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Sample records for anisotropic magnetocaloric effect

  1. Anisotropic magnetocaloric effect in antiferromagnetic systems: Application to EuTiO3

    Science.gov (United States)

    Alho, B. P.; Carvalho, A. Magnus G.; von Ranke, P. J.

    2014-09-01

    In this work, we theoretically predicted an anisotropic magnetocaloric effect of the same order of magnitude of the usual magnetocaloric effect for antiferromagnetic systems. The anisotropic magnetic properties come from the anti-parallel alignment of the magnetic sites and can be optimized depending on the magnetic field change. This result highlights the applicability of antiferromagnetic compounds as refrigerants based on the anisotropic magnetocaloric effect. For this purpose, we considered a Hamiltonian model, including the exchange and Zeeman interactions in a two sublattices framework. It is worth noting that no anisotropy is explicitly included on the Hamiltonian model, although the system presents an anisotropic behavior. The calculations were applied to the G-type antiferromagnetic compound EuTiO3.

  2. Magnetocaloric effect (MCE): Microscopic approach within Tyablikov approximation for anisotropic ferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Kotelnikova, O.A.; Prudnikov, V.N. [Physical Faculty, Lomonosov State University, Department of Magnetism, Moscow (Russian Federation); Rudoy, Yu.G., E-mail: rudikar@mail.ru [People' s Friendship University of Russia, Department of Theoretical Physics, Moscow (Russian Federation)

    2015-06-01

    The aim of this paper is to generalize the microscopic approach to the description of the magnetocaloric effect (MCE) started by Kokorina and Medvedev (E.E. Kokorina, M.V. Medvedev, Physica B 416 (2013) 29.) by applying it to the anisotropic ferromagnet of the “easy axis” type in two settings—with external magnetic field parallel and perpendicular to the axis of easy magnetization. In the last case there appears the field induced (or spin-reorientation) phase transition which occurs at the critical value of the external magnetic field. This value is proportional to the exchange anisotropy constant at low temperatures, but with the rise of temperature it may be renormalized (as a rule, proportional to the magnetization). We use the explicit form of the Hamiltonian of the anisotropic ferromagnet and apply widely used random phase approximation (RPA) (known also as Tyablikov approximation in the Green function method) which is more accurate than the well known molecular field approximation (MFA). It is shown that in the first case the magnitude of MCE is raised whereas in the second one the MCE disappears due to compensation of the critical field renormalized with the magnetization.

  3. Enhanced magnetocaloric effect material

    Science.gov (United States)

    Lewis, Laura J. H.

    2006-07-18

    A magnetocaloric effect heterostructure having a core layer of a magnetostructural material with a giant magnetocaloric effect having a magnetic transition temperature equal to or greater than 150 K, and a constricting material layer coated on at least one surface of the magnetocaloric material core layer. The constricting material layer may enhance the magnetocaloric effect by restriction of volume changes of the core layer during application of a magnetic field to the heterostructure. A magnetocaloric effect heterostructure powder comprising a plurality of core particles of a magnetostructural material with a giant magnetocaloric effect having a magnetic transition temperature equal to or greater than 150 K, wherein each of the core particles is encapsulated within a coating of a constricting material is also disclosed. A method for enhancing the magnetocaloric effect within a giant magnetocaloric material including the step of coating a surface of the magnetocaloric material with a constricting material is disclosed.

  4. Anisotropic Magnetocaloric Effect in Single Crystalline NiTa2O6

    Science.gov (United States)

    Schye, Aaron T.; Masunaga, Sueli H.; Christian, Aaron B.; Neumeier, John J.; Yu, Yi-Kuo

    2015-03-01

    Magnetic susceptibility and heat capacity measurements were made on the low-dimensional antiferromagnet NiTa2O6. The antiferromagnetic structure most consistent with our measurements is the two sub-lattice model proposed by Law et al.[1] in which magnetic moments in the z = 0 plane are aligned parallel to [110] and those in the z = 1/2 plane are aligned parallel to [1 1 0]. Applying a magnetic field along [110] causes the peak in the heat capacity to split into two with one remaining at TN and the other shifting to lower temperatures as the field is increased with a maximum ΔT ~ 3 K at 8 T. This splitting indicates that each sub-lattice orders at different Néel temperatures. Calculation of the magnetic entropy change associated with an increase in magnetic field(ΔSm (T , ΔH)) reveals ΔSm (T , ΔH) ~ 0.7 J/kg K for H ∥ [110] and ΔSm (T , ΔH) ~ 0 J/kg K for H ∥ [001] if ΔH = 8 T. This anisotropy in the magnetocaloric effect suggests that rotating the sample in constant magnetic field will result in a change in sample temperature. Supported by NSF Grant DMR-0907036.

  5. The Giant Magnetocaloric Effect

    Science.gov (United States)

    Pecharsky, Vitalij K.

    1998-03-01

    Since the discovery of the magnetocaloric effect in pure iron by E.Warburg in 1881, it has been measured experimentally on many magnetic metals and compounds. The majority of the materials studied order magnetically undergoing a second order phase transformation. The magnetocaloric effect, typically peaking near the Curie or the Néel temperature, generally ranges from 0.5 to 2 K (in terms of adiabatic temperature change) or at 1 to 4 J/kg K (in terms of isothermal magnetic entropy change) per 1 T magnetic field change. The giant magnetocaloric effect recently discovered in Gd_5(Si_xGe_1-x)4 alloys, where x refrigerant capacity, which is the measure of how much heat can be transferred from a cold to a hot reservoir in one ideal thermodynamic cycle, is larger than that of the best second order phase transition materials by 25 to 100%. When the Gd_5(Si_xGe_1-x)4 alloys are compared with other known materials, which show first order magnetic phase transition, such as Dy, Ho, Er, HoCo_2, NdMn_2Si_2, Fe_0.49Rh_0.51, and (Hf_0.83Ta_0.17)Fe_2+x, only Fe_0.49Rh_0.51 has comparable magnetocaloric properties. However, the first order magnetic phase transition in Fe_0.49Rh_0.51 is irreversible, and the magnetocaloric effect disappears after one magnetizing/demagnetizing cycle. A study of the crystal structure, thermodynamics, and magnetism of the Gd_5(Si_xGe_1-x)4 alloys, where 0 basic relations between the composition, the crystal structure, and the change in thermodynamics and magnetocaloric properties, which occur in the Gd_5(Si_xGe_1-x)4 system, and which brings about the giant magnetocaloric effect when x <= 0.5.

  6. Anisotropic thermal conductivity in epoxy-bonded magnetocaloric composites

    Science.gov (United States)

    Weise, Bruno; Sellschopp, Kai; Bierdel, Marius; Funk, Alexander; Bobeth, Manfred; Krautz, Maria; Waske, Anja

    2016-09-01

    Thermal management is one of the crucial issues in the development of magnetocaloric refrigeration technology for application. In order to ensure optimal exploitation of the materials "primary" properties, such as entropy change and temperature lift, thermal properties (and other "secondary" properties) play an important role. In magnetocaloric composites, which show an increased cycling stability in comparison to their bulk counterparts, thermal properties are strongly determined by the geometric arrangement of the corresponding components. In the first part of this paper, the inner structure of a polymer-bonded La(Fe, Co, Si)13-composite was studied by X-ray computed tomography. Based on this 3D data, a numerical study along all three spatial directions revealed anisotropic thermal conductivity of the composite: Due to the preparation process, the long-axis of the magnetocaloric particles is aligned along the xy plane which is why the in-plane thermal conductivity is larger than the thermal conductivity along the z-axis. Further, the study is expanded to a second aspect devoted to the influence of particle distribution and alignment within the polymer matrix. Based on an equivalent ellipsoids model to describe the inner structure of the composite, numerical simulation of the thermal conductivity in different particle arrangements and orientation distributions were performed. This paper evaluates the possibilities of microstructural design for inducing and adjusting anisotropic thermal conductivity in magnetocaloric composites.

  7. Who discovered the magnetocaloric effect?

    DEFF Research Database (Denmark)

    Smith, Anders

    2013-01-01

    A magnetic body changes its thermal state when subjected to a changing magnetic field. In particular, if done under adiabatic conditions, its temperature changes. For the past 15 years the magnetocaloric effect has been the focus of significant research due to its possible application for efficient...... refrigeration near room temperature. At the same time, it has become common knowledge within the magnetic refrigeration research community that the magnetocaloric effect was discovered by the German physicist E. Warburg in 1881. We re-examine the original literature and show that this is a misleading reading...

  8. The magnetocaloric effect in dysprosium

    Science.gov (United States)

    Benford, S. M.

    1979-01-01

    The magnetocaloric effect in polycrystalline Dy was measured in the 84-280-K range in measuring fields from 1 to 7 T. These adiabatic temperature changes reflect structural changes in Dy with applied field and temperature, and include the first magnetocaloric data for a helical antiferromagnet. Above the Neel point (179 K) a field increase always caused heating; below the Neel point fields less than about 2 T cause cooling for some values of initial temperature. The largest temperature increase with a 7 T field occurs at the Neel point and at fields below 2 T near the Curie point. For refrigeration purposes the optimal working region for a Dy cooling element is field dependent.

  9. The effect of demagnetization on the magnetocaloric properties of gadolinium

    DEFF Research Database (Denmark)

    Bahl, Christian Robert Haffenden; Nielsen, Kaspar Kirstein

    2009-01-01

    Gadolinium displays a strong magnetocaloric effect at temperatures close to room temperature making it useful in the field of room temperature magnetic refrigeration. We discuss the importance of including the effects of the demagnetization field when considering the magnetocaloric properties...

  10. Magnetocaloric effect at cryogenic temperature in gadolinium oxide nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Rima, E-mail: rima.paul@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Paramanik, Tapas; Das, Kalipada [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Sen, Pintu [Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata 700064 (India); Satpati, B.; Das, I. [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)

    2016-11-01

    We have synthesized fascinating nano-structure of Gadolinium oxide (Gd{sub 2}O{sub 3}) using controlled template-assisted electrochemical deposition technique which showed interesting anisotropic magnetic behavior. The nanotubes of Gd{sub 2}O{sub 3} with average diameter 200 nm, length 10 µm and wall thickness 20 nm are constituted of nanoclusters with average diameter 7.5 nm. The tubes are aligned and are almost uniform throughout their length. Detailed magnetic measurements of aligned Gd{sub 2}O{sub 3} nanotubes have been performed for both parallel and perpendicular magnetic field orientations with respect to the axis of the Gd{sub 2}O{sub 3} nanotube array. Significant differences in magnetization values have been observed between the parallel and perpendicular orientations. Experimental results indicate the superparamagnetic nature of the nanomaterial. Large magnetocaloric effect, associated with the sharp change in magnetization of the Gd{sub 2}O{sub 3} nanotubes, has been observed in the cryogenic temperature regime that shows anisotropic behavior. - Highlights: • Gd{sub 2}O{sub 3} nanotubes of diameter ~200 nm synthesized through electrochemical technique. • The nanotubes are superparamagnetic in nature. • At cryogenic temperature, the nanotubes exhibit large magnetocaloric anisotropic effect.

  11. Magnetic Refrigeration and the Magnetocaloric Effect

    DEFF Research Database (Denmark)

    Petersen, Thomas Frank; Pryds, Nini; Smith, Anders;

    2006-01-01

    material are plased in a magnetic field. This paper introduces and describes magnetic refrigeration cycles and the magnetocaloric effect, and shows how magnetic refrigeration can be an alternative to vapour-compression refrigeration,. A review of the Danish research on magnetic refrigeration at Risø......Magnetic refrigeration at room temperature is an emerging technology for refrigeration, which promises low energy consumption and is environmentalle friendly. Magnetic refrigeration is based on the magnetocaloric effect, which manifests itself as a reversibel increase in temperature when magnetic...

  12. Magnetocaloric effect at cryogenic temperature in gadolinium oxide nanotubes

    Science.gov (United States)

    Paul, Rima; Paramanik, Tapas; Das, Kalipada; Sen, Pintu; Satpati, B.; Das, I.

    2016-11-01

    We have synthesized fascinating nano-structure of Gadolinium oxide (Gd2O3) using controlled template-assisted electrochemical deposition technique which showed interesting anisotropic magnetic behavior. The nanotubes of Gd2O3 with average diameter 200 nm, length 10 μm and wall thickness 20 nm are constituted of nanoclusters with average diameter 7.5 nm. The tubes are aligned and are almost uniform throughout their length. Detailed magnetic measurements of aligned Gd2O3 nanotubes have been performed for both parallel and perpendicular magnetic field orientations with respect to the axis of the Gd2O3 nanotube array. Significant differences in magnetization values have been observed between the parallel and perpendicular orientations. Experimental results indicate the superparamagnetic nature of the nanomaterial. Large magnetocaloric effect, associated with the sharp change in magnetization of the Gd2O3 nanotubes, has been observed in the cryogenic temperature regime that shows anisotropic behavior.

  13. Electric field control of the magnetocaloric effect.

    Science.gov (United States)

    Gong, Yuan-Yuan; Wang, Dun-Hui; Cao, Qing-Qi; Liu, En-Ke; Liu, Jian; Du, You-Wei

    2015-02-04

    Through strain-mediated magnetoelectric coupling, it is demonstrated that the magnetocaloric effect of a ferromagnetic shape-memory alloy can be controlled by an electric field. Large hysteresis and the limited operating temperature region are effectively overcome by applying an electric field on a laminate comprising a piezoelectric and the alloy. Accordingly, a model for an active magnetic refrigerator with high efficiency is proposed in principle.

  14. Investigation on the magnetocaloric effect in TbN compound

    Energy Technology Data Exchange (ETDEWEB)

    Ranke, P.J. von, E-mail: von.ranke@uol.com.br [Instituto de Física, Universidade do Estado do Rio de Janeiro—UERJ, Rua São Francisco Xavier, 524, 20550-013 RJ (Brazil); Alvarenga, T.S.T.; Nóbrega, E.P.; Alho, B.P.; Ribeiro, P.O. [Instituto de Física, Universidade do Estado do Rio de Janeiro—UERJ, Rua São Francisco Xavier, 524, 20550-013 RJ (Brazil); Carvalho, A. Magnus G. [Divisão de Metrologia de Materiais (DIMAT), Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Duque de Caxias, RJ 25250-020 (Brazil); Sousa, V.S.R. de; Caldas, A.; Oliveira, N.A. de [Instituto de Física, Universidade do Estado do Rio de Janeiro—UERJ, Rua São Francisco Xavier, 524, 20550-013 RJ (Brazil)

    2013-09-15

    One of the biggest challenges in materials science is to understand the microscopic mechanisms responsible in storage and release material entropy. TbN compound, which presents non-degeneracy in ground state, was studied and the calculated magnetocaloric effect is in good agreement with the recent experimental data. Also inverse magnetocaloric effect and spin reorientation transition were predicted in TbN. The theoretical investigations were carried out using a Hamiltonian, which includes the crystalline electrical field, Zeeman and exchange interactions. - Highlights: • Theoretical description of the magnetocaloric effect in TbN. • Influence of the crystalline electrical field anisotropy on TbN. • Predictions of inverse and anomalous magnetocaloric effect in TbN.

  15. Magnetocaloric Refrigeration.

    Science.gov (United States)

    1987-03-01

    material having a magnetocaloric effect. Larger temperature spans require a cycle with some type of heat exchange. One such cycle is the Brayton cycle... heat capacity of the rare-earth metals, which had a small magnetocaloric effect at the higher temperatures. In order to optimize the small... magnetocaloric effect and minimize the heat capacities of the inactive rare- earth metals while they are being cooled to their Curie points, half the volume of

  16. Understanding the inverse magnetocaloric effect in antiferro- and ferrimagnetic arrangements.

    Science.gov (United States)

    von Ranke, P J; de Oliveira, N A; Alho, B P; Plaza, E J R; de Sousa, V S R; Caron, L; Reis, M S

    2009-02-04

    The inverse magnetocaloric effect occurs when a magnetic material cools down under applied magnetic field in an adiabatic process. Although the existence of the inverse magnetocaloric effect was recently reported experimentally, a theoretical microscopic description is almost nonexistent. In this paper we theoretically describe the inverse magnetocaloric effect in antiferro- and ferrimagnetic systems. The inverse magnetocaloric effects were systematically investigated as a function of the model parameters. The influence of the Néel and the compensation temperature on the magnetocaloric effect is also analyzed using a microscopic model.

  17. Consequenses of the magnetocaloric effect on magnetometry measurements

    DEFF Research Database (Denmark)

    Hansen, Britt Rosendahl; Bahl, Christian Robert Haffenden; Kuhn, Luise Theil;

    2010-01-01

    Magnetization curves recorded at high sweep-rates on magnetic materials near a phase transition temperature can be affected by temperature changes in the material due to the magnetocaloric effect. This change in the sample temperature is a result of the quasiadiabatic conditions that can occur...... under such conditions and we demonstrate its effects on magnetization curves of two magnetocaloric materials, La(Fe0.945Co0.055)11.9Si1.1 and Gd5Si2Ge2. We show how a quantity calculated from isothermal magnetization curves, the magnetic entropy change, ΔSM, is affected by the erroneous data. As ΔSM...... is a measure of the magnetocaloric effect, the discrepancies demonstrated here are more severe close to a peak in ΔSM, which is precisely the quantity that is of interest and reported on in the literature from possibly erroneous magnetization data. We also demonstrate how, through simple measurements...

  18. Tunable magnetocaloric effect in transition metal alloys.

    Science.gov (United States)

    Belyea, Dustin D; Lucas, M S; Michel, E; Horwath, J; Miller, Casey W

    2015-10-28

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based "high entropy alloys" in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants.

  19. Tunable magnetocaloric effect in transition metal alloys

    Science.gov (United States)

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-10-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants.

  20. Negative magnetocaloric effect in Fe 1-x Rh x compounds

    OpenAIRE

    2007-01-01

    International audience; On increasing temperature, the Fe1-xRhx alloys present a transition from an antiferromagnetic to a ferromagnetic state, which induces a negative magnetocaloric effect (MCE). The magnetocaloric effect, in particular of the Fe0.49Rh0.51 alloy, was studied by direct measurements and accordingto specific heat measurements. Here, we report the recent results obtained on the annealed Fe0.48Rh0.52 compound we prepared by arc melting. The isothermal entropy change ΔS allowing ...

  1. Evaluating the effect of magnetocaloric properties on magnetic refrigeration performance

    DEFF Research Database (Denmark)

    Engelbrecht, Kurt; Bahl, Christian Robert Haffenden

    2010-01-01

    on developing materials with a high entropy change with magnetization while placing lower emphasis on the adiabatic temperature change. This work uses model magnetocaloric materials and a numerical AMR model to predict how the temperature change and entropy change with magnetization interact and how they affect...... the performance of a practical system. The distribution of the magnetocaloric effect as a function of temperature was also studied. It was found that the adiabatic temperature change in a magnetocaloric material can be more important than the isothermal entropy change for certain conditions. A material...... that exhibits a sharp peak in isothermal entropy change was shown to produce a significantly lower cooling power than a material with a wide peak in a practical AMR system. © 2010 American Institute of Physics...

  2. Shape-anisotropic heterogeneous nucleation and magnetic Gibbs-Thomson effect in itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 magnetocaloric compound

    Science.gov (United States)

    Fujita, A.; Kondo, T.; Kano, M.; Yako, H.

    2013-01-01

    Macroscopic anisotropy of spatial selectivity in magnetic nucleation and growth was clarified for itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 by the time-dependent Ginzburg-Landau model combined with the Maxwell electromagnetic equation. Spontaneous generation of voltage supports symmetric growth in the longitudinal direction of the specimen as predicted by the simulation. The difference between nucleation-growth behaviors in thermally induced transition and those in field-induced transition is also elucidated. Electrical resistivity measurements also detect anisotropic growth of the induced phase. These results imply that the magnetic-dipole version of Gibbs-Thomson effect governs growth behavior.

  3. Magnetocaloric pump

    Science.gov (United States)

    Brown, G. V.

    1973-01-01

    Very cold liquids and gases such as helium, neon, and nitrogen can be pumped by using magnetocaloric effect. Adiabatic magnetization and demagnetization are used to alternately heat and cool slug of pumped fluid contained in closed chamber.

  4. Enhanced magnetocaloric effects and tunable thermal hysteresis in transition metal pnictides

    NARCIS (Netherlands)

    Brück, E.; Trung, N.T.; Ou, Z.Q.; Buschow, K.H.J.

    2012-01-01

    The effect of Co and Ni substitutions for Fe on the magnetocaloric properties of MnFe(P,Ge) compounds crystallizing in the hexagonal Fe2P type of structure was studied. It was found that, by changing composition, a small thermal hysteresis and a giant magnetocaloric effect can be obtained simultaneo

  5. Tuning the giant inverse magnetocaloric effect in Mn2−xCrxSb compounds

    NARCIS (Netherlands)

    Caron, L.; Miao, X.F.; Klaasse, J.C.P.; Gama, S.; Brück, E.

    2013-01-01

    Structural, magnetic, and magnetocaloric properties of Mn2-xCrxSb compounds have been studied. In these compounds, a first order magnetic phase transition from the ferrimagnetic to the antiferromagnetic state occurs with decreasing temperature, giving rise to giant inverse magnetocaloric effects tha

  6. Gadolinium oxalate derivatives with enhanced magnetocaloric effect via ionothermal synthesis.

    Science.gov (United States)

    Meng, Yan; Chen, Yan-Cong; Zhang, Ze-Min; Lin, Zhuo-Jia; Tong, Ming-Liang

    2014-09-02

    Two new oxalate-bridged Gd(III) coordination polymers, namely, (choline)[Gd(C2O4)(H2O)3Cl]Cl·H2O (1) and [Gd(C2O4)(H2O)3Cl] (2), were first obtained ionothermally by using a deep eutectic solvent (DES). The magnetic studies and heat capacity measurements reveal that the two-dimensional Gd(III)-based coordination polymer of 2 has the higher magnetic density and exhibits a larger cryogenic magnetocaloric effect (MCE) (ΔS(m) = 48 J kg(-1) K(-1) for ΔH = 7 T at 2.2 K).

  7. Magnetocaloric effect in quantum spin-s chains

    Directory of Open Access Journals (Sweden)

    A. Honecker

    2009-01-01

    Full Text Available We compute the entropy of antiferromagnetic quantum spin-s chains in an external magnetic field using exact diagonalization and Quantum Monte Carlo simulations. The magnetocaloric effect, i. e., temperature variations during adiabatic field changes, can be derived from the isentropes. First, we focus on the example of the spin-s=1 chain and show that one can cool by closing the Haldane gap with a magnetic field. We then move to quantum spin-s chains and demonstrate linear scaling with s close to the saturation field. In passing, we propose a new method to compute many low-lying excited states using the Lanczos recursion.

  8. Theoretical description of magnetocaloric effect in the shape memory alloy exhibiting metamagnetic behavior

    Energy Technology Data Exchange (ETDEWEB)

    L' vov, Victor A. [Institute of Magnetism, Kyiv 03142 (Ukraine); Taras Shevchenko National University, Kyiv 01601 (Ukraine); Kosogor, Anna, E-mail: annakosogor@gmail.com [Institute of Magnetism, Kyiv 03142 (Ukraine); National University of Science and Technology ‘MISiS’, Moscow 119049 (Russian Federation); Barandiaran, Jose M. [BCMaterials and University of Basque Country, UPV/EHU, Bilbao 48080 (Spain); Chernenko, Volodymyr A. [BCMaterials and University of Basque Country, UPV/EHU, Bilbao 48080 (Spain); Ikerbasque, Basque Foundation for Science, Bilbao 48013 (Spain)

    2016-01-07

    A simple thermodynamic theory is proposed for the quantitative description of giant magnetocaloric effect observed in metamagnetic shape memory alloys. Both the conventional magnetocaloric effect at the Curie temperature and the inverse magnetocaloric effect at the transition from the ferromagnetic austenite to a weakly magnetic martensite are considered. These effects are evaluated from the Landau-type free energy expression involving exchange interactions in a system of a two magnetic sublattices. The findings of the thermodynamic theory agree with first-principles calculations and experimental results from Ni-Mn-In-Co and Ni-Mn-Sn alloys, respectively.

  9. Nonuniversal scaling of the magnetocaloric effect as an insight into spin-lattice interactions in manganites

    DEFF Research Database (Denmark)

    Smith, Anders; Nielsen, Kaspar Kirstein; Neves Bez, Henrique;

    2016-01-01

    We measure the magnetocaloric effect of the manganite series La0.67Ca0.33-xSrxMnO3 by determining the isothermal entropy change upon magnetization, using variable-field calorimetry. The results demonstrate that the field dependence of the magnetocaloric effect close to the critical temperature....... In this way the determination of the nonuniversal field dependence of the magnetocaloric effect close to a phase transition can be used as a method to gain insight into the strength of the spin-lattice interactions of magnetic materials. The approach is shown also to be applicable to first-order transitions....

  10. Magnetocaloric effect in the metamagnet ErRhSi compound

    Science.gov (United States)

    Debnath, J. C.; Nair, Harikrishnan S.; Strydom, André M.; Ramesh Kumar, K.; Wang, Jianli

    2016-12-01

    The magnetocaloric effect is observed in the 1:1:1 compound ErRhSi, which is a metamagnet is reported in this paper. ErRhSi crystallizes in the orthorhombic space group Pnma, adopting the TiNiSi structure type, with lattice parameters a(Å) = 6.7903(5), b(Å) = 4.1881(3), and c(Å) = 7.3847(4). Our magnetic measurements confirm an antiferromagnetic phase transition at TN ≈ 8.5 K, also supported by the specific heat measurement. Crystal field effects of Er3+ are suggested by the inverse magnetic susceptibility data which do not conform to an ideal Curie-Weiss behaviour and also by the total entropy that attains Rln (2) at TN. Although the magnetic hysteresis indicates ErRhSi to be a soft magnet, several clear metamagnetic features are observed at 2 K. Magnetic entropy change ΔSM = - 8.7 J/kg-K is observed at about 9 K with the application of 5 T magnetic field. The corresponding adiabatic temperature change ΔTad is about 4 K. Large magnetocaloric effects suggest that this material is suitable for the low temperature magnetic refrigeration.

  11. Inconvenient magnetocaloric effect in ferromagnetic shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Khovaylo, Vladimir, E-mail: khovaylo@misis.ru [National University of Science and Technology “MISiS”, Moscow 119049 (Russian Federation)

    2013-11-15

    Highlights: ► Critical analysis of the available experimental results on isothermal magnetic entropy change in ferromagnetic shape memory alloys Ni–Mn–X (X = Ga, In, Sn, Sb) is given. ► Based on available in literature experimental data on total entropy change at martensitic transformation it is shown that the isothermal magnetic entropy change in Ni–Mn–X (X = Ga, In, Sn, Sb) should not greatly exceed 30 J/kg K. -- Abstract: Critical analysis available in the literature experimental results on magnetocaloric effect in ferromagnetic shape memory alloys Ni–Mn–X (X = Ga, In, Sn, Sb) is given. Based on a model developed by Pecharsky et al. [22], it is shown that the isothermal magnetic field-induced entropy change in the Ni–Mn–X alloys should not greatly exceed 30 J/kg K. Considering thermodynamics of temperature- and magnetic field-induced martensitic transformations, it is demonstrated that a contribution of the structural subsystem to the magnetocaloric effect in the Ni–Mn–X alloys studied so far is irreversible in magnetic fields below 5 T. This makes ferromagnetic shape memory alloys an inconvenient system for the practical application in modern magnetic refrigeration technology.

  12. Observation of a large magnetocaloric effect in a 2D Gd(III)-based coordination polymer.

    Science.gov (United States)

    Biswas, Soumava; Adhikary, Amit; Goswami, Soumyabrata; Konar, Sanjit

    2013-10-07

    A new 2D Gd(III)-based coordination polymer has close to the highest cryogenic magnetocaloric effect of any MOF reported so far. The experimental results reveal its structural features and magnetic properties.

  13. Magnetocrystalline anisotropy and the magnetocaloric effect in Fe2P

    NARCIS (Netherlands)

    Caron, L.; Hudl, M.; Höglin, V.; Dung, N.H.; Gomez, C.P.; Sahlberg, M.; Brück, E.; Andersson, Y.; Nordblad, P.

    2013-01-01

    Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a moderate magnetic entropy change, which spans over 70 K and the presence of strong magnetization anisotropy proves this system is not fully itiner

  14. Specific heat and magnetocaloric effect in Pr1-xAgxMnO3 manganites

    OpenAIRE

    2010-01-01

    The magnetocaloric effect in alternating magnetic fields has been investigated in Pr1-xAgxMnO3 manganites with x=0.05-0.25. The stepwise reversal of the sign of the magnetocaloric effect has been revealed in a weakly doped sample (x=0.05) at low temperatures (~80 K). This reversal is attributed to the coexistence of the ferromagnetic and canted antiferromagnetic phases with different critical temperatures.

  15. Heat capacity and magnetocaloric effect in polycrystalline Gd1-xSmxMn2Si2

    OpenAIRE

    2006-01-01

    We report the magnetocaloric effect in terms of isothermal magnetic entropy change as well as adiabatic temperature change, calculated using the heat capacity data. Using the zero field heat capacity data, the magnetic contribution to the heat capacity has been estimated. The variations in the magnetocaloric behavior have been explained on the basis of the magnetic structure of these compounds. The refrigerant capacities have also been calculated for these compounds.

  16. Influence of Domain Wall on Magnetocaloric Effect in GdPt$_{2}$

    OpenAIRE

    2006-01-01

    The resistivity, magnetoresistance and in-field heat capacity measurements were performed on GdPt$_{2}$ intermetallic compound. The magnetocaloric parameters $\\Delta T_{ad}$ and $-\\Delta S$ were derived from the in-field heat capacity data. Comparison has been made between the magnetocaloric effect $-\\Delta S$ and difference in resistivity $-\\Delta \\rho$ $(=\\rho(H)-\\rho(0))$ as a function of temperature. There is distinct difference in the temperature dependence of $-\\Delta S$ and $-\\Delta \\r...

  17. Large magnetocaloric effect in sintered ferromagnetic EuS

    Science.gov (United States)

    Matsumoto, Koichi; Li, Liang; Hirai, Shinji; Nakamura, Eiji; Murayama, Daiki; Ura, Yutaro; Abe, Satoshi

    2016-10-01

    We present magnetocaloric effect measurements of the ferromagnetic semiconductor EuS in the vicinity of its ordering temperature. Single phase EuS powder was synthesized by CS2 gas sulfurization of Eu2O3. A sintered compact with relative density over 95% was prepared by pulsed electric current sintering of the powder. Temperature and magnetic field dependence of the magnetization and specific heat were characteristic of a paramagnetic to ferromagnetic second order phase transition. The entropy change induced by an external magnetic field and the specific heat were both close to those of a single crystal. We obtained an entropy-temperature (S-T) diagram of the EuS sintered compact. Carnot cycle liquefaction of hydrogen using EuS was compared with several other materials, with results indicating that sintered EuS is an excellent magnetic refrigerant for hydrogen liquefaction.

  18. Magnetocaloric effect in rare-earth intermetallics: Recent trends

    Indian Academy of Sciences (India)

    R Nirmala; A V Morozkin; S K Malik

    2015-06-01

    Magnetocaloric effect (MCE) is the change in isothermal magnetic entropy (m)and adiabatic temperature (ad) that accompany magnetic transitions in materials during the application or the removal of magnetic field under adiabatic conditions. The physics of MCE gets enriched by correlated spin-lattice degrees of freedom. This phenomenon has been actively investigated over the past few decades as it holds a promise for an alternate method of refrigeration/heat pumping. This has already resulted in several reviews on this topic. This paper focusses on some recent trends in this field and prospects of using rare-earth-based materials as active magnetic refrigerants over a broad temperature range that includes gas liquefaction and near-room temperature refrigeration/heating.

  19. Rotating Magnetocaloric Effect in an Anisotropic Molecular Dimer.

    Science.gov (United States)

    Lorusso, Giulia; Roubeau, Olivier; Evangelisti, Marco

    2016-03-01

    In contrast to the mainstream research on molecular refrigerants that seeks magnetically isotropic molecules, we show that the magnetic anisotropy of dysprosium acetate tetrahydrate, [{Dy(OAc)3 (H2 O)2}2]⋅4 H2O (1), can be efficiently used for cooling below liquid-helium temperature. This is attained by rotating aligned single-crystal samples in a constant applied magnetic field. The envisioned advantages are fast cooling cycles and potentially compact refrigerators.

  20. The effect of external pressure on the magnetocaloric effect of Ni-Mn-In alloy.

    Science.gov (United States)

    Sharma, V K; Chattopadhyay, M K; Roy, S B

    2011-09-14

    The martensitic transition in Ni(50)Mn(34)In(16) alloy has been studied by measuring the magnetization of the alloy as a function of temperature, magnetic field and pressure. Magnetic field and pressure have opposite effects on the martensitic transition in this alloy; the martensitic transition temperature decreases with increasing magnetic field but it increases with increasing pressure. The effect of pressure on the magnetocaloric properties of this large magnetocaloric effect alloy has been investigated in detail. The magnitude of the peak in the isothermal magnetic entropy change in Ni(50)Mn(34)In(16) increases with pressure. The temperature at which the magnetocaloric effect reaches the peak value in this alloy increases from near 240 K under ambient pressure to near 280 K under an external pressure of 9.5 kbar. The temperature corresponding to the peak in the isothermal magnetic entropy change increases with increasing pressure at a rate which matches the rate of increase of the martensite start temperature with increasing pressure. The temperature dependence of the isothermal magnetic entropy change under different pressures is found to follow a universal curve for a particular magnetic field change. These results show that pressure as a control parameter can be used to tune the temperature regime of the magnetocaloric effect in the alloy. The effect of pressure on the martensitic transition also gives a clue as regards the possibility of tuning this temperature regime with elemental substitution.

  1. Influence of random substitution on magnetocaloric effect in a spinel ferrite

    Energy Technology Data Exchange (ETDEWEB)

    Mamiya, Hiroaki, E-mail: MAMIYA.Hiroaki@nims.go.j [National Institute for Materials Science, Tsukuba 305-0047 (Japan); Terada, Noriki; Furubayashi, Takao; Suzuki, Hiroyuki S.; Kitazawa, Hideaki [National Institute for Materials Science, Tsukuba 305-0047 (Japan)

    2010-05-15

    Influence of random substitution of nonmagnetic ions on magnetocaloric effect is studied on manganese zinc ferrites from the viewpoints of Griffiths effects and frustration effects. The obtained results show that these side effects are insignificant at the ferrimagnetic transition in the range of zinc content below 70%. Consequently, the ferrite can keep a large magnetocaloric effect even when the transition temperature is lowered to a half of the original. This finding indicates that the nonmagnetic substitution is useful in adjusting the working temperature, if we utilize popular magnets such as ferrites with high Curie temperatures for the refrigerant consisting ubiquitous and nontoxic elements.

  2. Magneto-Caloric Effect of Gd5Si2Ge2Compounds under Different Processing Conditions

    Institute of Scientific and Technical Information of China (English)

    Zeng Hong; Yue Ming; Niu Peili; Zhang Jiuxing

    2004-01-01

    The magneto-caloric effect of Gd5 Si2Ge2 compounds produced by various techniques is investigated in terms of their magnetization behaviors in the magnetic field from 0 to 2.0 T.The studied materials include arc-melted, annealed and sintered alloys.The results demonstrate that the Gd5Si2Ge2 alloys obtained under different processing conditions possess distinct magneto-caloric effect due to their various microstructures.Proper annealing treatment can enhance the magneto-caloric effect of the alloy remarkably.While the sintered alloy bears relatively lower value of magnetic entropy change ( △ SM) than arc-melted one.The magnetic entropy change of the annealed Gd5 Si2Ge2 alloy arrives the arrives the maximum value of - △SM = 15.29 J· kg-1· K-1 for magnetic field change under 2.0 T in the present work.

  3. Nonuniversal scaling of the magnetocaloric effect as an insight into spin-lattice interactions in manganites

    Science.gov (United States)

    Smith, Anders; Nielsen, Kaspar K.; Bez, Henrique N.; Bahl, Christian R. H.

    2016-08-01

    We measure the magnetocaloric effect of the manganite series La0.67Ca0.33 -xSrxMnO3 by determining the isothermal entropy change upon magnetization, using variable-field calorimetry. The results demonstrate that the field dependence of the magnetocaloric effect close to the critical temperature is not given uniquely by the critical exponents of the ferromagnetic-paramagnetic phase transition, i.e., the scaling is nonuniversal. A theoretical description based on the Bean-Rodbell model and taking into account compositional inhomogeneities is shown to be able to account for the observed field dependence. In this way the determination of the nonuniversal field dependence of the magnetocaloric effect close to a phase transition can be used as a method to gain insight into the strength of the spin-lattice interactions of magnetic materials. The approach is shown also to be applicable to first-order transitions.

  4. Magnetocaloric effect of Gd5Si2Ge2 alloys in low magnetic field

    Indian Academy of Sciences (India)

    Hong Zeng; Chunjiang Kuang; Jiuxing Zhang; Ming Yue

    2011-07-01

    The magnetocaloric effect of Gd5Si2Ge2 alloys under heat treatment conditions are investigated in low magnetic fields. The magnetocaloric effect (MCE) is studied by measuring magnetic entropy change ( M) and adiabatic temperature change ( ad) in a magnetic field of 1.5 T using a vibrating sample magnetometer (VSM) and a home-made magnetocaloric effect measuring apparatus, respectively. The maximum M of the alloys increases by 200% from 4.38 to 13.32 J kg-1 K-1, the maximum ad increases by 105% from 1.9 to 3.9 K when compared to the as-cast due to the homogeneous composition distribution and microstructure, while the magnetic ordering temperature is slightly reduced. These results indicate that the annealed Gd5Si2Ge2 compounds are promising as high-performance magnetic refrigerants working room temperature in relatively low magnetic fields.

  5. Giant enhancement of magnetocaloric effect in metallic glass matrix composite

    Institute of Scientific and Technical Information of China (English)

    WANG YongTian; BAI HaiYang; PAN MingXiang; ZHAO DeQian; WANG WeiHua

    2008-01-01

    The magnetocaloric effect (MCE) has made great success in very low temperature refrigeration, which is highly desirable for application to the extended higher tem-perature range. Here we report the giant enhancement of MCE in the metallic glass composite. The large magnetic refrigerant capacity (RC) up to 103 J·kg-1 is more than double the RC of the well-known crystalline magnetic refrigerant compound Gd5Si2Ge1.9Fe0.1 (357 J·kg-1) and MnFeP0.45As0.55 (390 J·kg-1)(containing either ex-orbitant-cost Ge or poisonous As). The full width at half maximum of the magnetic entropy change (△Sm) peak almost spreads over the whole low-temperature range (from 303 to 30 K), which is five times wider than that of the Gd5Si2Ge1.9Fe0.1 and pure Gd. The maximum △Sm approaches a nearly constant value in a wide tem-perature span over 100 K, and however, such a broad table-like region near room temperature has seldom been found in alloys and compounds. In combination with the intrinsic amorphous nature, the metallic glass composite may be potential for the ideal Ericsson-cycle magnetic refrigeration over a broad temperature range near room temperature.

  6. Giant enhancement of magnetocaloric effect in metallic glass matrix composite

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The magnetocaloric effect (MCE) has made great success in very low temperature refrigeration, which is highly desirable for application to the extended higher tem-perature range. Here we report the giant enhancement of MCE in the metallic glass composite. The large magnetic refrigerant capacity (RC) up to 103 J·kg-1 is more than double the RC of the well-known crystalline magnetic refrigerant compound Gd5Si2Ge1.9Fe0.1 (357 J·kg-1) and MnFeP0.45As0.55 (390 J·kg-1)(containing either ex-orbitant-cost Ge or poisonous As). The full width at half maximum of the magnetic entropy change (ΔSm) peak almost spreads over the whole low-temperature range (from 303 to 30 K), which is five times wider than that of the Gd5Si2Ge1.9Fe0.1 and pure Gd. The maximum ΔSm approaches a nearly constant value in a wide tem-perature span over 100 K, and however, such a broad table-like region near room temperature has seldom been found in alloys and compounds. In combination with the intrinsic amorphous nature, the metallic glass composite may be potential for the ideal Ericsson-cycle magnetic refrigeration over a broad temperature range near room temperature.

  7. Review of magnetocaloric effect in perovskite-type oxides

    Institute of Scientific and Technical Information of China (English)

    Zhong Wei; Au Chak-Tong; Du You-Wei

    2013-01-01

    We survey the magnetocaloric effect in perovskite-type oxides (including doped ABO3-type manganese oxides,A3B2O7-type two-layered perovskite oxides,and A2B'B''O6-type ordered double-perovskite oxides).Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La(Ⅰ)-xCaxMnO3 and alkali-metal (Na or K)doped La0.8Ca0.2MnO3 perovskite-type manganese oxides.The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature.Considerable magnetic entropy changes can also be observed in two-layered perovskites La1.6Ca1.4Mn2O7 and La2.5-xK0.5+xMn2O7+δ(0 < x < 0.5),and double-perovskite Ba2Fe1+xMo1-xO6(0 ≤ x ≤ 0.3) near their respective Curie temperatures.Compared with rare earth metals and their alloys,the perovskite-type oxides are lower in cost,and they exhibit higher chemical stability and higher electrical resistivity,which together favor lower eddy-current heating.They are potential magnetic refrigerants at high temperatures,especially near room temperature.

  8. Magnetocaloric effect in Ni-Fe-Ga Heusler alloys with Co and Al substitutions

    Directory of Open Access Journals (Sweden)

    Tolea F.

    2015-01-01

    Full Text Available The functionality of the ferromagnetic shape memory alloys is related to the martensitic and magnetic order-disorder transformations, both of which may be tailored by doping with other elements or by suitable thermal treatments, so that alloys with concomitant (or sequential but close structural and magnetic phase transitions may be obtained. Concerning the magnetocaloric applications, it is assumed that the thin melt-spun ribbons assure a more efficient heat transfer. In the present work we investigate the influence of Co and Al substitutions on magnetocaloric effect characteristics of NiFeGa in bulk and also in ribbons prepared by melt spinning method and subjected to different thermal treatments. X-ray diffraction, differential scanning calorimetry, magnetocaloric and magnetoresistive characterizations have been performed. The results highlight the differences between the bulk and the ribbons (both as prepared and annealed and the role of substitutions.

  9. Structure and giant inverse magnetocaloric effect of epitaxial Ni-Co-Mn-Al films

    Science.gov (United States)

    Teichert, N.; Kucza, D.; Yildirim, O.; Yuzuak, E.; Dincer, I.; Behler, A.; Weise, B.; Helmich, L.; Boehnke, A.; Klimova, S.; Waske, A.; Elerman, Y.; Hütten, A.

    2015-05-01

    The structural, magnetic, and magnetocaloric properties of epitaxial Ni-Co-Mn-Al thin films with different compositions have been studied. The films were deposited on MgO(001) substrates by co-sputtering on heated substrates. All films show a martensitic transformation, where the transformation temperatures are strongly dependent on the composition. The structure of the martensite phase is shown to be 14 M . The metamagnetic martensitic transformation occurs from strongly ferromagnetic austenite to weakly magnetic martensite. The structural properties of the films were investigated by atomic force microscopy and temperature dependent x-ray diffraction. Magnetic and magnetocaloric properties were analyzed using temperature dependent and isothermal magnetization measurements. We find that Ni41Co10.4Mn34.8Al13.8 films show giant inverse magnetocaloric effects with magnetic entropy change of 17.5 J kg-1K-1 for μ0Δ H =5 T.

  10. Magnetocaloric effect in temperature-sensitive magnetic fluids

    Indian Academy of Sciences (India)

    Kinnari Parekh; R V Upadhyay; R V Mehta

    2000-04-01

    The magnetocaloric properties of three different temperature-sensitive magnetic fluids were studied. The pyromagnetic coefficient for all the materials were obtained and it was found that this property depends on physical and magnetic properties like size, magnetization and Curie temperature. A theoretical model was developed to explain the behaviour of change in entropy with temperature.

  11. Magnetocaloric effect in sandwich structures of La1- x K x MnO3 manganites

    Science.gov (United States)

    Gamzatov, A. G.; Aliev, A. M.; Kamilov, I. K.; Kaul', A. R.

    2016-07-01

    This paper reports on the results of the investigation into the magnetocaloric properties of sandwich structures of La1- x K x MnO3 manganites with x = 0.11 (LKM11), 0.13 (LKM13), and 0.15 (LKM15) in magnetic fields of up to 18 kOe. The results of the analysis of the field and temperature dependences of the magnetocaloric effect in the structures LKM11 + LKM13 and LKM13 + LKM15 have demonstrated that the use of sandwich structures increases the efficiency of magnetic cooling in a magnetic field of 18 kOe by 45%.

  12. Magnetocaloric materials

    Energy Technology Data Exchange (ETDEWEB)

    Jeppesen, Stinus

    2008-10-15

    New and improved magnetocaloric materials are one of the cornerstones in the development of room temperature magnetic refrigeration. Magnetic refrigeration has been used since the 1930ies in cryogenic applications, but has since the discovery of room temperature refrigerants received enormous attention. This Ph.D. work has been mainly concerned with developing a new technique to characterize the magnetocaloric effect (MCE) and using this technique in the investigations on new and improved magnetocaloric materials. For this purpose a novel differential scanning calorimeter (DSC) with applied magnetic fields was developed for measuring heat capacity as function of magnetic field. Measurements using the developed DSC demonstrate a very high sensitivity, fast measurements and good agreement with results obtained by other techniques. Furthermore, two material systems have been described in this work. Both systems take basis in the mixed-valence manganite system La{sub 1-x}Ca{sub x}MnO{sub 3} well known from research on colossal magnetoresistance (CMR). The mixed-valence manganite crystallizes in the perovskite structure of general formula ABO{sub 3}. The first material system is designed to investigate the influence of low level Cu doping on the B-site. Six different samples were prepared with over-stoichiometric compositions La{sub 0.67}Ca{sub 0.33}Mn{sub 1.05}Cu{sub x}O{sub 3}, x=0, 1, 2, 3, 4 and 5%. All compositions crystallized well in the same perovskite structure, but the morphology of the samples changed drastically with doping. Investigation on the magnetocaloric properties revealed that small levels of Cu up to around 3% could improve the magnetocaloric performance of the materials. Furthermore, Cu could be used to tune the temperature interval without deteriorating the MCE, which is a much desired characteristic for potential use in magnetic refrigerators. A less comprehensive part of the work has been concerned with the investigation of doping on the A

  13. Giant rotating magnetocaloric effect in the region of spin-reorientation transition in the NdCo₅ single crystal.

    Science.gov (United States)

    Nikitin, S A; Skokov, K P; Koshkid'ko, Yu S; Pastushenkov, Yu G; Ivanova, T I

    2010-09-24

    We have investigated the anisotropy of the magnetocaloric effect in a NdCo₅ single crystal in a wide range of temperatures, including the spin-reorientation temperature region. In the field μ(0)H =1.3 T in the spin-reorientation region 250-310 K, we discovered a giant rotating magnetocaloric effect of ~ 1.6 K, caused by rotation of the magnetization vector. The calculations of the anisotropy magnetocaloric effect for the field μ(0)H =1.3 T have been carried out.

  14. Measuring the effect of demagnetization in stacks of gadolinium plates using the magnetocaloric effect

    DEFF Research Database (Denmark)

    Lipsø, Hans Kasper Wigh; Nielsen, Kaspar Kirstein; Christensen, Dennis;

    2011-01-01

    on which the temperature is measured are varied. The orientation of the magnetic field is also varied. The measurements are compared to a magnetostatic model previously described. The results show that the magnetocaloric effect, due to the change in the internal field, is sensitive to the stack...... configuration and the orientation of the applied field. This may have significant implications for the construction of a magnetic cooling device...

  15. Effects of relative orientation of magnetocaloric inserts with the magnetic flux

    Energy Technology Data Exchange (ETDEWEB)

    Risser, M.; Vasile, C. [National Institute of Applied Sciences (INSA) Strasbourg, 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France); Laboratoire de Genie de la Conception (LGeCo), 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France); Engel, T. [National Institute of Applied Sciences (INSA) Strasbourg, 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France); Laboratoire des Systemes Photoniques (LSP), 24 Bd de la Victoire, 67084 Strasbourg, Cedex (France)

    2009-08-15

    This paper presents the study of the magnetic change of the magnetic flux density into the magnetocaloric materials (MCMs). The MCMs are shaped in thin parallel plates separated by a fluid forming together an insert. It is shown that keeping all the parameters equal, the unique modification of the orientation of the insert induces a change of the magnetic flux density into the magnetocaloric materials. Like all paramagnetic and ferromagnetic materials, the MCMs have variable magnetic permeability according to the density of flux that crosses them. The influence of a thermal circuit on a permanent magnetic circuit assembly is also evaluated. In order to ensure the heat exchange between the magnetocaloric materials and the outside space, the use of a heat transfer fluid is needed. The heat transfer fluid goes along the mini plates and is also placed inside the magnetic field. Because a fluid is generally a diamagnetic element, this increases the total magnetic reluctance of the assembly. Two different configurations named serial and parallel have been studied and evaluated in order to find the configuration that causes minimal disturbances to the magnetic flux and thus increases the magnetocaloric effect (MCE). Both configurations were also compared in respect to the induction obtained inside the vacuum gap of the magnet assembly. (author)

  16. Effect of low temperature annealing on magneto-caloric effect of Ni–Mn–Sn–Al ferromagnetic shape memory alloy

    Energy Technology Data Exchange (ETDEWEB)

    Agarwal, Sandeep [Haldia Institute of Technology, Haldia 721657, West Bengal (India); LCMP, Department of Condensed Matter Physics and Material Sciences, S.N. Bose National Centre for Basic Sciences, JD Block, Salt Lake, Kolkata 700098 (India); Stern-Taulats, Enric; Mañosa, Lluís [Departament d’Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, 08028 Barcelona, Catalonia (Spain); Mukhopadhyay, P.K., E-mail: pkm@bose.res.in [LCMP, Department of Condensed Matter Physics and Material Sciences, S.N. Bose National Centre for Basic Sciences, JD Block, Salt Lake, Kolkata 700098 (India)

    2015-08-25

    Highlights: • Magnetic properties of the system changed after secondary heat treatment. • MCE was enhanced after Al was partially replaced with Sn in Ni–Mn–Al system. • Suitable heat treatment further increased overall MCE in the sample. • Change in magnetic properties occurred due to change in atomic ordering. - Abstract: We studied the effect of low temperature annealing on the atomic ordering and consequent changes in the magnetization and magnetocaloric effect of the sample. The annealing at lower temperatures initially decreased the magnetization and magnetocaloric effect in the sample, but at higher annealing temperatures both increased. The changes in magnetization and magnetocaloric effect arise from the change in atomic ordering. We have shown that post quenching heat treatment offers easy way of optimizing the alloy for magnetocaloric effect. In order to verify that there was no overestimation in the measurement of magnetocaloric effect we also performed an infield calorimetric measurements and compared them with those from the magnetization measurements. We did not find remarkable difference between them.

  17. Inverse barocaloric effect in the giant magnetocaloric La-Fe-Si-Co compound.

    Science.gov (United States)

    Mañosa, Lluís; González-Alonso, David; Planes, Antoni; Barrio, Maria; Tamarit, Josep-Lluís; Titov, Ivan S; Acet, Mehmet; Bhattacharyya, Amitava; Majumdar, Subham

    2011-12-20

    Application of hydrostatic pressure under adiabatic conditions causes a change in temperature in any substance. This effect is known as the barocaloric effect and the vast majority of materials heat up when adiabatically squeezed, and they cool down when pressure is released (conventional barocaloric effect). There are, however, materials exhibiting an inverse barocaloric effect: they cool when pressure is applied, and they warm when it is released. Materials exhibiting the inverse barocaloric effect are rather uncommon. Here we report an inverse barocaloric effect in the intermetallic compound La-Fe-Co-Si, which is one of the most promising candidates for magnetic refrigeration through its giant magnetocaloric effect. We have found that application of a pressure of only 1 kbar causes a temperature change of about 1.5 K. This value is larger than the magnetocaloric effect in this compound for magnetic fields that are available with permanent magnets.

  18. Magnetocaloric effect at the exchange–inversion with magnetoelastic coupling

    Energy Technology Data Exchange (ETDEWEB)

    Piazzi, Marco, E-mail: m.piazzi@inrim.it; Basso, Vittorio

    2015-09-15

    We develop a thermodynamic model to describe antiferro- (AFM) to ferromagnetic (FM) phase transitions through magnetoelastic coupling in the framework of Kittel's exchange–inversion mechanism. By including both magnetic and structural contributions to the free energy, we derive the conditions to have a direct AFM–FM transition. These are represented either by the presence of a non-zero intra-sublattice coupling constant or by a sufficiently high value of the magnetoelastic coupling parameter. In the paper we establish these conditions by analytical means and we discuss the physical meaning of the model in relation to possible applications to magnetocaloric materials with AFM–FM transitions.

  19. Magnetocaloric effect at the exchange-inversion with magnetoelastic coupling

    Science.gov (United States)

    Piazzi, Marco; Basso, Vittorio

    2015-09-01

    We develop a thermodynamic model to describe antiferro- (AFM) to ferromagnetic (FM) phase transitions through magnetoelastic coupling in the framework of Kittel's exchange-inversion mechanism. By including both magnetic and structural contributions to the free energy, we derive the conditions to have a direct AFM-FM transition. These are represented either by the presence of a non-zero intra-sublattice coupling constant or by a sufficiently high value of the magnetoelastic coupling parameter. In the paper we establish these conditions by analytical means and we discuss the physical meaning of the model in relation to possible applications to magnetocaloric materials with AFM-FM transitions.

  20. Review of the Magnetocaloric Effect in RMnO3 and RMn2O5 Multiferroic Crystals

    Directory of Open Access Journals (Sweden)

    Mohamed Balli

    2017-02-01

    Full Text Available It is known that some of RMnO3 and RMn2O5 (R = rare earth multiferroic crystals reveal a strong interplay between their magnetic and electric order parameters, paving the way for applications in spintronic technologies. Additionally, recent works have also pointed out their potential utilization as refrigerants in magnetocaloric cooling systems for cryogenic tasks. In this paper, recent advances regarding the magnetocaloric properties of both RMnO3 and RMn2O5 families of multiferroics are reviewed. With the aim of understanding the RMnO3 and RMn2O5 magnetocaloric features, their structural and magnetic properties are discussed. The physics behind the magnetocaloric effect as well as some of its key thermodynamic aspects are also considered.

  1. Sample dependence of giant magnetocaloric effect in a cluster-glass system Ho5Pd2

    Science.gov (United States)

    Toyoizumi, Saori; Kitazawa, Hideaki; Kawamura, Yukihiko; Mamiya, Hiroaki; Terada, Noriki; Tamura, Ryo; Dönni, Andreas; Morita, Kengo; Tamaki, Akira

    2015-05-01

    In order to investigate the effect of vacancy on the magnetocaloric effect in Ho5Pd2, we have carried out X-ray diffraction, magnetization, and specific heat measurements in the rare-earth intermetallic compound Ho5+xPd2(-0.4 ≤ x ≤ 0.4). The maximum magnetic entropy change -ΔSmmax , the maximum adiabatic temperature change ΔTadmax , and the relative cooling power of Ho5+xPd2 take large values at x = 0-0.4 for the field change of 5 T. The paramagnetic Curie temperature θp increases with an increase of x. This fact suggests that the enhancement of ferromagnetic coupling among the correlated spins leads to the increase of magnetocaloric effect.

  2. Large magnetocaloric effect, moment, and coercivity enhancement after coating Ni nanoparticles with Ag.

    Science.gov (United States)

    Srinath, Sanyadanam; Poddar, Pankaj; Das, Raja; Sidhaye, Deepti; Prasad, Bhagavatula Lakshmi Vara; Gass, James; Srikanth, Hariharan

    2014-06-06

    We observe a large magnetocaloric effect in monodisperse Ni and Ni(core)Ag(shell) nanoparticles in the superparamagnetic region. The organically passivated Ni nanospheres show a large magnetic entropy change of 0.9 J kg(-1)  K for a 3 T magnetic field change. In comparison to the surfactant-coated Ni nanoparticles, the Ni(core)Ag(shell) nanoparticles show an enhanced coercivity, magnetization, and magnetocaloric effect (1.3 kg K for a 3 T magnetic field change). The coercivity at 10 K increases from 360 Oe for Ni nanoparticles to nearly 610 Oe for Ni(core)Ag(shell) particles. This large enhancement is attributed to the enhanced inter-particle interaction, which is mediated by the metallic shell, over the relatively weaker dipolar interaction in the surfactant-coated Ni nanoparticles, and to modification of the surface spin structure.

  3. AC measurement of heat capacity and magnetocaloric effect for pulsed magnetic fields.

    Science.gov (United States)

    Kohama, Yoshimitsu; Marcenat, Christophe; Klein, Thierry; Jaime, Marcelo

    2010-10-01

    A new calorimeter for measurements of the heat capacity and magnetocaloric effect of small samples in pulsed magnetic fields is discussed for the exploration of thermal and thermodynamic properties at temperatures down to 2 K. We tested the method up to μ(0)H=50 T, but it could be extended to higher fields. For these measurements we used carefully calibrated bare-chip Cernox(®) and RuO(2) thermometers, and we present a comparison of their performances. The monotonic temperature and magnetic field dependences of the magnetoresistance of RuO(2) allow thermometry with a precision as good as ±4 mK at T=2 K. To test the performance of our calorimeter, heat capacity and magnetocaloric effect for the spin-dimer compound Sr(3)Cr(2)O(8) and the triangular lattice antiferromagnet RbFe(MoO(4))(2) are presented.

  4. Monte Carlo simulation study of magnetocaloric effect in NdMnO3 perovskite

    Science.gov (United States)

    Masrour, R.; Jabar, A.; Benyoussef, A.; Hamedoun, M.; Hlil, E. K.

    2016-03-01

    The magnetocaloric effect in NdMnO3 perovskite is investigated by using the Monte Carlo simulations. The Curie temperature TC of NdMnO3 compound is deduced from the variation of the magnetization vs. the temperature with different values of external magnetic field. The variation of magnetization with the external magnetic field H is given. The specific heat with the temperature is established for different external magnetic field. The thermal magnetic entropy for different external magnetic field and different exchange interactions in NdMnO3 compound is obtained. The adiabatic temperature change is obtained. The relative cooling power with different external magnetic field is established. The magnetocaloric effect has been investigated from magnetization.

  5. The magnetocaloric effect at the first-order magneto-elastic phase transition.

    Science.gov (United States)

    Basso, Vittorio

    2011-06-08

    This paper presents a study of the magnetocaloric effect at the first-order magneto-elastic phase transition. The entropy change Δs at the transition temperature is given by the sum of the magnetic and the structural contributions. By using a thermodynamic model, it is shown that the sign and amplitude of the structural contribution to Δs are determined by the dimensionless parameter ζ (zeta) which depends on β, the steepness of the change of exchange forces with volume, and on α(p), the thermal expansion coefficient of the structural lattice. For ζ magnetocaloric effect. For 0 1 the structural entropy dominates and a transition occurs upon heating from a low temperature paramagnet to a high temperature ferromagnet.

  6. Magnetic properties and magnetocaloric effects of Mn5Ge3-xGax

    Institute of Scientific and Technical Information of China (English)

    Liu Xi-Bin; Zhang Shao-Ying; Shen Bao-Gen

    2004-01-01

    We report on the magnetic properties and magnetocaloric effects of Mn5Ge3-xGax compounds with x=0.1, 0.2,0.3, 0.4, 0.6 and 0.9. All samples crystallize in the hexagonal Mn5Si3-type structure with space group P63/mcm and order ferromagnetically. The Curie temperature of these compounds decreases with increasing x, from 306K (x=0.1) to 274K (x=0.9). The average Mn magnetic moments increases with increasing Ga content, reaching a maximum value at x=0.6. The magnetic entropy changes in these compounds are determined from the temperature and field dependence of the magnetization using the thermodynamic Maxwell relation. The Ga substitution has two kinds of influence on the magnetocaloric effect (MCE) of Mn5Ge3. One is that the magnitude of the magnetic entropy change decreases, the other is that the MCE peak becomes broadened.

  7. The magnetocaloric effect in Er2Fe17 near the magnetic phase transition.

    Science.gov (United States)

    Alvarez-Alonso, Pablo; Gorria, Pedro; Sánchez Marcos, Jorge; Sánchez Llamazares, José L; Blanco, Jesús A

    2013-12-11

    Recent investigations in R2Fe17 intermetallic compounds have evidenced that these materials present a moderate magnetocaloric effect (MCE) near room temperature. A series of accurate magnetization measurements was carried out to show that the value of the demagnetizing factor has a significant influence on the absolute MCE value of Er2Fe17. In addition, the critical exponents determined from heat capacity and magnetization measurements allow us to describe the field dependence of the observed MCE around the Curie temperature.

  8. Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

    Energy Technology Data Exchange (ETDEWEB)

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2016-01-18

    Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (-8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

  9. The influence of magnetocrystalline anisotropy on the magnetocaloric effect: A case study on Co 2 B

    Science.gov (United States)

    Fries, M.; Skokov, K. P.; Karpenkov, D. Yu.; Franco, V.; Ener, S.; Gutfleisch, O.

    2016-12-01

    The influence of magnetocrystalline anisotropy on the magnetocaloric effect (MCE) was studied on single crystals of Co2B and compared to measurements on polycrystalline samples. Large differences in adiabatic temperature change Δ T a d and magnetic entropy change Δ S M were found along the different crystallographic directions. The magnetocaloric effect differs by 40% in the case of Δ T a d in a field change of 1.9 T when applying the field along the hard axis and easy plane of magnetization. In the case of Δ S M , the values differ 50% and 35% from each other in field changes of 1 and 1.9 T, respectively. It was found that this anisotropy effect does not saturate in fields up to 4 T, which is higher than the anisotropy field of Co2B ( ≈2 T). A simple model was developed to illustrate the possible effect on magnetocrystalline anisotropy, showing large differences especially in application relevant fields of about 1 T. The results strongly suggest that the MCE could be maximized when orienting single crystalline powders in an easy axis parallel to the applied field in active magnetocaloric regenerator structures, and therefore the overall device efficiency could be increased.

  10. Effective medium theory for anisotropic metamaterials

    KAUST Repository

    Zhang, Xiujuan

    2015-01-20

    Materials with anisotropic material parameters can be utilized to fabricate many fascinating devices, such as hyperlenses, metasolids, and one-way waveguides. In this study, we analyze the effects of geometric anisotropy on a two-dimensional metamaterial composed of a rectangular array of elliptic cylinders and derive an effective medium theory for such a metamaterial. We find that it is possible to obtain a closed-form analytical solution for the anisotropic effective medium parameters, provided the aspect ratio of the lattice and the eccentricity of the elliptic cylinder satisfy certain conditions. The derived effective medium theory not only recovers the well-known Maxwell-Garnett results in the quasi-static regime, but is also valid beyond the long-wavelength limit, where the wavelength in the host medium is comparable to the size of the lattice so that previous anisotropic effective medium theories fail. Such an advance greatly broadens the applicable realm of the effective medium theory and introduces many possibilities in the design of structures with desired anisotropic material characteristics. A real sample of a recently theoretically proposed anisotropic medium, with a near-zero index to control the flux, is achieved using the derived effective medium theory, and control of the electromagnetic waves in the sample is clearly demonstrated.

  11. Magnetocaloric effect in Sr2FeMoO6/Ag composites

    Directory of Open Access Journals (Sweden)

    Mahmoud A. Hamad

    2015-03-01

    Full Text Available The enhanced low-field magnetocaloric effect was investigated for double perovskite Sr2FeMoO6 - silver (SFMO/Ag composites with 0, 5 and 10 wt.% of Ag. A phenomenological model was used to predict magnetocaloric properties of SFMO/Ag composites, such as magnetic entropy change, heat capacity change and relative cooling power. It was shown that magnetic entropy change (∆S M peaks of SFMO/Ag span over a wide temperature region, which can significantly improve the global efficiency of the magnetic refrigeration. Furthermore, the ∆S M distribution of the SFMO/Ag composites is much more uniform than that of gadolinium. Through these results, SFMO/Ag composite has some potential application for magnetic refrigerants in an extended high-temperature range.

  12. Metamagnetism-enhanced magnetocaloric effect in the rare earth intermetallic compound Ho5Ge4

    Science.gov (United States)

    Nirmala, R.; Morozkin, A. V.; Rajivgandhi, R.; Nigam, A. K.; Quezado, S.; Malik, S. K.

    2016-11-01

    Magnetic and magnetocaloric properties of polycrystalline Ho5Ge4 (orthorhombic, Sm5Ge4-type, Space group Pnma, No. 62, oP36) compound have been studied. This compound orders antiferromagnetically at ~24 K (TN). From the magnetization vs field isotherms obtained close to the magnetic transition temperature, magnetocaloric effect (MCE) has been estimated. The isothermal magnetic entropy change (ΔSM) reaches a maximum value of ~-27 J/kg-K at ~30 K for a field change of 140 kOe. A metamagnetic transition is observed in the field dependent magnetization data at temperatures below 20 K, for critical fields above 20 kOe, giving rise to a ferromagnetic order and hence a large MCE. The magnetic moment value at 2.5 K is ~8μB/Ho3+ in 90 kOe field.

  13. Normal and inverse magnetocaloric effect in magnetic multilayers with antiferromagnetic interlayer coupling.

    Science.gov (United States)

    Szałowski, Karol; Balcerzak, Tadeusz

    2014-09-24

    The thermodynamics of a spin-1/2 magnetic multilayer system with antiferromagnetic interplanar couplings is studied using the pair approximation method. Special attention is paid to magnetocaloric properties, quantified by isothermal entropy change. The multilayer consists of two kinds of magnetic planes, one of which is diluted. The intraplanar couplings in both planes have arbitrary anisotropy ranging between Ising and isotropic Heisenberg interactions. The phase diagram related to the occurrence of magnetic compensation phenomenon is constructed and discussed. Then the isothermal entropy change is discussed as a function of interaction parameters, magnetic component concentration and external magnetic field amplitude. The ranges of normal and inverse magnetocaloric effect are found and related to the presence or absence of compensation.

  14. Non-contact direct measurement of the magnetocaloric effect in thin samples.

    Science.gov (United States)

    Cugini, F; Porcari, G; Solzi, M

    2014-07-01

    An experimental setup, based on a non-contact temperature sensor, is proposed to directly measure the magnetocaloric effect of samples few micrometers thick. The measurement of the adiabatic temperature change of foils and ribbons is fundamental to design innovative devices based on magnetocaloric thin materials or micro-structuring bulk samples. The reliability of the proposed setup is demonstrated by comparing the measurements performed on a bulk gadolinium sample with the results obtained by an experimental setup based on a Cernox bare chip thermoresistance and by in-field differential scanning calorimetry. We show that this technique can measure the adiabatic temperature variation on gadolinium sheets as thin as 27 μm. Heat transfer simulations are added to describe the capability of the presented technique.

  15. Non-contact direct measurement of the magnetocaloric effect in thin samples

    Energy Technology Data Exchange (ETDEWEB)

    Cugini, F., E-mail: francesco.cugini1@difest.unipr.it; Porcari, G.; Solzi, M. [Department of Physics and Earth Sciences, University of Parma, Parco Area delle Scienze 7/A, 43124 Parma (Italy)

    2014-07-15

    An experimental setup, based on a non-contact temperature sensor, is proposed to directly measure the magnetocaloric effect of samples few micrometers thick. The measurement of the adiabatic temperature change of foils and ribbons is fundamental to design innovative devices based on magnetocaloric thin materials or micro-structuring bulk samples. The reliability of the proposed setup is demonstrated by comparing the measurements performed on a bulk gadolinium sample with the results obtained by an experimental setup based on a Cernox bare chip thermoresistance and by in-field differential scanning calorimetry. We show that this technique can measure the adiabatic temperature variation on gadolinium sheets as thin as 27 μm. Heat transfer simulations are added to describe the capability of the presented technique.

  16. Influence of the transition width on the magnetocaloric effect across the magnetostructural transition of Heusler alloys.

    Science.gov (United States)

    Cugini, F; Porcari, G; Fabbrici, S; Albertini, F; Solzi, M

    2016-08-13

    We report a complete structural and magneto-thermodynamic characterization of four samples of the Heusler alloy Ni-Co-Mn-Ga-In, characterized by similar compositions, critical temperatures and high inverse magnetocaloric effect across their metamagnetic transformation, but different transition widths. The object of this study is precisely the sharpness of the martensitic transformation, which plays a key role in the effective use of materials and which has its origin in both intrinsic and extrinsic effects. The influence of the transition width on the magnetocaloric properties has been evaluated by exploiting a phenomenological model of the transformation built through geometrical considerations on the entropy versus temperature curves. A clear result is that a large temperature span of the transformation is unfavourable to the magnetocaloric performance of a material, reducing both isothermal entropy change and adiabatic temperature change obtainable in a given magnetic field and increasing the value of the maximum field needed to fully induce the transformation. The model, which is based on standard magnetometric and conventional calorimetric measurements, turns out to be a convenient tool for the determination of the optimum values of transformation temperature span in a trade-off between sheer performance and amplitude of the operating range of a material.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

  17. Research Advance on Magnetocaloric Effect of La-Fe-M(Al, Si) Compounds

    Institute of Scientific and Technical Information of China (English)

    肖素芬; 陈云贵; 郝春; 吴金平; 涂铭旌

    2004-01-01

    Recent research progress on magnetocaloric effect of La-Fe-M(M=Al,Si)compounds was presented.La-Fe-M(M=Al,Si)compounds of high Fe content are excellent soft magnetic materials with NaZn13 structure.The Curie temperature of the compounds can be increased by substituting small amount of Co for Si,Al.The La(Fe1-yCoy)xSi13-x compounds with an appropriate ratio of Co and Si can produce giant magnetocaloric effect comparable to that for Gd5Si2Ge2 at room temperature.The La(FexSi1-x)13 doped with H can also produce giant magnetocaloric effect at room temperature,which is much greater than that for Gd.For La(FexSi1-x)13 compounds with low Si or high Si contents.The nature of phase transition near Curie temperature induced by temperature and magnetic field was described in detail.

  18. Inverse magnetocaloric effect in Ce(Fe0.96Ru0.04)2: Effect of fast neutron irradiation

    Science.gov (United States)

    Dube, V.; Mishra, P. K.; Rajarajan, A. K.; Prajapat, C. L.; Sastry, P. U.; Thakare, S. V.; Singh, M. R.; Ravikumar, G.

    2013-02-01

    We have shown the effect of fast neutron irradiation on the magnetic phase transition and magnetocaloric effect (MCE) in a doped Ce(Fe0.96Ru0.04)2, intermettalic. We show that this leads to suppression of MCE and a to a disordered ferromagnetic phase.

  19. Tuning structural instability toward enhanced magnetocaloric effect around room temperature in MnCo1−xZnxGe

    Science.gov (United States)

    Choudhury, D.; Suzuki, T.; Tokura, Y.; Taguchi, Y.

    2014-01-01

    Magnetocaloric effect is the phenomenon that temperature change of a magnetic material is induced by application of a magnetic field. This effect can be applied to environmentally-benign magnetic refrigeration technology. Here we show a key role of magnetic-field-induced structural instability in enhancing the magnetocaloric effect for MnCo1−xZnxGe alloys (x = 0–0.05). The increase in x rapidly reduces the martensitic transition temperature while keeping the ferromagnetic transition around room temperature. Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition. Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics. PMID:25519919

  20. Tuning structural instability toward enhanced magnetocaloric effect around room temperature in MnCo(1-x)Zn(x)Ge.

    Science.gov (United States)

    Choudhury, D; Suzuki, T; Tokura, Y; Taguchi, Y

    2014-12-18

    Magnetocaloric effect is the phenomenon that temperature change of a magnetic material is induced by application of a magnetic field. This effect can be applied to environmentally-benign magnetic refrigeration technology. Here we show a key role of magnetic-field-induced structural instability in enhancing the magnetocaloric effect for MnCo(1-x)Zn(x)Ge alloys (x = 0-0.05). The increase in x rapidly reduces the martensitic transition temperature while keeping the ferromagnetic transition around room temperature. Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition. Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics.

  1. The metamagnetic behavior and giant inverse magnetocaloric effect in Ni–Co–Mn–(Ga, In, Sn) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Entel, Peter [Faculty of Physics and CENIDE, University of Duisburg-Essen, 47048 Duisburg (Germany); Sokolovskiy, Vladimir V. [Condensed Matter Physics Department, Chelyabinsk State University, 454001 Chelyabinsk (Russian Federation); Buchelnikov, Vasiliy D., E-mail: buche@csu.ru [Condensed Matter Physics Department, Chelyabinsk State University, 454001 Chelyabinsk (Russian Federation); Ogura, Masako [Department of Physics, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043 (Japan); Gruner, Markus E.; Grünebohm, Anna; Comtesse, Denis [Faculty of Physics and CENIDE, University of Duisburg-Essen, 47048 Duisburg (Germany); Akai, Hisazumi [The Institute for Solid State Physics, Center of Computational Materials Science, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8581 (Japan)

    2015-07-01

    The magnetic and magnetocaloric properties of Ni–Co–Mn–(Ga, In, Sn) Heusler intermetallics are discussed on the basis of ab initio and Monte Carlo calculations. The main emphasis is on the different reference spin states and magnetic exchange coupling constants of high-temperature austenite and low-temperature martensite which are very important for the calculation of magnetocaloric effect. The origin of metamagnetic behavior is considered in the framework of orbital resolved magnetic exchange parameters of austenite and martensite. The decomposition of exchange constants on orbital contributions has shown that a strong ferromagnetic interaction of magnetic moments in austenite is caused by the more itinerant d-electrons with t{sub 2g} states while a strong antiferromagnetic interaction in martensite is associated with the more localized e{sub g} states. In addition, the appearance of a paramagnetic gap between magnetically weak martensite and ferromagnetically ordered austenite can be realized because of strong competition of magnetic exchange interactions. As a result, large magnetization drop and giant inverse magnetocaloric effect can be achieved across the magnetostructural phase transition. - Highlights: • The magnetic and magnetocaloric properties of Ni–Co–Mn–(Ga, In, Sn) alloys are discussed. • The metamagnetic behavior results in a jump of magnetization. • The reason of metamagnetism is the antiferromagnetic interaction between Mn atoms. • The size of magnetocaloric effect is determined by the magnetic exchange parameters.

  2. High-resolution alternating-field technique to determine the magnetocaloric effect of metals down to very low temperatures.

    Science.gov (United States)

    Tokiwa, Y; Gegenwart, P

    2011-01-01

    The magnetocaloric effect or "magnetic Grüneisen ratio" Γ(H)=T(-1)(dT/dH)(S) quantifies the cooling or heating of a material when an applied magnetic field is changed under adiabatic conditions. Recently, this property has attracted considerable interest in the field of quantum criticality. Here, we report the development of a low-frequency alternating-field technique for measurements of the magnetocaloric effect down to very low temperatures, which is an important property for the study of quantum critical points. We focus, in particular, on highly conducting metallic samples and discuss the influence of eddy current heating. By comparison with magnetization and specific heat measurements, we demonstrate that our fast and accurate technique gives quantitatively correct values for the magnetocaloric effect under truly adiabatic conditions.

  3. Variations of magnetocaloric effect and magnetoresistance across RCuGe (R=Tb, Dy, Ho, Er) compounds

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Sachin; Suresh, K.G., E-mail: suresh@phy.iitb.ac.in

    2015-10-01

    RCuGe (R=Tb–Er) compounds have been studied by structural, magnetic, magnetocaloric and magnetotransport measurements. All these compounds are iso-structural and show antiferromagnetic ordering below their Néel temperatures (T{sub N}). Except TbCuGe, all the studied compounds show large magnetocaloric effect (MCE), arising due to the field induced metamagnetic transition. They also show a sign reversal of magnetoresistance (MR) with change in temperature or field. The non-monotonic variation of the magnitude of MR is attributed to the competing effects of Lorentz force, changes in the spin disorder scattering and the spin fluctuations. - Highlights: • RCuGe (R=Tb–Er) compounds show low temperature antiferromagnetic ordering. • All compounds show field induced metamagnetic transitions. • These compounds show large magnetocaloric effect and magnetoresistance.

  4. The influence of hysteresis on the determination of the magnetocaloric effect in Gd5Si2Ge2

    DEFF Research Database (Denmark)

    von Moos, Lars; Bahl, Christian; Nielsen, Kaspar Kirstein

    2015-01-01

    We present a non-equilibrium Preisach-type hysteresis model based on the first order magnetocaloric material Gd5Si2Ge2. The model is developed from isofield magnetization measurements and first order reversal curves, both of which constitute a new and detailed approach to characterizing and model......We present a non-equilibrium Preisach-type hysteresis model based on the first order magnetocaloric material Gd5Si2Ge2. The model is developed from isofield magnetization measurements and first order reversal curves, both of which constitute a new and detailed approach to characterizing...... continuous magnetization cycles, which effectively limits the adiabatic temperature change by the amount of thermal hysteresis present. We suggest a straightforward method for realistic estimation of the magnetocaloric effect from indirect measurements....

  5. Applications of the Magnetocaloric Effect in Single-Stage, Multi-Stage and Continuous Adiabatic Demagnetization Refrigerators

    Science.gov (United States)

    Shirron, Peter J.

    2014-01-01

    Adiabatic demagnetization refrigerators (ADR), based on the magnetocaloric effect, are solid-state coolers that were the first to achieve cooling well into the sub-kelvin regime. Although supplanted by more powerful dilution refrigerators in the 1960s, ADRs have experienced a revival due to the needs of the space community for cooling astronomical instruments and detectors to temperatures below 100 mK. The earliest of these were single-stage refrigerators using superfluid helium as a heat sink. Their modest cooling power (magnetocaloric effect and its application in single-stage systems, and then describing the challenges and capabilities of multi-stage and continuous ADRs.

  6. Magnetocaloric effect in the spin-1/2 Ising-Heisenberg diamond chain with the four-spin interaction

    Directory of Open Access Journals (Sweden)

    L. Gálisová

    2014-03-01

    Full Text Available The magnetocaloric effect in the symmetric spin-1/2 Ising–Heisenberg diamond chain with the Ising four-spin interaction is investigated using the generalized decoration-iteration mapping transformation and the transfer-matrix technique. The entropy and the Grüneisen parameter, which closely relate to the magnetocaloric effect, are exactly calculated to compare an ability of the system to cool in the vicinity of different field-induced ground-state phase transitions during the adiabatic demagnetization.

  7. Quantification of the effect of hysteresis on the adiabatic temperature change in magnetocaloric materials

    DEFF Research Database (Denmark)

    von Moos, Lars; Bahl, Christian R.H.; Nielsen, Kaspar Kirstein

    2014-01-01

    We quantify the effect of hysteresis on the performance of the magnetocaloric first order material Gd5Si2Ge2 undergoing an ideal active magnetic regenerator (AMR) cycle. The material is carefully characterized through magnetometry (VSM) and calorimetry (DSC) in order to enable an accurate model...... description of the phase transition at varying magnetic fields and temperatures. Using detailed experimental property data, a Preisach type model is used to describe the thermal hysteresis effects and simulate the material under realistic working conditions. We find that the adiabatic temperature change...... is limited by a significant fraction of the thermal hysteresis....

  8. Hydrostatic pressure effect on magnetic phase transition and magnetocaloric effect of metamagnetic TmZn compound

    Science.gov (United States)

    Li, Lingwei; Hu, Guanghui; Qi, Yang; Umehara, Izuru

    2017-02-01

    The magnetocaloric effect (MCE) is an intrinsic thermal response of all magnetic solids which has a direct and strong correlation with the corresponding magnetic phase transition. It has been well recognized that the magnetic phase transition can be tuned by adjusting applied pressure. Therefore, we perform the high hydrostatic pressure magnetization measurements (up to 1.4 GPa) on a recently reported giant MCE material of TmZn. The results indicate that the Curie temperature of TC increases from 8.4 K at the ambient pressure to 11.5 K under the pressure of 1.4 GPa. The field-induced first order metamagnetic transition is getting weak with increasing pressure, which results in a reduction of MCE. The hydrostatic pressure effect on the magnetic phase transition and MCE in the metamagnetic TmZn is discussed.

  9. Magnetic properties and magnetocaloric effect in Tb{sub 3}Al{sub 2} compound

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hu, E-mail: zhanghu@ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology of Beijing, Beijing 100083 (China); Yang, Li Hong [Department of Physics, University of Science and Technology of Beijing, Beijing 100083 (China); State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Jing Yang; Wang, Zhe [School of Materials Science and Engineering, University of Science and Technology of Beijing, Beijing 100083 (China); Niu, E. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Beijing Zhong ke San Huan Research, No. 10 Chuangxin Rd., Changping District, Beijing 102200 (China); Liu, Rong Ming; Li, Zhu Bai; Hu, Feng Xia; Sun, Ji Rong; Shen, Bao Gen [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2014-12-05

    Highlights: • Domain-wall-freezing effect may occur at low temperature due to magnetocrystalline anisotropy. • The ΔT{sub ad} for Tb{sub 3}Al{sub 2} is 9.0 K under 50 kOe, comparable to that of La(Fe{sub 0.88}Si{sub 0.12}){sub 13} compound. • The full width at half-maximum value of ΔT{sub ad} peak is much larger than that for La(Fe{sub 0.88}Si{sub 0.12}){sub 13}. - Abstract: Magnetic properties of intermetallic Tb{sub 3}Al{sub 2} compound have been investigated systematically by magnetization and heat capacity measurements. Tb{sub 3}Al{sub 2} compound undergoes a ferromagnetic–paramagnetic transition at Curie temperature T{sub C} = 190 K. Besides, another transition is observed around 86 K, which probably corresponds to a spin reorientation transition. In addition, a strong domain-wall-freezing effect may occur in low temperature range due to the high magnetocrystalline anisotropy, and thus resulting in the large intrinsic coercivity. Tb{sub 3}Al{sub 2} compound shows large magnetocaloric effect without hysteresis loss around T{sub C}, which is comparable to or even higher than those of some magnetocaloric materials in same temperature range. Furthermore, the full width at half-maximum value of adiabatic temperature change ΔT{sub ad} peak for Tb{sub 3}Al{sub 2} at 50 kOe is 55 K, more than three times of that (17 K) for typical magnetocaloric material La(Fe{sub 0.88}Si{sub 0.12}){sub 13}.

  10. Rate dependence of the magnetocaloric effect in La-Fe-Si compounds

    Directory of Open Access Journals (Sweden)

    Sasso C.P.

    2013-01-01

    Full Text Available The dynamic magnetocaloric effect in La(FexCoySi1-x-y13 with x=0.9 and low Co content of y=0.015 was analysed by calorimetric measurements at constant magnetic field and constant temperature as well as magnetisation relaxation measurements. It is shown that the rate dependence of the measurement, which leads to an increased entropy hysteresis with increasing rate of the driving force (temperature or magnetic field, can be mainly attributed to a thermal contact resistance R between sample and thermal bath of the measurement setup.

  11. Excellent Magnetocaloric Effect in Er6oAl18Co22 Bulk Metallic Glass

    Institute of Scientific and Technical Information of China (English)

    HUI Xi-Dong; XU Zhi-Yi; WANG En-Rui; CHEN Guo-Liang; LU Zhao-Ping

    2010-01-01

    @@ Excellent magnetocaloric effect with a maximum entropy change and refrigeration capacity of 17.6 J.kg-1.K-1 and 546 J.kg-1,respectively,has been discovered in the Er60Al18 Co22 bulk metallic glass under the fleld of 50 kOe in the temperature range of helium liquefaction.This MCE results from the second-order magnetic transition from the paramagnetic to the ferromagnetic state.Our analysis based on mean-field theory suggests that the excellent MCE is attributed to the strong exchange of magnetic moment in the glassy structure.

  12. Magnetic phase transitions and magnetocaloric effect in the Fe-doped MnNiGe alloys

    Institute of Scientific and Technical Information of China (English)

    Zhang Cheng-Liang; Wang Dun-Hui; Chen Jian; Wang Ting-Zhi; Xie Guang-Xi; Zhu Chun

    2011-01-01

    The magnetic phase transition and magnetocaloric effects in Fe-doped MnNiGe alloys are investigated. The substitution of Fe for Ni decreases the structural transition temperature remarkably,resulting in the magnetostructural transition occurring between antiferromagnetic and ferromagnetic states in MnNil-xFex Ge alloy. Owing to the enhanced ferromagnetic coupling induced by the substitution of Fe,metamagnetic behaviour is also observed in TiNiSi-type phase of MnNil_yFe.Ge alloys at temperature below the structural transition temperature.

  13. AC measurement of heat capacity and magnetocaloric effect for pulsed magnetic fields

    OpenAIRE

    2010-01-01

    International audience; A new calorimeter for measurements of the heat capacity and magnetocaloric effect of small samples in pulsed magnetic fields is discussed for the exploration of thermal and thermodynamic properties at temperatures down to 2 K. We tested the method up to 0H=50 T, but it could be extended to higher fields. For these measurements we used carefully calibrated bare-chip Cernox® and RuO2 thermometers, and we present a comparison of their performances. The monotonic temperatu...

  14. Magnetocaloric effect and refrigeration cooling power in amorphous Gd7Ru3 alloys

    Science.gov (United States)

    Kumar, Pramod; Kumar, Rachana

    2015-07-01

    In this paper, we report the magnetic, heat capacity and magneto-caloric effect (MCE) of amorphous Gd7Ru3 compound. Both, temperature dependent magnetization and heat capacity data reveals that two transitions at 58 K and 34 K. MCE has been calculated in terms of isothermal entropy change (ΔSM) and adiabatic temperature change (ΔTad) using the heat capacity data in different fields. The maximum values of ΔSM and ΔTad are 21 Jmol-1K-1 and 5 K respectively, for field change of 50 kOe whereas relative cooling power (RCP) is ˜735 J/kg for the same field change.

  15. Magnetocaloric effect and slow magnetic relaxation in two only azido bridged ferromagnetic tetranuclear metal clusters.

    Science.gov (United States)

    Zhao, Jiong-Peng; Zhao, Ran; Yang, Qian; Hu, Bo-Wen; Liu, Fu-Chen; Bu, Xian-He

    2013-10-28

    Two M(II) tetranuclear complexes bridged only by azido, Mn4(N3)(7.3)Cl(0.7)L4 (1) and Co4(N3)8L4 (2) in which the four M(II) ions are precisely coplanar bridged only by six azido anions, were obtained by using 4,5-diazafluoren-9-one (L) as a corner ligand. Magnetic studies indicate that ferromagnetic coupling was conducted by the azido anions between M(II) ions. At low temperature, 1 exhibits a large magnetocaloric effect and 2 shows field-induced multiple magnetic relaxations.

  16. Magnetocaloric effect in Gd-based ferromagnet GdZn2

    Science.gov (United States)

    Matsumoto, Keisuke T.; Hiraoka, Koichi

    2017-02-01

    Magnetic properties and magnetocaloric effect of the Gd-based compound GdZn2 have been investigated. GdZn2 shows a ferromagnetic transition at TC = 85 K and spin-reorientation transition at TSR = 58 K. The maximum entropy change and relative cooling power (RCP) are estimated to be 11.5 J/K kg and 690 J/kg, respectively, for a magnetic field change of 7 T. The large value of RCP is suggested that GdZn2 is an attractive candidate for a low-temperature magnetic refrigerant.

  17. Magnetic properties and magnetocaloric effect in TbCo2-xFex compounds

    Institute of Scientific and Technical Information of China (English)

    Zou Jun-Ding; Shen Bao-Gen; Sun Ji-Rong

    2007-01-01

    Magnetic properties and magnetocaloric effect in TbCo2-xFex compounds are studied by DC magnetic measurement. With increasing content of Fe, the entropy changes decrease slightly, though the Curie temperature is tuned from 231 K (x = 0) to 303 K (x = 0.1). Magnetic entropies of TbCo2 compound are calculated by using mean field approximation (MFA). Results estimated by using Maxwell relation are consistent with that of MFA calculation. It si shown that the entropy changes are mainly derived from the magnetic entropy change. The lattice has almost no contribution to the entropy change in the vicinity of phase transition.

  18. Normal and inverse magnetocaloric effects in LaCaMnNiO

    Science.gov (United States)

    Krishnamoorthi, C.; Barik, S. K.; Siu, Z.; Mahendiran, R.

    2010-09-01

    We have investigated magnetic and magnetocaloric properties of La 0.5Ca 0.5Mn 1- xNi xO 3 ( x=0, 0.02, 0.04, 0.06, & 0.08). It is shown that charge-ordered antiferromagnetic ground state of x=0 is destabilized and ferromagnetism is induced by just 2% Ni substitution. The ferromagnetic Curie temperature (TC) decreases from TC=220 K for x=0 to 85 K (x=0.08). Unusual field-induced metamagnetic transition is found above TC for x=0.02-0.06 and even below TC in the parent compound (x=0). Magnetic entropy change (ΔSm) was estimated from isothermal magnetization data and it is found that the parent compound (x=0) exhibits both normal (negative ΔSm) and inverse (positive ΔSm) magnetocaloric effects at TC and TN (Neel temperature), respectively. The ΔSm=+6.5 J kg K at TN is twice larger than that at TC(ΔSm=-3 JkgK) for a field change (ΔH) of 5 T. However, all the Ni doped samples in La 0.5Ca 0.5Mn 1- xNi xO 3 system show only normal magnetocaloric effect at TC. The largest MCE in the Ni doped series occurs for x=0.04 (ΔSm=-3.9 JkgK,ΔH=5 T) which also has the largest relative cooling power (RCP=235 J/kg,ΔH=5 T) in the series. We discuss our results in the scenario of phase separation induced by Ni substitution.

  19. Magnetic properties and magnetocaloric effect in Ni–Mn–Sn alloys

    Energy Technology Data Exchange (ETDEWEB)

    Dan, N.H., E-mail: dannh@ims.vast.ac.vn [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Duc, N.H.; Yen, N.H.; Thanh, P.T. [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Bau, L.V.; An, N.M. [Hong Duc University, 565 Quang Trung, Dong Ve, Thanh Hoa (Viet Nam); Anh, D.T.K.; Bang, N.A.; Mai, N.T. [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Hanoi (Viet Nam); Anh, P.K. [Vietnam Academy of Military Science, 322 Le Trong Tan, Thanh Xuan, Hanoi (Viet Nam); Thanh, T.D. [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Phan, T.L. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Yu, S.C., E-mail: scyu@chungbuk.ac.kr [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of)

    2015-01-15

    Magnetic and magnetocaloric properties in Ni{sub 50}Mn{sub 50−x}Sn{sub x} alloys with wide range of the Sn-concentration (x=0–40) were investigated. The alloys were prepared by arc-melting and subsequently annealing at 850 °C for 4 h. The X-ray diffraction analyses manifest the formation of the crystalline phases (Ni{sub 2}MnSn, NiMn, Ni{sub 3}Sn{sub 2}, Mn{sub 3}Sn, and MnSn{sub 2}) in the alloys with various compositions and fabrication conditions. With increasing x, the saturation magnetization first increases from near zero (at x=10) to above 40 emu/g (at x=20) and then decreases to below 10 emu/g (at x=40) for both the as-melted and annealed cases. The martensitic–austenitic transition was observed in the alloys with a narrow range of x (13–15). The magnetic transitions in the alloy can be controlled by changing Sn-concentration. The alloy reveals both the positive and negative entropy changes with quite large magnitude (∆S{sub m}>1 J/kg K with ∆H=12 kOe) with appropriate compositions and annealing conditions. - Highlights: • Crystalline phases and magnetic properties in Ni{sub 50}Mn{sub 50−x}Sn{sub x} alloys (x=0–40). • Simultaneous transitions of structural and magnetic phases. • Coexistence of positive and negative giant magnetocaloric effect in Heusler alloys. • Tuning giant magnetocaloric effect in room temperature region.

  20. Electromagnetic effects on cracking of anisotropic polytropes

    Energy Technology Data Exchange (ETDEWEB)

    Sharif, Muhammad; Sadiq, Sobia [University of the Punjab, Department of Mathematics, Lahore (Pakistan)

    2016-10-15

    In this paper, we study the electromagnetic effects on the stability of a spherically symmetric anisotropic fluid distribution satisfying two polytropic equations of state and construct the corresponding generalized Tolman-Oppenheimer-Volkoff equations. We apply perturbations on matter variables via the polytropic constant as well as the polytropic index and formulate the force distribution function. It is found that the compact object is stable for a feasible choice of perturbed polytropic index in the presence of charge. (orig.)

  1. Effect of inflation on anisotropic cosmologies

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, L.G.; Stein-Schabes, J.A.

    1986-03-01

    The effects of anisotropic cosmologies on inflation are studied. By properly formulating the field equations it is possible to show that any model that undergoes sufficient inflation will become isotropic on scales greater than the horizon today. Furthermore, we shall show that it takes a very long time for anisotropies to become visible in the observable part of the Universe. It is interesting to note that the time scale will be independent of the Bianchi Model and of the initial anisotropy. 6 refs.

  2. Electromagnetic Effects on Cracking of Anisotropic Polytropes

    CERN Document Server

    Sharif, M

    2016-01-01

    In this paper, we study the electromagnetic effects on stability of spherically symmetric anisotropic fluid distribution satisfying two polytropic equations of state and construct the corresponding generalized Tolman Oppenheimer Volkoff equations. We apply perturbations on matter variables via polytropic constant as well as polytropic index and formulate the force distribution function. It is found that the compact object is stable for feasible choice of perturbed polytropic index in the presence of charge.

  3. Effect of inflation on anisotropic cosmologies

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, L.G.; Stein-Schabes, J.A.

    1986-08-15

    We study the effects of anisotropic cosmologies on inflation. By properly formulating the field equations it is possible to show that any model that undergoes sufficient inflation will become isotropic on scales greater than the horizon today. Furthermore, we shall show that it takes a very long time for anisotropies to become visible in the observable part of the Universe. It is interesting to note that the time scale will be independent of the Bianchi model and of the initial anisotropy.

  4. Giant and reversible extrinsic magnetocaloric effects in La0.7Ca0.3MnO3 films due to strain.

    Science.gov (United States)

    Moya, X; Hueso, L E; Maccherozzi, F; Tovstolytkin, A I; Podyalovskii, D I; Ducati, C; Phillips, L C; Ghidini, M; Hovorka, O; Berger, A; Vickers, M E; Defay, E; Dhesi, S S; Mathur, N D

    2013-01-01

    Large thermal changes driven by a magnetic field have been proposed for environmentally friendly energy-efficient refrigeration, but only a few materials that suffer hysteresis show these giant magnetocaloric effects. Here we create giant and reversible extrinsic magnetocaloric effects in epitaxial films of the ferromagnetic manganite La(0.7)Ca(0.3)MnO(3) using strain-mediated feedback from BaTiO(3) substrates near a first-order structural phase transition. Our findings should inspire the discovery of giant magnetocaloric effects in a wide range of magnetic materials, and the parallel development of nanostructured bulk samples for practical applications.

  5. Magnetocaloric effect in magnetothermally-responsive nanocarriers for hyperthermia-triggered drug release.

    Science.gov (United States)

    Li, Jianbo; Qu, Yang; Ren, Jie; Yuan, Weizhong; Shi, Donglu

    2012-12-21

    The magnetocaloric effects and lower critical solution temperature (LCST) were investigated in a magnetothermally-responsive nanocarrier for magnetothermal drug release under alternating magnetic field (AMF). The Mn(0.2)Zn(0.8)Fe(2)O(4) nanoparticles with low T(c) were dispersed in a polymeric matrix consisting of N-Isopropyl acrylamide (NIPAAm) and N-hydroxymethyl acrylamide (HMAAm). The magnetocaloric effects and LCST of the nanocarriers were characterized by using high-resolution electron transmission microscopy, thermogravimetric analyses, and vibrating sample magnetometer. The maximum self-heating temperature of 42.9 °C was achieved by optimizing the Mn(0.2)Zn(0.8)Fe(2)O(4) concentration in the polymer matrix. By adjusting the NIPAAm to HMAAm ratio, the LCST was controlled at an ideal level of 40.1 °C for efficient thermosensitive drug delivery. Magnetothermally responsive drug release of Doxorubicin, an anticancer drug, was significantly enhanced by application of an external AMF on the nanocarriers. The cytotoxicity experimental results in vitro show good biocompatibility and efficient therapeutic effects in cancer treatment.

  6. Influence of the materials magnetic state on the accurate determination of the magnetocaloric effect

    Directory of Open Access Journals (Sweden)

    Forchelet J.

    2012-06-01

    Full Text Available In this paper, we report a detailed study of the magnetocaloric effect (MCE in different first order magnetic transition (FOMT materials with different situation of the magnetic state (magnetic order. For this purpose, R-Co2, MnAs based compounds were considered in this study. The MCE is discussed in terms of Maxwell relation (MR and Clausius-Clapeyron (C-C equation. The deviation observed between both methods is discussed and analyzed. On the other hand, practically all the reported data of the MCE in the literature are associated to the applied external magnetic field and have not been corrected taking into account the demagnetization effect related to the materials shape. The obtained results demonstrate that this phenomenon can alter drastically the MCE values by cancelling out a large part of the external field, resulting in spurious values of the measured MCE. The effect of the demagnetization field on the magnetocaloric performances is also the subject of this paper.

  7. Anomalous anisotropic magnetoresistance effects in graphene

    Directory of Open Access Journals (Sweden)

    Yiwei Liu

    2014-09-01

    Full Text Available We investigate the effect of external stimulus (temperature, magnetic field, and gases adsorptions on anisotropic magnetoresistance (AMR in multilayer graphene. The graphene sample shows superlinear magnetoresistance when magnetic field is perpendicular to the plane of graphene. A non-saturated AMR with a value of −33% is found at 10 K under a magnetic field of 7 T. It is surprisingly to observe that a two-fold symmetric AMR at high temperature is changed into a one-fold one at low temperature for a sample with an irregular shape. The anomalous AMR behaviors may be understood by considering the anisotropic scattering of carriers from two asymmetric edges and the boundaries of V+(V- electrodes which serve as active adsorption sites for gas molecules at low temperature. Our results indicate that AMR in graphene can be optimized by tuning the adsorptions, sample shape and electrode distribution in the future application.

  8. Ferromagnetic Order, Strong Magnetocrystalline Anisotropy, and Magnetocaloric Effect in the Layered Telluride Fe(3-δ)GeTe2.

    Science.gov (United States)

    Verchenko, Valeriy Yu; Tsirlin, Alexander A; Sobolev, Alexei V; Presniakov, Igor A; Shevelkov, Andrei V

    2015-09-08

    The ternary transition-metal compound Fe(3-δ)GeTe2 is formed for 0 magnetocaloric effect with the magnetic entropy change upon the ferromagnetic ordering transition, -ΔS ∼ 1.1 J·kg(-1)·K(-1) at 5 T, is found.

  9. Zero temperature non-plateau magnetization and magnetocaloric effect in an Ising-XYZ diamond chain structure

    Science.gov (United States)

    Torrico, J.; Rojas, M.; de Souza, S. M.; Rojas, Onofre

    2016-10-01

    Zero temperature non-plateau magnetization is a peculiar property of a quantum spin chain and it sometimes appears due to different gyromagnetic factors. In this study, we illustrate a quite unusual non-plateau magnetization property driven by XY-anisotropy in an Ising-XYZ diamond chain. Two particles with spin-1/2 are bonded by XYZ coupling and they are responsible for the emergence of non-plateau magnetization. These two quantum operator spins are bonded to two nodal Ising spins and this process is repeated infinitely to yield a diamond chain structure. Due to the non-plateau magnetization property, we focus our discussion on the magnetocaloric effect of this model by presenting the isentropic curves and the Grüneisen parameters, as well as showing the regions where the model exhibits an efficient magnetocaloric effect. Due to the existence of two phases located very close to each other, the strong XY-anisotropy exhibits a particular behavior with a magnetocaloric effect, with a wider interval in the magnetic field, where the magnetocaloric effect is efficient.

  10. Room temperature magnetocaloric effect in Ni-Mn-In-Cr ferromagnetic shape memory alloy thin films

    Science.gov (United States)

    Akkera, Harish Sharma; Singh, Inderdeep; Kaur, Davinder

    2017-02-01

    The influence of Cr substitution for In on the martensitic phase transformation and magnetocaloric effect (MCE) has been investigated in Ni-Mn-Cr-In ferromagnetic shape memory alloy (FSMA) thin films fabricated by magnetron sputtering. Temperature dependent magnetization (M-T) measurements demonstrated that the martensitic transformation temperatures (TM) monotonously increase with the increase of Cr content due to change in valence electron concentration (e/a) and cell volume. From the study of isothermal magnetization curves (M-H), magnetocaloric effect around the martensitic transformation has been investigated in these FSMA thin films. The magnetic entropy change ∆SM of 7.0 mJ/cm3-K was observed in Ni51.1Mn34.9In9.5Cr4.5 film at 302 K in an applied field of 2 T. Further, the refrigerant capacity (RC) was also calculated for all the films in an applied field of 2 T. These findings indicate that the Cr doped Ni-Mn-In FSMA thin films are potential candidates for room temperature micro-length-scale magnetic refrigeration applications.

  11. Universal field dependence of conventional and inverse magnetocaloric effects in DyCo2Si2

    Science.gov (United States)

    Karmakar, S. K.; Giri, S.; Majumdar, S.

    2017-01-01

    The rare-earth intermetallic compound DyCo2Si2 orders antiferromagnetically below TN = 23 K followed by a second magnetic anomaly at Tt = 9 K. The sample is known to show multiple metamagnetic transitions, which are reproduced in our present study. Our investigations on this sample indicate that the magnetocaloric effect (MCE) calculated from the magnetization data (in terms of change in entropy, ΔSM ) is quite fascinating, and it is characterized by multiple sign reversals around TN and Tt. The MCE is found to be conventional (i.e., ΔSM is negative) above TN and below Tt, while it is inverse (i.e., ΔSM is positive) between TN and Tt. We performed a comprehensive analysis of the field dependence of the observed MCE, and a universal quadratic variation is observed at temperatures above and below TN (including the region below Tt) as long as the applied field is lower than the critical field for metamagnetic transition. The present work is able to show that the field dependence of the MCE in this antiferromagnetic material is quadratic despite the fact that the magnetocaloric effect is conventional or inverse in different temperature regions.

  12. Giant magnetocaloric effect near room temperature in the off-stoichiometric Mn-Co-Ge alloy

    Science.gov (United States)

    Sharma, V. K.; Manekar, M. A.; Srivastava, Himanshu; Roy, S. B.

    2016-12-01

    We report a giant magnetocaloric effect near room temperature in an off-stoichiometric Mn-Co-Ge alloy, across the magnetostructural transition. The isothermal entropy change accompanying this transition has a peak value of nearly 40 J kg-1 K-1 near 297 K for a field excursion of 70 kOe, and a refrigerant capacity of 270 J kg-1 with the hot end at 302.5 K and cold end at 293.5 K. We also present an experimental protocol to avoid spurious peaks in the magnetocaloric effect across a sharp first order magnetostructural transition, not confined to Mn-Co-Ge alone, where metastability during the transition could influence the measured magnetization and thus the estimated entropy change. The estimated entropy change in the present off-stoichiometric Mn-Co-Ge alloy is possibly the highest reported value near room temperature in undoped Mn-Co-Ge alloys and underlines the potential of the alloy for technological applications in room temperature magnetic refrigeration.

  13. MnFe(PGe) compounds: Preparation, structural evolution, and magnetocaloric effects

    Science.gov (United States)

    Yue, Ming; Zhang, Hong-Guo; Liu, Dan-Min; Zhang, Jiu-Xing

    2015-01-01

    The interdependences of preparation conditions, magnetic and crystal structures, and magnetocaloric effects (MCE) of the MnFePGe-based compounds are reviewed. Based upon those findings, a new method for the evaluation of the MCE in these compounds, based on differential scanning calorimetry (DSC), is proposed. The MnFePGe-based compounds are a group of magnetic refrigerants with giant magnetocaloric effect (GMCE), and as such, have drawn tremendous attention, especially due to their many advantages for practical applications. Structural evolution and phase transformation in the compounds as functions of temperature, pressure, and magnetic field are reported. Influences of preparation conditions upon the homogeneity of the compounds’ chemical composition and microstructure, both of which play a key role in the MCE and thermal hysteresis of the compounds, are introduced. Lastly, the origin of the “virgin effect” in the MnFePGe-based compounds is discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 51171003, 51071007, and 51401002).

  14. Large magnetocaloric effect of GdNiAl{sub 2} compound

    Energy Technology Data Exchange (ETDEWEB)

    Dembele, S.N.; Ma, Z.; Shang, Y.F. [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Fu, H., E-mail: fuhao@uestc.edu.cn [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Balfour, E.A. [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Hadimani, R.L.; Jiles, D.C. [Department of Electrical and Computer Engineering, Iowa State University, Ames, IA 50011 (United States); Ames Laboratory, US Department of Energy, Ames, IA 50011 (United States); Teng, B.H.; Luo, Y. [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China)

    2015-10-01

    This paper presents the structure, magnetic properties, and magnetocaloric effect of the polycrystalline compound GdNiAl{sub 2}. Powder X-ray diffraction (XRD) measurement and Rietveld refinement revealed that GdNiAl{sub 2} alloy is CuMgAl{sub 2}-type phase structure with about 1 wt% GdNi{sub 2}Al{sub 3} secondary phase. Magnetic measurements suggest that the compound is ferromagnetic and undergoes a second-order phase transition near 28 K. The maximum value of magnetic entropy change reaches 16.0 J/kg K for an applied magnetic field change of 0–50 kOe and the relative cooling power was 6.4×10{sup 2} J/kg. It is a promising candidate as a magnetocaloric material working near liquid hydrogen temperature (~20 K) exhibiting large relative cooling power. - Highlights: • Preferred orientation with axis of [010] was found in the GdNiAl{sub 2} compound. • The ΔS{sub Mmax} and the RCP are 16.0 J/kg K and 640 J/kg, respectively, for ΔH=50 kOe. • Relative low rare earth content in GdNiAl{sub 2} comparing with other candidates.

  15. Exchange bias in a mixed metal oxide based magnetocaloric compound YFe0.5Cr0.5O3

    Science.gov (United States)

    Sharma, Mohit K.; Singh, Karan; Mukherjee, K.

    2016-09-01

    We report a detailed investigation of magnetization, magnetocaloric effect and exchange bias studies on a mixed metal oxide YFe0.5Cr0.5O3 belonging to perovskite family. Our results reveal that the compound is in canted magnetic state (CMS) where ferromagnetic correlations are present in an antiferromagnetic state. Magnetic entropy change of this compound follows a power law (∆SM∼Hm) dependence of magnetic field. In this compound, inverse magnetocaloric effect (IMCE) is observed below 260 K while conventional magnetocaloric effect (CMCE) above it. The exponent 'm' is found to be independent of temperature and field only in the IMCE region. Investigation of temperature and magnetic field dependence studies of exchange bias, reveal a competition between effective Zeeman energy of the ferromagnetic regions and anisotropic exchange energy at the interface between ferromagnetic and antiferromagnetic regions. Variation of exchange bias due to temperature and field cycling is also investigated.

  16. Fluctuating local moments, itinerant electrons, and the magnetocaloric effect: Compositional hypersensitivity of FeRh

    Science.gov (United States)

    Staunton, J. B.; Banerjee, R.; Dias, M. dos Santos; Deak, A.; Szunyogh, L.

    2014-02-01

    We describe an ab initio disordered local moment theory for materials with quenched static compositional disorder traversing first-order magnetic phase transitions. It accounts quantitatively for metamagnetic changes and the magnetocaloric effect. For perfect stoichiometric B2-ordered FeRh, we calculate the transition temperature of the ferromagnetic-antiferromagnetic transition to be Tt= 495 K and a maximum isothermal entropy change in 2 T of |ΔS|=21.1 J K-1 kg-1. A large (40%) component of |ΔS| is electronic. The transition results from a fine balance of competing electronic effects which is disturbed by small compositional changes; e.g., swapping just 2% Fe of "defects" onto the Rh sublattice makes Tt drop by 290 K. This hypersensitivity explains the narrow compositional range of the transition and impurity doping effects.

  17. Gadolinium(III)-hydroxy ladders trapped in succinate frameworks with optimized magnetocaloric effect.

    Science.gov (United States)

    Chen, Yan-Cong; Guo, Fu-Sheng; Zheng, Yan-Zhen; Liu, Jun-Liang; Leng, Ji-Dong; Tarasenko, Róbert; Orendáč, Martin; Prokleška, Jan; Sechovský, Vladimír; Tong, Ming-Liang

    2013-09-27

    Two kinds of inorganic gadolinium(III)-hydroxy "ladders", [2×n] and [3×n], were successfully trapped in succinate (suc) coordination polymers, [Gd2(OH)2(suc)2(H2O)]n·2nH2O (1) and [Gd6(OH)8(suc)5(H2O)2 ]n·4n H2O (2), respectively. Such coordination polymers could be regarded as alternating inorganic-organic hybrid materials with relatively high density. Magnetic and heat capacity studies reveal a large cryogenic magnetocaloric effect (MCE) in both compounds, namely (ΔH=70 kG) 42.8 J kg(-1) K(-1) for complex 1 and 48.0 J kg(-1) K(-1) for complex 2. The effect of the high density is evident, which gives very large volumetric MCEs up to 120 and 144 mJ cm(-3) K(-1) for complexes 1 and 2, respectively.

  18. Switching of the magnetocaloric effect of Mn(II) glycolate by water molecules.

    Science.gov (United States)

    Chen, Yan-Cong; Guo, Fu-Sheng; Liu, Jun-Liang; Leng, Ji-Dong; Vrábel, Peter; Orendáč, Martin; Prokleška, Jan; Sechovský, Vladimír; Tong, Ming-Liang

    2014-03-10

    The transformation of Mn(II) glycolates (glc) between the three-dimensional coordination polymer [Mn(glc)2]n (1) and discrete mononuclear phase [Mn(glc)2 (H2O)2] (2) can be reversibly switched by water molecules, which dramatically change the magnetocaloric effect (MCE) of Mn(II) glycolates from the maximum of 6.9 J kg(-1)  K(-1) in 1 to 60.3 J kg(-1)  K(-1) in 2. This case example reveals that the effect of magnetic coupling on MCE plays a dominant role over that of other factors such as magnetic density for 3d-type magnetic refrigerants.

  19. Magnetocaloric effect in a cluster-glass system Ho5Pd2-xNix

    Science.gov (United States)

    Toyoizumi, Saori; Kitazawa, Hideaki; Morita, Kengo; Tamaki, Akira

    2016-02-01

    In order to investigate the effect of chemical pressure on the large magnetocaloric effect in Ho5 Pd2, we conducted X-ray diffraction, magnetization, and specific heat measurements on Ho5Pd2-xNix(0≤ x ≤ 1.0) rare-earth intermetallic compounds. The linear x dependence of the lattice constant a suggests that Ni is replaced with Pd in the case of Ho5Pd2-xNix (0 ≤ x ≤ 0.5). The spin-glass transition temperature Tg and paramagnetic Curie temperature θP indicate a weak oscillatory x dependence. However, the magnetic entropy change —ΔSm and the relative cooling power (RCP) are rapidly suppressed with increasing x. These large reductions in —ΔSm and RCP cannot be explained only in terms of normal Ruderman-Kittel- Kasuya-Yoshida (RKKY)-type indirect exchange interactions.

  20. Amorphization Induced High Magneto-Caloric Effect of Gd55A120Ni25 Ternary Alloy

    Institute of Scientific and Technical Information of China (English)

    DING Ding; XIA Lei; YU Zhong-Hua; DONG Yuan-Da

    2008-01-01

    We report the amorphization induced high magneto-caloric effect (MCE) of recently developed Gd55Al15Ni30 bulk metallic glass (BMG). The magnetic properties of the Gd55Al15Ni30 BMG are investigated in comparison with that of its crystalline counterpart. It is found that amorphization can increase the saturation magnetization and decrease the hysteresis of Gd55Al15Ni30 alloys, which indicate the possible enhancement of MCE. The magnetic entropy changes and the refrigerant capacity of the BMG as well as the crystalline samples is calculated directly from isothermal magnetic measurements. The results show the amorphization induced high MCE of the alloy and the excellent refrigerant efficiency of Gd55A115Ni30 bulk metallic glass.

  1. Giant magnetocaloric effect in Gd5(Si2Ge2 alloy with low purity Gd

    Directory of Open Access Journals (Sweden)

    Cleber Santiago Alves

    2004-12-01

    Full Text Available Gd5(Ge1-xSi x, x < 4 based alloys are potential candidates for magnetic refrigeration in the range ~20 - ~290 K. However, one of the greatest obstacles for the use of that technology in large scale is the utilization of high pure Gd metal (99.99 wt. (% to produce the GdGeSi alloys, since the impurity elements decrease the intensity of the magnetocaloric effect (EMC¹. In this work, we prove that annealing of the Gd5Ge2Si2 can promote remarkable values for the EMC in comparison to those obtained for the alloy with high pure Gd. Also, the as cast alloy and the annealed alloy are not monophasic, but have at least two crystalline phases in their microstructure. Results for X-ray analysis, optical and electronic microscopy and magnetization measurements are reported.

  2. Magnetic properties and magnetocaloric effect in quaternary boroncarbides compound ErNiBC

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yikun, E-mail: zhangyk@epm.neu.edu.cn [Department of Material Science and Engineering, Shanghai University, Shanghai 200072 (China); Institute of Materials Physics, University of Münster, Wilhelm-Klemm-Straße 10, D-48149 Münster (Germany); Wilde, Gerhard [Institute of Materials Physics, University of Münster, Wilhelm-Klemm-Straße 10, D-48149 Münster (Germany)

    2015-09-01

    The magnetocaloric effect (MCE) of quaternary intermetallic compound ErNiBC has been investigated by magnetization and heat capacity measurements. The compound undergoes a paramagnetic (PM) to ferromagnetic (FM) transition at T{sub C}~5 K and the ground state of Er ion forms a Kramer's doublet state. The magnetic transition is found to be second order in nature. The maximum magnetic entropy change (−ΔS{sub M}{sup max}) and adiabatic temperature change (ΔT{sub ad}{sup max}) of ErNiBC are 24.8 J/kg K and 8.6 K, respectively, for a magnetic field change of 0–50 kOe, and the corresponding refrigerant capacity (RC) is 312 J/kg.

  3. Indirect measurement of the magnetocaloric effect using a novel differential scanning calorimeter with magnetic field

    DEFF Research Database (Denmark)

    Jeppesen, Stinus; Linderoth, Søren; Pryds, Nini

    2008-01-01

    A simple and high-sensitivity differential scanning calorimeter (DSC) unit operating under magnetic field has been built for indirect determination of the magnetocaloric effect. The principle of the measuring unit in the calorimeter is based on Peltier elements as heat flow sensors. The high...... sensitivity of the apparatus combined with a suitable calibration procedure allows very fast and accurate heat capacity measurements under magnetic field to be made. The device was validated from heat capacity measurements for the typical DSC reference material gallium (Ga) and a La0.67Ca0.33MnO3 manganite...... system and the results were highly consistent with previous reported data for these materials. The DSC has a working range from 200 to 340 K and has been tested in magnetic fields reaching 1.8 T. The signal-to-noise ratio is in the range of 102–103 for the described experiments. Finally the results have...

  4. Magnetic properties and magnetocaloric effects in Tb6Co1.67Si3 compound

    Institute of Scientific and Technical Information of China (English)

    Shen Jun; Wang Fang; Li Yang-Xian; Sun Ji-Rong; Shen Bao-Gen

    2007-01-01

    Magnetic properties and magnetocaloric effects of Tb6Co1.67Si3 have been investigated by magnetization measurement. This compound is of a hexagonal Ce6Ni2Si3-type structure with a saturation magnetization of 187 emu/g at 5 K and a reversible second-order magnetic transition at Curie temperature TC = 186 K. A magnetic entropy change is found to be 330 J/kg for fields ranging from 0 to 5 T. The large RC, the reversible magnetization around TC and the easy fabrication make the Tb6Co1.67Si3 compound a suitable candidate for magnetic refrigerants in a corresponding temperature range.

  5. Large reversible magnetocaloric effect in HoMn2O5

    Institute of Scientific and Technical Information of China (English)

    Ge Heng; Zhang Xiang-Qun; Ke Ya-Jiao; Jin Jin-Ling; Liao Zhi-Xin; Cheng Zhao-Hua

    2013-01-01

    Magnetocaloric effect (MCE) in polycrystalline HoMn2O5 was investigated by isothermal magnetization curves from 2 K to 50 K.A relatively large magnetic entropy change,ASM =7.8 J/(kg.K),was achieved with the magnetic field up to 70 kOe (1 Oe =79.5775 A·m-1).The magnetic entropy change is reversible in the whole range of temperature.The contributions of elastic and magnetoelastic energy to the changing of the magnetic entropy are discussed in terms of the Landau theory.The reversibility of MCE with maximal refrigerant capacity Rc =216.7 J/kg makes polycrystalline HoMn2O5 promising as a magnetic refrigerant.

  6. Achieving tailorable magneto-caloric effect in the Gd-Co binary amorphous alloys

    Directory of Open Access Journals (Sweden)

    C. Wu

    2016-03-01

    Full Text Available Tailorable magnetic properties and magneto-caloric effect were achieved in the Gd-Co binary amorphous alloys. It was found that the Curie temperature (Tc of the GdxCo100-x (x=50, 53, 56, 58, 60 metallic glasses can be tuned by changing the concentration of Gd as Tc =708.8-8.83x, and the mechanism involved was investigated. On the other hand, a linear correlation between the peak value of magnetic entropy change (-Δ Smpeak and Tc-2/3 is found in the amorphous alloys with a linear correlation coefficients of above 0.992. Therefore, the -ΔSmpeak of the Gd-Co binary amorphous alloys under different magnetic fields can be easily tailored by adjusting the composition of the alloy.

  7. Magnetocaloric Effect of Alloys Gd(Al1-xCox)2

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The magnetocaloric effect in alloys Gd(Al1-xCox)2 with x=0, 0.05, and 0.10 were investigated using X-ray diffraction (XRD) and magnetization measurements.It was found that three alloys crystallized in a single phase with MgCu2-type structure.The lattice parameter and Curie temperature decreased with increasing Co content, whereas the magnetic-entropy change increased.With a magnetic-field change of 2 T, the maximum of the magnetic-entropy change reached 4.6 J·kg-1·K-1 near Curie temperature at approximately 95 K in the alloy GdAl1.8Co0.2, which appeared to be an alternative candidate for active magnetic refrigerants working in the temperature range centered at 100 K.

  8. The giant magnetocaloric effect in Gd5Si2Ge2 with low purity gadolinium

    Institute of Scientific and Technical Information of China (English)

    ZHANG Tiebang; CHEN Yungui; FU Hao; TENG Baohua; TANG Yongbai; TU Mingjing

    2005-01-01

    The giant magnetocaloric effect Gd5Si2Ge2 alloy was prepared with 99wt% low purity commercial Gd. Powder XRD and magnetic measurements showed that the Gd5Si2Ge2 alloy annealed at 1200℃ for 1 h had a significant magnetic- crystallographic first order phase transition at about 270 K. The maximal magnetic entropy change is 17.55 J·kg-1·K-1 under a magnetic field change of 0―5 T. The distinct increase of magnetic entropy change belongs to the first-order phase transition from the orthorhombic Gd5Si4-type to the monoclinic Gd5Si2Ge2-type after high temperature heat-treatment.

  9. Large room-temperature rotating magnetocaloric effect in NdCo4Al polycrystalline alloy

    Science.gov (United States)

    Hu, Y.; Hu, Q. B.; Wang, C. C.; Cao, Q. Q.; Gao, W. L.; Wang, D. H.; Du, Y. W.

    2017-01-01

    The magnetic refrigeration based on rotating magnetocaloric effect (MCE) is promising to build a simplified magnetic cooling system. Until now, most magnetic refrigerants for rotating MCE are single crystal and work at low temperature, which hinder the development of this refrigeration technology. In present paper, we report a large room-temperature rotating MCE in a magnetic-field-aligned NdCo4Al polycrystalline alloy. A large rotating magnetic entropy change of 1.3 J kg-1 K-1 under 10 kOe and a broad operating temperature window of 52 K are achieved. The origin of large rotating MCE in NdCo4Al polycrystalline alloy and its advantages for rotating magnetic refrigeration are discussed.

  10. Observation of weak ferromagnetism and the sizable magnetocaloric effect in Co2V2O7

    Science.gov (United States)

    Sannigrahi, J.; Giri, S.; Majumdar, S.

    2017-02-01

    The magnetic behavior of cobalt pyrovanadate compound Co2V2O7 with dichromate structure is reported. The compound undergoes long range magnetic ordering below TC=8 K and our study identifies the ground state to be a canted antiferromagnetic type with a weak ferromagnetic component. The transition at TC is found to be first-order in nature as evident from the presence of distinct thermal hysteresis in the temperature dependent magnetization data. Below TC, a significantly large value of magnetic relaxation is observed which is possibly due to the metastability associated with the first order phase transition. Interestingly, the sample exhibits a sizable magneto-caloric effect around TC (∼4.1 J kg-1. K-1 for 50 kOe of field change) which is reasonably high among antiferromagnetic transition metal oxides with weak ferromagnetism.

  11. Giant magnetocaloric effect, magnetization plateaux and jumps of the regular Ising polyhedra

    Energy Technology Data Exchange (ETDEWEB)

    Strečka, Jozef, E-mail: jozef.strecka@upjs.sk [Institute of Physics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia); Karľová, Katarína [Institute of Physics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia); Madaras, Tomáš [Institute of Mathematics, Faculty of Science, P.J. Šafárik University, Jesenná 5, 040 01 Košice (Slovakia)

    2015-06-15

    Magnetization process and adiabatic demagnetization of the antiferromagnetic Ising spin clusters with the shape of regular polyhedra (Platonic solids) are exactly examined within the framework of a simple graph-theoretical approach. While the Ising cube as the only unfrustrated (bipartite) spin cluster shows just one trivial plateau at zero magnetization, the other regular Ising polyhedra (tetrahedron, octahedron, icosahedron and dodecahedron) additionally display either one or two intermediate plateaux at fractional values of the saturation magnetization. The nature of highly degenerate ground states emergent at intermediate plateaux owing to a geometric frustration is clarified. It is evidenced that the regular Ising polyhedra exhibit a giant magnetocaloric effect in a vicinity of magnetization jumps, whereas the Ising octahedron and dodecahedron belong to the most prominent geometrically frustrated spin clusters that enable an efficient low-temperature refrigeration by the process of adiabatic demagnetization.

  12. The normal and inverse magnetocaloric effect in RCu2 (R=Tb, Dy, Ho, Er) compounds

    Science.gov (United States)

    Zheng, X. Q.; Xu, Z. Y.; Zhang, B.; Hu, F. X.; Shen, B. G.

    2017-01-01

    Orthorhombic polycrystalline RCu2 (R=Tb, Dy, Ho and Er) compounds were synthesized and the magnetic properties and magnetocaloric effect (MCE) were investigated in detail. All of the RCu2 compounds are antiferromagnetic (AFM) ordered. As temperature increases, RCu2 compounds undergo an AFM to AFM transition at Tt and an AFM to paramagnetic (PM) transition at TN. Besides of the normal MCE around TN, large inverse MCE around Tt was found in TbCu2 compound. Under a field change of 0-7 T, the maximal value of inverse MCE is even larger than the value of normal MCE around TN for TbCu2 compound. Considering of the normal and inverse MCE, TbCu2 shows the largest refrigerant capacity among the RCu2 (R=Tb, Dy, Ho and Er) compounds indicating its potential applications in low temperature multistage refrigeration.

  13. Phase structure and magnetocaloric effect of (Tb1-xDyx)Co2 alloys

    Institute of Scientific and Technical Information of China (English)

    ZHUANG Yinghong; CHEN Xiang; ZHOU Kaiwen; LI Kefeng; MA Chunhua

    2008-01-01

    Phase structure and magnetocaloric effect of (Tb1-xDyx)Co2 alloys with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu2- type structure; with the increase of Dy content, Tc decreased from 240 K (TbCo2) to 130 K (DyCo2), and the maximum magnetic entropy change |ΔSM,max| increased from 3.133 to 8.176 J/kg-K under low magnetic field of 0-2 T. The Arrott plot and the change of |ΔSM,max| showed that magnetic phase transition from second order to first order occurred with the increase of Dy content between x=0.6 and 0.8.

  14. Magnetocaloric effect and refrigeration cooling power in amorphous Gd7Ru3 alloys

    Directory of Open Access Journals (Sweden)

    Pramod Kumar

    2015-07-01

    Full Text Available In this paper, we report the magnetic, heat capacity and magneto-caloric effect (MCE of amorphous Gd7Ru3 compound. Both, temperature dependent magnetization and heat capacity data reveals that two transitions at 58 K and 34 K. MCE has been calculated in terms of isothermal entropy change (ΔSM and adiabatic temperature change (ΔTad using the heat capacity data in different fields. The maximum values of ΔSM and ΔTad are 21 Jmol−1K−1 and 5 K respectively, for field change of 50 kOe whereas relative cooling power (RCP is ∼735 J/kg for the same field change.

  15. Magnetization Process and Magnetocaloric Effect of the Spin-1/2 XXZ Heisenberg Cuboctahedron

    Science.gov (United States)

    Karľová, Katarína; Strečka, Jozef

    2016-10-01

    Magnetic properties of the spin-1/2 XXZ Heisenberg cuboctahedron are examined using exact numerical diagonalization depending on a relative strength of the exchange anisotropy. While the Ising cuboctahedron exhibits in a low-temperature magnetization curve only one-third magnetization plateau, the XXZ Heisenberg cuboctahedron displays another four intermediate plateaux at zero, one-sixth, one-half and two-thirds of the saturation magnetization. The novel magnetization plateaux generally extend over a wider range of magnetic fields with increasing of a quantum (xy) part of the XXZ exchange interaction. It is shown that the XXZ Heisenberg cuboctahedron exhibits in the vicinity of all magnetization jumps anomalous thermodynamic behavior accompanied by an enhanced magnetocaloric effect.

  16. Large magnetocaloric effects in magnetic intermetallics: First-principles and Monte Carlo studies

    Directory of Open Access Journals (Sweden)

    Entel Peter

    2015-01-01

    Full Text Available We have performed ab initio electronic structure calculations and Monte Carlo simulations of frustrated ferroic materials where complex magnetic configurations and chemical disorder lead to rich phase diagrams. With lowering of temperature, we find a ferromagnetic phase which transforms to an antiferromagnetic phase at the magnetostructural (martensitic phase transition and to a cluster spin glass at still lower temperatures. The Heusler alloys Ni-(Co-Mn-(Cr-(Ga, Al, In, Sn, Sb are of particular interest because of their large inverse magnetocaloric effect associated with the magnetostructural transition and the influence of Co/Cr doping. Besides spin glass features, strain glass behavior has been observed in Ni-Co-Mn-In. The numerical simulations allow a complete characterization of the frustrated ferroic materials including the Fe-Rh-Pd alloys.

  17. Acoustic Detection of the Magnetocaloric Effect in Gadolinium Thin Films: Influence of the Substrate

    Science.gov (United States)

    Nogal, U.; Mansanares, A. M.; Gandra, F. C. G.; Soffner, M. E.; Guimarães, A. O.; da Silva, E. C.; Vargas, H.; Marín, E.; Calderón, A.

    2015-06-01

    The magnetocaloric effect (temperature change) in gadolinium thin films is investigated as a function of the external magnetic field using the magnetoacoustic technique. The measured signal evidences the magnetic anisotropy of the sample, and it is in good agreement with results obtained from magnetization measurements. The thermal coupling of the film with the substrate invalidates the adiabatic condition usually achieved when measuring bulk magnetic samples using the magnetoacoustic technique. The influence of the substrate on the temperature of the film is therefore investigated using a simple model for the heat diffusion within the sample. The temperature distribution is calculated as a function of the thermal parameters of the substrate and the results compared to the magnetoacoustic measurements.

  18. Universally diverging Grüneisen parameter and the magnetocaloric effect close to quantum critical points.

    Science.gov (United States)

    Zhu, Lijun; Garst, Markus; Rosch, Achim; Si, Qimiao

    2003-08-08

    At a generic quantum critical point, the thermal expansion alpha is more singular than the specific heat c(p). Consequently, the "Grüneisen ratio," Gamma=alpha/c(p), diverges. When scaling applies, Gamma approximately T(-1/(nu z)) at the critical pressure p=p(c), providing a means to measure the scaling dimension of the most relevant operator that pressure couples to; in the alternative limit T-->0 and p not equal p(c), Gamma approximately 1/(p-p(c)) with a prefactor that is, up to the molar volume, a simple universal combination of critical exponents. For a magnetic-field driven transition, similar relations hold for the magnetocaloric effect (1/T) partial differential T/ partial differential H|(S). Finally, we determine the corrections to scaling in a class of metallic quantum critical points.

  19. Magnetic properties and magnetocaloric effect in quaternary boroncarbides compound ErNiBC

    Science.gov (United States)

    Zhang, Yikun; Wilde, Gerhard

    2015-09-01

    The magnetocaloric effect (MCE) of quaternary intermetallic compound ErNiBC has been investigated by magnetization and heat capacity measurements. The compound undergoes a paramagnetic (PM) to ferromagnetic (FM) transition at TC~5 K and the ground state of Er ion forms a Kramer's doublet state. The magnetic transition is found to be second order in nature. The maximum magnetic entropy change (-ΔSMmax) and adiabatic temperature change (ΔTadmax) of ErNiBC are 24.8 J/kg K and 8.6 K, respectively, for a magnetic field change of 0-50 kOe, and the corresponding refrigerant capacity (RC) is 312 J/kg.

  20. Magnetization and Magnetocaloric Effect in Sol-Gel Derived Nanocrystalline Copper-Zinc Ferrite.

    Science.gov (United States)

    Anwar, M S; Ahmed, Faheem; Koo, Bon Heun

    2015-02-01

    We report the sol-gel synthesis and magnetocaloric effect in nanocrystalline copper-zinc ferrite (Cu0.5Zn0.5Fe2O4). The synthesized powder was characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and magnetization measurements. The XRD results confirm the formation of single phase spinel structure. The average particle size was found to be ~58 nm. FE-SEM results suggested that the nanoparticles are agglomerated and spherical in shape. Magnetization measurement reveals that Cu0.5Zn0.5Fe2O4 nanoparticles exhibit transition temperature (Tc) above room temperature. The maximum magnetic entropy change (ΔSM)max shows interesting behaviour and was found to vary with the applied magnetic field. This nanopowder can be considered as potential material for magnetic refrigeration above room temperature.

  1. Magnetocaloric Effect in MnCo_(1-x)Al_xGe Compounds

    Institute of Scientific and Technical Information of China (English)

    Weiguang Zhang; O. Tegus; Yongli Wu; Yirgeltu; Huanying Yan; Song Lin

    2009-01-01

    The effects of substitution of Al for Co on magnetic and magnetocaloric properties of MnCo_(1-x)Al_xGe (x=0.00, 0.03, 0.05, 0.08, 0.10, 0.13, 0.15, and 0.20) compounds have been investigated by X-ray diffraction (XRD) and magnetization measurements. XRD exhibits that MnCo_(1-x)Al_xGe compounds crystallize in the orthorhombic TiNiSi-type structure for x0.03. Magnetic measurements show that the Curie temperature can be tuned between 286 and 347 K by changing the Co/Al ratio. The maximum magnetic entropy change determined from the isothermal magnetization measurement by Maxwell relation reaches 1.52 J/(kgK) for x=0.08 in a field change from 0 to 1.5 T around 310 K.

  2. Sample dependence of giant magnetocaloric effect in a cluster-glass system Ho{sub 5}Pd{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Toyoizumi, Saori, E-mail: 14udb03@ms.dendai.ac.jp; Tamaki, Akira [Graduate School of Advanced Science and Technology, Tokyo Denki University, 5 Senju Asahi-cho, Adachi, Tokyo 120–8551 (Japan); Kitazawa, Hideaki; Mamiya, Hiroaki; Terada, Noriki; Tamura, Ryo; Dönni, Andreas [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305–0047 (Japan); Kawamura, Yukihiko [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305–0047 (Japan); Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society, 162-1 Shirane Shirakata, Tokai-mura, Naka-gun, Ibaraki 319–1106 (Japan); Morita, Kengo [School of Engineering, Tokyo Denki University, 5 Senju Asahi-cho, Adachi, Tokyo 120-8551 (Japan)

    2015-05-07

    In order to investigate the effect of vacancy on the magnetocaloric effect in Ho{sub 5}Pd{sub 2}, we have carried out X-ray diffraction, magnetization, and specific heat measurements in the rare-earth intermetallic compound Ho{sub 5+x}Pd{sub 2}(−0.4 ≤ x ≤ 0.4). The maximum magnetic entropy change −ΔS{sub m}{sup max}, the maximum adiabatic temperature change ΔT{sub ad}{sup max}, and the relative cooling power of Ho{sub 5+x}Pd{sub 2} take large values at x = 0−0.4 for the field change of 5 T. The paramagnetic Curie temperature θ{sub p} increases with an increase of x. This fact suggests that the enhancement of ferromagnetic coupling among the correlated spins leads to the increase of magnetocaloric effect.

  3. Effective orthorhombic anisotropic models for wavefield extrapolation

    KAUST Repository

    Ibanez-Jacome, W.

    2014-07-18

    Wavefield extrapolation in orthorhombic anisotropic media incorporates complicated but realistic models to reproduce wave propagation phenomena in the Earth\\'s subsurface. Compared with the representations used for simpler symmetries, such as transversely isotropic or isotropic, orthorhombic models require an extended and more elaborated formulation that also involves more expensive computational processes. The acoustic assumption yields more efficient description of the orthorhombic wave equation that also provides a simplified representation for the orthorhombic dispersion relation. However, such representation is hampered by the sixth-order nature of the acoustic wave equation, as it also encompasses the contribution of shear waves. To reduce the computational cost of wavefield extrapolation in such media, we generate effective isotropic inhomogeneous models that are capable of reproducing the firstarrival kinematic aspects of the orthorhombic wavefield. First, in order to compute traveltimes in vertical orthorhombic media, we develop a stable, efficient and accurate algorithm based on the fast marching method. The derived orthorhombic acoustic dispersion relation, unlike the isotropic or transversely isotropic ones, is represented by a sixth order polynomial equation with the fastest solution corresponding to outgoing P waves in acoustic media. The effective velocity models are then computed by evaluating the traveltime gradients of the orthorhombic traveltime solution, and using them to explicitly evaluate the corresponding inhomogeneous isotropic velocity field. The inverted effective velocity fields are source dependent and produce equivalent first-arrival kinematic descriptions of wave propagation in orthorhombic media. We extrapolate wavefields in these isotropic effective velocity models using the more efficient isotropic operator, and the results compare well, especially kinematically, with those obtained from the more expensive anisotropic extrapolator.

  4. Magnetocaloric effect in GdCu intermetallic compound

    Energy Technology Data Exchange (ETDEWEB)

    Oboz, M.; Talik, E.; Winiarski, A. [Institiute of Physics, University of Silesia, Katowice (Poland)

    2012-03-15

    A single crystal of GdCu of FeB-type was grown by the Czochralski method from a levitating melt and characterized using X-ray diffraction, dc -magnetization M(T) and ac -magnetic susceptibility (ac-{chi}). From ac and dc magnetic susceptibility a transition to the antiferromagnetic state has been found below T{sub N} = 37 K. The paramagnetic Curie temperature {theta}{sub p} and the effective magnetic moment {mu}{sub eff}were estimated assuming the Curie-Weiss law in the 100 to 300 K range and were found to be {theta}{sub p}=-37 K and {mu}{sub eff}=8.5 {mu}{sub B}. The last value is enhanced relatively to the free ion value of 7.94 {mu}{sub B} for Gd{sup 3+}. The calculated entropy changes {delta}S{sub m} for the examined compound amount to -1.22 J/K.kg, -0.6 J/K.kg and -0.09 J/K.kg at 7, 5 and 2 T respectively. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Improved magneto-caloric effect of the Gd50Co50 metallic glass by minor Si addition

    Science.gov (United States)

    Tang, B. Z.; Yu, P.; Ding, D.; Wu, C.; Xia, L.

    2017-02-01

    In the present work, we studied the effect of minor Si addition on the magneto-caloric effect (MCE) of the Gd50Co50 metallic glass. The Gd50Co50-xSix (x=2, 5) as-spun ribbons show typical amorphous characteristics in structure and magneto-caloric behaviors. The peak values for the magnetic entropy change (-ΔSmpeak) of the Gd50Co50-xSix (x=0, 2, 5) metallic glasses increase significantly with the addition of Si. The mechanism for the enhanced MCE by minor addition of Si was investigated by revealing the relationship between -ΔSmpeak and the Curie temperature in the Gd-Co-based amorphous ribbons.

  6. Magnetic properties,magnetoresistivity and magnetocaloric effect in GdxLa1-x-MnSi alloys

    Institute of Scientific and Technical Information of China (English)

    T.I.Ivanova; S.A.Nikitin; W.Suski; GA.Tskhadadze; I.A.Ovtchenkova; D.Badurski

    2009-01-01

    The results of magnetization,magnetoresistivity and magnetocaloric effect (MCE) studies performed on polycrystalline samples of the GdxLa1-xMnSi (x=0.5,0.6,0.7,0.8,0.9,1.0) compounds were presented.Complex measurements were carried out on the GdxLa1-xMnSi compounds to determine the influence of substitution in the rare earth (R) sublattice on the magnetic and related properties of these compounds.The compounds with x≤0.6 demonstrated two magnetic phase transitions (ferromagnetic to paramagnetic and antiferromagnetic to ferromagnetic) both of which were first order.Anomalies in the magnetocaloric effect,electroresistivity and magnetoresistivity were observed in the temperature ranges of the magnetic phase transitions.The temperature dependences of MCE and magnetoresistivity for these compounds correlated with the temperature dependence of magnetization.

  7. Magnetocaloric and Hopkinson effects in slowly and rapidly cooled Gd{sub 7}Pd{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Talik, Ewa; Guzik, Adam; Oboz, Monika; Zajdel, Pawel; Ziolkowski, Grzegorz [Silesia Univ., Katowice (Poland). Inst. of Physics

    2016-01-15

    Gd{sub 7}Pd{sub 3} intermetallic compound was prepared as slowly cooled polycrystal and rapidly cooled (rc) casts. The slowly cooled polycrystalline samples were obtained by melting in an induction coil. The rc-cast Gd{sub 7}Pd{sub 3} sample was obtained by means of a mould casting technique. The samples were characterized by means of X-ray diffraction, SQUID magnetometry and scanning electron microscopy in order to elucidate the Hopkinson effect and magnetocaloric properties in relation to the technological aspects. The investigated ferromagnetic system is sensitive to grain size. The magnetocaloric and Hopkinson effect decreases with the decrease of the grain size. The results were compared to the data of single crystal obtained by the Czochralski method from a levitating melt.

  8. Phase transitions and magnetocaloric effects in intermetallic compounds MnFeX (X=P, As, Si, Ge)

    Institute of Scientific and Technical Information of China (English)

    O.Tegus; Bao Li-Hong; Song Lin

    2013-01-01

    Since the discovery of giant magnetocaloric effect in MnFeP1-xAsx compounds,much valuable work has been performed to develop and improve Fe2P-type transition-metal-based magnetic refrigerants.In this article,the recent progress of our studies on fundamental aspects of theoretical considerations and experimental techniques,effects of atomic substitution on the magnetism and magnetocalorics of Fe2P-type intermetallic compounds MnFeX (X=P,As,Ge,Si) is reviewed.Substituting Si (or Ge) for As leads to an As-free new magnetic material MnFeP1-xSi(Ge)x.These new materials show large magnetocaloric effects resembling MnFe(P,As) near room temperature.Some new physical phenomena,such as huge thermal hysteresis and 'virgin' effect,were found in new materials.On the basis of Landau theory,a theoretical model was developed for studying the mechanism of phase transition in these materials.Our studies reveal that MnFe(P,Si) compound is a very promising material for room-temperature magnetic refrigeration and thermo-magnetic power generation.

  9. Large Magnetization and Reversible Magnetocaloric Effect at the Second-Order Magnetic Transition in Heusler Materials.

    Science.gov (United States)

    Singh, Sanjay; Caron, Luana; D'Souza, Sunil Wilfred; Fichtner, Tina; Porcari, Giacomo; Fabbrici, Simone; Shekhar, Chandra; Chadov, Stanislav; Solzi, Massimo; Felser, Claudia

    2016-05-01

    In contrast to rare-earth-based materials, cheaper and more environmentally friendly candidates for cooling applications are found within the family of Ni-Mn Heusler alloys. Initial interest in these materials is focused on the first-order magnetostructural transitions. However, large hysteresis makes a magnetocaloric cycle irreversible. Alternatively, here it is shown how the Heusler family can be used to optimize reversible second-order magnetic phase transitions for magnetocaloric applications.

  10. Structure and magnetocaloric effect in melt-spun La(Fe,Si)13 and MnFePGe compounds

    Institute of Scientific and Technical Information of China (English)

    YAN Aru

    2006-01-01

    The magnetocaloric properties of melt-spun La(Fe,Si) 13 and MnFePGe compounds were investigated. Very large value of magnetic entropy change |ΔS|=31 and 35.4J·(kg·K)-1 under 5 T were obtained at 201 K in LaFe11.8Si1.2 melt-spun ribbons and at around 317 K in Mn1.1Fe0.9P0.76Ge0.24 melt-spun ribbons, respectively. The large magnetocaloric effect results from a more homogenous element distribution related to the very high cooling rate during melt-spinning. The excellent MCE properties, the low materials cost and the accelerated aging regime make the melt-spun-type La(Fe,Si)13 and MnFePGe materials an excellent candidate for magnetic refrigerant applications.

  11. Atomic ordering effect in Ni{sub 50}Mn{sub 37}Sn{sub 13} magnetocaloric ribbons

    Energy Technology Data Exchange (ETDEWEB)

    Wu Dianzhen; Xue Sichuang [Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China); Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072 (China); Frenzel, Jan; Eggeler, Gunther [Institute of Materials, Ruhr University Bochum, Bochum 44801 (Germany); Zhai Qijie [Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072 (China); Zheng Hongxing, E-mail: hxzheng@shu.edu.cn [Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China); Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, Shanghai 200072 (China)

    2012-02-01

    Highlights: Black-Right-Pointing-Pointer High-performance Ni-Mn-Sn magnetocaloric materials are produced. Black-Right-Pointing-Pointer Ni{sub 50}Mn{sub 37}Sn{sub 13} demonstrates great potential for magnetic refrigeration applications. Black-Right-Pointing-Pointer A strong atomic order dependence is revealed in Ni{sub 50}Mn{sub 37}Sn{sub 13} materials. - Abstract: High-performance Ni{sub 50}Mn{sub 37}Sn{sub 13} magnetocaloric materials are produced using melt spinning technique in the present work and the atomic order dependence of phase transition behaviors and magnetic properties is established. The effective refrigeration capacity of the melt-spun ribbon annealed at 1273 K for 15 min reaches 95.27 J/kg for a magnetic field change of 18 kOe, demonstrating great potential for magnetic refrigeration applications near ambient temperature.

  12. Magneto-caloric effect of FexZryB100-x-y metallic ribbons for room temperature magnetic refrigeration

    Science.gov (United States)

    Guo, D. Q.; Chan, K. C.; Xia, L.; Yu, P.

    2017-02-01

    Among various amorphous magnetic materials, even though Fe-based materials do not have high magnetocaloric effect (MCE), their advantages of tunable Curie temperature (TC) and low cost have attracted considerable attention in regard to room temperature magnetic refrigeration applications. With the aim of enhancing the MCE, the influence of boron addition on Fe-based amorphous materials was investigated in this study. Fe94-xZr6Bx (x=5, 6, 8 and 10), Fe91-yZr9By (y=3, 4, 5, 6, 8 and 10) and Fe89-zZr11Bz (z=3, 4, 5, 6, 8 and 10) specimens were made in ribbon form and their magnetocaloric effect was investigated. The Curie temperature (TC) of all three series of ribbons underwent an almost linear increase, and the peak magnetic entropy change, | Δ SMpeak | (obtained in a magnetic field of 1.5 T), generally increases with increasing boron content. The results further show that the Fe86Zr9B5 ribbon exhibits a relatively large | Δ SMpeak | value of 1.13 J/kgK at 330 K and a large refrigerant capacity value of 135.6 J/kg under 1.5 T. On the basis of these results, although there is still much scope for improvement before totally replacing the conventional cooling method, the Fe-based amorphous ribbon can be seen as a promising magnetocaloric material for room temperature magnetic refrigeration applications.

  13. Magnetism and magnetocaloric effect study of CaFe0.7Co0.3O3

    Science.gov (United States)

    Xia, H. L.; Y Yin, Y.; Dai, J. H.; Y Yang, J.; Qin, X. M.; Jin, C. Q.; Long, Y. W.

    2015-04-01

    The CaFe0.7Co0.3O3 single crystal was grown for the first time by a two-step method and its magnetism and magnetocaloric effect were investigated. This compound experiences a second-order paramagnetism-to-ferromagnetism transition in a wide temperature window between 200 and 150 K due to the presence of multiple ferromagnetic interactions. Since the spin entropy is gradually released above the ferromagnetic Curie temperature (˜177 K), no sharp λ-type anomaly is observed in specific heat. On the basis of magnetization measurements, however, a considerable entropy change is found in this perovskite oxide. More interesting, this compound exhibits a broadening working temperature, and a significant refrigerant capacity (˜355 J kg-1 at 6 T) which is comparable with those found in some giant magnetocaloric alloys with first-order magnetic transitions. The present study therefore provides an example on how to enhance the refrigerant capacity by extending the working temperature of magnetocaloric material.

  14. Inverse magnetocaloric effect in Ce(Fe{sub 0.96}Ru{sub 0.04}){sub 2}: Effect of fast neutron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Dube, V.; Mishra, P. K.; Prajapat, C. L.; Singh, M. R.; Ravikumar, G. [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai-4000085 (India); Rajarajan, A. K.; Sastry, P. U. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai-4000085 (India); Thakare, S. V. [Radio Pharmaceuticals Division, Bhabha Atomic Research Centre, Mumbai-4000085 (India)

    2013-02-05

    We have shown the effect of fast neutron irradiation on the magnetic phase transition and magnetocaloric effect (MCE) in a doped Ce(Fe{sub 0.96}Ru{sub 0.04}){sub 2}, intermettalic. We show that this leads to suppression of MCE and a to a disordered ferromagnetic phase.

  15. Three isostructural one-dimensional Ln(III) chains with distorted cubane motifs showing dual fluorescence and slow magnetic relaxation/magnetocaloric effect.

    Science.gov (United States)

    Li, Yan; Yu, Jia-Wen; Liu, Zhong-Yi; Yang, En-Cui; Zhao, Xiao-Jun

    2015-01-05

    Three new homometallic lanthanide complexes with mixed carboxylate-modified rigid ligands, [Ln(μ3-OH)(na)(pyzc)]n (na(-) = 1-naphtholate, pyzc(-) = 2-pyrazinecarboxylate, Ln = Dy (1), Yb (2), and Gd (3)), were solvothermally synthesized, and their structures and magnetic as well as photophysical properties were completely investigated. Complexes 1-3 are crystallographically isostructural, exhibiting linear chains with four bidentate bridging μ-COO(-) moieties encapsulated cubic {Ln4(μ3-OH)4}(8+) clusters repeatedly extended by 4-fold chelating-bridging-pyzc(-) connectors. Magnetically, the former two complexes with highly anisotropic Dy(III) and weak anisotropic Yb(III) ions in the distorted NO7 triangular dodecahedron coordination environment display field-induced slow relaxation of magnetization. Fitting the dynamic magnetic data to the Arrhenius law gives energy barrier ΔE/kB = 39.6 K and pre-exponential factor τo = 1.52 × 10(-8) s for 1 and ΔE/kB = 14.1 K and τo = 2.13 × 10(-7) s for 2. By contrast, complex 3 with isotropic Gd(III) ion and weak intracluster antiferromagnetic coupling shows a significant cryogenic magnetocaloric effect, with a maximum -ΔSm value of 30.0 J kg(-1) K(-1) at 2.5 K and 70 kOe. Additionally, the chromophoric na(-) and pyzc(-) ligands can serve as antenna groups, selectively sensitizing the Dy(III)- and Yb(III)-based luminescence of 1 and 2 in the UV-visible region by an intramolecular energy transfer process. Thus, complexes 1-3, incorporating field-induced slow magnetic magnetization and interesting luminescence together, can be used as composite magneto-optical materials. More importantly, these interesting results further demonstrate that the mixed-ligand system with rigid carboxylate-functionalized chromophores can be excellent candidates for the preparations of new bifunctional magneto-optical materials.

  16. Giant rotating magnetocaloric effect induced by highly texturing in polycrystalline DyNiSi compound.

    Science.gov (United States)

    Zhang, Hu; Li, YaWei; Liu, Enke; Ke, YaJiao; Jin, JinLing; Long, Yi; Shen, BaoGen

    2015-07-10

    Large rotating magnetocaloric effect (MCE) has been observed in some single crystals due to strong magnetocrystalline anisotropy. By utilizing the rotating MCE, a new type of rotary magnetic refrigerator can be constructed, which could be more simplified and efficient than the conventional one. However, compared with polycrystalline materials, the high cost and complexity of preparation for single crystals hinder the development of this novel magnetic refrigeration technology. For the first time, here we observe giant rotating MCE in textured DyNiSi polycrystalline material, which is larger than those of most rotating magnetic refrigerants reported so far. This result suggests that DyNiSi compound could be attractive candidate of magnetic refrigerants for novel rotary magnetic refrigerator. By considering the influence of demagnetization effect on MCE, the origin of large rotating MCE in textured DyNiSi is attributed to the coexistence of strong magnetocrystalline anisotropy and highly preferred orientation. Our study on textured DyNiSi not only provides a new magnetic refrigerant with large rotating MCE for low temperature magnetic refrigeration, but also opens a new way to exploit magnetic refrigeration materials with large rotating MCE, which will be highly beneficial to the development of rotating magnetic refrigeration technology.

  17. Practical system for the direct measurement of magneto-caloric effect by micro-thermocouples.

    Science.gov (United States)

    Kamarád, J; Kaštil, J; Arnold, Z

    2012-08-01

    A system for direct measurements of the magneto-caloric effect (MCE) exploits a rapid transport of a sample into or from magnetic field in permanent Halbach-type (1 T) or superconducting (4.7 T) magnets. Time dependence of induced changes of the sample temperature, ΔT(t), is detected directly by the differential Cu-Constantan-Cu micro-thermocouples with time steps of 300 ms. A sample placed inside an evacuated simple LN(2) cryostat is either totally isolated (adiabatic conditions) or partly connected with the copper sample holder (non-adiabatic conditions). The last arrangement (a model of the Brayton cycle) is used to simulate an application of MCE in refrigeration techniques. The relations describing ΔT(t) that allow an analysis of MCE of the studied materials are based on the general cooling law. The effect of the first-order magnetic transition on MCE of selected sample is also demonstrated by non-standard ΔT(t) curves measured in the last mentioned experimental arrangements.

  18. Magnetocaloric effect in (La1-xAx)2/3Ba1/3Mn1.05O3-δ

    DEFF Research Database (Denmark)

    Ancona-Torres, Carlos Eugenio; Menon, Mohan; Bahl, Christian Robert Haffenden

    Recently, a large magnetocaloric effect has been reported in La2/3Ba1/3MnO3-δ at about 300 K. In this paper, we investigate the effect of the ion size distribution at the A site on the magnetocaloric effect of this perovskite material. This is accomplished by replacing the lanthanum by Ce, Pr......, and Nd, which allows us to study the effect of both the average size, , and the distribution, σrA, on the magnetic properties of the system. Using magnetization and heat capacity measurements, we determine the important magnetocaloric parameters ΔSM and ΔTad of (La1-xAx)2/3Ba1/3Mn1.05O3-δ powders...

  19. PURCELL EFFECT IN EXTREMELY ANISOTROPIC ELLIPTIC METAMATERIALS

    Directory of Open Access Journals (Sweden)

    Alexander V. Chebykin

    2014-11-01

    Full Text Available The paper deals with theoretical demonstration of Purcell effect in extremely anisotropic metamaterials with elliptical isofrequency surface. This effect is free from association with divergence in density of states unlike the case of hyperbolic metamaterials. It is shown that a large Purcell factor can be observed without excitation of modes with large wave vectors in one direction, and the component of the wave vector normal to the layers is less than k0. For these materials the possibility is given for increasing of the power radiated in the medium, as well as the power radiated from material into free space across the medium border situated transversely to the layers. We have investigated isofrequency contours and the dependence of Purcell factor from the frequency for infinite layered metamaterial structure. In the visible light range strong spatial dispersion gives no possibility to obtain enhancement of spontaneous emission in metamaterial with unit cell which consists of two layers. This effect can be achieved in periodic metal-dielectric layered nanostructures with a unit cell containing two different metallic layers and two dielectric ones. Analysis of the dependences for Purcell factor from the frequency shows that the spontaneous emission is enhanced by a factor of ten or more only for dipole orientation along metamaterial layers, but in the case of the transverse orientation radiation can be enhanced only 2-3 times at most. The results can be used to create a new type of metamaterials with elliptical isofrequency contours, providing a more efficient light emission in the far field.

  20. Tailoring of Magnetocaloric Effect in Ni45.5Mn43.0In11.5 Metamagnetic Shape Memory Alloy

    Directory of Open Access Journals (Sweden)

    W. O. Rosa

    2012-01-01

    Full Text Available We investigate the direct and inverse magnetocaloric effect in Ni45.5Mn43.0In11.5 Heusler alloy ribbons comparing the results obtained for the as-quenched sample with the ones after different annealing procedures. An enhancement and shift of the entropy maximum to near room temperature is observed in all annealed samples. A remarkable magnetocaloric effect is observed in samples with short-time treatment (10 minutes and at the lowest annealing temperature. We show that the suppressing of uncompensated martensitic transition and thermal hysteresis are both influenced by the heat treatment. Also, an improvement on Curie’s temperature is observed and, at low magnetic field, it has been risen up to 310 K. Our results demonstrate that the martensitic transformation is highly sensitive to the applied magnetic field and also to the annealing treatment, which means that the magnetocaloric effect can be tuned showing different behaviors for each sample.

  1. Magnetocaloric effects in Fe4MnSi3Bxr interstitial compounds

    Institute of Scientific and Technical Information of China (English)

    Yongli WU; O.Tegus; Weiguang ZHANG; S.Yiriyoltu; B.Mend; Songlin

    2009-01-01

    The magnetic properties and magnetocaloric effect in Fe_4MnSi_3B_x compounds with x=0, 0.05, 0.10, 0.15, 0.20, 0.25 have been investigated. X-ray diffraction study shows that all these compounds investigated crystallize in the Mn_5Si_3-type structure with space group P6_3/mcm. Boron insertion in the host ternary silicide Fe_4MnSi_3 does not change the crystal symmetry, only leads to an increase of the lattice parameters, indicating the B atoms entered the interstitial sites. With increasing B content, the Curie temperature shifts to higher temperatures. The maximal magnetic-entropy changes of the Fe_4MnSi_3B_x compounds with x=0, 0.10 and 0.20 are about 1.8 J/(kg·K), 1.8 J/(kg·K) and 1.6 J/(kg·K), respectively, for a field change from 0 to 1.5 T.

  2. Effect of Milling Time on the Blocking Temperature of Nanoparticles of Magnetocaloric Gd5Si4

    Science.gov (United States)

    Hadimani, Ravi; Gupta, Shalbh; Harstad, Shane; Pecharsky, Vitalij; Jiles, David; David C Jiles Team; Vitalij Pecharsky Collaboration

    Extensive research has been done on giant magnetocaloric material Gd5(SixGe1-x)4 to improve adiabatic temperature/isothermal entropy change. However, there have been only a few reports on fabrication of nanostructure/nanoparticles that can be used to tune various properties by changing the length scale. Recently we have reported fabrication of room temperature ferromagnetic nanoparticles of Gd5Si4 using high energy ball milling. These nanoparticles have potential applications in biomedical engineering such as better T2 MRI contrast agents and in hypothermia. Here we report the effect of milling time on the blocking temperature, micro-structure, crystal structure, and magnetic properties of these nanoparticles. Magnetization vs. temperature at an applied field of 100 Oe is measured for all the ball milled samples. Bulk Gd5Si4 has a transition temperature of ~340 K. There are two phase transitions observed in the nanoparticles, one near 300 K corresponding to the Gd5Si4 phase and another between 75-150 K corresponding to Gd5Si3. Zero Field Cooling (ZFC) and Field Cooling (FC) were measured. The blocking temperatures for the nanoparticles increase with decrease in milling time.

  3. Criticality-Enhanced Magnetocaloric Effect in Quantum Spin Chain Material Copper Nitrate

    Science.gov (United States)

    Xiang, Jun-Sen; Chen, Cong; Li, Wei; Sheng, Xian-Lei; Su, Na; Cheng, Zhao-Hua; Chen, Qiang; Chen, Zi-Yu

    2017-01-01

    In this work, a systematic study of Cu(NO3)2·2.5 H2O (copper nitrate hemipentahydrate, CN), an alternating Heisenberg antiferromagnetic chain model material, is performed with multi-technique approach including thermal tensor network (TTN) simulations, first-principles calculations, as well as magnetization measurements. Employing a cutting-edge TTN method developed in the present work, we verify the couplings J = 5.13 K, α = 0.23(1) and Landé factors g∥= 2.31, g⊥ = 2.14 in CN, with which the magnetothermal properties have been fitted strikingly well. Based on first-principles calculations, we reveal explicitly the spin chain scenario in CN by displaying the calculated electron density distributions, from which the distinct superexchange paths are visualized. On top of that, we investigated the magnetocaloric effect (MCE) in CN by calculating its isentropes and magnetic Grüneisen parameter. Prominent quantum criticality-enhanced MCE was uncovered near both critical fields of intermediate strengths as 2.87 and 4.08 T, respectively. We propose that CN is potentially a very promising quantum critical coolant. PMID:28294147

  4. Adiabatic magnetocaloric effect in Ni50Mn35In15 ribbons

    Science.gov (United States)

    Álvarez-Alonso, P.; Aguilar-Ortiz, C. O.; Camarillo, J. P.; Salazar, D.; Flores-Zúñiga, H.; Chernenko, V. A.

    2016-11-01

    Heusler-type Ni-Mn-based metamagnetic shape memory alloys (MetaMSMAs) are promising candidates for magnetic refrigeration. To increase heat exchange rate and efficiency of cooling, the material should have a high surface/volume ratio. In this work, the typical Ni50Mn35In15 MetaMSMA was selected to fabricate thin ribbons by melt-spinning. The characteristic transformations of the ribbons were determined by calorimetry, X-ray diffraction, scanning electron microscopy and thermomagnetization measurements. The inverse and conventional magnetocaloric effects (MCEs) associated with the martensitic transformation (MT) and the ferromagnetic transition of the austenite (TCA), respectively, were measured directly by the adiabatic method (ΔTad) and indirectly by estimating the magnetic entropy change from magnetization measurements. It is found that the ribbons exhibit large values of ΔTad = -1.1 K at μ0ΔH = 1.9 T, in the vicinity of the MT temperature of 300 K for inverse MCE, and ΔTad = 2.3 K for conventional MCE at TCA = 309 K. This result strongly motivates further development of different MetaMSMA refrigerants shaped as ribbons.

  5. Structure and Magnetocaloric Effect in Tb( Co1-xSnx )2 Alloys

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The phases and magnetocaloric effect in the alloys Tb (Co1 - xSnx) 2 with x = 0, 0.025, 0.050, 0.075, 0.100were investigated by X-ray diffraction analysis and magnetization measurement. The substitution of Sn in TbCo2 was limited. The cubic MgCu2-type structure for the sample of TbCo2 was confirmed by the results of X-ray powder diffraction and the rest samples consist of the TbCo2 phase mainly, together with some TbCo3 and Tb5Sn3 impurity phases. The impurity phases increase with the increase of Sn contents. The magnetic phase transition in all samples keeps second-order transition. TC increases slightly by Sn substitution from 230 K of the alloy with x = 0 to 233 K of the alloy with x = 0. 050 and then a slight decrease for higher concentration of x. The maximum magnetic entropy change in the samples Tb (Co1- x change from 0 to 2.0 T.

  6. Magnetic transitions and magnetocaloric effect in MnAs0.9P0.1

    Institute of Scientific and Technical Information of China (English)

    Naikun SUN; Feng LIU; Yinbo GAO; Jinjun LIU

    2012-01-01

    The compound MnAs0.9P0.1 exhibits a multistep magnetic order-order transition from a helimagnetic γ-phase with Hα-type magnetic order to a ferromagnetic β-phase at 80 K and then to a helimagnetic α-phase at 203 K.The γ-β transition exhibits the characteristics of a first-order transition with a thermal hysteresis as large as 6 K,while the β-α transition is of second order with a thermal hysteresis smaller than 2 K and without magnetic hysteresis.With these two successive helimagnetism-related transitions,magnetic-entropy changes of -2.1 J/(kg·K) at 203 K for a field change from 0 to 5 T and 0.1 J/(kg.K) at 83 K for a field change from 0 to 1 T are obtained.Investigation of the magnetocaloric effect associated with a transition from Hα-type magnetic order to FM order may open a new route to explore candidates for magnetic refrigeration.

  7. Magnetocaloric effect in amorphous and partially crystallized Fe40Ni38Mo4B18 alloys

    Directory of Open Access Journals (Sweden)

    T. Thanveer

    2016-05-01

    Full Text Available A study of magnetocaloric effect in amorphous and partially crystallized Fe40Ni38Mo4B18 alloys is reported. Amorphous Fe40Ni38Mo4B18, near its magnetic ordering temperature (600K showed a magnetic entropy change ΔSM of 1.1 J/KgK and a relative cooling power of 36J/Kg in a field change of 10 kOe. Amorphous samples were partially crystallized by annealing at 700 K at different time intervals. Partially crystallized samples showed two distinct magnetic ordering temperature, one corresponding to the precipitated FeNi nanocrystals and the other one corresponding to the boron rich amorphous matrix. Magnetic ordering temperature of the residual amorphous matrix got shifted to the lower temperatures on increasing the annealing duration. Partially crystallised samples showed a magnetic entropy change of about 0.27J/kgK near the magnetic ordering temperature of the amorphous matrix (540K in a field change of 10 kOe. The decrease in ΔSM on partial crystallisation is attributed to the biphasic magnetic nature of the sample.

  8. Magnetocaloric effect of (Gd1-xNdx)Co2 alloys in low magnetic field

    Institute of Scientific and Technical Information of China (English)

    CHEN Xiang; ZHUANG Yinghong; YAN Jialin; ZHOU Kaiwen; LI Kefeng

    2008-01-01

    The phases and magnetocaloric effect in the alloys (Gd1-xNdx)Co2 with x = 0,0.1,0.2,0.3,and 0.4 were investigated by X-ray diffraction analysis and magnetization measurement.The samples are single phase with a cubic MgCu2-type structure.The Tc decreases obviously with increasing Nd content from 404 K of the alloy with x = 0 to 272 K of the alloy with x = 0.4;for x = 0.3,the Tc is 296 K,which is near room temperature.In the samples (Gd1-xNdx)Co2 with x = 0.0,0.1,0.2,0.3,and 0.4,the maximum magnetic entropy change is 1.471,1.228,1.280,1.381 and 1.610 J.kg-1.K-1,respectively,in the applied field range of 0-2.0 T.The results of Arrott plots confirmed that the transition type were second order magnetic transition for x = 0,0.3,and 0.4.

  9. Large magnetocaloric effect and adiabatic demagnetization refrigeration with YbPt2Sn.

    Science.gov (United States)

    Jang, Dongjin; Gruner, Thomas; Steppke, Alexander; Mitsumoto, Keisuke; Geibel, Christoph; Brando, Manuel

    2015-10-23

    Adiabatic demagnetization is currently gaining strong interest in searching for alternatives to (3)He-based refrigeration techniques for achieving temperatures below 2 K. The main reasons for that are the recent shortage and high price of the rare helium isotope (3)He. Here we report the discovery of a large magnetocaloric effect in the intermetallic compound YbPt2Sn, which allows adiabatic demagnetization cooling from 2 K down to 0.2 K. We demonstrate this with a home-made refrigerator. Other materials, for example, paramagnetic salts, are commonly used for the same purpose but none of them is metallic, a severe limitation for low-temperature applications. YbPt2Sn is a good metal with an extremely rare weak magnetic coupling between the Yb atoms, which prevents them from ordering above 0.25 K, leaving enough entropy free for use in adiabatic demagnetization cooling. The large volumetric entropy capacity of YbPt2Sn guarantees also a good cooling power.

  10. Tricarboxylate-based Gd(III) coordination polymers exhibiting large magnetocaloric effects.

    Science.gov (United States)

    Liu, Sui-Jun; Cao, Chen; Xie, Chen-Chao; Zheng, Teng-Fei; Tong, Xiao-Lan; Liao, Jin-Sheng; Chen, Jing-Lin; Wen, He-Rui; Chang, Ze; Bu, Xian-He

    2016-05-31

    Two Gd(III) coordination polymers with the formula [Gd(cit)(H2O)]∞ () and [Gd(nta)(H2O)2]∞ () (H4cit = citric acid, H3nta = nitrilotriacetic acid) have been successfully prepared under hydrothermal conditions. Complex exhibits a three-dimensional (3D) structure based on carboxylate-bridged layers, while complex is a double-layer structure containing eight-coordinated Gd(III). Magnetic investigations reveal that weak antiferromagnetic couplings between adjacent Gd(III) ions in both and with different Weiss values result in large cryogenic magnetocaloric effects. It is notable that the maximum entropy changes (-ΔS) of and reach 31.3 J kg(-1) K(-1) and 32.2 J kg(-1) K(-1) at 2 K for a moderate field change (ΔH = 3 T), and a remarkable -ΔS (41.5 J kg(-1) K(-1) for and 42.0 J kg(-1) K(-1) for ) could be obtained for ΔH = 7 T.

  11. Large reversible magnetocaloric effect induced by metamagnetic transition in antiferromagnetic HoNiGa compound

    Science.gov (United States)

    Wang, Yi-Xu; Zhang, Hu; Wu, Mei-Ling; Tao, Kun; Li, Ya-Wei; Yan, Tim; Long, Ke-Wen; Long, Teng; Pang, Zheng; Long, Yi

    2016-12-01

    The magnetic properties and magnetocaloric effects (MCE) of HoNiGa compound are investigated systematically. The HoNiGa exhibits a weak antiferromagnetic (AFM) ground state below the Ńeel temperature TN of 10 K, and the AFM ordering could be converted into ferromagnetic (FM) ordering by external magnetic field. Moreover, the field-induced FM phase exhibits a high saturation magnetic moment and a large change of magnetization around the transition temperature, which then result in a large MCE. A large -ΔSM of 22.0 J/kg K and a high RC value of 279 J/kg without magnetic hysteresis are obtained for a magnetic field change of 5 T, which are comparable to or even larger than those of some other magnetic refrigerant materials in the same temperature range. Besides, the μ0H2/3 dependence of well follows the linear fitting according to the mean-field approximation, suggesting the nature of second-order FM-PM magnetic transition under high magnetic fields. The large reversible MCE induced by metamagnetic transition suggests that HoNiGa compound could be a promising material for magnetic refrigeration in low temperature range. Project supported by the National Natural Science Foundation of China (Grant Nos. 51671022 and 51427806), the Beijing Natural Science Foundation, China (Grant No. 2162022), and the Fundamental Research Funds for the Central Universities, China (Grant No. FRF-TP-15-002A3).

  12. Giant magnetocaloric effect in MnCoGe with minimal Ga substitution

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Danlu [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Nie, Zhihua, E-mail: zhihua_nie@yahoo.com [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Wang, Zilong; Huang, Lian; Zhang, Qinghua [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Wang, Yan-dong, E-mail: ydwang@mail.neu.edu.cn [The State Key Laboratory of Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-08-01

    The effects of Ga-doping on the phase transition behaviors and magnetocaloric properties of MnCoGe alloys are systematically investigated through calorimetry and magnetic measurements. The magneto-structural coupling between the structural and magnetic transitions is achieved in the MnCoGe{sub 1–x}Ga{sub x} alloys by decreasing the structural transition temperature via Ga substitution. An 80 K Curie-temperature window is established between Curie temperatures of austenite and martensite phases. Within the window, a magnetic entropy change of 34 J kg{sup −1} K{sup −1} can be obtained near room temperature under the application of a 5 T magnetic field. - Highlights: • The magnetostructural coupling is achieved in MnCoGe alloys with Ga substitution. • An 80 K Curie-temperature window is established in MnCoGe{sub 1–x}Ga{sub x} alloys. • A magnetic entropy change of 34 J kg{sup −1} K{sup −1} is obtained under magnetic field of 5 T.

  13. Indirect measurement of the magnetocaloric effect using a novel differential scanning calorimeter with magnetic field.

    Science.gov (United States)

    Jeppesen, S; Linderoth, S; Pryds, N; Kuhn, L Theil; Jensen, J Buch

    2008-08-01

    A simple and high-sensitivity differential scanning calorimeter (DSC) unit operating under magnetic field has been built for indirect determination of the magnetocaloric effect. The principle of the measuring unit in the calorimeter is based on Peltier elements as heat flow sensors. The high sensitivity of the apparatus combined with a suitable calibration procedure allows very fast and accurate heat capacity measurements under magnetic field to be made. The device was validated from heat capacity measurements for the typical DSC reference material gallium (Ga) and a La(0.67)Ca(0.33)MnO(3) manganite system and the results were highly consistent with previous reported data for these materials. The DSC has a working range from 200 to 340 K and has been tested in magnetic fields reaching 1.8 T. The signal-to-noise ratio is in the range of 10(2)-10(3) for the described experiments. Finally the results have been compared to results from a Quantum Design(R) physical properties measuring system. The configuration of the system also has the advantage of being able to operate with other types of magnets, e.g., permanent magnets or superconducting coils, as well as the ability to be expanded to a wider temperature range.

  14. Giant low field magnetocaloric effect and field-induced metamagnetic transition in TmZn

    Science.gov (United States)

    Li, Lingwei; Yuan, Ye; Zhang, Yikun; Namiki, Takahiro; Nishimura, Katsuhiko; Pöttgen, Rainer; Zhou, Shengqiang

    2015-09-01

    The magnetic properties and the magnetocaloric effect (MCE) in TmZn have been studied by magnetization and heat capacity measurements. The TmZn compound exhibits a ferromagnetic state below a Curie temperature of TC = 8.4 K and processes a field-induced metamagnetic phase transition around and above TC. A giant reversible MCE was observed in TmZn. For a field change of 0-5 T, the maximum values of magnetic entropy change (-ΔSMmax) and adiabatic temperature change (ΔTadmax) are 26.9 J/kg K and 8.6 K, the corresponding values of relative cooling power and refrigerant capacity are 269 and 214 J/kg, respectively. Particularly, the values of -ΔSMmax reach 11.8 and 19.6 J/kg K for a low field change of 0-1 and 0-2 T, respectively. The present results indicate that TmZn could be a promising candidate for low temperature and low field magnetic refrigeration.

  15. Impact of cycle-hysteresis interactions on the performance of giant magnetocaloric effect refrigerants

    Science.gov (United States)

    Brown, T. D.; Karaman, I.; Shamberger, P. J.

    2016-07-01

    Magnetic refrigeration technology based on the giant magnetocaloric effect in solid-state refrigerants is known qualitatively to be limited by dissipative mechanisms accompanying hysteresis in the magneto-structural solid-solid phase transition. In this paper, we quantitatively explore the dependence of cycle performance metrics (cooling power, temperature span, work input, and fractional Carnot efficiency) on hysteresis properties (thermal hysteresis, one-way transition width) of the magneto-structural phase transition in a Ni45Co5Mn36.6In13.4 alloy system. We investigate a variety of Ericsson-type magnetic refrigeration cycles, using a Preisach-based non-equilibrium thermodynamic framework to model the evolution of the alloy's magnetic and thermal properties. Performance metrics are found to depend strongly on hysteresis parameters, regardless of the cycle chosen. However, for a given hysteresis parameter set, the material's transformation temperatures determine a unique cycle that maximizes efficiency. For the model system used undergoing Ericsson cycles with 5 and 1.5 {{T}} maximum field constraint, fractional Carnot efficiencies in excess of 0.9 require thermal hysteresis below 1.5 {{K}} and 0.5 {{K}}, respectively. We conclude briefly with some general materials considerations for mitigating these hysteresis inefficiencies through microstructure design and other materials processing strategies.

  16. Magnetostructural transition and magnetocaloric effect in highly textured Ni-Mn-Sn alloy

    Science.gov (United States)

    Czaja, P.; Chulist, R.; Szczerba, M. J.; Przewoźnik, J.; Olejnik, E.; Chrobak, A.; Maziarz, W.; Cesari, E.

    2016-04-01

    Ni49.4Mn38.5Sn12.1 near single crystal was obtained by the Bridgman method. At room temperature, it consisted of a mixture of the parent austenite phase with the cubic L21 Heusler structure (ac = 5.984 Å) and modulated, tetragonal martensite phase 4M (at = 4.337 Å, ct = 5.655 Å). Under the application of a magnetic field, the specimen undergoes field induced reverse martensitic transformation, which combined with the Curie transition in austenite leads to the coexistence of direct and inverse magnetocaloric effects. The maximum entropy change at 280 K and under 5 T amounts to 3.4 J.kg-1.K-1 for the structural transition and at 316 K reaches -2.7 J.kg-1.K-1 for the magnetic transformation. The magnetic entropy change occurs over a wide temperature span leading to improved refrigerant capacity of 101 J.kg-1 (5 T). Hysteretic losses are considerably reduced, which is promising with respect to improved cyclic stability of such a material.

  17. Giant magnetocaloric effect and temperature induced magnetization jump in GdCrO3 single crystal

    Science.gov (United States)

    Yin, L. H.; Yang, J.; Kan, X. C.; Song, W. H.; Dai, J. M.; Sun, Y. P.

    2015-04-01

    We report on a systematic study of the single-crystal GdCrO3, which shows various novel magnetic features, such as temperature-induced magnetization reversal (TMR), temperature-induced magnetization jump (TMJ), spin reorientation, and giant magnetocaloric effect (MCE). In the field-cooled cooling process with modest magnetic field along the c axis, GdCrO3 first shows a TMR at T c o m p ˜ 120 - 130 K and then an abrupt TMJ with a sign change of magnetization at T j u m p ˜ 52 - 120 K , and finally a spin reorientation at T S R ˜ 4 - 7 K . Interestingly, the remarkable TMJ behavior, which was not reported ever before, persists at higher fields up to 10 kOe even when TMR disappears. In addition, giant MCE with the maximum value of magnetic entropy change reaching ˜31.6 J/kg K for a field change of 44 kOe was also observed in GdCrO3 single crystal, suggesting it could be a potential material for low-T magnetic refrigeration. A possible mechanism for these peculiar magnetic behaviors is discussed based on the various competing magnetic interactions between the 3d electrons of Cr3+ ions and 4f electrons of Gd3+ ions.

  18. Magnetocaloric effect in Mn2-pyrazole-[Nb(CN)8] molecular magnet by relaxation calorimetry

    Science.gov (United States)

    Pełka, R.; Gajewski, M.; Miyazaki, Y.; Yamashita, S.; Nakazawa, Y.; Fitta, M.; Pinkowicz, D.; Sieklucka, B.

    2016-12-01

    Magnetocaloric effect in {[Mn(pyrazole)4]2[Nb(CN)8]·4 H2O}n molecular magnet is reported. It crystallizes in tetragonal I41/a space group. The compound exhibits a phase transition to a long range magnetically ordered state at TN ≈ 22.8 K. Temperature dependences of the magnetic entropy change ΔSM as well as the adiabatic temperature change ΔTad due to applied field change μ0 ΔH in the range of 0.1-9 T have been inferred from the relaxation calorimetry measurements. A systematic approximate approach has been used to determine the lattice contribution to the heat capacity. The maximum value of ΔSM for μ0 ΔH = 5 T is 6.83 J mol-1 K-1 (6.65 J kg-1 K-1) at 24.3 K. The corresponding maximum value of ΔTad is 1.4 K at 23.8 K. The temperature dependence of the exponent n characterizing the field dependence of ΔSM has been estimated. It attains the value of 0.64 at the transition temperature, which is consistent with the 3D Heisenberg universality class. A hitherto unobserved two-peak structure has been revealed in the temperature dependence of ΔTad.

  19. Magnetic Anisotropic Energy Gap and Strain Effect in Au Nanoparticles

    Directory of Open Access Journals (Sweden)

    Shih Po-Hsun

    2009-01-01

    Full Text Available Abstract We report on the observation of the size effect of thermal magnetization in Au nanoparticles. The thermal deviation of the saturation magnetization departs substantially from that predicted by the Bloch T3/2-law, indicating the existence of magnetic anisotropic energy. The results may be understood using the uniaxial anisotropy Heisenberg model, in which the surface atoms give rise to polarized moments while the magnetic anisotropic energy decreases as the size of the Au nanoparticles is reduced. There is a significant maximum magnetic anisotropic energy found for the 6 nm Au nanoparticles, which is associated with the deviation of the lattice constant due to magnetocrystalline anisotropy.

  20. Magnetocaloric properties of metallic nanostructures

    Directory of Open Access Journals (Sweden)

    Khurram S. Khattak

    2015-12-01

    Full Text Available A compilation of magnetocaloric properties of metallic nanostructures with Curie temperature (TC between 260 and 340 K has been tabulated. The tabulated data show that nanostructure plays an important role in enhancing the magnetocaloric properties of a material, namely by reducing the peak of magnetic entropy, but broadening of the magnetocaloric effect curve with an average of 10 K sliding window for Curie temperature. A second table lists all bulk metallic and intermetallic materials, in which there is no nanostructural data, with an entropy change of at least 20 J/kg K and a Curie temperature between 260 and 340 K. We propose that further experiments should be made on the nanostructured form of these materials.

  1. Second Law Violation By Magneto-Caloric Effect Adiabatic Phase Transition of Type I Superconductive Particles

    Directory of Open Access Journals (Sweden)

    Peter Keefe

    2004-03-01

    Full Text Available Abstract: The nature of the thermodynamic behavior of Type I superconductor particles, having a cross section less than the Ginzburg-Landau temperature dependent coherence length is discussed for magnetic field induced adiabatic phase transitions from the superconductive state to the normal state. Argument is advanced supporting the view that when the adiabatic magneto-caloric process is applied to particles, the phase transition is characterized by a decrease in entropy in violation of traditional formulations of the Second Law, evidenced by attainment of a final process temperature below that which would result from an adiabatic magneto-caloric process applied to bulk dimensioned specimens.

  2. Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn1+χCo1-χGe alloys

    Institute of Scientific and Technical Information of China (English)

    Ma Sheng-Can; Wang Dun-Hui; Xuan Hai-Cheng; Shen Ling-Jia; Cao Qing-Qi; Du You-Wei

    2011-01-01

    We have investigated the magnetic transition and magnetocaloric effects of Mn1+χCo1-χGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn (χ = 0.11) gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.

  3. Tuneable Giant Magnetocaloric Effect in (Mn,Fe)2(P,Si) Materials by Co-B and Ni-B Co-Doping

    OpenAIRE

    Nguyen Thang; Niels Harmen van Dijk; Ekkes Brück

    2016-01-01

    The influence of Co (Ni) and B co-doping on the structural, magnetic and magnetocaloric properties of (Mn,Fe) 2 (P,Si) compounds is investigated by X-ray diffraction (XRD), differential scanning calorimetry, magnetic and direct temperature change measurements. It is found that Co (Ni) and B co-doping is an effective approach to tune both the Curie temperature and the thermal hysteresis of (Mn,Fe) 2 (P,Si) materials without losing either the giant magnetocaloric effect or the pos...

  4. Magnetocaloric Effect in Colossal Magnetoresistance Material (La0.6Dy0.1)Sr0.3MnO3

    Institute of Scientific and Technical Information of China (English)

    Cai Zhirang; Xu Sujun; Liu Ning; Sun Yong; Tong Wei; Zhang Yuheng

    2005-01-01

    The magnetocaloric effect in the A-site doping colossal magnetoresistance material (La0.6Dy0.1)Sr0.3MnO3 was studied. From the measurement and calculation of isothermal magnetization (M-H) curves under various temperatures, a large magnetocaloric effect with ferromagnetic-paramagnetic transition, additional magnetism exchange action introduces additional magnetic entropy change was discovered. This result suggests that (La0.6Dy0.1)Sr0.3MnO3 is a suitable candidate as working substance at room temperature in magnetic refrigeration technology.

  5. Spatially resolved measurements of the magnetocaloric effect and the local magnetic field using thermography

    DEFF Research Database (Denmark)

    Christensen, Dennis; Bjørk, Rasmus; Nielsen, Kaspar Kirstein

    2010-01-01

    The magnetocaloric effect causes a magnetic material to change temperature upon application of a magnetic field. Here, spatially resolved measurements of the adiabatic temperature change are performed on a plate of gadolinium using thermography. The adiabatic temperature change is used to extract...

  6. Reentrant phenomenon and inverse magnetocaloric effect in a generalized spin-(1/2,  s) Fisher’s super-exchange antiferromagnet

    Science.gov (United States)

    Gálisová, Lucia

    2016-11-01

    The thermodynamic and magnetocaloric properties of a generalized spin-(1/2,  s) Fisher’s super-exchange antiferromagnet are investigated precisely by using the decoration-iteration mapping transformation. Besides the critical temperature, sublattice magnetization, total magnetization, entropy and specific heat, the isothermal entropy change and adiabatic temperature change are also rigorously calculated in order to examine the cooling efficiency of the model in the vicinity of the first- and second-order phase transitions. It is shown that an enhanced inverse magnetocaloric effect occurs around the temperature interval {{T}\\text{c}}(B\

  7. Understanding the role played by Fe on the tuning of magnetocaloric effect in Tb5Si2Ge2

    Energy Technology Data Exchange (ETDEWEB)

    Pereira, Andre [University of Porto, Portugal; Moreira Dos Santos, Antonio F [ORNL; Magen Dominguez, Cesar [ORNL; Sousa, Joao Bessa [University of Porto, Portugal; Algarabel, Pedro A. [University of Zaragoza, Spain; Ren, Yang [Argonne National Laboratory (ANL); Ritter, Clemens [Institut Laue-Langevin (ILL); Morellon, Luis [University of Zaragoza, Spain; Ibarra, M. Ricardo [University of Zaragoza, Spain; Araujo, Joao Pedro [University of Porto, Portugal

    2011-01-01

    In this work, it is shown that when replacing Ge by Fe in Tb5Si2Ge2 the structural transition still occurs and enhances the Magnetocaloric effect (up to 66%) with maximum of MCE at a critical Fe amount where the magnetic and structural transitions become fully coupled. It is observed that Fe concentration is able to mimic the e?ect of external pressure as it induces a complex microstructure, that tunes long range strain ?elds. This knowledge is crucial for the development of strategies towards materials with improved performance for e?cient magnetic refrigeration applications.

  8. Adiabatic Magnetooptical and Magnetocaloric Effects of Tb3GasO12 at Low Temperature in Strong Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    ZHANG Guo-Ying; CHEN Hui; YANG Dan; HU Feng; LIU Hai-Shun

    2012-01-01

    In a strong magnetic field, the magnetic susceptibility χ and equivalent magnetic susceptibility λχ of some paramagnetic materials depend sensitively on the applied field He. Here A is the coefficient of the effective field Hm, which relates to the superexchange interaction between the electrons in different magnetic ions. We present the forms of the adiabatic equivalent λχ and the effective field Hm. The adiabatic magneto-caloric and magneto-optical effects of paramagnetic terbium gallate garnet Tb3 Ga5 O12 are calculated at 6K in strong magnetic fields. Our calculated results are in agreement with the experimental data.%In a strong magnetic field,the magnetic susceptibility χ and equivalent magnetic susceptibility λχ of some paramagnetic materials depend sensitively on the applied field He.Here λ is the coefficient of the effective field Hm,which relates to the superexchange interaction between the electrons in different magnetic ions.We present the forms of the adiabatic equivalent λχ and the effective field Hm.The adiabatic magneto-caloric and magnetooptical effects of paramagnetic terbium gallate garnet Tb3Ga5O12 are calculated at 6 K in strong magnetic fields.Our calculated results are in agreement with the experimental data.

  9. Critical dependence of magnetostructural coupling and magnetocaloric effect on particle size in Mn-Fe-Ni-Ge compounds

    Science.gov (United States)

    Wu, Rongrong; Shen, Feiran; Hu, Fengxia; Wang, Jing; Bao, Lifu; Zhang, Lei; Liu, Yao; Zhao, Yingying; Liang, Feixiang; Zuo, Wenliang; Sun, Jirong; Shen, Baogen

    2016-01-01

    Magnetostructural coupling, which is the coincidence of crystallographic and magnetic transition, has obtained intense attention for its abundant magnetoresponse effects and promising technological applications, such as solid-state refrigeration, magnetic actuators and sensors. The hexagonal Ni2In-type compounds have attracted much attraction due to the strong magnetostructural coupling and the resulted giant negative thermal expansion and magnetocaloric effect. However, the as-prepared samples are quite brittle and naturally collapse into powders. Here, we report the effect of particle size on the magnetostructural coupling and magnetocaloric effect in the Ni2In-type Mn-Fe-Ni-Ge compound, which undergoes a large lattice change across the transformation from paramagnetic austenite to ferromagnetic martensite. The disappearance of martensitic transformation in a large amount of austenitic phase with reducing particle size, to our best knowledge, has not been reported up to now. The ratio can be as high as 40.6% when the MnNi0.8Fe0.2Ge bulk was broken into particles in the size range of 5~15 μm. Meanwhile, the remained magnetostructural transition gets wider and the magnetic hysteresis becomes smaller. As a result, the entropy change drops, but the effective cooling power RCeffe increases and attains to the maximum at particles in the range of 20~40 μm. These observations provide constructive information and highly benefit practical applications for this class of novel magnetoresponse materials. PMID:26883719

  10. Critical dependence of magnetostructural coupling and magnetocaloric effect on particle size in Mn-Fe-Ni-Ge compounds

    Science.gov (United States)

    Wu, Rongrong; Shen, Feiran; Hu, Fengxia; Wang, Jing; Bao, Lifu; Zhang, Lei; Liu, Yao; Zhao, Yingying; Liang, Feixiang; Zuo, Wenliang; Sun, Jirong; Shen, Baogen

    2016-02-01

    Magnetostructural coupling, which is the coincidence of crystallographic and magnetic transition, has obtained intense attention for its abundant magnetoresponse effects and promising technological applications, such as solid-state refrigeration, magnetic actuators and sensors. The hexagonal Ni2In-type compounds have attracted much attraction due to the strong magnetostructural coupling and the resulted giant negative thermal expansion and magnetocaloric effect. However, the as-prepared samples are quite brittle and naturally collapse into powders. Here, we report the effect of particle size on the magnetostructural coupling and magnetocaloric effect in the Ni2In-type Mn-Fe-Ni-Ge compound, which undergoes a large lattice change across the transformation from paramagnetic austenite to ferromagnetic martensite. The disappearance of martensitic transformation in a large amount of austenitic phase with reducing particle size, to our best knowledge, has not been reported up to now. The ratio can be as high as 40.6% when the MnNi0.8Fe0.2Ge bulk was broken into particles in the size range of 5~15 μm. Meanwhile, the remained magnetostructural transition gets wider and the magnetic hysteresis becomes smaller. As a result, the entropy change drops, but the effective cooling power RCeffe increases and attains to the maximum at particles in the range of 20~40 μm. These observations provide constructive information and highly benefit practical applications for this class of novel magnetoresponse materials.

  11. Critical dependence of magnetostructural coupling and magnetocaloric effect on particle size in Mn-Fe-Ni-Ge compounds.

    Science.gov (United States)

    Wu, Rongrong; Shen, Feiran; Hu, Fengxia; Wang, Jing; Bao, Lifu; Zhang, Lei; Liu, Yao; Zhao, Yingying; Liang, Feixiang; Zuo, Wenliang; Sun, Jirong; Shen, Baogen

    2016-02-17

    Magnetostructural coupling, which is the coincidence of crystallographic and magnetic transition, has obtained intense attention for its abundant magnetoresponse effects and promising technological applications, such as solid-state refrigeration, magnetic actuators and sensors. The hexagonal Ni2In-type compounds have attracted much attraction due to the strong magnetostructural coupling and the resulted giant negative thermal expansion and magnetocaloric effect. However, the as-prepared samples are quite brittle and naturally collapse into powders. Here, we report the effect of particle size on the magnetostructural coupling and magnetocaloric effect in the Ni2In-type Mn-Fe-Ni-Ge compound, which undergoes a large lattice change across the transformation from paramagnetic austenite to ferromagnetic martensite. The disappearance of martensitic transformation in a large amount of austenitic phase with reducing particle size, to our best knowledge, has not been reported up to now. The ratio can be as high as 40.6% when the MnNi0.8Fe0.2Ge bulk was broken into particles in the size range of 5~15 μm. Meanwhile, the remained magnetostructural transition gets wider and the magnetic hysteresis becomes smaller. As a result, the entropy change drops, but the effective cooling power RCeffe increases and attains to the maximum at particles in the range of 20~40 μm. These observations provide constructive information and highly benefit practical applications for this class of novel magnetoresponse materials.

  12. Magnetism and magnetocaloric effect in multicomponent Laves-phase compounds: Study and comparative analysis

    Energy Technology Data Exchange (ETDEWEB)

    Ćwik, J., E-mail: cwikjac@ml.pan.wroc.pl

    2014-01-15

    This paper presents a review and results of comparative study of the influence of Gd on some physical properties of (R{sub 0.9}R′{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2} solid solutions with R=Dy, Ho and R′=Er, Ho and x varied from 0.05 to 0.15. Powder X-ray diffraction analysis performed at room temperature revealed that all studied solid solutions solidify with the formation of a Laves-phase MgCu{sub 2}-type structure (space group Fd−3m). The magnetization behavior and the magnetic transition are analyzed in terms of the Landau theory. The studies of magnetic properties and heat capacity showed that a relatively small Gd addition significantly increases T{sub C} of the compounds. The maximum percentage increase in T{sub C}, namely, ∼43% was observed for (Ho{sub 0.9}Er{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2}. However, the highest temperature was noted for the (Dy{sub 0.9}Ho{sub 0.1}){sub 0.85}Gd{sub 0.15}Co{sub 2} solid solution; it is T{sub C}=183.4 K. Below the ordering temperature, all samples are ferrimagnetically ordered; at high temperatures, they are Curie–Weiss paramagnets. Moreover, a small Gd addition eliminates the field-induced magnetic transition near T{sub C} and, as consequence, transforms the nature of magnetic transition from the first- to second-order. The magnetocaloric effect has been estimated in terms of both isothermal magnetic entropy and adiabatic temperature changes. The highest adiabatic temperature change ΔT{sub ad}=3 K and highest isothermal entropy change ΔS{sub mag}=12.1 J/kg K were observed for (Ho{sub 0.9}Er{sub 0.1}){sub 0.95}Gd{sub 0.05}Co{sub 2} at ∼90 K in magnetic fields of 2 T and 3 T, respectively. A decrease in the entropy change has been observed with increasing Gd content in all studied samples. The smallest values of ΔS{sub mag} were observed for the (Dy{sub 0.9}Ho{sub 0.1}){sub 1−x}Gd{sub x}Co{sub 2} solid solutions. Under an external field change of from 0 to 3 T, the maximum entropy change for (Dy{sub 0

  13. Magneto-caloric effect in the pseudo-binary intermetallic YPrFe{sub 17} compound

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez, Pablo [Departamento de Fisica, Universidad de Oviedo, Calvo Sotelo, s/n, 33007 Oviedo (Spain); Gorria, Pedro, E-mail: pgorria@uniovi.es [Departamento de Fisica, Universidad de Oviedo, Calvo Sotelo, s/n, 33007 Oviedo (Spain); Sanchez Llamazares, Jose L. [Division de Materiales Avanzados, Instituto Potosino de Investigacion Cientifica y Tecnologica, Camino a la presa San Jose 2055, CP 78216, San Luis Potosi (Mexico); Perez, Maria J. [Departamento de Fisica, Universidad de Oviedo, Calvo Sotelo, s/n, 33007 Oviedo (Spain); Franco, Victorino [Departamento de Fisica de la Materia Condensada, ICMSE-CSIC, Universidad de Sevilla, P.O. Box 1065, 41080 Sevilla (Spain); Reiffers, Marian; Kovac, Jozef [Institute of Experimental Physics, Watsonova 47, SK-04001 Kosice (Slovakia); Puente-Orench, Ines [Institute Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble (France); Blanco, Jesus A. [Departamento de Fisica, Universidad de Oviedo, Calvo Sotelo, s/n, 33007 Oviedo (Spain)

    2011-12-15

    Highlights: Black-Right-Pointing-Pointer YPrFe{sub 17} exhibits a broad {Delta}S{sub M}(T) associated with the ferro-to-paramagnetic phase transition (T{sub C} Almost-Equal-To 290 K). Black-Right-Pointing-Pointer We obtain |{Delta}S{sub M}| Almost-Equal-To 2.3 J kg{sup -1} K{sup -1} and RCP Almost-Equal-To 100 J kg{sup -1}for a magnetic field change of 1.5 T. Black-Right-Pointing-Pointer A single master curve for {Delta}S{sub M} is found when compared with other isostructural R{sub 2}Fe{sub 17} binary alloys. - Abstract: We have synthesized the intermetallic YPrFe{sub 17} compound by arc-melting. X-ray and neutron powder diffraction show that the crystal structure is rhombohedral with R3{sup Macron }m space group (Th{sub 2}Zn{sub 17}-type). The investigated compound exhibits a broad isothermal magnetic entropy change {Delta}S{sub M}(T) associated with the ferro-to-paramagnetic phase transition (T{sub C} Almost-Equal-To 290 K). The |{Delta}S{sub M}| ( Almost-Equal-To 2.3 J kg{sup -1} K{sup -1}) and the relative cooling power ( Almost-Equal-To 100 J kg{sup -1}) have been calculated for applied magnetic field changes up to 1.5 T. A single master curve for {Delta}S{sub M} under different values of the magnetic field change can be obtained by a rescaling of the temperature axis. The results are compared and discussed in terms of the magneto-caloric effect in the isostructural R{sub 2}Fe{sub 17} (R = Y, Pr and Nd) binary intermetallic alloys.

  14. Magnetocaloric effect in M-pyrazole-[Nb(CN)(8)] (M = Ni, Mn) molecular compounds.

    Science.gov (United States)

    Fitta, Magdalena; Bałanda, Maria; Mihalik, Marian; Pełka, Robert; Pinkowicz, Dawid; Sieklucka, Barbara; Zentkova, Maria

    2012-12-19

    We report a study of magnetocaloric effect (MCE) in cyanido-bridged {[M(II)(pyrazole)(4)](2)[Nb(IV)(CN)(8)]·4H(2)O}(n) molecular compounds where M = Ni, Mn, pyrazole = C(3)H(4)N(2). The substances show a sharp phase transition to a long range magnetically ordered state, with ferromagnetic coupling between M and Nb sublattices in the case of the Ni-based sample 1 (T(c) = 13.4 K) and ferrimagnetic coupling for the Mn-based sample 2 (T(c) = 23.8 K). The magnetic entropy change ΔS due to applied field change ΔH as a function of temperature was determined by the magnetization and heat capacity measurements. The maximum value of ΔS at μ(0)ΔH = 5 T is 6.1 J mol(-1) K(-1) (5.9 J kg(-1) K(-1)) for 1 at T = 14 K and 6.7 J mol(-1) K(-1) (6.5 J kg(-1) K(-1)) for 2 at T = 25 K. MCE data at different applied fields have been presented as one universal curve, which confirms magnetic transitions in 1 and 2 to be of second order. The temperature dependences of the n exponent characterizing the dependence of ΔS on ΔH have been obtained. The n(T(c)) values, consistent with the shape of the magnetization curves, pointed to the 3D Heisenberg behaviour for 2 and some anisotropy, probably of the XY type, for 1. The (H/T(c))(2/3) dependence of the maximum entropy change has been tested in the ferrimagnetic Mn(2)-L-[Nb(CN)(8)] (L = C(3)H(4)N(2), C(4)H(4)N(2)) series.

  15. Magnetocaloric Materials and the Optimization of Cooling Power Density

    Science.gov (United States)

    Wikus, Patrick; Canavan, Edgar; Heine, Sarah Trowbridge; Matsumoto, Koichi; Numazawa, Takenori

    2014-01-01

    The magnetocaloric effect is the thermal response of a material to an external magnetic field. This manuscript focuses on the physics and the properties of materials which are commonly used for magnetic refrigeration at cryogenic temperatures. After a brief overview of the magnetocaloric effect and associated thermodynamics, typical requirements on refrigerants are discussed from a standpoint of cooling power density optimization. Finally, a compilation of the most important properties of several common magnetocaloric materials is presented.

  16. The physical mechanism of magnetic field controlled magnetocaloric effect and magnetoresistance in bulk PrGa compound.

    Science.gov (United States)

    Zheng, X Q; Wu, H; Chen, J; Zhang, B; Li, Y Q; Hu, F X; Sun, J R; Huang, Q Z; Shen, B G

    2015-10-12

    The PrGa compound shows excellent performance on the magnetocaloric effect (MCE) and magnetoresistance (MR). The physical mechanism of MCE and MR in PrGa compound was investigated and elaborated in detail on the basis of magnetic measurement, heat capacity measurement and neutron powder diffraction (NPD) experiment. New types of magnetic structure and magnetic transition are found. The results of the NPD along with the saturation magnetic moment (MS) and magnetic entropy (SM) indicate that the magnetic moments are randomly distributed within the equivalent conical surface in the ferromagnetic (FM) temperature range. PrGa compound undergoes an FM to FM transition and an FM to paramagnetic (PM) transition as temperature increases. The magnetizing process was discussed in detail and the physical mechanism of the magnetic field controlled magnetocaloric effect (MCE) and the magnetoresistance (MR) was studied. The formation of the plateau on MCE curve was explained and MR was calculated in detail on the basis of the magnetic structure and the analysis of the magnetizing process. The experimental results are in excellent agreement with the calculations. Finally, the expression of MR = β(T)X(2) and its application conditions were discussed, where X is M(H)/Meff, and Meff is the paramagnetic effective moment.

  17. The physical mechanism of magnetic field controlled magnetocaloric effect and magnetoresistance in bulk PrGa compound

    Science.gov (United States)

    Zheng, X. Q.; Wu, H.; Chen, J.; Zhang, B.; Li, Y. Q.; Hu, F. X.; Sun, J. R.; Huang, Q. Z.; Shen, B. G.

    2015-10-01

    The PrGa compound shows excellent performance on the magnetocaloric effect (MCE) and magnetoresistance (MR). The physical mechanism of MCE and MR in PrGa compound was investigated and elaborated in detail on the basis of magnetic measurement, heat capacity measurement and neutron powder diffraction (NPD) experiment. New types of magnetic structure and magnetic transition are found. The results of the NPD along with the saturation magnetic moment (MS) and magnetic entropy (SM) indicate that the magnetic moments are randomly distributed within the equivalent conical surface in the ferromagnetic (FM) temperature range. PrGa compound undergoes an FM to FM transition and an FM to paramagnetic (PM) transition as temperature increases. The magnetizing process was discussed in detail and the physical mechanism of the magnetic field controlled magnetocaloric effect (MCE) and the magnetoresistance (MR) was studied. The formation of the plateau on MCE curve was explained and MR was calculated in detail on the basis of the magnetic structure and the analysis of the magnetizing process. The experimental results are in excellent agreement with the calculations. Finally, the expression of MR = β(T)X2 and its application conditions were discussed, where X is M(H)/Meff, and Meff is the paramagnetic effective moment.

  18. Direct and indirect measurement of the magnetocaloric effect in a La0.6Ca0.4MnO3 ceramic perovskite

    DEFF Research Database (Denmark)

    Dinesen, A.R.; Linderoth, Søren; Mørup, Steen

    2002-01-01

    The adiabatic temperature change DeltaT(ad) due to a change of the external magnetic field (the magnetocaloric effect) for a perovskite-type La0.6Ca0.4MnO3 sample has been measured directly and indirectly (from the entropy change) and the results are compared. From the indirect method, involving...

  19. Reversible crystal-to-amorphous-to-crystal phase transition and a large magnetocaloric effect in a spongelike metal organic framework material.

    Science.gov (United States)

    Tian, Chong-Bin; Chen, Rui-Ping; He, Chao; Li, Wei-Jin; Wei, Qi; Zhang, Xu-Dong; Du, Shao-Wu

    2014-02-21

    Reversible crystal-to-amorphous-to-crystal phase transition accompanied by changes in magnetic and NLO properties was first observed in a rigid non-porous spongelike MOF material. The crystal phase exhibits a high magnetocaloric effect, while the amorphous phase has potential application as a magnetic DMF sensor.

  20. Magnetocaloric effect and critical behaviour in Mn2-pyridazine-[Nb(CN)8] molecular compound under press.

    Science.gov (United States)

    Fitta, Magdalena; Bałanda, Maria; Pełka, Robert; Konieczny, Piotr; Pinkowicz, Dawid; Sieklucka, Barbara

    2013-12-11

    A comprehensive study of magnetocaloric effect (MCE) and critical behaviour in the ferrimagnetic Mn2–pyridazine–[Nb(CN)8] molecular magnet under hydrostatic pressure is reported. The pressure-induced structural changes provoke the strengthening of magnetic interaction between Mn and Nb centres. Consequently, an increase of critical temperature Tc is observed from 43 K for a sample at ambient pressure (A) to 52.5 K for a sample under a pressure of 1.19 GPa (AHP). The magnetocaloric effect was determined by the magnetization measurements. The application of a hydrostatic pressure of 1.19 GPa causes a decrease in the maximum value of magnetic entropy change ΔS, which for AHP is equal to 4.63 J mol−1 K−1 (7.73 J kg−1 K−1) at μ0ΔH = 5 T, while for A it is 5.36 J mol−1 K−1 (8.95 J kg−1 K−1) for the same magnetic field change. The temperature-dependent parameter n obtained for AHP, describing the field dependence of MCE, is consistent with other critical exponents determined from magnetization measurements. The critical exponents allow us to classify AHP to the 3D Heisenberg universality class, similar to the case of the non-pressurized sample.

  1. Nitronyl nitroxide based 2p-3d-4f chains with the magnetocaloric effect and slow magnetic relaxation.

    Science.gov (United States)

    Wang, Xiufeng; Li, Cun; Sun, Juan; Li, Licun

    2015-11-14

    Four new nitronyl nitroxide radical based hetero-tri-spin one-dimensional compounds, namely [{Ln(hfac)3}3{Cu(hfac)2}{NIT-Ph(OMe)2}4]n (Ln = Gd (1), Tb (2), Dy (3), Er (4); hfac = hexafluoroacetylacetonate; NIT-Ph(OMe)2 = 2-(2',4'-dimethoxyphenyl)-4,4,5,5-tetramethyl-imidazolyl-1-oxyl-3-oxide) have been successfully prepared. Single crystal X-ray crystallographic analysis reveals that complexes 1-4 possess a 1D chain structure with a repeating [Cu-Rad-Ln-Rad-Ln-Rad-Ln-Rad] moiety in which Ln(hfac)3 and Cu(hfac)2 units are bridged by nitronyl nitroxide radicals through the NO groups. DC magnetic studies found that ferromagnetic interactions between metals and the coordinated NO groups are active in all four compounds. The Tb derivative displays frequency dependent ac magnetic susceptibilities, indicating slow magnetic relaxation behavior. The Gd complex shows an important cryogenic magnetocaloric effect with the entropy change (-ΔSm) of 13.5 J kg(-1) K(-1) at 2 K and a magnetic field of 7 T, representing the first example of Gd-radical molecular species exhibiting the magnetocaloric effect.

  2. Debonding analyses in anisotropic materials with strain- gradient effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2012-01-01

    A unit cell approach is adopted to numerically analyze the effect of plastic anisotropy on damage evolution in a micro-reinforced composite. The matrix material exhibit size effects and a visco-plastic anisotropic strain gradient plasticity model accounting for such size effects is adopted. A con...

  3. Debonding Analyses in Anisotropic Materials with Strain-Gradient Effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2012-01-01

    A unit cell approach is adopted to numerically analyze the effect of plastic anisotropy on damage evolution in a microreinforced composite. The matrix material exhibit size effects and a visco-plastic anisotropic strain gradient plasticity model accounting for such size effects is adopted....... A conventional cohesive law is extended such that both the average as well as the jump in plastic strain across the fiber-matrix interface are accounted for. Results are shown for both conventional isotropic and anisotropic materials as well as for higher order isotropic and anisotropic materials...... with and without debonding. Generally, the strain gradient enhanced material exhibits higher load carry capacity compared to the corresponding conventional material. A sudden stress drop occurs in the macroscopic stress-strain response curve due to fiber-matrix debonding and the results show that a change in yield...

  4. A universal curve for the magnetocaloric effect: an analysis based on scaling relations

    Energy Technology Data Exchange (ETDEWEB)

    Franco, V; Conde, A; Blazquez, J S [Departamento de Fisica de la Materia Condensada, ICMSE-CSIC, Universidad de Sevilla, PO Box 1065, 41080 Sevilla (Spain); Romero-Enrique, J M [Departamento de Fisica Atomica, Molecular y Nuclear, Area de Fisica Teorica, Universidad de Sevilla, PO Box 1065, 41080 Sevilla (Spain)

    2008-07-16

    The universal character of the recent experimentally found master curve for the magnetic entropy change, {delta}S{sub M}, in studies of the magnetocaloric response of materials is analytically justified by using scaling arguments. The validity of the obtained scaling relations is checked against experimental data as well as the mean field and Heisenberg models. The curves are unique for each universality class. It is shown that the universal curve can be practically constructed in two different ways, reducing the number of required parameters with respect to the previous phenomenological derivation. This opens the possibility of an inexpensive screening of the performance of magnetocaloric materials, as it allows extrapolations to magnetic fields or temperatures not available in some laboratories.

  5. Microstructural Anisotropy of Magnetocaloric Gadolinium Cylinders: Effect on the Mechanical Properties of the Material

    Directory of Open Access Journals (Sweden)

    Darja Steiner Petrovič

    2016-05-01

    Full Text Available The development of advanced materials and technologies based on magnetocaloric Gd and its compounds requires an understanding of the dependency of mechanical properties on their underlying microstructure. Therefore, the aim of the study was to characterize microstructural inhomogeneities in the gadolinium that can be used in magnetocaloric refrigeration systems. Microstructures of magnetocaloric gadolinium cylinders were investigated by light microscopy and FE-SEM (Field Emission Scanning Electron Microscopy, EDS (Energy-dispersive X-ray Spectroscopy, and BSE (Back-scattered Electrons in both the extrusion and the extrusion-transversal directions. XRD (X-ray Diffraction analyses were performed to reveal the presence of calcium- and fluorine-based compounds. Metallographic characterization showed an oxidized and inhomogeneous microstructure of the cross-sections. The edges and the outer parts of the cylinders were oxidized more intensively on the surfaces directly exposed to the processing tools. Moreover, a significant morphological anisotropy of the non-metallic inclusions was observed. CaF inclusions act as active nucleation sites for internal oxidation. The non-metallic, Ca- and F-containing inclusions can be classified as complex calciumoxyfluorides. The solubility of Er and Yb in the CaF was negligible compared to the Gd matrix and/or the oxide phase. Lower mechanical properties of the material are a consequence of the lower structural integrity due to selective oxidation of surfaces and interfaces.

  6. Magnetocaloric effect in Ni-Zn ferrite nanoparticles prepared by using solution combustion

    Energy Technology Data Exchange (ETDEWEB)

    Lee, K. D.; Kambale, R. C.; Hur, N. [Inha University, Incheon (Korea, Republic of)

    2014-12-15

    Ni{sub x}Zn{sub 1-x}Fe{sub 2}O{sub 4} (x = 0.2 and 0.3) ferrite nanoparticles with sizes ranging from 65 to 70 nm were synthesized employing the solution combustion route. The magnetocaloric behavior was investigated within the 50 K ≤ T ≤ 400 K range of temperatures (T). The entropy change (ΔS) and the adiabatic temperature change (ΔT) were derived from magnetization (M) and specific heat (C{sub P} ) measurements. Both compositions exhibited broad peaks for the isothermal entropy change. The magnetic field (H)-dependent ΔT was analyzed within the mean-field approximation scheme, and the observed magnetocaloric properties of the nanoparticle samples were compared with those of a bulk sample. Our study suggests that the magnetocaloric properties of magnetic oxides strongly depend on the particle size; thus, particle size should be considered as a key tuning parameter in the optimization of magnetic refrigeration.

  7. Assessment of the magnetocaloric effect in La,Pr(Fe,Si) under cycling

    Science.gov (United States)

    Kaeswurm, B.; Franco, V.; Skokov, K. P.; Gutfleisch, O.

    2016-05-01

    The response of a magnetocaloric material to periodic variations of magnetic field and temperature corresponding to those occurring during a magnetic refrigeration process is studied. A series of simple measurement protocols are suggested which are used to obtain a value for the cyclic response of the magnetic entropy change associated with the magnetic transition. The entropy values are compared to direct measurements of the temperature change under adiabatic conditions. The procedure is illustrated on the first order magnetocaloric material La0.6Pr0.4Fe11.6Si1.4 and provides a basis for comparison of the suitability of different hysteretic magnetocaloric materials for application in a magnetic refrigerator. For the alloy studied here the peak magnetic entropy change of -28±1 J kg-1 K-1 in a field change of 2 T is not affected by cycling, but the full width at half maximum of the peak decreases from 8.7 K to 3.8 K.

  8. Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metals

    Science.gov (United States)

    Ling-Wei, Li

    2016-03-01

    The magnetocaloric effect (MCE) in many rare earth (RE) based intermetallic compounds has been extensively investigated during the last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress on studying the magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal(s) (Zn, Mg, and Cd). Some of them exhibit promising MCE properties, which make them attractive for low temperature magnetic refrigeration. Characteristics of the magnetic transition, origin of large MCE, as well as the potential application of these compounds are thoroughly discussed. Additionally, a brief review of the magnetic and magnetocaloric properties in the quaternary rare earth nickel boroncarbides RENi2B2C superconductors is also presented. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374081 and 11004044), the Fundamental Research Funds for the Central Universities, China (Grant Nos. N150905001, L1509006, and N140901001), the Japan Society for the Promotion of Science Postdoctoral Fellowships for Foreign Researchers (Grant No. P10060), and the Alexander von Humboldt (AvH) Foundation (Research stipend to L. Li).

  9. Martensitic transformation and magnetocaloric effect in Mn-Ni-Nb-Sn shape memory alloys: The effect of 4d transition-metal doping

    Energy Technology Data Exchange (ETDEWEB)

    Han Zhida, E-mail: zhida.han@gmail.com [Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Jiangsu Laboratory of Advanced Functional Materials, Changshu Institute of Technology, Changshu 215500 (China); Department of Physics, Nanjing University, Nanjing 210093 (China); Chen Xi; Zhang Yao; Chen Jie [Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Qian Bin; Jiang Xuefan [Department of Physics, Changshu Institute of Technology, Changshu 215500 (China); Jiangsu Laboratory of Advanced Functional Materials, Changshu Institute of Technology, Changshu 215500 (China); Wang Dunhui; Du Youwei [Department of Physics, Nanjing University, Nanjing 210093 (China)

    2012-02-25

    Highlights: Black-Right-Pointing-Pointer The first study of 4d transition-metal addition in Ni-Mn-based ferromagnetic shape memory alloys. Black-Right-Pointing-Pointer The martensitic transformation temperatures decrease with the increase of Nb content. Black-Right-Pointing-Pointer 4d transition-metal doping provide an alternative way to tailor the phase transitions and magnetocaloric effect Ni-Mn-X (X = In, Sn, Sb) alloys. - Abstract: The influence of 4d transition-metal Nb substitution for Ni in Mn{sub 50}Ni{sub 50-y}Sn{sub y} (y = 9, 10) alloys on the phase transitions and magnetocaloric effect was investigated. Austenitic phase of Nb-doped Mn{sub 50}Ni{sub 50-y}Sn{sub y} alloys have the cubic structure, and Nb addition results in the expansion of cell volume. The martensitic transformation temperatures decrease with the increase of Nb content, which could be explained by the decrease of valence electron concentration. Our results indicate that 4d transition-metal doping may provide an alternative way to tailor the martensitic transformation and the magnetocaloric effect in ferromagnetic shape memory alloys.

  10. The magnetocaloric effect with critical behavior of a periodic Anderson-like organic polymer.

    Science.gov (United States)

    Ding, L J; Zhong, Y; Fan, S W; Zhu, L Y

    2016-01-07

    We study the magnetocaloric effect and the critical behavior of a periodic Anderson-like organic polymer using Green's function theory, in which the localized f orbitals hybridize with the conduction orbitals at even sites. The field-induced metal-insulator transitions with the magnetic Grüneisen parameter showing |Γh|∼T(-1) power-law critical behaviour are revealed, which provides a new thermodynamic means for probing quantum phase transitions. It is found that the competition of up-spin and down-spin hole excitations is responsible for the double peak structure of magnetic entropy change (-ΔS) for the dominant Kondo coupling case, implying a double magnetic cooling process via demagnetization, which follows a power law dependence of the magnetic field h: -ΔS∼h(n). The local exponent n tends to 1 and 2 below and above TC, while has a minimum of 0.648 at TC, which is in accordance with the experimental observation of perovskite manganites Pr0.55Sr0.45MnO3 and Nd0.55Sr0.45MnO3 (J. Y. Fan et al., Appl. Phys. Lett., 2011, 98, 072508; Europhys. Lett., 2015, 112, 17005) corresponding to the conventional ferromagnets within the mean field theory -ΔS∼h(2/3). At TC, the -ΔS∼h curves with a convex curvature superpose each other for small V values, which are separated by the large V case, distinguishing the RKKY interaction and Kondo coupling explicitly. Furthermore, the critical scaling law n(TC) = 1 + (β- 1)/(β + γ) = 1 + 1/δ(1 - 1/β) is related to the critical exponents (β, γ, and δ) extracted from the Arrott-Noakes equation of state and the Kouvel-Fisher method, which fulfill the Widom scaling relation δ = 1 + γβ(-1), indicating the self-consistency and reliability of the obtained results. In addition, based on the scaling hypothesis through checking the scaling analysis of magnetization, the M-T-h curves collapse into two independent universal branches below and above TC.

  11. Effect of Zn doping on the magneto-caloric effect and critical constants of Mott insulator MnV{sub 2}O{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Shahi, Prashant; Kumar, A.; Shukla, K. K.; Chatterjee, Sandip, E-mail: schatterji.app@iitbhu.ac.in [Department of Applied Physics, Indian Institute of Technology (Banaras Hindu University), Varanasi-221005 (India); Singh, Harishchandra [Indus Synchrotron Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore - 452013 (India); Ghosh, A. K. [Department of Physics, Banaras Hindu University, Varanasi-221005 (India); Yadav, A. K. [Atomic and Molecular Physics Division, Bhabha Atomic Research Centre, Mumbai – 400 094 (India); Nigam, A. K. [Department of CMP and MS, Tata Institute of Fundamental Research, Mumbai-400005 (India)

    2014-09-15

    X-ray absorption near edge spectra (XANES) and magnetization of Zn doped MnV{sub 2}O{sub 4} have been measured and from the magnetic measurement the critical exponents and magnetocaloric effect have been estimated. The XANES study indicates that Zn doping does not change the valence states in Mn and V. It has been shown that the obtained values of critical exponents β, γ and δ do not belong to universal class and the values are in between the 3D Heisenberg model and the mean field interaction model. The magnetization data follow the scaling equation and collapse into two branches indicating that the calculated critical exponents and critical temperature are unambiguous and intrinsic to the system. All the samples show large magneto-caloric effect. The second peak in magneto-caloric curve of Mn{sub 0.95}Zn{sub 0.05}V{sub 2}O{sub 4} is due to the strong coupling between orbital and spin degrees of freedom. But 10% Zn doping reduces the residual spins on the V-V pairs resulting the decrease of coupling between orbital and spin degrees of freedom.

  12. Effect of Zn doping on the magneto-caloric effect and critical constants of Mott insulator MnV2O4

    Science.gov (United States)

    Shahi, Prashant; Singh, Harishchandra; Kumar, A.; Shukla, K. K.; Ghosh, A. K.; Yadav, A. K.; Nigam, A. K.; Chatterjee, Sandip

    2014-09-01

    X-ray absorption near edge spectra (XANES) and magnetization of Zn doped MnV2O4 have been measured and from the magnetic measurement the critical exponents and magnetocaloric effect have been estimated. The XANES study indicates that Zn doping does not change the valence states in Mn and V. It has been shown that the obtained values of critical exponents β, γ and δ do not belong to universal class and the values are in between the 3D Heisenberg model and the mean field interaction model. The magnetization data follow the scaling equation and collapse into two branches indicating that the calculated critical exponents and critical temperature are unambiguous and intrinsic to the system. All the samples show large magneto-caloric effect. The second peak in magneto-caloric curve of Mn0.95Zn0.05V2O4 is due to the strong coupling between orbital and spin degrees of freedom. But 10% Zn doping reduces the residual spins on the V-V pairs resulting the decrease of coupling between orbital and spin degrees of freedom.

  13. Effect of Zn doping on the magneto-caloric effect and critical constants of Mott insulator MnV2O4

    Directory of Open Access Journals (Sweden)

    Prashant Shahi

    2014-09-01

    Full Text Available X-ray absorption near edge spectra (XANES and magnetization of Zn doped MnV2O4 have been measured and from the magnetic measurement the critical exponents and magnetocaloric effect have been estimated. The XANES study indicates that Zn doping does not change the valence states in Mn and V. It has been shown that the obtained values of critical exponents β, γ and δ do not belong to universal class and the values are in between the 3D Heisenberg model and the mean field interaction model. The magnetization data follow the scaling equation and collapse into two branches indicating that the calculated critical exponents and critical temperature are unambiguous and intrinsic to the system. All the samples show large magneto-caloric effect. The second peak in magneto-caloric curve of Mn0.95Zn0.05V2O4 is due to the strong coupling between orbital and spin degrees of freedom. But 10% Zn doping reduces the residual spins on the V-V pairs resulting the decrease of coupling between orbital and spin degrees of freedom.

  14. Anisotropic Effects on Magnetoelastic Transition in Magnetic Molecular Rings

    Institute of Scientific and Technical Information of China (English)

    LI Peng-Fei; CHEN Yu-Guang; CHEN Hong

    2006-01-01

    @@ We numerically study the anisotropic effects on the magnetoelastic transition in an S = 1/2 XXZ model with a finite lattice number. It is found that the order of the magnetoelastic transition is strongly affected by the anisotropy parameter A and there may exist a critical λc dividing the first-order transition and the continuous transition.

  15. Giant magnetocaloric effect in GdAlO3 and a comparative study with GdMnO3

    Science.gov (United States)

    Mahana, Sudipta; Manju, U.; Topwal, D.

    2017-01-01

    The magnetic properties and magnetocaloric effect of polycrystalline GdAlO3 and GdMnO3 have been investigated to assess their potential usage as magnetic refrigerants at cryogenic temperatures. These compounds undergo antiferromagnetic transitions at low temperatures which are associated with the giant magnetic entropy change effect (-\\bigtriangleup {{S}M} )  ˜40.9 J Kg · K-1 under a field change of 0-9 T for GdAlO3 while the moderate effect of 18 J Kg · K-1 is observed for polycrystalline GdMnO3. Though the relative cooling power of both the stated materials is similar however, the absence of magnetic and thermal hysteresis makes GdAlO3 a more efficient magnetic refrigerant than GdMnO3.

  16. Effect of grain constraint on the field requirements for magnetocaloric effect in Ni45Co5Mn40Sn10 melt-spun ribbons

    Science.gov (United States)

    Bruno, N. M.; Huang, Y. J.; Dennis, C. L.; Li, J. G.; Shull, R. D.; Ross, J. H.; Chumlyakov, Y. I.; Karaman, I.

    2016-08-01

    The influence of grain constraint on the magnetic field levels required to complete the isothermal martensitic transformation in magnetic shape memory alloys has been demonstrated for a NiCoMnSn alloy, and the magnetocaloric performance of an optimally heat treated alloy was quantified. Ni45CoxMn45-xSn10 melt spun ribbons with x = 2, 4, 5, and 6 were characterized. The x = 5 sample was determined to exhibit the lowest transformation thermal hysteresis (7 K) and transformation temperature range during transformation from paramagnetic austenite to non-magnetic martensite, as well as a large latent heat of transformation (45 J kg-1 K-1). For this composition, it was found that increasing the grain size to thickness ratio of the ribbons from 0.2 to 1.2, through select heat treatments, resulted in a decrease in the magnetic field required to induce the martensitic transformation by about 3 T due to the corresponding reduction in the martensitic transformation temperature range. This decrease in the field requirement ultimately led to a larger magnetocaloric entropy change achieved under relatively smaller magnetic field levels. The giant inverse magnetocaloric effect of the optimized alloy was measured and showed that up to 25 J kg-1 K-1 was generated by driving the martensitic transition with magnetic fields up to 7 T.

  17. Effect of Gd polarization on the large magnetocaloric effect of GdCrO4 in a broad temperature range

    Science.gov (United States)

    Palacios, E.; Tomasi, C.; Sáez-Puche, R.; Dos santos-García, A. J.; Fernández-Martínez, F.; Burriel, R.

    2016-02-01

    The ferromagnetic zircon-type phase of GdCrO4 presents high values for the magnetocaloric (MC) parameters. This compound has large isothermal entropy changes Δ ST under the magnetic field action in a wide temperature range, from 5 to 35 K, reaching a maximum |Δ ST|=29.0 ±0.1 J /kg K at 22 K, for a field increment Δ B =9 T. It orders ferromagnetically at TC=21.3 K via the Cr-Cr exchange interaction and shows a second transition at 4.8 K due to the ordering of the Gd sublattice. The large MC effect is enhanced by the polarization of the Gd3 + ions by the Cr5 + ones via a weaker Gd-Cr interaction. This effect is an interesting feature to be considered in the search for new compounds with a high MC effect in the range of liquid hydrogen or natural gas, regarding the liquefaction of gases by magnetization-demagnetization cycles. This paper contains experimental measurements of magnetization, heat capacity, and direct determinations of the MC effect. The magnetic contribution to the heat capacity Cm has been obtained after subtracting the lattice component. Approximate values for the exchange constants J1 (Cr-Cr) and J3 (Gd-Cr) have been deduced from Cm.

  18. Giant magnetocaloric effect in isostructural MnNiGe-CoNiGe system by establishing a Curie-temperature window

    KAUST Repository

    Liu, E. K.

    2013-03-28

    An effective scheme of isostructural alloying was applied to establish a Curie-temperature window in isostructural MnNiGe-CoNiGe system. With the simultaneous accomplishment of decreasing structural-transition temperature and converting antiferromagnetic martensite to ferromagnetic state, a 200 K Curie-temperature window was established between Curie temperatures of austenite and martensite phases. In the window, a first-order magnetostructural transition between paramagnetic austenite and ferromagnetic martensite occurs with a sharp jump in magnetization, showing a magnetic entropy change as large as −40 J kg−1 K−1 in a 50 kOe field change. This giant magnetocaloric effect enables Mn1− x Co x NiGe to become a potential magnetic refrigerant.

  19. Effect of Fe on the Martensitic Transition, Magnetic and Magnetocaloric Properties in Ni-Mn-In Melt-spun Ribbons

    Directory of Open Access Journals (Sweden)

    D.M. Raj kumar

    2016-06-01

    Full Text Available The effect of Fe on the martensitic transitions, magnetic and inverse magnetocaloric effect in Ni47Mn40-xFexIn13 ribbons (x = 1, 2, 3 and 5 has been investigated. All the ribbon compositions under study have shown the presence of austenite phase at room temperature. The variation of martensitic transition with the increase in Fe-content is non-monotonic. The thermal hysteresis of the martensitic transition increased with the increase in Fe-content. The martensitic transitions shifted to lower temperatures in the presence of high magnetic fields. A maximum magnetic entropy change (∆SM of 50 Jkg-1K-1 has been achieved in the Ni47Mn38Fe2In13 (x = 1 ribbon at 282 K for an applied field of 5 T.

  20. Evolution of magnetostructural transition and magnetocaloric effect with Al doping in MnCoGe1-xAlx compounds

    KAUST Repository

    Bao, Lifu

    2014-01-03

    The effect of Al doping in MnCoGe1-xAlx compounds has been investigated. The substitution of Al for Ge enhances Mn-Mn covalent bonding by shortening the distance of nearest Mn atom layers, and thus stabilizes the hexagonal structure. As a result, first-order magnetostructural transition between ferromagnetic martensite and paramagnetic austenite takes place for the optimized compositions (x = 0.01, 0.02). Accompanied with the magnetostructural transition, large magnetocaloric effect (MCE) is observed. More doping of Al(x = 0.03, 0.04) leads to the separation of magnetic and structural transitions and remarkable reduction of MCE. © 2014 IOP Publishing Ltd.

  1. Magnetocaloric effect in heavy rare-earth elements doped Fe-based bulk metallic glasses with tunable Curie temperature

    Science.gov (United States)

    Li, Jiawei; Huo, Juntao; Law, Jiayan; Chang, Chuntao; Du, Juan; Man, Qikui; Wang, Xinmin; Li, Run-Wei

    2014-08-01

    The effects of heavy rare earth (RE) additions on the Curie temperature (TC) and magnetocaloric effect of the Fe-RE-B-Nb (RE = Gd, Dy and Ho) bulk metallic glasses were studied. The type of dopping RE element and its concentration can easily tune TC in a large temperature range of 120 K without significantly decreasing the magnetic entropy change (ΔSM) and refrigerant capacity (RC) of the alloys. The observed values of ΔSM and RC of these alloys compare favorably with those of recently reported Fe-based metallic glasses with enhanced RC compared to Gd5Ge1.9Si2Fe0.1. The tunable TC and large glass-forming ability of these RE doped Fe-based bulk metallic glasses can be used in a wide temperature range with the final required shapes.

  2. Theoretical investigation on the magnetocaloric effect in amorphous Eu80 Au20 system

    Science.gov (United States)

    Costa, S. S.; Roriz, O. A. V.; Silvano, N. de O.; von Ranke, P. J.; Nóbrega, E. P.

    2016-09-01

    In this work, we investigated the magnetic and magnetocaloric properties of the amorphous system Eu80 Au20. The magnetic state equation and entropy were considered in the framework of Handrich-Kaneyoshi model, which takes into account the amorphization through the symmetric exchange fluctuation in the mean field approximation. The exchange and structural fluctuations parameters were chosen based on the experimental data of Eu80 Au20. The isothermal entropy change was calculated for several variations of external magnetic field. Furthermore, the adiabatic temperature change and the refrigerant capacity were calculated for a magnetic field change from 0 to 5 T.

  3. Strong Purcell effect in anisotropic $\\varepsilon$-near-zero metamaterials

    CERN Document Server

    Chebykin, A V; Shalin, A S; Poddubny, A N; Belov, P A

    2014-01-01

    We theoretically demonstrate the strong Purcell effect in $\\varepsilon$-near-zero ultra-anisotropic uniaxial metamaterials with elliptic isofrequency surface. Contrary to the hyperbolic metamaterials, the effect does not rely on the diverging density of states and evanescent waves. As a result, both the radiative decay rate and the far-field emission power are enhanced. The effect can be realized in the periodic layered metal-dielectric nanostructures with complex unit cell containing two different metallic layers.

  4. Magnetocaloric effect of(Tb_(1-x)Ce_x)Co_2 alloys in low magnetic field

    Institute of Scientific and Technical Information of China (English)

    陈湘; 庄应烘

    2009-01-01

    The phases in alloys(Tb1-xCex)Co2 with x=0,0.1,0.2,0.3,0.4 and 0.5 were investigated by X-ray diffraction analysis,and the magnetocaloric effect for x=0-0.4 was studied by magnetization measurement.The samples were almost single phase with MgCu2-type cubic structure.The magnetization decreased with the increase of Ce.The Curie temperatures(Tc) of Tb1-xCexCo2 alloys with x from 0.1 to 0.4 were 180,165,160 and 152 K,respectively.For x=0.5 in the range from 100 K to 230 K,the point of magnetic transition was n...

  5. Magnetocaloric Effect of Ni56Mn18.8Ga24.5Gd0.7 Alloy

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    With the addition of Gd, the Ni56Mn18.8Ga24.5Gd0.7 alloy exhibits non-modulated martensite phase at room temperature. From the illustration of Gd microstructure, it can be found that Gd exists along the subgrain boundaries. Hence,he crystalline size decreases and the mechanical properties improve. Ac-susceptibility results show that Ni56Mn18.8Ga24.5Gd0.7 alloy still undergoes simultaneous structural and magnetic transitions and transforms from ferromagnetic martensitic phase to paramagnetic austenitic phase with increasing temperature. The maximum magnetic entropy change is 13.4 J· (kg· K) - 1 under 1.9 T field at 338 K. The giant magnetocaloric effect found in Ni56Mn18.8Ga24.5Gd0.7 alloy is attributed to the concurrently occurring first-order structural- and magnetic-phase transitions.

  6. Magnetic transition and large reversible magnetocaloric effect in EuCu1.75P2 compound

    Institute of Scientific and Technical Information of China (English)

    Huo De-Xuan; Liao Luo-Bing; Li Ling-Wei; Li Miao; Qian Zheng-Hong

    2013-01-01

    The magnetocaloric effect (MCE) in EuCul.75P2 compound is studied by the magnetization and heat capacity measurements.Magnetization and modified Arrott plots indicate that the compound undergoes a second-order phase transition at Tc ~ 51 K.A large reversible MCE is observed around Tc.The values of maximum magnetic entropy change (-△SMmax)reach 5.6 J.kg-1.K-1 and 13.3 J.kg 1.K-1 for the field change of 2 T and 7 T,respectively,with no obvious hysteresis loss in the vicinity of Curie temperature.The corresponding maximum adiabatic temperature changes (△Taadmax) are evaluated to be 2.1 K and 5.0 K.The magnetic transition and the origin of large MCE in EuCu1.75P2 are also discussed.

  7. The effects of substituting Ag for In on the magnetoresistance and magnetocaloric properties of Ni-Mn-In Heusler alloys

    Directory of Open Access Journals (Sweden)

    Sudip Pandey

    2016-05-01

    Full Text Available The effect of substituting Ag for In on the structural, magnetocaloric, and thermomagnetic properties of Ni50Mn35In15−xAgx (x = 0.1, 0.2, 0.5, and 1 Heusler alloys was studied. The magnitude of the magnetization change at the martensitic transition temperature (TM decreased with increasing Ag concentration. Smaller magnetic entropy changes (ΔSM were observed for the alloys with larger Ag concentrations and the martensitic transition shifted to higher temperature. A shift of TM by about 25 K to higher temperature was observed for an applied hydrostatic pressure of P = 6.6 kbar with respect to ambient pressure. A large drop in resistivity was observed for large Ag concentration. The magnetoresistance was dramatically suppressed due to an increase in the disorder of the system with increasing Ag concentration. Possible mechanisms responsible for the observed behavior are discussed.

  8. Enhanced magnetocaloric effect in a Co-doped Heusler Mn50Ni37Co3In10 unidirectional crystal

    Science.gov (United States)

    Ren, Jian; Feng, Shutong; Fang, Yue; Zhai, Qijie; Luo, Zhiping; Zheng, Hongxing

    2016-11-01

    A high-pressure optical zone-melting technique was employed to grow a Mn-rich Heusler Mn50Ni37Co3In10 unidirectional crystal in the present study. It was found that the Co-doped Mn50Ni37Co3In10 unidirectional crystal showed a low magnetic hysteretic loss and a widened working temperature interval in the vicinity of the martensitic transformation. The inverse magnetic entropy change (∆SM) reached 7.84 Jkg-1K-1 around 237.5 K under a magnetic field change of 30 kOe, and the corresponding effective refrigeration capacity (RCeff) was about 127.2 Jkg-1. The experimental results demonstrated a high potential to develop high-performance Mn-rich Heusler Mn-Ni-In magnetocaloric materials by means of Co doping in combination with the high-pressure optical zone-melting fabrication technique.

  9. Room-temperature Magnetocaloric Effect in (Co0.35Mn0.65)2P Compound

    Institute of Scientific and Technical Information of China (English)

    Naikun Sun; Da Li; Songning Xu; Zhenhua Wang; Zhidong Zhang

    2011-01-01

    The (Co0.35Mn0.65)2P compound, prepared by a mechanical alloying plus solid sintering process, exhibits a second-order transition from a ferromagnetic state to a paramagnetic one at Curie temperature of about 320 K with no clear thermal hysteresis. A magnetic-entropy change (△SM) value above 1.6 J·kg-1·K-1 for a 5 T field change is obtained in the whole temperature range of 292.5-352.5 K and the maximum value of the △SM is 2.3 J·kg-1·K-1 at 337.5 K. The study on the magnetocaloric effect of the (Co0.35Mn0.65)2P compound may be helpful for exploring good candidates for room-temperature magnetic refrigeration.

  10. Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys

    Science.gov (United States)

    Salazar Mejía, C.; Ghorbani Zavareh, M.; Nayak, A. K.; Skourski, Y.; Wosnitza, J.; Felser, C.; Nicklas, M.

    2015-05-01

    The present pulsed high-magnetic-field study on Ni50Mn35In15 gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields.

  11. Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Salazar Mejía, C., E-mail: Catalina.Salazar@cpfs.mpg.de; Nayak, A. K.; Felser, C.; Nicklas, M. [Max Planck Institute for Chemical Physics of Solids, 01187 Dresden (Germany); Ghorbani Zavareh, M.; Wosnitza, J. [Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden (Germany); Institut für Festkörperphysik, TU Dresden, 01062 Dresden (Germany); Skourski, Y. [Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden (Germany)

    2015-05-07

    The present pulsed high-magnetic-field study on Ni{sub 50}Mn{sub 35}In{sub 15} gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields.

  12. Enhanced magnetocaloric effect in the proximity of magnetization steps and jumps of spin-1/2 XXZ Heisenberg regular polyhedra

    Science.gov (United States)

    KarǏová, Katarína; Strečka, Jozef; Richter, Johannes

    2017-03-01

    The magnetization process and adiabatic demagnetization of antiferromagnetic spin-1/2 XXZ Heisenberg clusters in the shape of regular polyhedra (tetrahedron, octahedron, cube, icosahedron and dodecahedron) are examined using the exact diagonalization method. It is demonstrated that a quantum (xy) part of the XXZ exchange interaction is a primary cause for the presence of additional intermediate magnetization plateaux and steps, which are totally absent in the limiting Ising case. The only exception to this rule is the spin-1/2 XXZ Heisenberg tetrahedron, which shows just a quantitative shift of the level-crossing fields related to two magnetization steps. It is shown that spin-1/2 XXZ Heisenberg regular polyhedra exhibit an enhanced magnetocaloric effect in the proximity of magnetization steps and jumps, which are accompanied with a rapid drop (rise) of temperature just above (below) the level-crossing field when the magnetic field is removed adiabatically.

  13. Effective wavefield extrapolation in anisotropic media: Accounting for resolvable anisotropy

    KAUST Repository

    Alkhalifah, Tariq Ali

    2014-04-30

    Spectral methods provide artefact-free and generally dispersion-free wavefield extrapolation in anisotropic media. Their apparent weakness is in accessing the medium-inhomogeneity information in an efficient manner. This is usually handled through a velocity-weighted summation (interpolation) of representative constant-velocity extrapolated wavefields, with the number of these extrapolations controlled by the effective rank of the original mixed-domain operator or, more specifically, by the complexity of the velocity model. Conversely, with pseudo-spectral methods, because only the space derivatives are handled in the wavenumber domain, we obtain relatively efficient access to the inhomogeneity in isotropic media, but we often resort to weak approximations to handle the anisotropy efficiently. Utilizing perturbation theory, I isolate the contribution of anisotropy to the wavefield extrapolation process. This allows us to factorize as much of the inhomogeneity in the anisotropic parameters as possible out of the spectral implementation, yielding effectively a pseudo-spectral formulation. This is particularly true if the inhomogeneity of the dimensionless anisotropic parameters are mild compared with the velocity (i.e., factorized anisotropic media). I improve on the accuracy by using the Shanks transformation to incorporate a denominator in the expansion that predicts the higher-order omitted terms; thus, we deal with fewer terms for a high level of accuracy. In fact, when we use this new separation-based implementation, the anisotropy correction to the extrapolation can be applied separately as a residual operation, which provides a tool for anisotropic parameter sensitivity analysis. The accuracy of the approximation is high, as demonstrated in a complex tilted transversely isotropic model. © 2014 European Association of Geoscientists & Engineers.

  14. Magnetic properties and magnetocaloric effects in NaZn13-type La(Fe, Al)13-based compounds

    Institute of Scientific and Technical Information of China (English)

    Shen Bao-Gen; Hu Feng-Xia; Dong Qiao-Yan; Sun Ji-Rong

    2013-01-01

    In this article,our recent progress concerning the effects of atomic substitution,magnetic field,and temperature on the magnetic and magnetocaloric properties of the LaFe13-xAlx compounds are reviewed.With an increase of the aluminum content,the compounds exhibit successively an antiferromagnetic (AFM) state,a ferromagnetic (FM) state,and a mictomagnetic state.Furthermore,the AFM coupling of LaFe13-xAlx can be converted to an FM one by substituting Si for Al,Co for Fe,and magnetic rare-earth R for La,or introducing interstitial C or H atoms.However,low doping levels lead to FM clusters embedded in an AFM matrix,and the resultant compounds can undergo,under appropriate applied fields,first an AFM-FM and then an FM-AFM phase transition while heated,with significant magnetic relaxation in the vicinity of the transition temperature.The Curie temperature of LaFe13-xAlx can be shifted to room temperature by choosing appropriate contents of Co,C,or H,and a strong magnetocaloric effect can be obtained around the transition temperature.For example,for the LaFe11.5Al1.5C0.2H1.0 compound,the maximal entropy change reaches 13.8 J·kg-1·K-1 for a field change of 0-5 T,occurring around room temperature.It is 42% higher than that of Gd,and therefore,this compound is a promising room-temperature magnetic refrigerant.

  15. Direct magnetocaloric characterization and simulation of thermomagnetic cycles

    NARCIS (Netherlands)

    Porcari, G.; Buzzi, M.; Cugini, F.; Pellicelli, R.; Pernechele, C.; Caron, L.; Brück, E.; Solzi, M.

    2013-01-01

    n experimental setup for the direct measurement of the magnetocaloric effect capable of simulating high frequency magnetothermal cycles on laboratory-scale samples is described. The study of the magnetocaloric properties of working materials under operative conditions is fundamental for the developm

  16. Constraints on the Adiabatic Temperature Change in Magnetocaloric Materials

    DEFF Research Database (Denmark)

    Nielsen, Kaspar Kirstein; Bahl, Christian Robert Haffenden; Smith, Anders

    2010-01-01

    The thermodynamics of the magnetocaloric effect implies constraints on the allowed variation in the adiabatic temperature change for a magnetocaloric material. An inequality for the derivative of the adiabatic temperature change with respect to temperature is derived for both first- and second...

  17. Effect of Fe substitution on the structure and magnetocaloric effect of Mn5-xFexGeSi2 alloys

    Science.gov (United States)

    Sun, Y. W.; Yan, J. L.; Feng, E. L.; Tang, G. W.; Zhou, K. W.

    2017-01-01

    The structure and magnetocaloric effect of Mn5-xFexGeSi2 compounds were studied. Analysis of X-ray powder diffraction and energy dispersive X-Ray spectroscopy revealed that Mn5-xFexGeSi2 alloys with x<1 crystallize in the Mn5Si3-type structure (space group P63/mcm), maintaining the structure of Mn5Ge3; and alloys with x=1.5 and 2 consist of the major Mn5Si3-type phase and the minor Ni2In-type phase (space group P63/mmc). The results of Rietveld refinement showed that the cell parameters for the Mn5Si3-type phase decrease with increasing Fe content. The positive slopes in Arrott plots indicate that a second-order ferromagnetic to paramagnetic transition occurs. The Curie temperature increases with increasing Fe content from 182 K for x=0.6 to 224 K for x=2. The maximum magnetic entropy change of 3.7 J/(kg K) for x=0.8 was found under a magnetic field change of 0-20 kOe.

  18. Hysteresis in Magnetocaloric Materials

    DEFF Research Database (Denmark)

    von Moos, Lars

    , obtained at the initial low and final high field. However, in first order materials thermal entropy hysteresis loops are obtained through characterization, corresponding to measurements done in an increasing and a decreasing temperature mode. Indirectly determining the MCE through the use of the Maxwell...... characterization of the magnetocaloric effect (MCE) in these materials is done through conventional indirect magnetometric and calorimetric methods, as well as newly developed direct methods. The determination of the MCE due to a magnetic field change is in principle given by the isofield material entropy curves...... relation or calorimetric measurements done only in a heating or cooling mode, estimate the MCE as the reversible difference between the set isofield heating-heating or cooling-cooling entropy curves. Here it is shown that direct measurements suggest that the real MCE is given by the difference between...

  19. Efficient anisotropic wavefield extrapolation using effective isotropic models

    KAUST Repository

    Alkhalifah, Tariq Ali

    2013-06-10

    Isotropic wavefield extrapolation is more efficient than anisotropic extrapolation, and this is especially true when the anisotropy of the medium is tilted (from the vertical). We use the kinematics of the wavefield, appropriately represented in the high-frequency asymptotic approximation by the eikonal equation, to develop effective isotropic models, which are used to efficiently and approximately extrapolate anisotropic wavefields using the isotropic, relatively cheaper, operators. These effective velocity models are source dependent and tend to embed the anisotropy in the inhomogeneity. Though this isotropically generated wavefield theoretically shares the same kinematic behavior as that of the first arrival anisotropic wavefield, it also has the ability to include all the arrivals resulting from a complex wavefield propagation. In fact, the effective models reduce to the original isotropic model in the limit of isotropy, and thus, the difference between the effective model and, for example, the vertical velocity depends on the strength of anisotropy. For reverse time migration (RTM), effective models are developed for the source and receiver fields by computing the traveltime for a plane wave source stretching along our source and receiver lines in a delayed shot migration implementation. Applications to the BP TTI model demonstrates the effectiveness of the approach.

  20. Correlation theory of crystal field and anisotropic exchange effects

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker

    1985-01-01

    A general theory for including correlation effects in static and dynamic properties is presented in terms of Raccah or Stevens operators. It is explicitly developed for general crystal fields and anisotropic interactions and systems with several sublattices, like the rare earth compounds. The the......A general theory for including correlation effects in static and dynamic properties is presented in terms of Raccah or Stevens operators. It is explicitly developed for general crystal fields and anisotropic interactions and systems with several sublattices, like the rare earth compounds....... The theory gives explicitly a temperature dependent renormalization of both the crystal field and the interactions, and a damping of the excitations and in addition a central park component. The general theory is illustrated by a discussion of the singlet-doublet system. The correlation effects...... on the susceptibility, the first and second moment frequencies and the line shape are calculated self-consistently....

  1. The magnetocaloric effect and critical behaviour of the Mn(0.94)Ti(0.06)CoGe alloy.

    Science.gov (United States)

    Shamba, P; Wang, J L; Debnath, J C; Kennedy, S J; Zeng, R; Din, M F Md; Hong, F; Cheng, Z X; Studer, A J; Dou, S X

    2013-02-06

    Structural, magnetic and magnetocaloric properties of the Mn(0.94)Ti(0.06)CoGe alloy have been investigated using x-ray diffraction, DC magnetization and neutron diffraction measurements. Two phase transitions have been detected, at T(str) = 235 K and T(C) = 270 K. A giant magnetocaloric effect has been obtained at around T(str) associated with a structural phase transition from the low temperature orthorhombic TiNiSi-type structure to the high temperature hexagonal Ni(2)In-type structure, which is confirmed by neutron study. In the vicinity of the structural transition, at T(str), the magnetic entropy change, -ΔS(M) reached a maximum value of 14.8 J kg(-1) K(-1) under a magnetic field of 5 T, which is much higher than that previously reported for the parent compound MnCoGe. To investigate the nature of the magnetic phase transition around T(C) = 270 K from the ferromagnetic to the paramagnetic state, we performed a detailed critical exponent study. The critical components γ, β and δ determined using the Kouvel-Fisher method, the modified Arrott plot and the critical isotherm analysis agree well. The values deduced for the critical exponents are close to the theoretical prediction from the mean-field model, indicating that the magnetic interactions are long range. On the basis of these critical exponents, the magnetization, field and temperature data around T(C) collapse onto two curves obeying the single scaling equation M(H,ε) = ε(β)f ± (H/ε(β+γ)).

  2. Large magnetocaloric effect and near-zero thermal hysteresis in the rare earth intermetallic Tb1-x Dy x Co2 compounds

    Science.gov (United States)

    Zeng, Yuyang; Tian, Fanghua; Chang, Tieyan; Chen, Kaiyun; Yang, Sen; Cao, Kaiyan; Zhou, Chao; Song, Xiaoping

    2017-02-01

    We report the magnetocaloric effect in a Tb1-x Dy x Co2 compound which exhibits a wide working temperature window around the Curie temperature (T C) and delivers a large refrigerant capacity (RC) with near-zero thermal hysteresis. Specifically, the wide full width at half maxima ({δ\\text{WFHM}} ) can reach up to 62 K and the RC value changes from 216.5 to 274.3 J Kg-1 when the external magnetic field increases to 5 T. Such magnetocaloric effects are attributed to a magnetic and structural transition from a paramagnetic and cubic phase to a ferromagnetic (M S along [1 1 1] direction) and rhombohedral phase or ferromagnetic (M S along [0 0 1] direction) and tetragonal phase.

  3. Analysis of the Magnetocaloric Effect in Heusler Alloys: Study of Ni50CoMn36Sn13 by Calorimetric Techniques

    Directory of Open Access Journals (Sweden)

    Elias Palacios

    2015-03-01

    Full Text Available Direct determinations of the isothermal entropy increment, \\(-\\Delta S_T\\, in the Heusler alloy Ni\\(_{50}\\CoMn\\(_{36}\\Sn\\(_{13}\\ on demagnetization gave positive values, corresponding to a normal magnetocaloric effect. These values contradict the results derived from heat-capacity measurements and also previous results obtained from magnetization measurements, which indicated an inverse magnetocaloric effect, but showing different values depending on the technique employed. The puzzle is solved, and the apparent incompatibilities are quantitatively explained considering the hysteresis, the width of the martensitic transition and the detailed protocol followed to obtain each datum. The results show that these factors should be analyzed in detail when dealing with Heusler alloys.

  4. Effective Elliptic Models for Efficient Wavefield Extrapolation in Anisotropic Media

    KAUST Repository

    Waheed, Umair bin

    2014-05-01

    Wavefield extrapolation operator for elliptically anisotropic media offers significant cost reduction compared to that of transversely isotropic media (TI), especially when the medium exhibits tilt in the symmetry axis (TTI). However, elliptical anisotropy does not provide accurate focusing for TI media. Therefore, we develop effective elliptically anisotropic models that correctly capture the kinematic behavior of the TTI wavefield. Specifically, we use an iterative elliptically anisotropic eikonal solver that provides the accurate traveltimes for a TI model. The resultant coefficients of the elliptical eikonal provide the effective models. These effective models allow us to use the cheaper wavefield extrapolation operator for elliptic media to obtain approximate wavefield solutions for TTI media. Despite the fact that the effective elliptic models are obtained by kinematic matching using high-frequency asymptotic, the resulting wavefield contains most of the critical wavefield components, including the frequency dependency and caustics, if present, with reasonable accuracy. The methodology developed here offers a much better cost versus accuracy tradeoff for wavefield computations in TTI media, considering the cost prohibitive nature of the problem. We demonstrate the applicability of the proposed approach on the BP TTI model.

  5. Anisotropic Paramagnetic Meissner Effect by Spin-Orbit Coupling

    Science.gov (United States)

    Espedal, Camilla; Yokoyama, Takehito; Linder, Jacob

    2016-03-01

    Conventional s -wave superconductors repel an external magnetic field. However, a recent experiment [A. Di Bernardo et al., Phys. Rev. X 5, 041021 (2015)] has tailored the electromagnetic response of superconducting correlations via adjacent magnetic materials. We consider another route of altering the Meissner effect where spin-orbit interactions induce an anisotropic Meissner response that changes sign depending on the field orientation. The tunable electromagnetic response opens new paths in the utilization of hybrid systems comprising magnets and superconductors.

  6. Highly Sensitive Flexible Magnetic Sensor Based on Anisotropic Magnetoresistance Effect.

    Science.gov (United States)

    Wang, Zhiguang; Wang, Xinjun; Li, Menghui; Gao, Yuan; Hu, Zhongqiang; Nan, Tianxiang; Liang, Xianfeng; Chen, Huaihao; Yang, Jia; Cash, Syd; Sun, Nian-Xiang

    2016-11-01

    A highly sensitive flexible magnetic sensor based on the anisotropic magnetoresistance effect is fabricated. A limit of detection of 150 nT is observed and excellent deformation stability is achieved after wrapping of the flexible sensor, with bending radii down to 5 mm. The flexible AMR sensor is used to read a magnetic pattern with a thickness of 10 μm that is formed by ferrite magnetic inks.

  7. Magnetocaloric effect across the coupled structural and ferromagnetic transition in Pr0.1Ce0.4Sr0.5MnO3

    Indian Academy of Sciences (India)

    C Madhu; A Sundaresan

    2008-11-01

    We have investigated the magnetocaloric effect across a first order structural transition coupled to the ferromagnetic transition (C ∼ 270 K) in Pr0.1Ce0.4Sr0.5MnO3 using magnetization and heat capacity measurements. The adiabatic magnetic entropy change || obtained from magnetization measurements for a magnetic field change of 2 T is around 1.3 J/kg K. A similar value of || was obtained from the analysis of heat capacity data.

  8. The thermomechanical stability of Fe-based amorphous ribbons exhibiting magnetocaloric effect

    Science.gov (United States)

    Shishkin, D. A.; Volegov, A. S.; Baranov, N. V.

    2016-12-01

    The Fe-Nb-B and Fe71.5Cr2Si13.5B9Nb3Cu1 alloys have been prepared by rapid quenching from the melt, and the magnetic properties of alloys in the vicinity of the magnetic ordering have been studied before and after thermomechanical processing. It has been shown that change in the Fe:Nb:B ratio allows tuning the magnetic ordering temperature and the position of maximum of the isothermal magnetic entropy change | { - Δ Sm } | from 256 to 333 K. The thermomechanical treatment of alloys at 623 K under applied tensile stresses observed does not affect remarkably the magnetocaloric properties of alloys. The combination of high thermomechanical stability, good electrical, anti-corrosive and thermomagnetic properties makes these alloys promising for use in magnetic refrigeration devices.

  9. Giant magnetocaloric effect in antiferromagnetic DyVO{sub 4} compound

    Energy Technology Data Exchange (ETDEWEB)

    Midya, A., E-mail: arindam.midya@saha.ac.in; Khan, N.; Bhoi, D.; Mandal, P.

    2014-09-01

    We have investigated the magnetic and magnetocaloric properties of DyVO{sub 4} by magnetization and heat capacity measurements. χ(T) shows antiferromagnetic to paramagnetic transition at T{sub N}{sup Dy}∼3.5K. The compound undergoes a metamagnetic transition and exhibits a huge entropy change. The maximum values of magnetic entropy change (ΔS{sub M}), adiabatic temperature change (ΔT{sub ad}) and refrigerant capacity (RC) reach 26 J kg{sup −1} K{sup −1}, 17 K, and 526 J kg{sup −1}, respectively for a field change of 0–8 T. Moreover, the material is highly insulating and exhibits no thermal and field hysteresis, satisfying the necessary conditions for a good magnetic refrigerant material.

  10. Giant low-field magnetocaloric effect in single-crystalline EuTi0.85Nb0.15O3

    Directory of Open Access Journals (Sweden)

    S. Roy

    2016-02-01

    Full Text Available The magnetocaloric effect in ferromagnetic single crystal EuTi0.85Nb0.15O3 has been investigated using magnetization and heat capacity measurements. EuTi0.85Nb0.15O3 undergoes a continuous ferromagnetic phase transition at TC = 9.5 K due to the long range ordering of magnetic moments of Eu2+ (4f7. With the application of magnetic field, the spin entropy is strongly suppressed and a giant magnetic entropy change is observed near TC. The values of entropy change ΔSm and adiabatic temperature change ΔTad are as high as 51.3 J kg−1 K−1 and 22 K, respectively, for a field change of 0–9 T. The corresponding magnetic heating/cooling capacity is 700 J kg−1. This compound also shows large magnetocaloric effect even at low magnetic fields. In particular, the values of ΔSm reach 14.7 and 23.8 J kg−1 K−1 for field changes of 0–1 T and 0–2 T, respectively. The low-field giant magnetocaloric effect, together with the absence of thermal and field hysteresis makes EuTi0.85Nb0.15O3 a very promising candidate for low temperature magnetic refrigeration.

  11. Giant low-field magnetocaloric effect in single-crystalline EuTi0.85Nb0.15O3

    Science.gov (United States)

    Roy, S.; Khan, N.; Mandal, P.

    2016-02-01

    The magnetocaloric effect in ferromagnetic single crystal EuTi0.85Nb0.15O3 has been investigated using magnetization and heat capacity measurements. EuTi0.85Nb0.15O3 undergoes a continuous ferromagnetic phase transition at TC = 9.5 K due to the long range ordering of magnetic moments of Eu2+ (4f7). With the application of magnetic field, the spin entropy is strongly suppressed and a giant magnetic entropy change is observed near TC. The values of entropy change ΔSm and adiabatic temperature change ΔTad are as high as 51.3 J kg-1 K-1 and 22 K, respectively, for a field change of 0-9 T. The corresponding magnetic heating/cooling capacity is 700 J kg-1. This compound also shows large magnetocaloric effect even at low magnetic fields. In particular, the values of ΔSm reach 14.7 and 23.8 J kg-1 K-1 for field changes of 0-1 T and 0-2 T, respectively. The low-field giant magnetocaloric effect, together with the absence of thermal and field hysteresis makes EuTi0.85Nb0.15O3 a very promising candidate for low temperature magnetic refrigeration.

  12. Phase relationship, microstructure and magnetocaloric effect in Gd{sub 1-x}(Si{sub 0.5}Ge{sub 0.5}){sub x} alloys

    Energy Technology Data Exchange (ETDEWEB)

    Raja, M Manivel; Gopalan, R; Rajkumar, D M; Balamuralikrishnan, R; Chandrasekaran, V [Defence Metallurgical Research Laboratory, Hyderabad-500 058 (India); Suresh, K G [Department of Physics, Indian Institute of Technology, Mumbai-400 076 (India); Hono, K [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba-305 0047 (Japan)], E-mail: rg_gopy@yahoo.com

    2008-03-07

    Microstructure and magnetocaloric effect were investigated in Gd{sub 1-x}(Si{sub 0.5}Ge{sub 0.5}){sub x} alloys with x = 0.38, 0.41, 0.45, 0.47 and 0.50. The phase identification and compositional analysis were carried out by a combination of x-ray powder diffraction, scanning electron microscopy and electron probe microanalysis. The Gd{sub 5}(Si,Ge){sub 4} phase was found to have an orthorhombic Gd{sub 5}Si{sub 4}-type structure when the coexisting phase was Gd-rich (Gd{sub 5}Si{sub 3}-type) and a monoclinic Gd{sub 5}Si{sub 2}Ge{sub 2}-type structure when the coexisting phase was Gd-depleted (Gd{sub 5}Ge{sub 5}-type). The magnetocaloric effect was found to depend on the volume fraction and the Si/Ge ratio of the ferromagnetic 5 : 4 phase in the above series of alloys. A maximum magnetocaloric effect ({delta}S){sub M} of 14.3 J kg{sup -1} K{sup -1} for a magnetic field change from 0 to 5 T was obtained for the x = 0.45 alloy.

  13. Europium substitution effects on structural, magnetic and magnetocaloric properties in La0.5Ca0.5MnO3

    Directory of Open Access Journals (Sweden)

    Boujelben W.

    2012-06-01

    Full Text Available We have investigated structural, magnetic and magnetocaloric properties of polycrystalline samples La0.5-xEuxCa0.5MnO3 (x=0 and 0.1. Rietveld refinement of the X-ray diffraction patterns show that our samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Magnetization measurements versus temperature at a magnetic applied field of 500 Oe indicate that La0.4Eu0.1Ca0.5MnO3 sample exhibits a paramagnetic to ferromagnetic transition with decreasing temperature. Magnetic measurements reveal strong magnetocaloric effect in the vicinity of the Curie temperature TC. The parent compound shows a negative magnetic entropy change of ∆SM=−1.13Jkg−1K−1 at 220K and a positive magnetocaloric effects ∆SM=1Jkg−1K−1 at 150K under a magnetic applied field of 2T. La0.4Eu0.1Ca0.5MnO3 exhibits a maximum value of magnetic entropy change ∆SM=−1.15Jkg−1K−1 at 130K under an applied field of 2T and a large relative cooling power RCP with a maximum value of 72 J/kg.

  14. Reentrant phenomenon and inverse magnetocaloric effect in a generalized spin-(1/2,  s) Fisher's super-exchange antiferromagnet.

    Science.gov (United States)

    Gálisová, Lucia

    2016-11-30

    The thermodynamic and magnetocaloric properties of a generalized spin-(1/2,  s) Fisher's super-exchange antiferromagnet are investigated precisely by using the decoration-iteration mapping transformation. Besides the critical temperature, sublattice magnetization, total magnetization, entropy and specific heat, the isothermal entropy change and adiabatic temperature change are also rigorously calculated in order to examine the cooling efficiency of the model in the vicinity of the first- and second-order phase transitions. It is shown that an enhanced inverse magnetocaloric effect occurs around the temperature interval [Formula: see text] for any magnetic-field change [Formula: see text]. The most pronounced inverse magnetocaloric effect can be found nearby the critical field, which corresponds to the zero-temperature phase transition from the long-range ordered ground state to the paramagnetic one. The observed phenomenon increases with an increasing value of decorating spins. Furthermore, sufficiently high values of decorating spins have also been linked to the possibility of observing reentrant phase transitions at finite temperatures.

  15. Effect of annealing on the magnetic, magnetocaloric and magnetoresistance properties of Ni-Co-Mn-Sb melt spun ribbons 

    Energy Technology Data Exchange (ETDEWEB)

    Sahoo, Roshnee [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Raj Kumar, D.M.; Arvindha Babu, D. [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India); Suresh, K.G., E-mail: suresh@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Nigam, A.K. [Tata Institute of Fundamental Research, Mumbai 400005 (India); Manivel Raja, M. [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India)

    2013-12-15

    The structural, magnetic, magnetocaloric and magnetotransport properties of Ni{sub 46}Co{sub 4}Mn{sub 38}Sb{sub 12} melt spun ribbons have been systematically investigated. The partially ordered B2 phase of the as-spun ribbon transforms to fully ordered L2{sub 1} phase upon annealing, which signifies a considerable change of the atomic ordering in the system. The presence of atomic disorder in the as-spun ribbon gives rise to a higher martensitic transition temperature and a lower magnetization as compared to the bulk sample. However, annealing the ribbons helps in regaining the bulk properties to a large extent. Significant changes in magnetocaloric effect, exchange bias and magnetoresistance have been observed between the as-spun and the annealed ribbons, indicating the role of atomic ordering on the functional as well as fundamental properties in the Heusler system. Importantly, the study shows that one can reduce the hysteresis loss by preparing melt spun alloys and subjecting them to appropriate annealing conditions, which enable them to become practical magnetic refrigerants. - Highlights: • In this paper we have systematically studied various phenomenon caused by the heat treatment of the melt spun NiCoMnSb samples. • Significant changes in magnetocaloric effect, exchange bias and magnetoresistance have been observed between the as-spun and the annealed ribbons. • Another important result is annealing the ribbons helps in regaining the bulk properties to a large extent.

  16. Scaling and universality in magnetocaloric materials

    DEFF Research Database (Denmark)

    Smith, Anders; Nielsen, Kaspar Kirstein; Bahl, Christian R. H.

    2014-01-01

    fields are not universal, showing significant variation for models in the same universality class. As regards the adiabatic temperature change, it is not determined exclusively by the singular part of the free energy and its derivatives. We show that the field dependence of the adiabatic temperature......The magnetocaloric effect of a magnetic material is characterized by two quantities, the isothermal entropy change and the adiabatic temperature change, both of which are functions of temperature and applied magnetic field. We discuss the scaling properties of these quantities close to a second...... the framework of the Bean-Rodbell model, we briefly consider the scaling properties of the magnetocaloric effect in first-order materials. Finally, we discuss the implications of our findings for a widely used phenomenological scaling procedure for magnetocaloric quantities....

  17. Effective stress law for anisotropic double porous media

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ying; CHEN Mian; ZHANG Guangqing

    2004-01-01

    An effective stress law is derived analytically to describe the effect of pore (fracture pore and matrix-block pore) fluid pressure on the linearly elastic response of anisotropic saturated dual-porous rocks, which exhibit anisotropy. For general anisotropy the difference between the effective stress and the applied stress is not hydrostatic simply multiplied by Biot coefficient. The effective stress law involves four constants for transversely isotropic response; these constants can be expressed in terms of the moduli of the single porous material, double porous material and of the solid material. These expressions are simplified considerably when the anisotropy is structural rather than intrinsic, i.e. in the case of an isotropic solid material with an anisotropic pore structure. In this case the effective stress law involves grain bulk modulus, four moduli and two compliances of the porous material for transverse isotropy. The law reduces, in the case of isotropic response, to that suggested by Li Shuiquan (2001). And reduction to the single-porosity (derived analytically by Carroll (1979)) is presented to demonstrate the conceptual consistency of the proposed law.

  18. Magnetocaloric materials for energy efficient cooling

    Science.gov (United States)

    Lyubina, Julia

    2017-02-01

    Solid-state magnetic cooling near room temperature has recently gained a prominent position among alternative cooling technologies that are deemed to have higher energy efficiency compared to vapour compression. This prospect has surged a rapid growth of the area of magnetocaloric materials. Although several breakthroughs were achieved, the extensive study revealed a number of challenges in the effective deployment of the magnetic refrigerants. This review focuses on fundamentally and technologically relevant aspects of the cooling with magnetocaloric materials. A critical evaluation of magnetic refrigerants and progress made in improvement of their performance is provided. Future development trends in the field of materials for the solid state cooling are highlighted.

  19. Spin Hall effect of a light beam in anisotropic metamaterials

    Institute of Scientific and Technical Information of China (English)

    Tang Ming; Zhou Xin-Xing; Luo Hai-Lu; Wen Shuang-Chun

    2012-01-01

    We theoretically investigate a switchable spin Hall effect of light (SHEL) in reflection for three specific dispersion relations at an air-anisotropic metamaterial interface.The displacements of horizontal and vertical polarization components vary with the incident angle at different dispersion relations.The transverse displacements can be obtained with the relevant metamaterial whose refractive index can be arbitrarily tailed.The results of the SHEL in the metamaterial provide a new way for manipulating the transverse displacements of a specific polarization component.

  20. Enhancement of the martensitic transformation and magnetocaloric effect of Ni-Mn-V-Sn ribbons by annealing treatment

    Energy Technology Data Exchange (ETDEWEB)

    Xuan, H.C. [College of Materials Science and Engineering, Taiyuan University of Technology (China); National Laboratory of Solid State Microstructures and Key Laboratory of Nanomaterials for Jiang Su Province, Nanjing University (China); Zhang, Y.Q.; Li, H.; Han, P.D. [College of Materials Science and Engineering, Taiyuan University of Technology (China); Wang, D.H.; Du, Y.W. [National Laboratory of Solid State Microstructures and Key Laboratory of Nanomaterials for Jiang Su Province, Nanjing University (China)

    2015-09-15

    The rapidly solidified Ni{sub 41.98}Mn{sub 42.97}V{sub 2.08}Sn{sub 12.97} ribbons are prepared by the melt-spinning technique. The microstructure, martensitic transformation (MT), and magnetocaloric effect of the ribbons are greatly affected by annealing treatment. The equiaxed crystallized grains with the relatively homogeneous size distribution are observed for these ribbons. After annealing, the grain size becomes obviously large, the lattice constants decreases, and the exchange bias effect gets improved. The MT temperatures increase obviously for the annealed ribbons. Large magnetic entropy change (ΔS) is obtained in the annealed Ni-Mn-V-Sn ribbons. The peak values of ΔS in the annealed ribbons are 41.6 and -2.3 J kg{sup -1} K{sup -1} in the vicinity of MT temperature and Curie temperature of austenite, respectively, for the field change of 30 kOe. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Magnetocaloric effects in a freestanding and flexible graphene-based superlattice synthesized with a spatially confined reaction.

    Science.gov (United States)

    Zhu, Haiou; Xiao, Chong; Cheng, Hao; Grote, Fabian; Zhang, Xiaodong; Yao, Tao; Li, Zhou; Wang, Chengming; Wei, Shiqiang; Lei, Yong; Xie, Yi

    2014-06-03

    Superlattices have attracted great interest because of their tailorable electronic properties at the interface. However, the lack of an efficient and low-cost synthetic method represents a huge challenge to implement superlattices into practical applications. Herein, we report a space-confined nanoreactor strategy to synthesize flexible freestanding graphene-based superlattice nanosheets, which consist of alternately intercalated monolayered metal-oxide frameworks and graphene. Taking vanadium oxide as an example, clear-cut evidences in extended X-ray absorption fine structure, high-resolution transmission electron microscopy and infrared spectra have confirmed that the vanadium oxide frameworks in the superlattice nanosheets show high symmetry derived from the space-confinement and electron-donor effect of graphene layers, which enable the superlattice nanosheets to show emerging magnetocaloric effect. Undoubtedly, this freestanding and flexible superlattice synthesized from a low-cost and scalable method avoids complex transferring processes from growth substrates for final applications and thus should be beneficial to a wide variety of functionalized devices.

  2. Multiple magnetic relaxation processes, magnetocaloric effect and fluorescence properties of rhombus-shaped tetranuclear rare earth complexes.

    Science.gov (United States)

    Gao, Hong-Ling; Jiang, Li; Liu, Shuang; Shen, Hai-Yun; Wang, Wen-Min; Cui, Jian-Zhong

    2016-01-07

    Seven new tetranuclear rare earth (RE) complexes [RE4(acac)4L6(μ3-OH)2] (HL = 5-(4-fluorobenzylidene)-8-hydroxylquinoline; acac = acetylacetonate; RE = Y (1), Eu (2), Gd (3), Tb (4), Dy (5), Tm (6) and Lu (7)) have been synthesized and completely characterized. Complex exhibits multiple zero-field slow magnetic relaxation processes typical of Single Molecule Magnets (SMMs). Two distinct slow magnetic relaxation processes, with effective energy barriers of Ueff = 48 K for the slow relaxation (SR) process and Ueff = 121 K for the fast relaxation (FR) process, are mainly attributed to the presence of two crystallographically independent Dy(III) sites. The magnetocaloric effect (MCE) was detected as -ΔSm(T) = 20.8 J kg(-1) K(-1) for complex . The fluorescence properties of complexes 1, 2, 4, 5 and 7 were also investigated. Complexes 2, 4 and 5 show the characteristic peaks for their corresponding RE(III) center, while complexes 1 and 7 show similar emission peaks to the Schiff base ligand when they are excited at the appropriate wavelength.

  3. Magnetocaloric effect in heavy rare-earth elements doped Fe-based bulk metallic glasses with tunable Curie temperature

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jiawei; Huo, Juntao; Chang, Chuntao, E-mail: ctchang@nimte.ac.cn, E-mail: dujun@nimte.ac.cn; Du, Juan, E-mail: ctchang@nimte.ac.cn, E-mail: dujun@nimte.ac.cn; Man, Qikui; Wang, Xinmin; Li, Run-Wei [Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201 (China); Zhejiang Province Key Laboratory of Magnetic Materials and Application Technology, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201 (China); Law, Jiayan [Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg (Sweden)

    2014-08-14

    The effects of heavy rare earth (RE) additions on the Curie temperature (T{sub C}) and magnetocaloric effect of the Fe-RE-B-Nb (RE = Gd, Dy and Ho) bulk metallic glasses were studied. The type of dopping RE element and its concentration can easily tune T{sub C} in a large temperature range of 120 K without significantly decreasing the magnetic entropy change (ΔS{sub M}) and refrigerant capacity (RC) of the alloys. The observed values of ΔS{sub M} and RC of these alloys compare favorably with those of recently reported Fe-based metallic glasses with enhanced RC compared to Gd{sub 5}Ge{sub 1.9}Si{sub 2}Fe{sub 0.1}. The tunable T{sub C} and large glass-forming ability of these RE doped Fe-based bulk metallic glasses can be used in a wide temperature range with the final required shapes.

  4. Accurate modelling of anisotropic effects in austenitic stainless steel welds

    Science.gov (United States)

    Nowers, O. D.; Duxbury, D. J.; Drinkwater, B. W.

    2014-02-01

    The ultrasonic inspection of austenitic steel welds is challenging due to the formation of highly anisotropic and heterogeneous structures post-welding. This is due to the intrinsic crystallographic structure of austenitic steel, driving the formation of dendritic grain structures on cooling. The anisotropy is manifested as both a `steering' of the ultrasonic beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the quantitative effects and relative impacts of these phenomena are not well-understood. A semi-analytical simulation framework has been developed to allow the study of anisotropic effects in austenitic stainless steel welds. Frequency-dependent scatterers are allocated to a weld-region to approximate the coarse grain-structures observed within austenitic welds and imaged using a simulated array. The simulated A-scans are compared against an equivalent experimental setup demonstrating excellent agreement of the Signal to Noise (S/N) ratio. Comparison of images of the simulated and experimental data generated using the Total Focusing Method (TFM) indicate a prominent layered effect in the simulated data. A superior grain allocation routine is required to improve upon this.

  5. Inverse magnetocaloric effect in Mn{sub 2}NiGa and Mn{sub 1.75}Ni{sub 1.25}Ga magnetic shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Sanjay, E-mail: sanju8419@gmail.com; Barman, S. R. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001 (India); Esakki Muthu, S.; Arumugam, S. [Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli 620024 (India); Senyshyn, A. [Forschungsneutronenquelle Heinz Maier-Leibnitz FRM-II, Technische Universität München, Lichtenbergstrasse 1, 85747 Garching b. München (Germany); Rajput, P. [European Synchrotron Radiation Facility, 6 rue Jules Horowitz, F-38000 Grenoble (France); Suard, E. [Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9 (France)

    2014-02-03

    Inverse magnetocaloric effect is demonstrated in Mn{sub 2}NiGa and Mn{sub 1.75}Ni{sub 1.25}Ga magnetic shape memory alloys. The entropy change at the martensite transition is larger in Mn{sub 1.75}Ni{sub 1.25}Ga, and it increases linearly with magnetic field in both the specimens. Existence of inverse magnetocaloric effect is consistent with the observation that magnetization in the martensite phase is smaller than the austenite phase. Although the Mn content is smaller in Mn{sub 1.75}Ni{sub 1.25}Ga, from neutron diffraction, we show that the origin of inverse magnetocaloric effect is the antiferromagnetic interaction between the Mn atoms occupying inequivalent sites.

  6. Magnetocaloric effect in La(Fe{sub x}Si{sub 1-x}){sub 13} ferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Valiev, E. Z., E-mail: valiev@imp.uran.ru; Kazantsev, V. A. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)

    2011-12-15

    The isothermal changes in the magnetic entropy and the lattice entropy and the adiabatic temperature change in La(Fe{sub 0.88}Si{sub 0.12}){sub 13} and La(Fe{sub 0.86}Si{sub 0.14}){sub 13} ferromagnets in a magnetic field are calculated. The calculations are performed with a generalized magnetostriction model of a ferromagnet; the calculation results are compared to experimental data. It is shown that the change in the lattice entropy decreases the magnetocaloric effect and makes it possible to explain the experimental data obtained for La(Fe{sub x}Si{sub 1-x}){sub 13} (x = 0.86, 0.88) ferromagnets. The temperature dependences of the bulk compression moduli of these ferromagnets are calculated, and these dependences indicate a strong lattice softening in the vicinity of the magnetic phase transition in them. The thermal expansion coefficient and some magnetic properties of the ferromagnet with x = 0.86 are measured to determine the numerical values of the parameters entering into calculation formulas.

  7. Heisenberg like critical properties, magnetocaloric effect and scaling in lead doped NdMnO{sub 3} single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Nilotpal [School of Advanced Sciences, VIT University, Vellore-632014, Tamilnadu (India)

    2013-07-01

    Magnetic isotherms for single crystals of Nd{sub 0.7}Pb{sub 0.3}MnO{sub 3} have been measured around the ferromagnetic(FM) to paramagnetic(PM) transition temperature T{sub C}. Critical exponents have been obtained by modified Arrott plots and the Kouvel Fisher method. The values of exponents are consistent with those expected for 3D Heisenberg universality class. Magnetocaloric effect (MCE) has been also studied from the magnetic isotherms. Relative cooling power (RCP) is estimated as 56.725, 66.252 and 77.163 J/Kg for 1.2, 2.2 and 4.8 T fields respectively. Universal scaling behaviour in the relative change of magnetic entropy ΔS{sub M} has been observed. The rescaled magnetic entropy change curves for different applied fields are noticed to collapse onto a single curve. It has been found that the peak entropy change, ΔS{sub M} peak at T{sub C} and RCP follow a scaling power law in magnetic field H with the exponents which are reduced in comparison to their theoretically estimated value.

  8. Insulating phase in Sr2IrO4: An investigation using critical analysis and magnetocaloric effect

    Science.gov (United States)

    Bhatti, Imtiaz Noor; Pramanik, A. K.

    2017-01-01

    The nature of insulating phase in 5d based Sr2IrO4 is quite debated as the theoretical as well as experimental investigations have put forward evidences in favor of both magnetically driven Slater-type and interaction driven Mott-type insulator. To understand this insulating behavior, we have investigated the nature of magnetic state in Sr2IrO4 through studying critical exponents, low temperature thermal demagnetization and magnetocaloric effect. The estimated critical exponents do not exactly match with any universality class, however, the values obey the scaling behavior. The exponent values suggest that spin interaction in present material is close to mean-field model. The analysis of low temperature thermal demagnetization data, however, shows dual presence of localized- and itinerant-type of magnetic interaction. Moreover, field dependent change in magnetic entropy indicates magnetic interaction is close to mean-field type. While this material shows an insulating behavior across the magnetic transition, yet a distinct change in slope in resistivity is observed around Tc. We infer that though the insulating phase in Sr2IrO4 is more close to be Slater-type but the simultaneous presence of both Slater- and Mott-type is the likely scenario for this material.

  9. Magnetocaloric effect in AlFe2B2: toward magnetic refrigerants from earth-abundant elements.

    Science.gov (United States)

    Tan, Xiaoyan; Chai, Ping; Thompson, Corey M; Shatruk, Michael

    2013-06-26

    AlFe2B2 was prepared by two alternative synthetic routes, arc melting and synthesis from Ga flux. In the layered crystal structure, infinite chains of B atoms are connected by Fe atoms into two-dimensional [Fe2B2] slabs that alternate with layers of Al atoms. As expected from the theoretical analysis of electronic band structure, the compound exhibits itinerant ferromagnetism, with the ordering temperature of 307 K. The measurement of magnetocaloric effect (MCE) as a function of applied magnetic field reveals isothermal entropy changes of 4.1 J kg(-1) K(-1) at 2 T and 7.7 J kg(-1) K(-1) at 5 T. These are the largest values observed near room temperature for any metal boride and for any magnetic material of the vast 122 family of layered structures. Importantly, AlFe2B2 represents a rare case of a lightweight material prepared from earth-abundant, benign reactants which exhibits a substantial MCE while not containing any rare-earth elements.

  10. Phase, microstructure, and magnetocaloric effect of the large disc LaFe11.6Si1.4 alloy

    Institute of Scientific and Technical Information of China (English)

    陈湘; 陈云贵; 肖定全; 唐永柏

    2015-01-01

    The large disc LaFe11.6Si1.4 alloy, which was prepared by medium-frequency induction furnace, was annealed at 1503 K for different time. The main phases were 1:13 phase in the edge parts of the large discs alloy;the impurity phases includedα-Fe phase, LaFeSi phase, and even very small amount of La5Si3 phase. The amounts of impurity phases reduced with increasing in annealing time. The magnetic properties in the edge parts of the large discs LaFe11.6Si1.4 alloy were investigated. The magnetic susceptibility had an abrupt change at Curie temperature (TC) as the magnetization in M-T curves. The alloys had almost the same TC (191 K), the mag-netocaloric effect (MCE) and relative cooling power (RCP) increased with increasing in annealing time. In addition, for the same al-loy, the magnetic hysteresis decreased with the increase in temperature.

  11. Magneto-caloric effect of a Gd50Co50 amorphous alloy near the freezing point of water

    Directory of Open Access Journals (Sweden)

    L. Xia

    2015-09-01

    Full Text Available In the present work, we report the magneto-caloric effect (MCE of a binary Gd50Co50 amorphous alloy near the freezing temperature of water. The Curie temperature of Gd50Co50 amorphous ribbons is about 267.5 K, which is very close to room temperature. The peak value of the magnetic entropy change (-ΔSmpeak and the resulting adiabatic temperature rise (ΔTad. of the Gd50Co50 amorphous ribbons is much higher than that of any other amorphous alloys previously reported with a Tc near room temperature. On the other hand, although the -ΔSmpeak of Gd50Co50 amorphous ribbons is not as high as those of crystalline alloys near room temperature, its refrigeration capacity (RC is still much larger than the RC values of these crystalline alloys. The binary Gd50Co50 amorphous alloy provides a basic alloy for developing high performance multi-component amorphous alloys near room temperature.

  12. Large magnetocaloric effect of HoxEr1-xNi (0 ≤ x ≤ 1) compounds

    Science.gov (United States)

    Zheng, X. Q.; Zhang, B.; Wu, H.; Hu, F. X.; Huang, Q. Z.; Shen, B. G.

    2016-10-01

    A secondary magnetic transition (spin reorientation transition) below Curie temperature in ErNi was observed via different characterization techniques. Ho-substitution for Er atoms has a great impact on the magnetic property and magnetocaloric effect. The two magnetic transitions change close to each other with 10% of Ho-substitution at the Er site. It is also found that 10% of Ho-substitution contributes up to ˜14.9% of enhancement on the maximal magnetic entropy change (ΔSM) and ˜21.9% of enhancement on the maximal adiabatic temperature change (ΔTad). The maximum value of ΔSM and ΔTad for Ho0.1Er0.9Ni compound is as high as 34 J/kg K and 8.9 K, respectively, under a field change of 0-5 T. The relationship between the maximal ΔSM and the refrigerant temperature width (δTFWHM) for HoxEr1-xNi (0 ≤ x ≤ 1) compounds is analyzed. The enhancement of MCE for Ho0.1Er0.9Ni compound is considered to be resulted from the tendency of merging of spin reorientation transition and ferromagnetic to paramagnetic transition.

  13. Table-like magnetocaloric effect in Gd56Ni15Al27Zr2 alloy and its field independence feature

    Science.gov (United States)

    Agurgo Balfour, E.; Ma, Z.; Fu, H.; Hadimani, R. L.; Jiles, D. C.; Wang, L.; Luo, Y.; Wang, S. F.

    2015-09-01

    In order to obtain "table-like" magnetocaloric effect (MCE), multiple-phase Gd56Ni15Al27Zr2 alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd2Al and GdNiAl further broadened the relatively wider magnetic entropy change (-ΔSM) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5 K to 77.5 K. The plateau feature of the MCE was found to be nearly independent of the applied magnetic field from 3 T to 5 T. The maximum -ΔSM value of the MCE platforms is 6.0 J/kg K under applied magnetic field change of 5 T. Below 3 T, the field independence of the table-like feature disappears. The relatively large constant values of -ΔSM for the respective applied magnetic fields have promising applications in magnetic refrigeration using regenerative Ericsson cycle.

  14. Magnetic Properties and Magnetocaloric Effect in Layered NdMn1.9V0.1Si2

    Directory of Open Access Journals (Sweden)

    Din M.F. Md

    2014-07-01

    Full Text Available The structural and magnetic properties of the compounds NdMn2-xVxSi2 have been studied by x-ray and high resolution neutron powder diffraction, specific heat, dc magnetization, and differential scanning calorimetry measurements over the temperature range 3-450 K. The Curie temperature and Néel temperature of layered NdMn1.9V0.1Si2 are been indicate at TC ~ 24 K and TN ~ 376 K respectively. The giant magnetocaloric effect (GMCE around TC is found in layered NdMn1.9V0.1Si2 associated with first order magnetic transition from antiferromagnetic [AFil-type] to ferromagnetic [F(Nd+Fmc]. This behaviorhas been confirmed as contribution of the magnetostructural coupling by using neutron powder diffraction. The magnetic entropy change −ΔSM ~ 25.4J kg-1 K-1 and adiabatic temperature change ΔTad~ 6.7 K have been determined using magnetization and specific heat measurement under 0-8 T field applied. This compound belongs with the small thermal ~ 0.8 K and magnetic ~ 0.1 T hysteresis characteristic providing high potential material for magnetic refrigerator.

  15. Magnetic Properties and Magnetocaloric Effect in Layered NdMn1.9Ti0.1Si2

    Directory of Open Access Journals (Sweden)

    M.F. Md Din

    2014-04-01

    Full Text Available The structural and magnetic properties of the NdMn1.9Ti0.1Si2 compund have been studied by high-intensity x-ray and high-resolution neutron powder diffraction, specific heat, dc magnetization, and differential scanning calorimetry measurements over the temperature range of 3-450 K. The Curie temperature and Néel temperature of layered NdMn1.9Ti0.1Si2 are indicated as TC ~ 22 K and TN ~ 374 K respectively. The first order magnetic transition from antiferromagnetic [AFil-type] to ferromagnetic [F(Nd+Fmc] around TC is found in layered NdMn1.9Ti0.1Si2 and is associated with large magnetocaloric effect. This behavior has been confirmed as a contribution of the magnetostructural coupling by using neutron and x-ray powder diffraction. The magnetic entropy change –ΔSM ~ 15.3 J kg-1 K-1 and adiabatic temperature change ΔTad ~ 4.7 K have been determined using magnetization and specific heat measurement under 0-5 T applied fields. This compound exhibits almost no thermal and magnetic hysteresis, thus potentially applicable in low temperature region for magnetic refrigerator material

  16. First order structural transformation and inverse magnetocaloric effect in melt-spun Ni-Mn-Sn ribbons

    Science.gov (United States)

    Babita, I.; Patil, S. I.; Ram, S.

    2010-05-01

    First order structural transformation (FOST) and inverse magnetocaloric effect (IMCE) were investigated in melt-spun ribbons of Ni49Mn37.4Sn13.6 and Ni50Mn34.5Sn15.5 Heusler alloys. Thermal and magnetic characterization of the ribbons revealed the existence of FOST. Interestingly, in the Ni49Mn37.4Sn13.6 ribbon, the structural transformation occurs prior to magnetic transition incongruous to that observed in the Ni50Mn34.5Sn15.5 ribbons. In addition to FOST, the ribbons also exhibit a large IMCE at low magnetic field. A maximum positive magnetic entropy change ΔSM ~ 6.0 J kg-1 K-1 and ~1.6 J kg-1 K-1 for a field change of 2 T was observed in the Ni49Mn37.4Sn13.6 and Ni50Mn34.5Sn15.5 ribbons, respectively.

  17. Phase transitions, magnetotransport and magnetocaloric effects in a new family of quaternary Ni-Mn-In-Z Heusler alloys.

    Science.gov (United States)

    Kazakov, Alexander; Prudnikov, Valerii; Granovsky, Alexander; Perov, Nikolai; Dubenko, Igor; Pathak, Arjun Kumar; Samanta, Tapas; Stadler, Shane; Ali, Naushad; Zhukov, Arcady; Ilyin, Maxim; Gonzalez, Julian

    2012-09-01

    The magnetic, magnetotransport, and magnetocaloric properties near compound phase transitions in Ni50Mn35In14Z (Z = In, Ge, Al), and Ni48Co2Mn35In15 Heusler alloys have been studied using VSM and SQUID magnetometers (at magnetic fields (H) up to 5 T), four-probe method (at H = 0.005-1.5 T), and an adiabatic magnetocalorimeter (for H changes up to deltaH = 1.8 T), respectively. The martensitic transformation (MT) is accompanied by large magnetoresistance (up to 70%), a significant change in resistivity (up to 200%), and a sign reversal of the ordinary Hall effect coefficient, all related to a strong change in the electronic spectrum at the MT. The field dependences of the Hall resistance are complex in the vicinity of the MT, indicating a change in the relative concentrations of the austenite and martensite phases at strong fields. Negative and positive changes in adiabatic temperatures of about -2 K and +2 K have been observed in the vicinity of MT and Curie temperatures, respectively, for deltaH = 1.8 T.

  18. Effect of changing P/Ge and Mn/Fe ratios on the magnetocaloric effect and structural transition in the (Mn,Fe2 (P,Ge intermetallic compounds

    Directory of Open Access Journals (Sweden)

    Wlodarczyk P.

    2016-09-01

    Full Text Available The magnetocaloric effect in the MnxFe2−xP1−yGey intermetallic compounds with the amount of Mn in the range of x = 1.05 to 1.17 and amount of Ge in the range of y = 0.19 to 0.22 has been studied. It was found that a higher Ge/P ratio causes an increase in Curie temperature, magnetocaloric effect at low field (up to 1 T, activation energy of structural transition and a decrease in thermal hysteresis, as well as transition enthalpy. Contrary to this observation, higher Mn/Fe ratio causes a decrease in Curie temperature, slight decrease of magnetocaloric effect at low magnetic field, and an increase in thermal hysteresis. Simultaneous increase of both ratios may be very advantageous, as the thermal hysteresis can be lowered and magnetocaloric effect can be enhanced without changing the Curie temperature. Some hints about optimization of the composition for applications at low magnetic fields (0.5 T to 2 T have been presented.

  19. Aeroelastic modal dynamics of wind turbines including anisotropic effects

    Energy Technology Data Exchange (ETDEWEB)

    Fisker Skjoldan, P.

    2011-03-15

    Several methods for aeroelastic modal analysis of a rotating wind turbine are developed and used to analyse the modal dynamics of two simplified models and a complex model in isotropic and anisotropic conditions. The Coleman transformation is used to enable extraction of the modal frequencies, damping, and periodic mode shapes of a rotating wind turbine by describing the rotor degrees of freedom in the inertial frame. This approach is valid only for an isotropic system. Anisotropic systems, e.g., with an unbalanced rotor or operating in wind shear, are treated with the general approaches of Floquet analysis or Hill's method which do not provide a unique reference frame for observing the modal frequency, to which any multiple of the rotor speed can be added. This indeterminacy is resolved by requiring that the periodic mode shape be as constant as possible in the inertial frame. The modal frequency is thus identified as the dominant frequency in the response of a pure excitation of the mode observed in the inertial frame. A modal analysis tool based directly on the complex aeroelastic wind turbine code BHawC is presented. It uses the Coleman approach in isotropic conditions and the computationally efficient implicit Floquet analysis in anisotropic conditions. The tool is validated against system identifications with the partial Floquet method on the nonlinear BHawC model of a 2.3 MW wind turbine. System identification results show that nonlinear effects on the 2.3 MW turbine in most cases are small, but indicate that the controller creates nonlinear damping. In isotropic conditions the periodic mode shape contains up to three harmonic components, but in anisotropic conditions it can contain an infinite number of harmonic components with frequencies that are multiples of the rotor speed. These harmonics appear in calculated frequency responses of the turbine. Extreme wind shear changes the modal damping when the flow is separated due to an interaction between

  20. Computational Study of Subdural Cortical Stimulation: Effects of Simulating Anisotropic Conductivity on Activation of Cortical Neurons.

    Directory of Open Access Journals (Sweden)

    Hyeon Seo

    Full Text Available Subdural cortical stimulation (SuCS is an appealing method in the treatment of neurological disorders, and computational modeling studies of SuCS have been applied to determine the optimal design for electrotherapy. To achieve a better understanding of computational modeling on the stimulation effects of SuCS, the influence of anisotropic white matter conductivity on the activation of cortical neurons was investigated in a realistic head model. In this paper, we constructed pyramidal neuronal models (layers 3 and 5 that showed primary excitation of the corticospinal tract, and an anatomically realistic head model reflecting complex brain geometry. The anisotropic information was acquired from diffusion tensor magnetic resonance imaging (DT-MRI and then applied to the white matter at various ratios of anisotropic conductivity. First, we compared the isotropic and anisotropic models; compared to the isotropic model, the anisotropic model showed that neurons were activated in the deeper bank during cathodal stimulation and in the wider crown during anodal stimulation. Second, several popular anisotropic principles were adapted to investigate the effects of variations in anisotropic information. We observed that excitation thresholds varied with anisotropic principles, especially with anodal stimulation. Overall, incorporating anisotropic conductivity into the anatomically realistic head model is critical for accurate estimation of neuronal responses; however, caution should be used in the selection of anisotropic information.

  1. Magnetocaloric refrigeration concepts: current state of the art

    DEFF Research Database (Denmark)

    Nielsen, Kaspar Kirstein

    2014-01-01

    Refrigeration devices based on the magnetocaloric effect have been prototyped in great numbers during the past decade. The search for the optimal combination of magnetic field source, regenerator geometry, magnetocaloric material composition and flow system design has resulted in a variety...... of designs and concepts. In this paper key parts constituting a magnetocaloric refrigeration device are reviewed in terms of how they have been implemented in actual machines. Some of the major design choices are then evaluated and, based on numerical modeling tools, recommendations on how to optimize...

  2. Fracture of anisotropic materials with plastic strain-gradient effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2013-01-01

    parameter is adopted. The fracture process along the fiber-matrix interface is modeled using a recently proposed cohesive law extension having an additional material length parameter. Due to the fiber-matrix fracture a sudden stress-drop is seen in the macroscopic stress-strain response which defines......A unit cell is adopted to numerically analyze the effect of plastic anisotropy on frac-ture evolution in a micro-reinforced fiber-composite. The matrix material exhibit size-effects and an anisotropic strain-gradient plasticity model accounting for such size-effects through a mate-rial length scale...... the failure strain of the composite. The effect of the two material length parameters on the failure strain of the composite is studied. For small values of the material length scale parameter conventional predictions are obtained. Larger values of the material length scale parameter result in corresponding...

  3. Effect of benzotriazole on the anisotropic electrolytic etching of copper

    Energy Technology Data Exchange (ETDEWEB)

    Papapanayiotou, D.; Deligianni, H.; Alkire, R.C. [Univ. of Illinois, Urbana, IL (United States)

    1998-09-01

    Electrolytic etching of copper foil at the base of cavities formed by patterned photoresist was investigated in 0.5 M sulfuric acid solutions which either contained 40 mM benzotriazole (BTA) or were free of BTA. It was found that undercutting (metal dissolution beneath the photoresist) was minimized by the action of surface films in both solutions. It was also found that the nature of the surface films and the mechanism by which they enhanced etch anisotropy differed. In additive-free solutions, anisotropic etching was observed under conditions of applied potential and flow for which mass transfer was suppressed in the interior corner regions of cavities. Such operating conditions in additive-free solutions displayed characteristic current transients. In BTA-containing solutions, the etch profiles were highly dependent on applied potential. In contrast to the additive-free solutions, the flow conditions in BTA-containing solutions had little effect on the current transients or on the degree of undercutting within the region of applied potential in which anisotropic etching was achievable.

  4. Effect of Interplanetary Transients on Cosmic Ray Anisotropic Variations

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In the present work the cosmic ray intensity data recorded with ground-based neutron monitor at Deep River has investigated taking into account the associated interplanetary magnetic field and solar wind plasma data during 1981-1994. A large number of days having abnormally high/low amplitudes for successive number of five or more days as compared to annual average amplitude of diurnal anisotropy have been taken as high/low amplitude anisotropic wave train events (HAE/LAE). The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth. The High-Speed Solar Wind Streams (HSSWS) do not play any significant role in causing these types of events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic ray decreases. Hα solar flares have a good positive correlation with both amplitude and direction of the anisotropy for HAEs,whereas PMSs have a good positive correlation with both amplitude and direction of the anisotropy for LAEs.The source responsible for these unusual anisotropic wave trains in CR has been proposed.

  5. Reciprocal relations for effective conductivities of anisotropic media

    Science.gov (United States)

    Nevard, John; Keller, Joseph B.

    1985-11-01

    Any pair of two-dimensional anisotropic media with local conductivity tensors that are functions of position and that are related to one another in a certain reciprocal way are considered. It is proved that their effective conductivity tensors are related to each other in the same way for both spatially periodic media and statistically stationary random media. An inequality involving the effective conductivity tensors of two three-dimensional media that are reciprocally related is also proved. These results extend the corresponding results for locally isotropic media obtained by Keller, Mendelsohn, Hansen, Schulgasser, and Kohler and Papanicolau. They also yield a relation satisfied by the effective conductivity tensor of a medium reciprocal to a translated or rotated copy of itself.

  6. Waveguide effect under 'antiguiding' conditions in graded anisotropic media

    Science.gov (United States)

    Kozlov, A. V.; Mozhaev, V. G.; Zyryanova, A. V.

    2010-02-01

    A new wave confinement effect is predicted in graded crystals with a concave slowness surface under conditions of growth of the phase velocity with decreasing distance from the waveguide axis. This finding overturns the common notion about the guiding and 'antiguiding' profiles of wave velocity in inhomogeneous media. The waveguide effect found is elucidated by means of ray analysis and particular exact wave solutions. The exact solution obtained for localized flexural waves in thin plates of graded cubic and tetragonal crystals confirms the predicted effect. Since this solution is substantially different with respect to the existence conditions from all others yet reported, and it cannot be deduced from the previously known results, the predicted waves can be classified as a new type of waveguide mode in graded anisotropic media. Although the concrete calculations are given in the article for acoustic waves, its general predictions are expected to be valid for waves of various natures, including spin, plasma, and optical waves.

  7. Monte Carlo Simulations of the Magnetic Behavior, Ordering Temperature and Magnetocaloric Effects in 1D, 2D and 3D Ferrimagnetic Systems.

    Science.gov (United States)

    Stanica, Nicolae; Cimpoesu, Fanica; Radu, Cosmin; Chihaia, Viorel; Suh, Soong-Hyuck

    2015-01-01

    As for the systematic investigations of magnetic behaviors and its related properties, computer simulations in extended quantum spin networks have been performed in good conditions via the generalized Ising model using the Monte Carlo-Metropolis algorithm with proven efficiencies. The present work, starting from a real magnetic system, provides detailed insights into the finite size effects and the ferrimagnetic properties in various 1 D, 2D and 3D geometries such as the magnetic moment, ordering temperature, and magnetocaloric effects with the different values of spins localized on the different coordinated sites.

  8. Giant low-field magnetocaloric effect in single-crystalline EuTi{sub 0.85}Nb{sub 0.15}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Roy, S.; Khan, N.; Mandal, P., E-mail: prabhat.mandal@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700 064 (India)

    2016-02-01

    The magnetocaloric effect in ferromagnetic single crystal EuTi{sub 0.85}Nb{sub 0.15}O{sub 3} has been investigated using magnetization and heat capacity measurements. EuTi{sub 0.85}Nb{sub 0.15}O{sub 3} undergoes a continuous ferromagnetic phase transition at T{sub C} = 9.5 K due to the long range ordering of magnetic moments of Eu{sup 2+} (4f{sup 7}). With the application of magnetic field, the spin entropy is strongly suppressed and a giant magnetic entropy change is observed near T{sub C}. The values of entropy change ΔS{sub m} and adiabatic temperature change ΔT{sub ad} are as high as 51.3 J kg{sup −1} K{sup −1} and 22 K, respectively, for a field change of 0–9 T. The corresponding magnetic heating/cooling capacity is 700 J kg{sup −1}. This compound also shows large magnetocaloric effect even at low magnetic fields. In particular, the values of ΔS{sub m} reach 14.7 and 23.8 J kg{sup −1} K{sup −1} for field changes of 0–1 T and 0–2 T, respectively. The low-field giant magnetocaloric effect, together with the absence of thermal and field hysteresis makes EuTi{sub 0.85}Nb{sub 0.15}O{sub 3} a very promising candidate for low temperature magnetic refrigeration.

  9. Conventional and inverse magnetocaloric effect in Pr{sub 2}CuSi{sub 3} and Gd{sub 2}CuSi{sub 3} compounds

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Fang, E-mail: jfzw2001@163.com [Ning Bo University of Technology, Ning Bo, Zhe Jiang 315211 (China); Yuan, Feng-ying [Tian Jin University of Science and Technology, Tian Jin 300222,China (China); Wang, Jin-zhi; Feng, Tang-fu; Hu, Guo-qi [Ning Bo University of Technology, Ning Bo, Zhe Jiang 315211 (China)

    2014-04-01

    Highlights: • Two phase transitions in a narrow temperature range were observed and studied. • Both typical and inverse magnetocaloric effect were observed and discussed. • The inverse magnetocaloric effect was attributed to the spin-glass behavior. - Abstract: Magnetic properties and magnetocaloric effect (MCE) in Pr{sub 2}CuSi{sub 3} and Gd{sub 2}CuSi{sub 3} compounds were investigated systematically. Both Pr{sub 2}CuSi{sub 3} and Gd{sub 2}CuSi{sub 3} compounds experienced two phase transitions in a relatively narrow temperature range: first a paramagnet (PM)–ferromagnet (FM) second-order phase transition at 12 and 26 K and then a FM–spin glass (SG) transition at 6 K and 7.5 K, respectively. The magnetic entropy change (ΔS{sub M}) was calculated based on Maxwell relation using the collected magnetization data. The maximum of ΔS{sub M} for Pr{sub 2}CuSi{sub 3} and Gd{sub 2}CuSi{sub 3} compounds was 7.6 and 5 J kg{sup −1} K{sup −1}, respectively, at the applied filed change of 0–5 T. The shape of the temperature dependence of ΔS{sub M} (ΔS{sub M}–T) curve was obviously different from that of the conventional magnetic materials undergoing only one typical phase transition. In the left half part of ΔS{sub M}–T curve, ΔS{sub M} is not very sensitive to the applied field and they tend to intersect with the decrease of temperature. Both typical conventional and inverse MCE behavior were observed in Gd{sub 2}CuSi{sub 3}, which would be originated from the two transition features at the low temperatures.

  10. Magnetocaloric effect in {[Fe(pyrazole)_4]_2[Nb(CN)_8]·4H_2O}{sub n} molecular magnet

    Energy Technology Data Exchange (ETDEWEB)

    Pełka, R., E-mail: robert.pelka@ifj.edu.pl [The H. Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342 Kraków (Poland); Konieczny, P.; Zieliński, P.M.; Wasiutyński, T. [The H. Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342 Kraków (Poland); Miyazaki, Y.; Inaba, A. [Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Pinkowicz, D.; Sieklucka, B. [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków (Poland)

    2014-03-15

    Magnetocaloric effect in {[Fe(pyrazole)_4]_2[Nb(Cn)_8]·4H_2O}{sub n} molecular magnet is reported. It crystallizes in tetragonal I4{sub 1}/a space group. The compound exhibits a phase transition to a long range magnetically ordered state at T{sub c}≈8.3K. The magnetic entropy change ΔS{sub M} as well as the adiabatic temperature change ΔT{sub ad} due to applied field change μ{sub 0}ΔH=0.1, 0.2, 0.5, 1, 2, 5, 9 T as a function of temperature have been determined by the relaxation calorimetry measurements. The maximum value of ΔS{sub M} for μ{sub 0}ΔH=5T is 4.9 J mol{sup −1} K{sup −1} (4.8 J kg{sup −1} K{sup −1}) at 10.3 K. The corresponding maximum value of ΔT{sub ad} is 2.0 K at 8.9 K. The temperature dependence of the exponent n characterizing the field dependence of ΔS{sub M} has been estimated. It attains the value of 0.64 at the transition temperature, which is consistent with the 3D Heisenberg universality class. - Highlights: • Using the technique of relaxation calorimetry the magnetocaloric effect of a novel molecular magnet is analyzed. • Temperature dependencies of isothermal magnetic entropy change and adiabatic temperature change are estimated. • Scaling behavior of the magnetocaloric effect is discussed.

  11. Effective Orthorhombic Anisotropic Models for Wave field Extrapolation

    KAUST Repository

    Ibanez Jacome, Wilson

    2013-05-01

    Wavefield extrapolation in orthorhombic anisotropic media incorporates complicated but realistic models, to reproduce wave propagation phenomena in the Earth\\'s subsurface. Compared with the representations used for simpler symmetries, such as transversely isotropic or isotropic, orthorhombic models require an extended and more elaborated formulation that also involves more expensive computational processes. The acoustic assumption yields more efficient description of the orthorhombic wave equation that also provides a simplified representation for the orthorhombic dispersion relation. However, such representation is hampered by the sixth-order nature of the acoustic wave equation, as it also encompasses the contribution of shear waves. To reduce the computational cost of wavefield extrapolation in such media, I generate effective isotropic inhomogeneous models that are capable of reproducing the first-arrival kinematic aspects of the orthorhombic wavefield. First, in order to compute traveltimes in vertical orthorhombic media, I develop a stable, efficient and accurate algorithm based on the fast marching method. The derived orthorhombic acoustic dispersion relation, unlike the isotropic or transversely isotropic one, is represented by a sixth order polynomial equation that includes the fastest solution corresponding to outgoing P-waves in acoustic media. The effective velocity models are then computed by evaluating the traveltime gradients of the orthorhombic traveltime solution, which is done by explicitly solving the isotropic eikonal equation for the corresponding inhomogeneous isotropic velocity field. The inverted effective velocity fields are source dependent and produce equivalent first-arrival kinematic descriptions of wave propagation in orthorhombic media. I extrapolate wavefields in these isotropic effective velocity models using the more efficient isotropic operator, and the results compare well, especially kinematically, with those obtained from the

  12. Gd2Cu(SO4)2(OH)4: a 3d-4f hydroxysulfate with an enhanced cryogenic magnetocaloric effect.

    Science.gov (United States)

    Tang, Yingying; Guo, Wenbin; Zhang, Suyun; Yang, Ming; Xiang, Hongping; He, Zhangzhen

    2015-10-21

    A 3d-4f hydroxysulfate, Gd2Cu(SO4)2(OH)4, is synthesized by means of a conventional hydrothermal method. Magnetic measurements confirm that the title compound exhibits a paramagnetic behavior down to 2 K, in which an enhanced magnetocaloric effect with a maximum -ΔSm (45.52(1) J kg(-1) K(-1), 212.8(6) mJ cm(-3) K(-1)) is observed at ∼4 K for ΔH = 8 T. The thermal stability using TG analysis and a FT-IR spectrum are also investigated.

  13. Magnetocaloric effect and thermal conductivity of Gd(OH)3 and Gd2O(OH)4(H2O)2.

    Science.gov (United States)

    Yang, Yan; Zhang, Qian-Chong; Pan, Yin-Yin; Long, La-Sheng; Zheng, Lan-Sun

    2015-04-30

    Magnetocaloric effect (MCE) and thermal conductivity of two gadolinium hydroxides, Gd(OH)3 (1) and Gd2O(OH)4(H2O)2 (2), are investigated. Magnetic studies indicate that both 1 and 2 exhibit antiferromagnetic interaction, and the MCE values for 1 and 2 at 2 K and ΔH = 7 T are 62.00 J kg(-1) K(-1) and 59.09 J kg(-1) K(-1), respectively. Investigation of their thermal conductivity reveals that the thermal conductivity for 1 is significantly better than that for 2.

  14. A large cryogenic magnetocaloric effect exhibited at low field by a 3D ferromagnetically coupled Mn(II)-Gd(III) framework material.

    Science.gov (United States)

    Guo, Fu-Sheng; Chen, Yan-Cong; Liu, Jun-Liang; Leng, Ji-Dong; Meng, Zhao-Sha; Vrábel, Peter; Orendáč, Martin; Tong, Ming-Liang

    2012-12-28

    The large cryogenic magnetocaloric effect of a 3D oxydiacetate-bridged gadolinium-manganese MOF material, [Mn(H(2)O)(6)][MnGd(oda)(3)](2)·6H(2)O (1), was evaluated by magnetization and heat capacity measurements. A maximum -ΔS(m) of 50.1 J kg(-1) K(-1) for ΔH = 70 kG along with significant entropy change at lower field was found on account of the weak Mn···Gd ferromagnetic interactions and the small molecular mass. This suggests that 1 could be considered as a potential coolant for liquid helium temperature applications.

  15. Monte Carlo simulation of the magnetocaloric effect in La2/3Ca1/3MnO3 single crystal

    Science.gov (United States)

    Zouari, R.; Chehaidar, A.

    2016-11-01

    The present work is devoted to a theoretical simulation study of the magnetocaloric effect in magnetically homogeneous La2/3 Ca1/3 Mn O3 single crystal. Using the standard Monte Carlo-Metropolis algorithm and the classical Heisenberg model Hamiltonian, we have computed the two main magnetocaloric properties such as the isothermal entropy change and the adiabatic temperature change upon an abrupt variation of the intensity of the applied magnetic field, as function of temperature. A good qualitative agreement is observed between our simulation and experiment. We have shown that the maximum entropy change increases by increasing the intensity of the applied magnetic field. In addition, it occurs at the ferromagnetic-paramagnetic transition temperature regardless of the intensity of the applied magnetic field. Our simulation shows, moreover, that the adiabatic temperature change behaves as the isothermal entropy change with respect to the material temperature and the applied magnetic field variation. Quantitatively, however, the experimental data deviate more or less, depending on powder preparation conditions, from our simulation data. This demonstrates the deviation of the prepared powders with respect to an ideal magnetic structure, as expected experimentally. Our simulation expects a maximum isothermal entropy change of - 5.2 J / kg K and a maximum adiabatic temperature change of 5.7 K under a magnetic field variation of 5 T. On approaching room temperature, the magnitude of the magnetocaloric effect in La2/3 Ca1/3 Mn O3 single crystal decreases but remains significant under a magnetic field variation of at least 2 T.

  16. Characterization of magnetocaloric effect, magnetic ordering and electronic structure in the GdFe{sub 1−x}Co{sub x}Si intermetallic compounds

    Energy Technology Data Exchange (ETDEWEB)

    Wlodarczyk, P., E-mail: patrykw@imn.gliwice.pl [Institute of Non-Ferrous Metals, ul. Sowinskiego 5, 44-100 Gliwice (Poland); Hawelek, L. [Institute of Non-Ferrous Metals, ul. Sowinskiego 5, 44-100 Gliwice (Poland); University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-008 Katowice (Poland); Zackiewicz, P. [Institute of Non-Ferrous Metals, ul. Sowinskiego 5, 44-100 Gliwice (Poland); Rebeda Roy, T. [SRM Research Institute, SRM University, Chennai 603203 (India); Chrobak, A. [University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-008 Katowice (Poland); Kaminska, M.; Kolano-Burian, A. [Institute of Non-Ferrous Metals, ul. Sowinskiego 5, 44-100 Gliwice (Poland); Szade, J. [University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40-008 Katowice (Poland)

    2015-07-15

    GdFeSi silicide is a strong ferromagnet with Curie temperature (T{sub c}) equal to 118 K. The substitution of cobalt for iron continuously suppresses ferromagnetism of the former compound, while it changes magnetic transition temperature nonlinearly. When the molar amount of cobalt reaches 0.4, the temperature of magnetic transition reaches minimal value i.e, 70 K. For larger amount of cobalt, magnetic transformation temperature rises well above 200 K and the antiferromagnetic interactions become dominant. In the present work we have found that the magnetic transformation temperature can be strictly correlated with the lattice constant c, which determines the distance between gadolinium layers as well as distance between neighboring gadolinium atoms in one layer. These results correspond to the change of amplitude of magnetocaloric effect which is being suppressed when the amount of cobalt increases. Adiabatic temperature change is equal to 2 K during the magnetic field cycle 0–1.7 T for pure GdFeSi, while no temperature change is observed during the same cycle for pure GdCoSi because of its antiferromagnetic character. - Highlights: • We have studied magnetocaloric properties of GdFe{sub x}Co{sub 1−x}Si intermetallic compounds. • It was found that when x is changing from 1 to 0, initially ferromagnetic compound becomes antiferromagnetic. • The highest magnetocaloric effect was found in pure GdFeSi (ΔT = 2 K at B = 1.7 T at T = 135 K)

  17. Anisotropic hydrodynamics, holography and the chiral magnetic effect

    Energy Technology Data Exchange (ETDEWEB)

    Gahramanov, Ilmar; Kalaydzhyan, Tigran; Kirsch, Ingo [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Hamburg Univ. (Germany). Zentrum fuer Mathematische Physik

    2012-03-15

    We discuss a possible dependence of the chiral magnetic effect (CME) on the elliptic flow coefficient {upsilon}{sub 2}. We first study this in a hydrodynamic model for a static anisotropic plasma with multiple anomalous U(1) currents. In the case of two charges, one axial and one vector, the CME formally appears as a first-order transport coefficient in the vector current. We compute this transport coefficient and show its dependence on {upsilon}{sub 2}. We also determine the CME-coefficient from first-order corrections to the dual AdS background using the fluid-gravity duality. For small anisotropies, we find numerical agreement with the hydrodynamic result. (orig.)

  18. An effective one-dimensional anisotropic fingerprint enhancement algorithm

    Science.gov (United States)

    Ye, Zhendong; Xie, Mei

    2012-01-01

    Fingerprint identification is one of the most important biometric technologies. The performance of the minutiae extraction and the speed of the fingerprint verification system rely heavily on the quality of the input fingerprint images, so the enhancement of the low fingerprint is a critical and difficult step in a fingerprint verification system. In this paper we proposed an effective algorithm for fingerprint enhancement. Firstly we use normalization algorithm to reduce the variations in gray level values along ridges and valleys. Then we utilize the structure tensor approach to estimate each pixel of the fingerprint orientations. At last we propose a novel algorithm which combines the advantages of onedimensional Gabor filtering method and anisotropic method to enhance the fingerprint in recoverable region. The proposed algorithm has been evaluated on the database of Fingerprint Verification Competition 2004, and the results show that our algorithm performs within less time.

  19. The Anisotropic Transport Effects On The Dilute Plasmas

    CERN Document Server

    Devlen, Ebru

    2012-01-01

    We examine the linear stability analysis of a hot, dilute and differentially rotating plasma by considering anisotropic transport effects. In the dilute plasmas, the ion Larmor radius is small compared with its collisional mean free path. In this case, the transport of heat and momentum along the magnetic field lines become important. This paper presents a novel linear instability that may more powerful and greater than ideal magnetothermal instability (MTI) and ideal magnetorotational instability (MRI) in the dilute astrophysical plasmas. This type of plasma is believed to be found in the intracluster medium of galaxy clusters and radiatively ineffective accretion flows around black holes. We derive the dispersion relation of this instability and obtain the instability condition. There is at least one unstable mode that is independent of the temperature gradient direction for a helical magnetic field geometry. This novel instability is driven by the gyroviscosity coupled with differential rotation. Therefore...

  20. Numerical analysis of anisotropic diffusion effect on ICF hydrodynamic instabilities

    Directory of Open Access Journals (Sweden)

    Olazabal-Loumé M.

    2013-11-01

    Full Text Available The effect of anisotropic diffusion on hydrodynamic instabilities in the context of Inertial Confinement Fusion (ICF flows is numerically assessed. This anisotropy occurs in indirect-drive when laminated ablators are used to modify the lateral transport [1,2]. In direct-drive, non-local transport mechanisms and magnetic fields may modify the lateral conduction [3]. In this work, numerical simulations obtained with the code PERLE [4], dedicated to linear stability analysis, are compared with previous theoretical results [5]. In these approaches, the diffusion anisotropy can be controlled by a characteristic coefficient which enables a comprehensive study. This work provides new results on the ablative Rayleigh-Taylor (RT, ablative Richtmyer-Meshkov (RM and Darrieus-Landau (DL instabilities.

  1. Magnetostructural transitions in Mn-rich Heusler Mn–Ni–In melt-spun ribbons with enhanced magnetocaloric effect

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hongwei; Feng, Shutong; Ren, Jian [State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072 (China); Laboratory for Microstructures, Shanghai University, Shanghai 200072 (China); Zhai, Qijie; Fu, Jianxun [State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072 (China); Luo, Zhiping [Department of Chemistry and Physics, Fayetteville State University, Fayetteville, NC 28301 (United States); Zheng, Hongxing, E-mail: hxzheng@shu.edu.cn [State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072 (China); Laboratory for Microstructures, Shanghai University, Shanghai 200072 (China)

    2015-10-01

    The magnetostructural transition behavior and magnetocaloric effect of Mn-rich Heusler Mn–Ni–In melt-spun ribbons have been investigated in the present study. Experimental results showed that the martensitic transition temperatures decreased by substituting small amounts of Ni with Mn in Mn{sub 49+x}Ni{sub 42−x}In{sub 9} (x=0,1,2). Within a temperature range from 100 K to 380 K, the Mn{sub 49}Ni{sub 41}In{sub 9} underwent a martensitic transformation from a paramagnetic L2{sub 1}-type cubic austenite to a ferromagnetic modulated fourteen-layered monoclinic (14M) martensite, followed with a ferromagnetic→weak-magnetic transition in martensite upon cooling. While for both Mn{sub 50}Ni{sub 41}In{sub 9} and Mn{sub 51}Ni{sub 40}In{sub 9}, the paramagnetic→ferromagnetic transition in austenite occurred prior to the martensitic transformation upon cooling. Under a magnetic field change of 30 kOe, the maximum magnetic entropy changes of the Mn{sub 50}Ni{sub 41}In{sub 9} melt-spun ribbons were found to be 5.7 J/kg K and −2.3 J/kg K in the vicinity of martensitic transformation and magnetic transition of austenite, respectively. An enhanced total effective refrigeration capacity as high as 184.2 J/kg was obtained in the Mn{sub 50}Ni{sub 41}In{sub 9} melt-spun ribbons. - Highlights: • Mn-rich Heusler Mn–Ni–In melt-spun ribbons were investigated in the present study. • The compositional dependence on the magnetostructural transition behavior was clarified. • An enhanced refrigeration capacity as high as 184.2 J/kg was obtained in Mn{sub 50}Ni{sub 41}In{sub 9}.

  2. New aspects of magnetocaloric effect in NiMn{sub 0.89}Cr{sub 0.11}Ge

    Energy Technology Data Exchange (ETDEWEB)

    Jaworska-Gołąb, T., E-mail: teresa.jaworska-golab@uj.edu.pl [Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków (Poland); Baran, S. [Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków (Poland); Duraj, R. [Institute of Physics, Cracow University of Technology, Podchorążych 1, 30-084 Kraków (Poland); Marzec, M. [Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków (Poland); Dyakonov, V. [Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warszawa (Poland); A.A. Galkin Donetsk Physico-Technical Institute, 83-114 Donetsk (Ukraine); Sivachenko, A. [A.A. Galkin Donetsk Physico-Technical Institute, 83-114 Donetsk (Ukraine); Tyvanchuk, Yu. [Chemistry Department, Ivan Franko National University of Lviv, 79-005 Lviv (Ukraine); Szymczak, H. [Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warszawa (Poland); Szytuła, A. [Institute of Physics, Jagiellonian University, Łojasiewicza 11, 30-348 Kraków (Poland)

    2015-07-01

    Investigations of structural and magnetic phase transitions in the NiMn{sub 0.89}Cr{sub 0.11}Ge half-Heusler alloy were carried out by DSC, XRD (80–400 K), magnetic susceptibility and magnetization (1.9–400 K, magnetic field up to 9.0 T, pressure up to 5.25 kbar) measurements. At high temperatures the sample is a single phase crystallizing in the hexagonal crystal structure (Ni{sub 2}In-type, space group P6{sub 3}/mmc) while below 260 K, down to 100 K, some amount of the hexagonal phase coexists with the orthorhombic (TiNiSi-type, space group Pnma) one. Strong magnetostructural coupling is observed. Magnetic data indicate that with increasing temperature magnetic properties of the sample change from antiferro- to ferro- and then to paramagnetic ones. The latter magnetic phase transition is associated with the crystal structure change and results in large magnetic entropy change equal to −51 J/kg K at μ{sub 0}H= 9.0 T near 260 K. Application of external pressure shifts T{sub C} towards lower temperatures. - Highlights: • # Pnma below 210 K, # P6{sub 3}/mmc above 260 K, for 210 K magnetocaloric effect observed about 260 K at ambient pressure. • Magnetostructural effect observed at 260 K (ΔV/V= 2.4%) at ambient pressure. • Magnetic measurements under hydrostatic pressure up to 5.25 kbar; (p, T) diagram.

  3. The Effect of Magnetic Domains on the Measurement of the Magnetocaloric effect

    DEFF Research Database (Denmark)

    Bahl, Christian R.H.; Smith, Anders; Nielsen, Kaspar Kirstein

    2014-01-01

    We discuss how magnetic domains influence the magnetic entropy change calculated from magnetisation data. In a simple qualitative model we show that the effect is to change the shape of the apparent isothermal entropy change curve compared to the true curve determined by the entropy. We further s...

  4. Effect of spin reorientation on magnetocaloric and transport properties of NdAl2

    Science.gov (United States)

    de Souza, M. V.; da Silva, J. A.; Silva, L. S.

    2017-01-01

    We report the magneto-thermal and resistive properties of rare-earth dialuminide NdAl2, including spin reorientation transition. To this purpose, we used a theoretical model that considers the interactions of exchange and Zeeman, besides the anisotropy due to the electrical crystal field. The theoretical results obtained were compared to experimental data of the NdAl2 in single crystal and bulk forms. Explicitly, we have calculated the anisotropic variation of magnetic entropy with the magnetic field oriented along the three principal crystallographic directions: [100], [110], and [111] of NdAl2 single crystal, where a signature of the spin reorientation is observed in the [110] and [111] directions. Moreover, of magnetoresistivity we consider the applied magnetic field along the crystallographic directions [100] and [110]. In turn, for the polycrystalline form, the good agreement between theory and experiment confirms the presence of spin reorientation, which was predicted theoretically in magnetization curves.

  5. Direct measurement of the magnetocaloric effect in MnFe(P,X)(X = As, Ge, Si) materials

    Science.gov (United States)

    Yibole, H.; Guillou, F.; Zhang, L.; van Dijk, N. H.; Brück, E.

    2014-02-01

    An investigation of the magnetocaloric effect (MCE) displayed by three generations of MnFe(P,X) (X = As, Ge, Si) materials has been carried out by combining indirect ΔS and direct ΔTad measurements. To be able to compare the performances of the new Si-based system with the already well-known As- and Ge-based materials in optimal conditions, both the Mn/Fe and P/Si ratios of the MnxFe1.95-xP1-ySiy compounds were optimized to display the largest MCE around room temperature. Here, we show that the maximum values of ΔTad (ΔB = 1.1 T) and ΔS (ΔB = 1 T) are respectively ˜2.2 K and ˜8 J kg-1 K-1 in the Si-based material Mn1.25Fe0.7P0.49Si0.51. These values are very close to the MCE performances of the As-based and Ge-based compounds. A critical comparison of these three MnFe(P,X) series highlights the role played by the non-magnetic elements on the latent heat at the Curie temperature. The combination of: (i) large ΔS and ΔTad in intermediate magnetic fields, (ii) limited thermal/magnetic hysteresis, (iii) easy tunability of the Curie temperatures and (iv) practical advantages like cheap, non-critical and non-toxic starting materials; makes the MnxFe1.95-xP1-ySiy family highly promising for magnetic refrigeration applications.

  6. Martensitic phase transformations and magnetocaloric effect in Al co-sputtered Ni–Mn–Sb alloy thin films

    Energy Technology Data Exchange (ETDEWEB)

    Akkera, Harish Sharma [Functional Nanomaterials Research Lab, Department of Physics, Indian Institute of Technology Roorkee, Uttarakhand 247667 (India); Choudhary, Nitin [Department of Materials Science and Engineering, University of North Texas, North Texas Discovery Park, 3940 North Elm St., Denton, TX 76207 (United States); Kaur, Davinder, E-mail: dkaurfph@iitr.ac.in [Functional Nanomaterials Research Lab, Department of Physics, Indian Institute of Technology Roorkee, Uttarakhand 247667 (India)

    2015-08-15

    Highlights: • The Al content leads to a increase in the martensitic transformation temperature. • A maximum ΔS{sub M} = 23 mJ/cm{sup 3} K at 300 K was observed in the N{sub 49.8}Mn{sub 32.97}Al{sub 4.43}Sb{sub 12.8}. • The refrigeration capacity RC = 64.4 mJ/cm{sup 3} at 2 T for N{sub 49.8}Mn{sub 32.97}Al{sub 4.43}Sb{sub 12.8} film. - Abstract: We systematically investigated the influence of aluminium (Al) content on the martensitic transformations and magnetocaloric effect (MCE) in Ni–Mn–Sb ferromagnetic shape memory alloy (FSMA) thin films. The temperature-dependent magnetization (M–T) and resistance (R–T) results displayed a monotonic increase in martensitic transformation temperature (T{sub M}) with increasing Al content. From the isothermal magnetization (M–H) curves, a large magnetic entropy change (ΔS{sub M}) of 23 mJ/cm{sup 3} K was observed in N{sub 49.8}Mn{sub 32.97}Al{sub 4.43}Sb{sub 12.8}. A remarkable enhancement of MCE could be attributed to the significant change in the magnetization of Ni–Mn–Sb films with increasing Al content. Furthermore, a high refrigerant capacity (RC) was observed in Ni–Mn–Sb–Al thin films as compared to pure Ni–Mn–Sb. The substitution of Al for Mn in Ni–Mn–Sb thin films with field induced MCE are potential candidates for micro length scale magnetic refrigeration applications where low magnetic fields are desirable.

  7. Lanthanide Coordination Polymers with 4,4'-Azobenzoic Acid: Enhanced Stability and Magnetocaloric Effect by Removing Guest Solvents.

    Science.gov (United States)

    Zhang, Shaowei; Duan, Eryue; Han, Zongsu; Li, Leilei; Cheng, Peng

    2015-07-06

    Three lanthanide coordination polymers (Ln-CPs) formulated as [Ln(azdc)(HCOO)]n [Ln = Gd(III) (1), Tb(III) (2), Dy(III) (3); H2azdc = 4,4'-azobenzoic acid] have been successfully obtained by the solvothermal reaction of Ln(III) ions with H2azdc ligands in the mixed solvent N,N-dimethylformamide (DMF)/H2O. Compared with our previous work on Ln-CPs with H2azdc ligands, [Gd2(azdc)3(DMA)2]n·2nDMA (1'; DMA = dimethylacetamide), in which the DMA molecules coordinate to Gd(III) ions that are replaced by HCOO(-) groups in 1, resulting in the distinct structures and properties of the final products. Adjacent Ln(III) ions in 1-3 are connected by HCOO(-) groups through bridging and chelating modes to give 2D layers, which are further linked by azdc(2-) ligands to produce 3D frameworks. Magnetic results declare that antiferromagnetic couplings exist in 1, although two different magnetic interactions among adjacent Gd(III) ions derived from antiferromagnetic interactions of the smaller Gd-O-Gd angles (Gd···Gd distances) and weak ferromagnetic interactions of the larger Gd-O-Gd angles (Gd···Gd distances) coexist in 1. Furthermore, the magnetocaloric effect (MCE) value of 1 is 1.5 times as large as that of 1'. More importantly, 1 exhibits excellent stabilities toward air, thermal, solvent, and acid/alkaline conditions. The results manifest that the crystalline structure of 1 can be stable at at least 425 °C supported by the in situ variable-temperature powder X-ray diffraction patterns and thermogravimetric analyses, in air for at least 3 months, and in common solvents for more than 1 week, as well as in aqueous solutions ranging from pH = 2 to 12 for more than 1 week.

  8. Magnetization reversal behavior and magnetocaloric effect in SmCr0.85Mn0.15O3 chromites

    Science.gov (United States)

    Kumar, Surendra; Coondoo, Indrani; Vasundhara, M.; Patra, Ajit K.; Kholkin, Andrei L.; Panwar, Neeraj

    2017-01-01

    We have synthesized SmCr0.85Mn0.15O3 (SCMO) chromites through the ceramic route. The compound crystallized into a distorted orthorhombic structure with the Pnma space group, which was confirmed from the Rietveld refinement of x-ray powder diffraction patterns. Neel temperature, noticed at 168 K from the temperature variation of magnetisation, smaller than that reported for SmCrO3, indicated the influence of Mn3+ substitution on decreasing the antiferromagnetic ordering. A phenomenon of magnetization reversal was observed in the SCMO compound. At low magnetic fields, i.e., 500 Oe, a single compensation temperature (defined as the temperature where magnetization became zero) around 106 K was observed in the field cooled magnetization curve. However, with the application of higher magnetic fields, i.e., under an applied field of 1000 Oe, a second compensation temperature was noticed around 8 K. With a further increase in the magnetic field, the magnetization remained positive in both field cooled and zero field cooled protocols. A normal magnetocaloric effect was observed through an indirect method of field dependence of magnetisation measured in the temperature range of 2-152 K. The magnetic entropy change (-ΔS) of ˜11.36 J kg-1 K-1 along with the relative cooling power (RCP) of ˜175.89 J kg-1 was obtained in the temperature range of 10-20 K for an applied field of 90 kOe, and their values at 50 kOe applied field were, respectively, almost twenty and forty times larger in magnitude in comparison to those for the SmCrO3 compound. The relatively large values of ΔS and RCP make the studied compound a potential candidate for magnetic refrigeration applications at low temperatures.

  9. Inverse magnetocaloric and exchange bias effects in single crystalline La0.5Sr0.5MnO3 nanowires.

    Science.gov (United States)

    Chandra, Sayan; Biswas, Anis; Datta, Subarna; Ghosh, Barnali; Raychaudhuri, A K; Srikanth, Hariharan

    2013-12-20

    We report the first observation of inverse magnetocaloric effect (IMCE) in hydrothermally synthesized single crystalline La0.5Sr0.5MnO3 nanowires. The core of the nanowires is phase separated with the development of double exchange driven ferromagnetism (FM) in the antiferromagnetic (AFM) matrix, whereas the surface is found to be composed of disordered magnetic spins. The FM phase scales with the effective magnetic anisotropy, which is directly probed by transverse susceptibility experiments. The surface exhibits a glassy behavior and undergoes spin freezing, which manifests as a positive peak (T(L) ~ 42 K) in the magnetic entropy change (-ΔS(M)) curves, thereby stabilizing the re-entrance of the conventional magnetocaloric effect. Precisely at T(L), the nanowires develop the exchange bias (EB) effect. Our results conclusively demonstrate that the mere coexistence of FM and AFM phases along with a disordered surface below their Néel temperature (T(N) ~ 210 K) does not trigger EB, but this develops only below the surface spin freezing temperature.

  10. Tuneable Giant Magnetocaloric Effect in (Mn,Fe2(P,Si Materials by Co-B and Ni-B Co-Doping

    Directory of Open Access Journals (Sweden)

    Nguyen Van Thang

    2016-12-01

    Full Text Available The influence of Co (Ni and B co-doping on the structural, magnetic and magnetocaloric properties of (Mn,Fe 2 (P,Si compounds is investigated by X-ray diffraction (XRD, differential scanning calorimetry, magnetic and direct temperature change measurements. It is found that Co (Ni and B co-doping is an effective approach to tune both the Curie temperature and the thermal hysteresis of (Mn,Fe 2 (P,Si materials without losing either the giant magnetocaloric effect or the positive effect of the B substitution on the mechanical stability. An increase in B concentration leads to a rapid decrease in thermal hysteresis, while an increase in the Co or Ni concentration hardly changes the thermal hysteresis of the (Mn,Fe 2 (P,Si compounds. However, the Curie temperature decreases slowly as a function of the Co or Ni content, while it increases dramatically for increasing B concentration. Hence, the co-substitution of Fe and P by Co (Ni and B, respectively, offers a new control parameter to adjust the Curie temperature and reduce the thermal hysteresis of the (Mn,Fe 2 (P,Si materials.

  11. Magnetotransport properties and magnetocaloric effects of Mn1.95Cr0.05Sb0.95Ga0.05 Compound

    Institute of Scientific and Technical Information of China (English)

    Liu Xi-Bin; Zhang Shao-Ying; Shen Bao-Gen; Yao Jin-Lei; Wang Fang

    2004-01-01

    The magnetotransport properties and magnetocaloric effects of the compound Mn1.95Cr0.05Sb0.95Ga0.05 have been studied. With decreasing temperature, a spontaneous first-order magnetic phase transition from ferrimagnetic (FI) to antiferromagnetic (AF) state takes place at Ts=200K. A metamagnetic transition from the AF to FI state can be induced by an external field, accompanied by a giant magnetoresistance effect of 57%. The magnetic entropy changes are determined from the temperature and field dependence of the magnetization using the thermodynamic Maxwell relation. Mn1.95Cr0.05Sb0.95Ga0.05 exhibits a negative magnetocaloric effect, and the absolute values of △Smax M (T, △H) are 4.4, 4.1, 3.6, 2.8 and 1.5 J/(kg.K) for magnetic field changes of 0-5T, 0-4T, 0-3T, 0-2T and 0-1T,respectively.

  12. Mastering hysteresis in magnetocaloric materials.

    Science.gov (United States)

    Gutfleisch, O; Gottschall, T; Fries, M; Benke, D; Radulov, I; Skokov, K P; Wende, H; Gruner, M; Acet, M; Entel, P; Farle, M

    2016-08-13

    Hysteresis is more than just an interesting oddity that occurs in materials with a first-order transition. It is a real obstacle on the path from existing laboratory-scale prototypes of magnetic refrigerators towards commercialization of this potentially disruptive cooling technology. Indeed, the reversibility of the magnetocaloric effect, being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and, therefore, it is necessary to understand the mechanisms causing hysteresis and to find solutions to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices. In this work, we discuss the fundamental aspects that can contribute to thermal hysteresis and the strategies that we are developing to at least partially overcome the hysteresis problem in some selected classes of magnetocaloric materials with large application potential. In doing so, we refer to the most relevant classes of magnetic refrigerants La-Fe-Si-, Heusler- and Fe2P-type compounds.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

  13. Anisotropic intrinsic spin Hall effect in quantum wires.

    Science.gov (United States)

    Cummings, A W; Akis, R; Ferry, D K

    2011-11-23

    We use numerical simulations to investigate the spin Hall effect in quantum wires in the presence of both Rashba and Dresselhaus spin-orbit coupling. We find that the intrinsic spin Hall effect is highly anisotropic with respect to the orientation of the wire, and that the nature of this anisotropy depends strongly on the electron density and the relative strengths of the Rashba and Dresselhaus spin-orbit couplings. In particular, at low densities, when only one subband of the quantum wire is occupied, the spin Hall effect is strongest for electron momentum along the [N110] axis, which is the opposite of what is expected for the purely 2D case. In addition, when more than one subband is occupied, the strength and anisotropy of the spin Hall effect can vary greatly over relatively small changes in electron density, which makes it difficult to predict which wire orientation will maximize the strength of the spin Hall effect. These results help to illuminate the role of quantum confinement in spin-orbit-coupled systems, and can serve as a guide for future experimental work on the use of quantum wires for spin-Hall-based spintronic applications.

  14. Electric control of magnetism and magnetocaloric effects in LaFe11.4Si1.6H1.5 using ferroelectric PMN-PT

    Science.gov (United States)

    Wang, Chuancong; Hu, Yong; Wang, Dunhui; Cao, Qingqi; Shao, Yanyan; Liu, Jian; Zhang, Hu; Du, Youwei

    2016-10-01

    The alloy with first-order magnetic phase transition has an advantage to exhibit large magnetoelectric effect in strain-mediated multiferroic composites, since the strain can drive its phase transition and consequently lead to a large magnetic change. In the present paper, we investigate the electric field manipulation of magnetic and magnetocaloric properties in LaFe11.4Si1.6H1.5/Pb(Mg1/3Nb2/3)O3-PbTiO3 laminate. By applying an electric field on the ferroelectric substrate, the relative change of magnetization has a peak value of  -8% around the Curie temperature, showing a large converse magnetoelectric effect. As for the magnetocaloric performance, the peak temperature of magnetic entropy change (ΔS M) has a shift of 3 K to low temperature and the maximal value of ΔS M keeps almost unchanged under an electric field of 8 kV cm-1. Moreover, the thermal and magnetic hysteresis can be reduced as well with the application of the electric field.

  15. Giant reversible magnetocaloric effect in flower-like β-Co(OH){sub 2} hierarchical superstructures self-assembled by nanosheets

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xianguo; Feng, Chao; Xiao, Feng; Jin, Chuangui; Xia, Ailin, E-mail: liuxianguohugh@gmail.com, E-mail: eeswor@polyu.edu.hk [Anhui Key Laboratory of Metal Materials and Processing, School of Materials Science and Engineering, Anhui University of Technology, Ma' anshan, PR (China); Or, Siu Wing [Department of Electrical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon (Hong Kong); Sun, Yuping [Center for Engineering Practice and Innovation Education, Anhui University of Technology, Ma' anshan, PR (China)

    2014-01-15

    A facile hydrothermal strategy is proposed to synthesize flower-like β- Co(OH){sub 2} hierarchical microspherical superstructures with a diameter of 0.5-1.5 µm, which are self-assembled by β - Co(OH){sub 2} nano sheets with the average thickness ranging between 20 and 40 nm. The magnetocaloric effect associated with magnetic phase transitions in Co(OH){sub 2} superstructures has been investigated. A sign change in the magnetocaloric effect is induced by a magnetic field, which is related to a filed-induced transition from the antiferromagnetic to the ferromagnetic state below the Néel temperature. The large reversible magnetic-entropy change –ΔS{sub m} (13.4 J/kg K at 15 K for a field change of 5 T) indicates that flower-like Co(OH){sub 2} superstructures is a potential candidate for application in magnetic refrigeration in the low-temperature range. (author)

  16. Magnetocaloric effect and critical behavior in melt-extracted Gd{sub 60}Co{sub 15}Al{sub 25} microwires

    Energy Technology Data Exchange (ETDEWEB)

    Xing, Dawei; Jiang, Sida; Chen, Dongming; Liu, Yanfen; Sun, Jianfei [School of Materials Science and Engineering, Harbin Institute of Technology (China); Shen, Hongxian [School of Materials Science and Engineering, Harbin Institute of Technology (China); Institute of Materials and Department of Physics, University of South Florida, Tampa, FL (United States); Liu, Jingshun [School of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot (China); Phan, Manh-Huong [Institute of Materials and Department of Physics, University of South Florida, Tampa, FL (United States); Wang, Huan; Qin, Faxiang [Institute for Composites Science and Innovation (InCSI), College of Materials Science and Engineering, Zhejiang University, Hangzhou (China)

    2015-09-15

    High-quality Gd{sub 60}Co{sub 15}Al{sub 25} microwires with an average diameter of 40 μm were successfully fabricated by the melt-extraction method. The as-cast microwires undergo a second-order paramagnetic to ferromagnetic (PM-FM) transition at ∝100 K. Large values of the magnetic entropy change (-ΔS{sub M} ∝9.73 J kg{sup -1} K{sup -1}) and the refrigerant capacity (RC ∝732 J kg{sup -1}) are achieved for a field change of 5 T. A careful analysis of critical exponents near the PM-FM transition indicates the significant effects of structural disorder on the long-range ferromagnetic interaction and the magnetocaloric response of the microwires. The excellent magnetocaloric properties make the Gd{sub 60}Co{sub 15}Al{sub 25} microwires very promising for use in magnetic refrigerators operating in the liquid nitrogen temperature range. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Effect of α-Fe impurities on the field dependence of magnetocaloric response in LaFe{sub 11.5}Si{sub 1.5}

    Energy Technology Data Exchange (ETDEWEB)

    Blázquez, J.S., E-mail: jsebas@us.es [Dpto. Física de la Materia Condensada, Universidad de Sevilla, ICMSE-CSIC. P.O. Box 1065, 41080 Sevilla (Spain); Moreno-Ramírez, L.M.; Ipus, J.J. [Dpto. Física de la Materia Condensada, Universidad de Sevilla, ICMSE-CSIC. P.O. Box 1065, 41080 Sevilla (Spain); Kiss, L.F.; Kaptás, D.; Kemény, T. [Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O.Box 49, 1525 Budapest (Hungary); Franco, V.; Conde, A. [Dpto. Física de la Materia Condensada, Universidad de Sevilla, ICMSE-CSIC. P.O. Box 1065, 41080 Sevilla (Spain)

    2015-10-15

    In this work, the theoretical field dependence of the magnetic entropy change far away from the transition is used to analyze the field dependence of composite materials formed by fcc La(Fe,Si){sub 13} and bcc α-Fe(Si) phases. A non-interacting phases approximation is followed in the analysis and results are in good agreement with microstructural data obtained from X-ray diffraction and Mössbauer spectroscopy. The range of validity of the approximation is estimated. It is concluded that the quadratic field dependence of magnetic entropy change is reached a few tens of kelvin above the transition temperature at 1.5 T. However, the linear dependence (characteristic of ferromagnets well below its Curie temperature) is only reached a few hundred kelvin below the transition. The results presented here can be used in the deconvolution of the contribution of impurities to the MCE signal in composites. - Highlights: • Field dependence of the magnetocaloric effect is analyzed for two-phase systems. • Fraction of impurity phases is directly obtained from the analysis of field dependence of the magnetocaloric response. • The thermal range of validity of the present analysis is discussed.

  18. Critical magnetic behavior and large magnetocaloric effect in Pr{sub 0.67}Ba{sub 0.33}MnO{sub 3} perovskite manganite

    Energy Technology Data Exchange (ETDEWEB)

    Varvescu, A.; Deac, I.G., E-mail: iosif.deac@phys.ubbcluj.ro

    2015-08-15

    We report results of critical magnetic behavior and magnetocaloric investigations of the perovskite manganite Pr{sub 0.67}Ba{sub 0.33}MnO{sub 3}. The compound exhibits a paramagnetic (PM) to ferromagnetic (FM) transition at the Curie temperature T{sub C}, and significant negative magnetoresistance in a wide temperature range. To probe the magnetic interactions responsible for the magnetic transitions, we performed a critical exponent analysis in the vicinity of the FM–PM transition region. Magnetic entropy change ΔS{sub M} was estimated from isothermal magnetization data. We have found a remarkable large value of |ΔS{sub M}| around T{sub C}’s, of about 5.50 J/kg K for μ{sub 0}ΔH=4 T and a large relative cooling power (~225 J/kg). The analysis was done by using the modified Arrot plot (MAP) method. The values of the obtained critical exponents associated with this transition, β=0.366, γ=1.375 and δ=4.743 are close to those expected for the short range 3D Heisenberg model. The model was also confirmed by using |ΔS{sub M}|∝(μ{sub 0}H){sup n}, the field dependence of magnetic entropy change method. The large measured magnetocaloric effect is presumed to arise as a consequence of the sample preparation route.

  19. Comparative analysis of magnetic and caloric determinations of the magnetocaloric effect in Mn0.99Co0.01As

    Directory of Open Access Journals (Sweden)

    Wang Gaofeng

    2014-07-01

    Full Text Available The results from direct and indirect determinations of the magnetocaloric parameters of Mn0.99Co0.01As have been analyzed. The isothermal entropy change (ΔST due to external magnetic field changes has been determined through direct measurements of the heat absorbed by the sample when the field is removed under isothermal conditions. It has also been calculated from isothermal magnetization and isofield heat capacity measurements. In addition to that, the adiabatic temperature change (ΔTS has been obtained from direct measurements and from isofield heat capacity measurements. The different results of both ΔST and ΔTS are compared. Due to the presence of a first-order phase transition, the studied sample exhibits giant magnetocaloric effect at room temperature. The observed maximum values, −ΔST,max = 32.1 J/kg·K and ΔTS,max = 17.7 K for a field change from 0 to 6 T, suggest that the Co-doped MnAs compounds are promising candidates for the preparation of useful materials for magnetic refrigeration near room temperature.

  20. Effect of microstructure and texture on the magnetic and magnetocaloric properties of the melt-spun rare earth intermetallic compound DyNi

    Science.gov (United States)

    Rajivgandhi, R.; Chelvane, J. Arout; Nigam, A. K.; Park, Je-Geun; Malik, S. K.; Nirmala, R.

    2016-11-01

    Magnetization measurements have been carried out on the melt-spun ribbon sample of the rare earth intermetallic compound DyNi (Orthorhombic, FeB-type, Space group Pnma) and its magnetic and magnetocaloric properties are compared with those of the arc-melted analog. The arc-melted DyNi orders ferromagnetically at around 61 K (TC) whereas the melt-spun DyNi orders ferromagnetically at about 47 K. The maximum isothermal magnetic entropy change, ∆Smmax , near TC of the arc-melted and the melt-spun DyNi is found to be -32.7 J/kg K and -22.4 J/kg K, respectively, for a field change of 140 kOe. For low magnetic field changes of ~20 kOe, the relative cooling power (RCP) is ~660 J/kg for the arc melted DyNi and ~460 J/kg for the melt-spun ribbon. The reduction in TC and magnetocaloric effect may be attributed to the microstructure-induced anisotropy developed during the melt-spinning process.

  1. Characterization and theoretical investigation of the magnetocaloric effect of La0.67Ba0.33Mn1-xSbxO3 compounds

    Science.gov (United States)

    Hassine, A. Ben; Dhahri, A.; Bouazizi, L.; Oumezzine, M.; Hlil, E. K.

    2016-05-01

    In this study, the structural, magnetic and magnetocaloric properties of the polycrystalline La0.67Ba0.33Mn1-xSbxO3 (x=0.01, x=0.03 and x=0.07) were consistently investigated. X-ray analysis revealed that the substitution of Mn by Sb produced no considerable structural change just the diffraction peaks of rhombohedric symmetry were obtained all the samples. The variation of the magnetization M versus temperature T, under an applied magnetic field of 1.5 T, shows a ferromagnetic-paramagnetic transition. The experimental results exhibit that with the increase of Sb substitution TC decreases from 326 K to 296 K. The prediction of magnetic entropy change, relative cooling power and specific heat for magnetic field variation were predicted with the help of a phenomenological model. A large magneto-caloric effect has been observed, the maximum of magnetic entropy change, | Δ S mmax|, reaches the highest value of 2.74 J kg-1 K-1 under a magnetic field of 1.5 T with an RCP value of 132.8 J kg-1 for La0.67Ba0.33Mn1-xSbxO3 (x=0.07) composition , which will be an interesting compound for application materials working as magnetic refrigerants near room temperature.

  2. Pauli paramagnetic effects on mixed-state properties in a strongly anisotropic superconductor: Application to Sr2RuO4

    Science.gov (United States)

    Amano, Yuujirou; Ishihara, Masahiro; Ichioka, Masanori; Nakai, Noriyuki; Machida, Kazushige

    2015-04-01

    We study theoretically the mixed-state properties of a strong uniaxially anisotropic type-II superconductor with the Pauli paramagnetic effect, focusing on their behaviors when the magnetic field orientation is tilted from the conduction layer a b plane. On the basis of Eilenberger theory, we quantitatively estimate significant contributions of the Pauli paramagnetic effects on a variety of physical observables, including transverse and longitudinal components of the flux-line lattice form factors, magnetization curves, Sommerfeld coefficient, field distributions, and magnetic torques. We apply these studies to Sr2RuO4 and quantitatively explain several seemingly curious behaviors, including the Hc 2 suppression for the a b -plane direction, the larger anisotropy ratio and intensity found by the spin-flip small-angle neutron scattering, and the first-order transition observed recently in magnetocaloric, specific-heat, and magnetization measurements in a coherent and consistent manner. Those lead us to conclude that Sr2RuO4 is either a spin-singlet or a spin-triplet pairing with the d -vector components in the a b plane.

  3. Single-Molecule Magnetism, Enhanced Magnetocaloric Effect, and Toroidal Magnetic Moments in a Family of Ln4 Squares.

    Science.gov (United States)

    Das, Chinmoy; Vaidya, Shefali; Gupta, Tulika; Frost, Jamie M; Righi, Mattia; Brechin, Euan K; Affronte, Marco; Rajaraman, Gopalan; Shanmugam, Maheswaran

    2015-10-26

    Three cationic [Ln4 ] squares (Ln=lanthanide) were isolated as single crystals and their structures solved as [Dy4 (μ4 -OH)(HL)(H2 L)3 (H2 O)4 ]Cl2 ⋅(CH3 OH)4 ⋅(H2 O)8 (1), [Tb4 (μ4 -OH)(HL)(H2 L)3 (MeOH)4 ]Cl2 ⋅(CH3 OH)4 ⋅(H2 O)4 (2) and [Gd4 (μ4 -OH)(HL)(H2 L)3 (H2 O)2 (MeOH)2 ]Br2 ⋅(CH3 OH)4 ⋅(H2 O)3 (3). The structures are described as hydroxo-centered squares of lanthanide ions, with each edge of the square bridged by a doubly deprotonated H2 L(2-) ligand. Alternating current magnetic susceptibility measurements show frequency-dependent out-of-phase signals with two different thermally assisted relaxation processes for 1, whereas no maxima in χM " appears above 2.0 K for complex 2. For 1, the estimated effective energy barrier for these two relaxation processes is 29 and 100 K. Detailed ab initio studies reveal that complex 1 possesses a toroidal magnetic moment. The ab initio calculated anisotropies of the metal ions in complex 1 were employed to simulate the magnetic susceptibility by using the Lines model (POLY_ANISO) and this procedure yields J1 =+0.01 and J2 =-0.01 cm(-1) for 1 as the two distinct exchange interactions between the Dy(III) ions. Similar parameters are also obtained for complex 1 (and 2) from specific heat measurements. A very weak antiferromagnetic super-exchange interaction (J1 =-0.043 cm(-1) and g=1.99) is observed between the metal centers in 3. The magnetocaloric effect (MCE) was estimated by using field-dependent magnetization and temperature-dependent heat-capacity measurements. An excellent agreement is found for the -ΔSm values extracted from these two measurements for all three complexes. As expected, 3 shows the largest -ΔSm variation (23 J Kg(-1)  K(-1) ) among the three complexes. The negligible magnetic anisotropy of Gd indeed ensures near degeneracy in the (2S+1) ground state microstates, and the weak super-exchange interaction facilitates dense population of low-lying excited states, all of

  4. Microstructure and magnetocaloric effect in as-quenched GdGeSi alloys with addition of Ni and Ce

    Energy Technology Data Exchange (ETDEWEB)

    Hasiak, Mariusz [Department of Mechanics and Materials Science, Wroclaw University of Science and Technology (Poland)

    2016-05-15

    Microstructure as well as AC and DC thermomagnetic properties were studied for the as-quenched Gd{sub 80}Ge{sub 15}Si{sub 5}, Gd{sub 75}Ge{sub 15}Si{sub 5}Ni{sub 5} and Gd{sub 75}Ge{sub 15}Si{sub 5}Ce{sub 5} (wt.%) alloys in a wide range of magnetic fields. The structural investigations performed by X-ray diffractometry show the presence of Gd-based phases in the investigated alloys. These results were also confirmed by structure investigations as temperature dependence of specific heat capacity. Besides the crystalline phases discovered in the samples the regions with different atom concentration were observed in Ni and Ce-containing alloys. The Curie temperature for the Gd{sub 80}Ge{sub 15}Si{sub 5}, Gd{sub 75}Ge{sub 15}Si{sub 5}Ni{sub 5} and Gd{sub 75}Ge{sub 15}Si{sub 5}Ce{sub 5} alloys is 272, 235, and 284 K, respectively. The magnetocaloric effect (MCE) calculated as magnetic entropy change (-ΔS{sub M}) depends on magnetizing field and for the Gd{sub 80}Ge{sub 15}Si{sub 5} and Gd{sub 75}Ge{sub 15}Si{sub 5}Ni{sub 5} alloys reaches almost the same maximum value of 12 J kg{sup -1} K{sup -1}. Ce-containing sample shows about 2.4 times lower MCE than the master alloy. Magnetic entropy change (-ΔS{sub M}) versus temperature for the Gd{sub 80}Ge{sub 15}Si{sub 5}, Gd{sub 75}Ge{sub 15}Si{sub 5}Ni{sub 5}, and Gd{sub 75}Ge{sub 15}Si{sub 5}Ce{sub 5} alloys calculated for the maximum magnetizing field of 3 T. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Efficient Modeling and Migration in Anisotropic Media Based on Prestack Exploding Reflector Model and Effective Anisotropy

    KAUST Repository

    Wang, Hui

    2014-05-01

    This thesis addresses the efficiency improvement of seismic wave modeling and migration in anisotropic media. This improvement becomes crucial in practice as the process of imaging complex geological structures of the Earth\\'s subsurface requires modeling and migration as building blocks. The challenge comes from two aspects. First, the underlying governing equations for seismic wave propagation in anisotropic media are far more complicated than that in isotropic media which demand higher computational costs to solve. Second, the usage of whole prestack seismic data still remains a burden considering its storage volume and the existing wave equation solvers. In this thesis, I develop two approaches to tackle the challenges. In the first part, I adopt the concept of prestack exploding reflector model to handle the whole prestack data and bridge the data space directly to image space in a single kernel. I formulate the extrapolation operator in a two-way fashion to remove he restriction on directions that waves propagate. I also develop a generic method for phase velocity evaluation within anisotropic media used in this extrapolation kernel. The proposed method provides a tool for generating prestack images without wavefield cross correlations. In the second part of this thesis, I approximate the anisotropic models using effective isotropic models. The wave phenomena in these effective models match that in anisotropic models both kinematically and dynamically. I obtain the effective models through equating eikonal equations and transport equations of anisotropic and isotropic models, thereby in the high frequency asymptotic approximation sense. The wavefields extrapolation costs are thus reduced using isotropic wave equation solvers while the anisotropic effects are maintained through this approach. I benchmark the two proposed methods using synthetic datasets. Tests on anisotropic Marmousi model and anisotropic BP2007 model demonstrate the applicability of my

  6. Investigating the Effects of Anisotropic Mass Transport on Dendrite Growth in High Energy Density Lithium Batteries

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Jinwang; Tartakovsky, Alexandre M.; Ferris, Kim F.; Ryan, Emily M.

    2016-01-01

    Dendrite formation on the electrode surface of high energy density lithium (Li) batteries causes safety problems and limits their applications. Suppressing dendrite growth could significantly improve Li battery performance. Dendrite growth and morphology is a function of the mixing in the electrolyte near the anode interface. Most research into dendrites in batteries focuses on dendrite formation in isotropic electrolytes (i.e., electrolytes with isotropic diffusion coefficient). In this work, an anisotropic diffusion reaction model is developed to study the anisotropic mixing effect on dendrite growth in Li batteries. The model uses a Lagrangian particle-based method to model dendrite growth in an anisotropic electrolyte solution. The model is verified by comparing the numerical simulation results with analytical solutions, and its accuracy is shown to be better than previous particle-based anisotropic diffusion models. Several parametric studies of dendrite growth in an anisotropic electrolyte are performed and the results demonstrate the effects of anisotropic transport on dendrite growth and morphology, and show the possible advantages of anisotropic electrolytes for dendrite suppression.

  7. Effective material parameter retrieval of anisotropic elastic metamaterials with inherent nonlocality

    Science.gov (United States)

    Lee, Hyung Jin; Lee, Heung Son; Ma, Pyung Sik; Kim, Yoon Young

    2016-09-01

    In this paper, the scattering (S-) parameter retrieval method is presented specifically for anisotropic elastic metamaterials; so far, no retrieval has been accomplished when elastic metamaterials exhibit fully anisotropic behavior. Complex constitutive property and intrinsic scattering behavior of elastic metamaterials make their characterization far more complicated than that for acoustic and electromagnetic metamaterials. In particular, elastic metamaterials generally exhibit anisotropic scattering behavior due to higher scattering modes associated with shear deformation. They also exhibit nonlocal responses to some degrees, which originate from strong multiple scattering interactions even in the long wavelength limit. Accordingly, the conventional S-parameter retrieval methods cannot be directly used for elastic metamaterials, because they determine only the diagonal components in effective tensor property. Also, the conventional methods simply use the analytic inversion formulae for the material characterization so that inherent nonlocality cannot be taken into account. To establish a retrieval method applicable to anisotropic elastic metamaterials, we propose an alternative S-parameter method to deal with full anisotropy of elastic metamaterials. To retrieve the whole effective anisotropic parameter, we utilize not only normal but also oblique wave incidences. For the retrieval, we first retrieve the ratio of the effective stiffness tensor to effective density and then determine the effective density. The proposed retrieval method is validated by characterizing the effective material parameters of various types of non-resonant anisotropic metamaterials. It is found that the whole effective parameters are retrieved consistently regardless of used retrieval conditions in spite of inherent nonlocality.

  8. Magnetocaloric effect in a dual-phase coupled LaFe11Si2 crystal prepared by a modified high-pressure zone-melting technique

    Science.gov (United States)

    Feng, Shutong; Fang, Yue; Zhai, Qijie; Luo, Zhiping; Zheng, Hongxing

    2016-10-01

    A modified high-pressure optical zone-melting technique was adopted to grow a rare-earth-based LaFe11Si2 crystal in the present work. Dual-phase coupled microstructure was obtained where aligned α(Fe) phase distributed in the La(Fe,Si)13 matrix. Magnetic measurements showed that the produced crystal underwent a second-order magnetic transition in the vicinity of 250 K. Under a magnetic field change of 30 kOe, the refrigeration capacity (RC) of the produced crystal reached up to 162 J/kg. It was confirmed that zone-melting crystal growth technique is an effective approach to strikingly enhance the magnetocaloric effect of La-Fe-Si refrigeration materials.

  9. Exchange Bias and Inverse Magnetocaloric Effect in Co and Mn Co-Doped Ni2MnGa Shape Memory Alloy

    Directory of Open Access Journals (Sweden)

    Yong Liu

    2013-01-01

    Full Text Available Exchange bias effect observed in the Ni1.68Co0.32Mn1.20Ga0.80 alloy confirms the coexistence of antiferromagnetic and ferromagnetic phases in the martensite phase. A large inverse magnetocaloric effect has been observed within the martensitic transformation temperature range, which is originated from modified magnetic order through magnetic-field-induced phase transformation from partially antiferromagnetic martensite to ferromagnetic austenite. The magnetic entropy change is 16.2 J kg−1 K−1 at 232 K under ΔH = 60 kOe, with the net refrigerant capacity of 68 J kg−1. These properties indicate Co and Mn co-doped Ni2MnGa alloy is a multifunctional material potentially suitable for magnetic refrigeration and spintronics applications.

  10. Magnetocaloric effect of a series of remarkably isostructural intermetallic [Ni(II)3Ln(III)] cubane aggregates.

    Science.gov (United States)

    Wang, Pei; Shannigrahi, Santiranjan; Yakovlev, Nikolai L; Hor, T S Andy

    2014-01-07

    A new series of remarkably isostructural 3d-4f compounds, [Ni3Ln(hmp)4(OAc)5]·H2O·CH2Cl2 (Ln = Gd (1), Tb (2), Dy (3), Ho (4), Y (5)) were synthesized based on a simple one-pot self-assembly method. Magnetic measurements demonstrated the ferromagnetic property of the [Ni3Ln] cores and the heterometallic influence on the magnetocaloric properties. This study suggested that robust and discrete intermetallic cubanes can be an alternative to other magnetically active materials such as high-nuclearity aggregates or clusters whose structures are not generally controlled by common synthetic methodological designs.

  11. Penetration Effect for Tangential Direction of the Anisotropy Axis in Anisotropic Medium

    Directory of Open Access Journals (Sweden)

    K.A. Vytovtov

    2012-07-01

    Full Text Available Anisotropic plane-parallel structure (both homogeneous and stratified with the direction of the anisotropy axis along the interfaces under tangential propagation of the incident wave is considered. The possibility of wave transmission through a plate (the penetration effect was analytically shown for the given particular case. Expressions for the wave-vector in anisotropic medium, field components, Poynting vector components were written and analyzed. It is shown that the structure has nonreciprocal properties.

  12. Effects of staggered magnetic field on entanglement in the anisotropic XY model

    CERN Document Server

    Sun, Z; Li, Y Q; Sun, Zhe; Wang, XiaoGuang; Li, You-Quan

    2004-01-01

    We investigate effects of staggered magnetic field on thermal entanglement in the anisotropic XY model. The analytic results of entanglement for the two-site cases are obtained. For the general case of even sites, we show that when the anisotropic parameter is zero, the entanglement in the XY model with a staggered magnetic field is the same as that with a uniform magnetic field.

  13. Influence of the Erbium Substitution for Gd in Gd5Si1.8Ge2.2Alloys on the Magnetocaloric Effect in Low-Field

    Institute of Scientific and Technical Information of China (English)

    Chen Xiang; Li Kefeng; Ma Chunhua; Zhuang Yinghong

    2007-01-01

    The phases and magnetocaloric effect in the alloys (Gd1-xErx)5Si1.8Ge2.2 with x=0,0.1,0.2 and 0.3 were investigated by X-ray diffraction analysis and magnetization measurement. The samples were single phase with the monoclinic Gd5Si2Ge2-type structure. With the increase of Er content, the Curie temperature (Tc) decreased obviously from 253K of the alloy with x=0 to 114K with x=0.3. The maximum magnetic entropy changed in the samples of (Gd1-xErx)5Si1.8Ge2.2 with x=0.0,0.1,0.2 and 0.3 were 6.88,8.32,9.59 and 10.24 J·kg-1·K-1 respectively in the applied field change of 0~2.0T.

  14. Magnetocaloric effect in gadolinium-oxalate framework Gd2(C2O43(H2O6⋅(0⋅6H2O

    Directory of Open Access Journals (Sweden)

    Romain Sibille

    2014-12-01

    Full Text Available Magnetic refrigerants incorporating Gd3+ ions and light organic ligands offer a good balance between isolation of the magnetic centers and their density. We synthesized the framework material Gd2(C2O43(H2O6⋅0.6H2O by a hydrothermal route and characterized its structure. The honeycomb lattice of Gd3+ ions interlinked by oxalate ligands in the (a,c plane ensures their decoupling in terms of magnetic exchange interactions. This is corroborated by magnetic measurements indicating negligible interactions between the Gd3+ ions in this material. The magnetocaloric effect was evaluated from isothermal magnetization measurements. The maximum entropy change −ΔSMmax reaches 75.9 mJ cm−3 K−1 (around 2 K for a moderate field change (2 T.

  15. Effect of ball milling and thermal treatment on exchange bias and magnetocaloric properties of Ni48Mn39.5Sn10.5Al2 ribbons

    Science.gov (United States)

    Czaja, P.; Przewoźnik, J.; Fitta, M.; Bałanda, M.; Chrobak, A.; Kania, B.; Zackiewicz, P.; Wójcik, A.; Szlezynger, M.; Maziarz, W.

    2016-03-01

    The combined effect of ball milling and subsequent heat treatment on microstructure, magnetic, magnetocaloric and exchange bias properties of Ni48Mn39.5Sn10.5Al2 ribbons is reported. The annealing treatment results in the increase of the critical martensitic transformation temperature. The magnetic entropy change ΔSM of the order of 7.9 and -2.3 J kg K-1 for the annealed 50-32 μm powder fraction is determined. This is less than in the as melt spun ribbon but appears at a considerably higher temperature. At the same time EB is decreased due to annealing treatment. This decrease is attributed to the strengthened ferromagnetic exchange coupling due heat induced stress and structural relaxation.

  16. Two lanthanide(III)-copper(II) organic frameworks based on {OLn6 } clusters that exhibited a large magnetocaloric effect and slow relaxation of the magnetization.

    Science.gov (United States)

    Bing, Yanmin; Xu, Na; Shi, Wei; Liu, Ke; Cheng, Peng

    2013-07-01

    Two new 3D lanthanide(III)-copper(II) organic frameworks based on unusual {OLn6} clusters have been successfully synthesized and fully characterized. Crystallographic studies showed that the {OLn6} clusters acted as 12-connected nodes that were linked together by [CuL2] (H2L = 3-hydroxypyrazine-2-carboxylic acid) moieties to construct an interesting 4,12-c net with the point symbol {4(36).6(30)}{4(4).6(2)}3. Magnetic studies revealed that these two isostructural heterometallic frameworks exhibited different magnetic properties, depending on the different anisotropies of the lanthanide spin carriers: Gd-Cu showed a large magnetocaloric effect, with an entropy change (-ΔS(m)) of 35.76 J  kg(-1)  K(-1), which is one of the largest values in high-dimensional complexes, whilst Dy-Cu exhibited slow relaxation of the magnetization at low temperatures.

  17. Magnetocaloric effect in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe0.92Al0.0812O22

    Directory of Open Access Journals (Sweden)

    Wenfei Xu

    2014-06-01

    Full Text Available Magnetocaloric effect is investigated in multiferroic Ba0.5Sr1.5Zn2(Fe0.92Al0.0812O22 ceramic with Y-type hexagonal system. Three magnetic transitions, from alternating longitudinal conical to mixed conical at ∼240 K, to ferrimagnetic at ∼297 K, further to paramagnetic at ∼702 K, are unambiguously determined. Furthermore, obvious MCE is shown, and the maximum values of the magnetic entropy change and relative cooling power are evaluated to be 1.53 JKg−1K−1 and 280 JKg−1 for a field change of 7 T, respectively. In addition, inverse MCE is also observed, which might be associated with the first-order magnetic phase transition between two incommensurate longitudinal conical phases.

  18. Magnetic and calorimetric investigations of inverse magnetocaloric effect in Pr0.46Sr0.54MnO3

    Science.gov (United States)

    Naik, V. B.; Barik, S. K.; Mahendiran, R.; Raveau, B.

    2011-03-01

    We investigated magnetic entropy change (ΔSm) in the A-type antiferromagnet Pr0.46Sr0.54MnO3 by magnetic and differential scanning calorimetry (DSC) methods. The field-induced antiferromagnetic to ferromagnetic transition is first-order in nature and is accompanied by a large change in the latent heat as evidenced by the DSC data. The ΔSm shows an inverse magnetocaloric effect (ΔSm=+9 J kg-1 K-1 for ΔH =7 T) around the Neel temperature (TN=210±2 K) by magnetic measurement, which closely agrees with the calorimetric results. It is suggested that the large positive ΔSm results from a field-induced structural transition that accompanies the destruction of antiferromagnetism.

  19. Anisotropic magnetoresistance and piezoelectric effect in GaAs Hall samples

    Science.gov (United States)

    Ciftja, Orion

    2017-02-01

    Application of a strong magnetic field perpendicular to a two-dimensional electron system leads to a variety of quantum phases ranging from incompressible quantum Hall liquid to Wigner solid, charge density wave, and exotic non-Abelian states. A few quantum phases seen in past experiments on GaAs Hall samples of electrons show pronounced anisotropic magnetoresistance values at certain weak magnetic fields. We argue that this might be due to the piezoelectric effect that is inherent in a semiconductor host such as GaAs. Such an effect has the potential to create a sufficient in-plane internal strain that will be felt by electrons and will determine the direction of high and low resistance. When Wigner solid, charge density wave, and isotropic liquid phases are very close in energy, the overall stability of the system is very sensitive to local order and, thus, can be strongly influenced even by a weak perturbation such as the piezoelectric-induced effective electron-electron interaction, which is anisotropic. In this work, we argue that an anisotropic interaction potential may stabilize anisotropic liquid phases of electrons even in a strong magnetic field regime where normally one expects to see only isotropic quantum Hall or isotropic Fermi liquid states. We use this approach to support a theoretical framework that envisions the possibility of an anisotropic liquid crystalline state of electrons in the lowest Landau level. In particular, we argue that an anisotropic liquid state of electrons may stabilize in the lowest Landau level close to the liquid-solid transition region at filling factor ν =1 /6 for a given anisotropic Coulomb interaction potential. Quantum Monte Carlo simulations for a liquid crystalline state with broken rotational symmetry indicate stability of liquid crystalline order consistent with the existence of an anisotropic liquid state of electrons stabilized by anisotropy at filling factor ν =1 /6 of the lowest Landau level.

  20. Magnetocaloric heat pump device, a heating or cooling system and a magnetocaloric heat pump assembly

    DEFF Research Database (Denmark)

    2014-01-01

    The invention provides a magnetocaloric heat pump device, comprising a magnetocaloric bed; a magnetic field source, the magnetocaloric bed and the magnetic field source being arranged to move relative to each other so as to generate a magnetocaloric refrigeration cycle within the heat pump, wherein...

  1. Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Vladimir Sokolovskiy

    2014-09-01

    Full Text Available The complex magnetic and structural properties of Co-doped Ni-Mn-Ga Heusler alloys have been investigated by using a combination of first-principles calculations and classical Monte Carlo simulations. We have restricted the investigations to systems with 0, 5 and 9 at% Co. Ab initio calculations show the presence of the ferrimagnetic order of austenite and martensite depending on the composition, where the excess Mn atoms on Ga sites show reversed spin configurations. Stable ferrimagnetic martensite is found for systems with 0 (5 at% Co and a c=a ratio of 1.31 (1.28, respectively, leading to a strong competition of ferro- and antiferro-magnetic exchange interactions between nearest neighbor Mn atoms. The Monte Carlo simulations with ab initio exchange coupling constants as input parameters allow one to discuss the behavior at finite temperatures and to determine magnetic transition temperatures. The Curie temperature of austenite is found to increase with Co, while the Curie temperature of martensite decreases with increasing Co content. This behavior can be attributed to the stronger Co-Mn, Mn-Mn and Mn-Ni exchange coupling constants in austenite compared to the corresponding ones in martensite. The crossover from a direct to inverse magnetocaloric effect in Ni-Mn-Ga due to the substitution of Ni by Co leads to the appearance of a “paramagnetic gap” in the martensitic phase. Doping with In increases the magnetic jump at the martensitic transition temperature. The simulated magnetic and magnetocaloric properties of Co- and In-doped Ni-Mn-Ga alloys are in good qualitative agreement with the available experimental data.

  2. Magnetocaloric effect and its implementation in critical behaviour study of La$_{0.67}$Ca$_{0.33}$Mn$_{0.9}$Fe$_{0.1}$O$_3$

    Indian Academy of Sciences (India)

    M’NASSRI R

    2016-04-01

    The magnetocaloric effect (MCE) and the field dependence of the magnetic entropy changes in the perovskite-type a$_{0.67}$Ca$_{0.33}$Mn$_{0.9}$Fe$_{0.1}$O$_3$ were studied using the phenomenological model. The model parameters were determined from the magnetization data adjustment and used to give better fits to magnetic transition and to calculate the magnetocaloric properties. The entropy curves have been observed to behave a symmetrical broadning of $\\Delta$S$_M$ peak with the increase in magnetic field. The values of maximum magnetic entropy change, full-width at half-maximum, relative cooling power (RCP) and the refrigerant capacity (RC), at several magnetic field variations, were calculated. The maximum magnetic entropy change of 1.17 J kg$^{−1}$K$^{−1}$ was obtained for 3 T. The theoretical calculations were compared with the available experimental data. The results were found to be in good accordance. The critical exponents associated with ferromagnetic transition have been determined from the MCE methods. By using the field dependence of $\\Delta S_{\\rm max} \\approx a (\\mu_0 H)^n$ and the ${\\rm RCP} \\approx v(\\mu_0H)^w$, the critical behaviour of La$_{0.67}$Ca$_{0.33}$Mn$_{0.9}$Fe$_{0.1}$O$_3$ was investigated. From the analysis of the relationship between the local exponent$n$ and $w$, other exponents $\\beta$, $\\gamma$ and $\\delta$ were calculated. Our results indicated that the ferromagnetic coupling in the La$_{0.67}$Ca$_{0.33}$Mn$_{0.9}$Fe$_{0.1}$O$_3$ can be well described by the 3D Heisenberg model. This reflects an existence of ferromagnetic short-range order in the sample.

  3. Thermodynamical Evaluation on Magnetocaloric Effect of Magnetic Refrigerating Materials Near Room Temperature

    Institute of Scientific and Technical Information of China (English)

    肖素芬; 陈云贵; 管登高; 杨涛; 涂铭旌

    2003-01-01

    The relationship between isothermal magnetic entropy change ΔS and adiabatic temperature change ΔTad was deduced according to the principles of thermodynamics. The MCE and the engineering application were discussed for Gd and several new kinds of magnetic refrigerating materials near room temperature, Gd5Si2Ge2, MnFeP0.45As0.55 and LaFe11.2Co0.7Si 1.1. Isothermal entropy change is proportional to adiabatic temperature change with a factor of T/C (T is temperature, C is heat capacity). When the comparison of magnetacoloric effect is made for two different mate rials, we should consider isothermal entropy change as well as adiabatic tempera ture change.

  4. Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Emre, Baris [Department of Engineering Physics, Ankara University, 06100 Ankara (Turkey); Bruno, Nickolaus M. [Department of Mechanical Engineering, Texas A and M University, College Station, Texas 77843 (United States); Yuce Emre, Suheyla [Department of Physics, Ondokuz Mayis University, 55139 Samsun (Turkey); Karaman, Ibrahim, E-mail: ikaraman@tamu.edu [Department of Mechanical Engineering, Texas A and M University, College Station, Texas 77843 (United States); Department of Materials Science and Engineering, Texas A and M University, College Station, Texas 77843 (United States)

    2014-12-08

    The effect of Nb substitution for Ni in Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloys potential candidates for solid state refrigeration near room temperature.

  5. Effect of gallium doping on the magnetocaloric effect of LaFe11.2Co0.7Si1.1

    Institute of Scientific and Technical Information of China (English)

    DENG Jianqiu; CHEN Xiang; ZHUANG Yinghong

    2008-01-01

    The lattice parameter and magnetocaloric properties of three samples of LaFe11.2Co0.7Si1.1-xGax with x = 0,0.03 and 0.05 have been investigated by X-ray powder diffraction and magnetization measurements.The lattice parameter increases slightly and the Curie temperature increases somewhat with increasing gallium content.However,a small amount of Ga doping into the sample decreases the magnetic entropy change of the sample.All the samples remain in the first-order magnetic phase transition.The most striking effect of the Ga doping is that the cooling capacity in the samples increases significantly.The maximum magnetic entropy change,-△SM,max,and the cooling capacity of the sample LaFe11.2Co0.7Si1.07Ga0.03 are 11.9 J·kg-1.K-1 and 254.8 J.kg-1,respectively.

  6. Particle Size Effect on Charge Ordering and Magnetocaloric Effect in Nanosized Nd0.5Sr0.5MnO3.

    Science.gov (United States)

    Xu, Shujuan; Shi, Qianyi; Ju, Jinghua; Han, Zhida; Qian, Bin; Wang, Dunhui; Zhang, Ping; Jiang, Xuefan; Du, Youwei

    2016-02-01

    Nd0.5Sr0.5MnO3 nanoparticles with average sizes of 32-1000 nm in diameter were prepared by sol-gel method. The synthesized nanoparticles were characterized using X-ray diffraction, high- resolution transmission microscopy, scanning electron microscopy, and vibrating sample magnetometer. All samples have the single-phase orthorhombic structure, and the grain size increases with the increase in annealing temperature. A charge ordering (CO) transition at T(CO) and a ferromagnetic-paramagnetic transition at Tc were observed in 1000 nm nanoparticles. With the decrease in particle size, CO transition gradually shifts to lower temperature, becomes increasingly weak, and disappears for 85 nm nanoparticles. An inverse magnetocaloric effect with positive magnetic entropy change was observed around T(CO), and it decreases with the decrease in size due to the suppression of CO phase. The observed negative magnetic entropy change at Tc shows a surprising nonmonotonic behavior with the variation of particles size. All these results may give rise to a new insight into the magnetothermal behaviors in nanosized CO perovskite manganites.

  7. Magnetocaloric effect and H gradient in bulk La(Fe,Si)13Hy magnetic refrigerants obtained by HDSH

    DEFF Research Database (Denmark)

    Neves Bez, Henrique; Eggert, Bruno G.F.; Lozano, Jaime;

    2015-01-01

    Results are reported on the preparation of bulk parts of La(Fe,Si)13Hy via the Hydrogen-Decrepitation-Sintering-Hydrogenation (HDSH) process. Net shape parts for application in room-temperature magnetic refrigeration have been produced in only 8 h of heat treatment which is considerably faster than...... the conventional ingot homogenization heat treatment of 7 days. The samples produced by HDSH showed higher amounts of hydrogen than the parts hydrogenated by the conventional method of thermal homogenization (20 h at 1423 K), milling to fine powder and subsequent hydrogenation. Hydrogenation parameters play...... and 4 h of hydrogenation exhibited different magnetocaloric behaviours. For a hydrogenation step of 4 h, parts with a demagnetization factor of 0.49 showed an adiabatic temperature change (ΔTadΔTad) higher than 1 K for a temperature range of 40 K with a maximum value of 1.57 K for an applied magnetic...

  8. Strain dependent magnetocaloric effect in La0.67Sr0.33MnO3 thin-films

    Directory of Open Access Journals (Sweden)

    V. Suresh Kumar

    2013-05-01

    Full Text Available The strain dependent magnetocaloric properties of La0.67Sr0.33MnO3 thin films deposited on three different substrates (001 LaAlO3 (LAO, (001 SrTiO3 (STO, and (001 La0.3Sr0.7Al0.65Ta0.35O9 (LSAT have been investigated under low magnetic fields and around magnetic phase transition temperatures. Compared to bulk samples, we observe a remarkable decrease in the ferromagnetic transition temperature that is close to room temperature, closely matched isothermal magnetic entropy change and relative cooling power values in tensile strained La0.67Sr0.33MnO3 films. The epitaxial strain plays a significant role in tuning the peak position of isothermal magnetic entropy change towards room temperature with improved cooling capacity.

  9. Magnetocaloric effect in Gd6Co1.67Si3 compound with a second-order phase transition

    Institute of Scientific and Technical Information of China (English)

    Shen Jun; Li Yang-Xian; Dong Qiao-Yan; Wang Fang; Sun Ji-Rong

    2008-01-01

    The magnetic properties and the magnetic entropy change ΔS have been investigated for Gd6Co1.67Si3 compounds with a second-order phase transition. The saturation moment at 5 K and the Curie temperature TC are 38.1μB and 298 K, respectively. The AS originates from a reversible second-order magnetic transition around TC and its value reaches 5.2J/kg.K for a magnetic field change from 0 to 5T. The refrigerant capacity (RC) of Gd6Co1.67Si3 are calculated by using the methods given in Refs.[12] and [21], respectively, for a field change of 0-5 T and its values are 310 and 440 J/kg, which is larger than those of some magnetocaloric materials with a first-order phase transition.

  10. Experimental study of the anisotropic magneto-Seebeck effect in (Ga,Mn)As thin films

    Energy Technology Data Exchange (ETDEWEB)

    Althammer, Matthias; Krupp, Alexander T.; Brenninger, Thomas; Venkateshvaran, Deepak; Opel, Matthias; Gross, Rudolf; Goennenwein, Sebastian T.B. [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Dreher, Lukas [Walter Schottky Institut, Technische Universitaet Muenchen, Garching (Germany); Schoch, Wladimir; Limmer, Wolfgang [Abteilung Halbleiterphysik, Universitaet Ulm, Ulm (Germany)

    2011-07-01

    In analogy to anisotropic magnetoresistance (AMR), the thermopower of ferromagnetic materials also characteristically depends on the orientation of the magnetization vector. This anisotropic magneto-thermopower - or anisotropic magneto-Seebeck effect (AMS) - has only scarcely been studied to date. Taking the ferromagnetic semiconductor (Ga,Mn)As with its large magneto-resistive effects as a prototype example, we have measured the evolution of both the AMR and the AMS effects at liquid He temperatures as a function of the orientation of a magnetic field applied in the (Ga,Mn)As film plane, for different, fixed magnetic field magnitudes. Our data show that the AMS effect can be adequately modeled only if the symmetry of the (Ga,Mn)As crystal is explicitly taken into account. We quantitatively compare our AMR and AMS measurements with corresponding model calculations, and address the validity of the Mott relations linking the magneto-resistance and the magneto-Seebeck coefficients.

  11. Enhanced magnetocaloric effect in quasi-one-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(dmen){sub 2}(H{sub 2}O)]SiF{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Orendáč, M., E-mail: martin.orendac@upjs.sk; Čižmár, E.; Orendáčová, A.; Tkáčová, J.; Kuchár, J.; Černák, J.

    2014-02-15

    Highlights: • Low-dimensional magnetic behavior was found in [Cu(dmen){sub 2}(H{sub 2}O)]SiF{sub 6}. • Enhanced magnetocaloric effect occurs at low enough temperatures (T ≪ J/k{sub B}). • The isothermal change of entropy can be 20 times larger than that in paramagnet. -- Abstract: The results of specific heat and electron-spin resonance of [Cu(dmen){sub 2}(H{sub 2}O)]SiF{sub 6} (dmen = N,N-dimethyl-1,2-diaminoethane) are reported. The studied material can be considered as an S = 1/2 quasi-one-dimensional Heisenberg antiferromagnet with dominant intrachain interaction J{sub intra}/k{sub B} = −3.59 K. The appearance of both normal and inverse magnetocaloric effect in various field ranges below saturation field B{sub sat} is tentatively attributed to weaker ferromagnetic interchain interactions. Pronounced magnetocaloric effect is found in the vicinity of B{sub sat,} where at temperatures T ≪ |J{sub intra}/k{sub B}|, the isothermal change of entropy was found to be about 20 times higher than that in S = 1/2 paramagnet. The potential origin of the observed behavior is discussed.

  12. Exploring the details of the martensitic phase transition and magnetocaloric effect of CoMnGe{sub 0.95}Ga{sub 0.05} by synchrotron and magnetic measurements

    Energy Technology Data Exchange (ETDEWEB)

    Dincer, I., E-mail: idincer@eng.ankara.edu.tr [Department of Engineering Physics, Faculty of Engineering, Ankara University, 06100 Besevler, Ankara (Turkey); Yuezueak, E.; Durak, G.; Elerman, Y. [Department of Engineering Physics, Faculty of Engineering, Ankara University, 06100 Besevler, Ankara (Turkey); Bell, A.M.T. [HASYLAB/DESY, Notkestrasse 85, 22607 Hamburg (Germany); Ehrenberg, H. [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, D-76344, Eggenstein-Leopoldshafen (Germany)

    2012-11-05

    Highlights: Black-Right-Pointing-Pointer CoMnGe{sub 0.95}Ga{sub 0.05} alloy shows a structural phase transformation from hexagonal to orthorhombic. Black-Right-Pointing-Pointer In CoMnGe{sub 0.95}Ga{sub 0.05}, the giant magnetocaloric effect is observed around room temperature. Black-Right-Pointing-Pointer The maximum magnetic entropy change is -5.2 J kg{sup -1} K{sup -1} in magnetic field change of 1 T. - Abstract: The structural, magnetic and magnetocaloric properties of CoMnGe{sub 0.95}Ga{sub 0.05} have been investigated by using electron microscopy, calorimetric, synchrotron and magnetic measurements. The substitution of Ga for Ge leads to decreasing on the martensitic transition temperature from 650 K to 315 K. CoMnGe{sub 0.95}Ga{sub 0.05} has hexagonal structure (space group P6{sub 3}/mmc) above the martensitic transition temperature and orthorhombic structure (space group Pnma) below this temperature. The magnetic field dependence of magnetization measurements are performed in the heating and cooling processes around the martensitic transition temperature to determine magnetocaloric effect. It is observed that the magnetic entropy change associated with the martensitic transition temperature can be as high as -5.2 J kg{sup -1} K{sup -1} in field of 1 T.

  13. Direct magnetocaloric characterization and simulation of thermomagnetic cycles.

    Science.gov (United States)

    Porcari, G; Buzzi, M; Cugini, F; Pellicelli, R; Pernechele, C; Caron, L; Brück, E; Solzi, M

    2013-07-01

    An experimental setup for the direct measurement of the magnetocaloric effect capable of simulating high frequency magnetothermal cycles on laboratory-scale samples is described. The study of the magnetocaloric properties of working materials under operative conditions is fundamental for the development of innovative devices. Frequency and time dependent characterization can provide essential information on intrinsic features such as magnetic field induced fatigue in materials undergoing first order magnetic phase transitions. A full characterization of the adiabatic temperature change performed for a sample of Gadolinium across its Curie transition shows the good agreement between our results and literature data and in-field differential scanning calorimetry.

  14. Crack growth resistance for anisotropic plasticity with non-normality effects

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Legarth, Brian Nyvang

    2006-01-01

    For a plastically anisotropic solid a plasticity model using a plastic flow rule with non-normality is applied to predict crack growth. The fracture process is modelled in terms of a traction–separation law specified on the crack plane. A phenomenological elastic–viscoplastic material model...... is applied, using one of two different anisotropic yield criteria to account for the plastic anisotropy, and in each case the effect of the normality flow rule is compared with the effect of non-normality. Conditions of small scale yielding are assumed, with mode I loading conditions far from the crack...

  15. Theoretical investigation of the magnetocaloric effect on La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 compound at room temperature

    Science.gov (United States)

    Tlili, R.; Hammouda, R.; Bejar, M.; Dhahri, E.

    2015-07-01

    Based on a phenomenological model, the magnetic and magnetocaloric properties of La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 oxide have been studied. Indeed, the magnetic measurements have demonstrated that the sample exhibits a ferromagnetic-paramagnetic transition at room temperature. The value of the magnetocaloric effect such as magnetic entropy change, full width at half-maximum, relative cooling power and magnetic specific heat change has been determined from the calculation of magnetization as a function of temperature under different external magnetic fields. The maximum magnetic entropy change (- ΔSMmax) and the relative cooling power (RCP) are, respectively, 0.57 J kg-1 K-1 and 28.68 J kg-1 for a 10 kOe field change at 300 K, which are the characteristics of a good magnetocaloric material. Hence, the La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 compound can be considered as a promising material in magnetic refrigeration technology. According to the master curve behavior for the temperature dependence of ΔSM predicted for different maximum fields, this work has confirmed that the paramagnetic-ferromagnetic phase transition observed for our sample is of a second order.

  16. Aeroelastic modal dynamics of wind turbines including anisotropic effects

    DEFF Research Database (Denmark)

    Skjoldan, Peter Fisker

    , damping, and periodic mode shapes of a rotating wind turbine by describing the rotor degrees of freedom in the inertial frame. This approach is valid only for an isotropic system. Anisotropic systems, e.g., with an unbalanced rotor or operating in wind shear, are treated with the general approaches...... of Floquet analysis or Hill's method which do not provide a unique reference frame for observing the modal frequency, to which any multiple of the rotor speed can be added. This indeterminacy is resolved by requiring that the periodic mode shape be as constant as possible in the inertial frame. The modal...... frequency is thus identified as the dominant frequency in the response of a pure excitation of the mode observed in the inertial frame. A modal analysis tool based directly on the complex aeroelastic wind turbine code BHawC is presented. It uses the Coleman approach in isotropic conditions...

  17. The Effect of Anisotropic Conduction on the Thermal Instability in the Interstellar Medium

    CERN Document Server

    Choi, Ena

    2011-01-01

    Thermal instability (TI) can strongly affect the structure and dynamics of the interstellar medium (ISM) in the Milky Way and other disk galaxies. Thermal conduction plays an important role in the TI by stabilizing small scales and limiting the size of the smallest condensates. In the magnetized ISM, however, heat is conducted anisotropically (primarily along magnetic field lines). We investigate the effects of anisotropic thermal conduction on the nonlinear regime of the TI by performing two-dimensional magnetohydrodynamic simulations. We present models with magnetic fields of different initial geometries and strengths, and compare them to hydrodynamic models with isotropic conduction. We find anisotropic conduction does not significantly alter the overall density and temperature statistics in the saturated state of the TI. However, it can strongly affect the shapes and sizes of cold clouds formed by the TI. For example, for uniform initial fields long filaments of cold gas are produced that are reminiscent ...

  18. Effects of the Biot and the squirt-flow coupling interaction on anisotropic elastic waves

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Considering the velocity anisotropy of the solid/fluid relative motion and employment of the BISQ theory[1] based on the one-dimensional porous isotropic case, we establish a two-phase anisotropic elastic wave equation to simultaneously include the Biot and the squirt mechanisms in terms of both the basic principles of the fluid's mass conservation and the elastic-wave dynamical equations in the two-phase anisotropic rock. Numerical results, while the Biot-flow and the squirt-flow effects are simultaneously considered in the transversely isotropic (TI) poroelastic medium, show that the attenuation of the quasi P-wave and the quasi SV-wave strongly depend on the permeability anisotropy, and the attenuation behavior at low and high frequencies is contrary. Meanwhile, the attenuation and dispersion of the quasi P-wave are also affected seriously by the anisotropic solid/fluid coupling additional density.

  19. Necking of anisotropic micro-films with strain-gradient effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2008-01-01

    Necking of stubby micro-films of aluminum is investigated numerically by considering tension of a specimen with an initial imperfection used to onset localisation. Plastic anisotropy is represented by two different yield criteria and strain-gradient effects are accounted for using the visco......-plastic finite strain model. Furthermore, the model is extended to isotropic anisotropic hardening (evolving anisotropy). For isotropic hardening plastic anisotropy affects the predicted overall nominal stress level, while the peak stress remains at an overall logarithmic strain corresponding to the hardening...... exponent. This holds true for both local and nonlocal materials. Anisotropic hardening delays the point of maximum overall nominal stress....

  20. Simulated magnetocaloric properties of MnCr2O4 spinel

    OpenAIRE

    2016-01-01

    The magnetocaloric properties of MnCr2O4 spinel have been simulated based on a phenomenological model. The simulation of magnetization as function of temperature is used to explore magnetocaloric properties such as magnetic entropy change, heat capacity change, and relative cooling power. The results imply the prospective application of MnCr2O4 spinel to achieve magnetocaloric effect at cryogenic temperatures (20–60 K) near Curie temperatures (38–44 K). According to the obtained results it is...

  1. Gd3Al2-xGax系合金磁热效应的研究%Study on Magnetocaloric Effect of Gd3Al2-xGax

    Institute of Scientific and Technical Information of China (English)

    生利英; 曹朝霞; 黄焦宏; 齐勇田; 宋博宇

    2016-01-01

    The organization structure and the magnetocaloric effect of Gd3 Al2-x Gax (0.1 x =0,0.2,0.3) series alloy prepared by smelting in a a high-frequency floating furnace and annealing treatment at 900 ℃ for 30 h were investigated.The results show that Gd3Al2-xGax series alloy keeps simple tetragonal crystal structure of Gd3Al2.The content of base phase Gd3Al2 increases after heat treatment.The Curie temperature of Gd3 Al2-xGaxseries alloy changes between 1 K ~ 2 K along with the increase of the content of Ga.The half peak width of △Sm-T curve is almost the same.The maximum magnetic entropy changes of Gd3Al1.8Ga0.2 alloy is the largest under magnetic field changes of 1.5 T,which exceeds 30% of Gd3Al2 alloy.A small amount of Ga to replace Al can improve the magnetocaloric effect of Gd3Al2 alloy.%对经真空高频磁悬浮炉熔炼、900℃30 h热处理的Gd3 Al2-XGax(x=0,0.1,0.2,0.3)系列合金的组织结构和磁热效应进行了研究.研究发现,Gd3Al2-XGax系列合金保持了Gd3Al2的简单正方晶体结构,热处理后基相Gd3Al2的含量增加,随着Ga含量的增加,Gd3Al2-XGax合金的居里温度变化在1K~2K之间,在1.5T的外加磁场下,△Sm-T曲线半峰宽几乎不变,Gd3Al1.8Ga0.2合金的最大磁熵变最大,超过Gd3Al2的最大磁熵变30%.少量Ga替代Al可以提高Gd3Al2合金的磁热效应.

  2. Magnetocaloric Pumping of Liquid Oxygen

    Science.gov (United States)

    Immer, Christopher; Kandula, Max; Lane, John; Youngquist, Robert

    2004-01-01

    The field-induced force density on a magnetic fluid is proportional to the magnetic susceptibility times the gradient of the magnetic field squared. The direction of the force is towards increasing magnetic field (positive gradient). Applying a magnetic field to a magnetic fluid will result in a force from all directions towards the location of peak field. Since the magnetic field is conservative and there are no magnetic monopoles, the net field-induced force on any fluid of constant susceptibly will be zero. The only manner to obtain a nonzero net field-induced force is to vary the susceptibility of the fluid. At the gas/liquid interface of liquid oxygen, the susceptibility varies drastically, and the exploitation of the resultant large net forces. An alternative method of varying the magnetic susceptibility is to vary the temperature of the fluid. The magnetic susceptibility of paramagnetic liquid oxygen obeys the Curie-Weiss law: it is inversely proportional to temperature. By applying a temperature gradient in the presence of a symmetric magnetic field, a nonzero net force results. Much of the theory of the so-called Magnetocaloric Effect has previously been developed for and applied to ferromagnetic fluids, or ferrofluids, but is readily applied to paramagnetic liquid oxygen.

  3. Table-like magnetocaloric effect of Fe{sub 88−x}Nd{sub x}Cr{sub 8}B{sub 4} composite materials

    Energy Technology Data Exchange (ETDEWEB)

    Lai, J.W.; Zheng, Z.G.; Zhong, X.C. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Franco, V. [Departamento Física de la Materia Condensada, ICMSE-CSIC, Universidad de Sevilla, P.O. Box 1065, 41080 Sevilla (Spain); Montemayor, R.; Liu, Z.W. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Zeng, D.C., E-mail: medczeng@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China)

    2015-09-15

    The narrow working temperature range due to the sharp magnetic entropy change |ΔS{sub M}| peak and large thermal or magnetic hysteresis restricts the practical application of magnetocaloric materials. In this work, the table-like magnetocaloric effect (MCE) was obtained in the multilayer composite of Fe{sub 88−x}Nd{sub x}Cr{sub 8}B{sub 4} alloys with various Nd substitutions for Fe (x=5, 8, 10, 12, and 15), which were prepared by arc-melting followed by melt-spinning. The substation of Nd was found to enhance the glass-forming ability. For the alloys with Nd substitution from 5 at% to 15 at%, the Curie temperature (T{sub C}) ranged from 322 K to 350 K and the peak value of |ΔS{sub M}| remained almost constant, 3.4–3.5 J/(kg K) under an applied field of 0–5 T. The composite with various Nd contents was prepared by stocking the ribbons layer by layer. The |ΔS{sub M}| of the composite approached a nearly constant value of ∼3.2 J/(kg K) in a field change of 0–5 T in a wide temperature span over 40 K, resulting in large refrigerant capacity value of >408 J/kg. This |ΔS{sub M}| value was much larger than the previous reported Fe-based amorphous composite Fe{sub 78−x}Ce{sub x}Si{sub 4}Nb{sub 5}B{sub 12}Cu{sub 1}. This composite can be used as the working material in the Ericsson-cycle magnetic regenerative refrigerator around room temperature. - Highlights: • The T{sub C} ranges from 322 K to 350 K when increasing Nd substitution from 5 to 15 at%. • |ΔS{sub M}| remains relatively constant, about 3.4–3.5 J/(kg K) under H=0–5 T. • RC decreases from 93 to 78 J/kg in a field change of 1.5 T when Nd increasing. • Table-like MCE ,|ΔS{sub M}| ~3.2J/kg K under 0–5 T, appeared in the composite. • A wide working temperature range (40 K) and enhanced RC (>408J/kg) were obtained in the composite.

  4. Theoretical investigations on magnetocaloric effect in Er{sub 1−y}Tb{sub y}Al{sub 2} series

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, P.O., E-mail: paula.ribeiro@gmail.com [Instituto de Física, Universidade do Estado do Rio de Janeiro – UERJ, Rua São Francisco Xavier, 524, 20550-013 RJ (Brazil); Alho, B.P.; Alvarenga, T.S.T.; Nóbrega, E.P.; Sousa, V.S.R. de [Instituto de Física, Universidade do Estado do Rio de Janeiro – UERJ, Rua São Francisco Xavier, 524, 20550-013 RJ (Brazil); Carvalho, A. Magnus G. [Laboratório Nacional de Luz Síncrotron, CNPEM, 13083-970 Campinas, SP (Brazil); Caldas, A. [Sociedade Unificada de Ensino Superior e Cultura, SUESC, 20211-351 Rio de Janeiro, RJ (Brazil); Oliveira, N.A. de; Ranke, P.J. von [Instituto de Física, Universidade do Estado do Rio de Janeiro – UERJ, Rua São Francisco Xavier, 524, 20550-013 RJ (Brazil)

    2015-04-01

    We report on the magnetic and magnetocaloric effect calculations in rare earth Er{sub 1−y}Tb{sub y}Al{sub 2} compounds (y=0.00, 0.25, 0.5, 0.75 and 1.00). Our model Hamiltonian has contributions of the crystalline electrical field anisotropy in both Er and Tb magnetic sublattices, disorder in exchange interactions among Er–Er, Tb–Tb and Er–Tb magnetic ions and the Zeeman effect. The magnetization, the isothermal entropy change (ΔS{sub T}) and the adiabatic temperature change (ΔT{sub ad}) dependence on temperature were simulated and, compared with the experimental data available. - Highlights: • Modeling Er{sub (1−y)}Tb{sub y}Al{sub 2} intermetallic compounds. • Magnetic entropy changes in Er{sub (1−y)}Tb{sub y}Al{sub 2}. • Adiabatic temperature changes in Er{sub 0.75}Tb{sub 0.25}Al{sub 2} and Er{sub 0.65}Tb{sub 0.35}Al{sub 2} compounds.

  5. Large inverse magnetocaloric effect and magnetoresistance in nickel rich Ni{sub 52}Mn{sub 34}Sn{sub 14} Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Pal, D., E-mail: deba.phy@gmail.com [S.N. Bose National Center for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata 700098, West Bengal (India); Kandi Raj College, Kandi 742137, West Bengal (India); Ghosh, A.; Mandal, K. [S.N. Bose National Center for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata 700098, West Bengal (India)

    2014-06-01

    Nickel rich Ni{sub 52}Mn{sub 34}Sn{sub 14} Heusler alloy was prepared by arc melting and subsequent homogenization by annealing. Existence of first order magneto-structural transition (FOMST) was confirmed by various measurements. In comparison to conventional Ni{sub 50−x}Mn{sub 36+x}Sn{sub 14} alloys, a larger magnetic entropy change (∆S{sub M}≈8 J/kg K using Maxwell's thermodynamic equation and ∆S{sub M}≈18 J/kg K using Clasius–Clapeyron equation) and large negative magnetoresistance (MR≈−30%) were observed in the vicinity of martensitic transition temperature due to a change of 3 T and 8 T magnetic fields respectively. Effect of excess Ni content was discussed by considering other nearer compositions as reported by other researchers. Irreversibility in FOMST due to kinetic arrest was also studied from MR vs magnetic fields curves taken at a single temperature in two different initial phases. The exchange bias behavior in this alloy was studied by various magnetic measurements. - Highlights: • Large magnetocaloric effect was observed in Ni-rich Ni{sub 52}Mn{sub 34}Sn{sub 14} Heusler alloy. • A large negative magnetoresistance was observed near the structural transition. • We investigated the exchange bias behavior in this alloy. • The resistivity shows irreversibility due to field cycling.

  6. Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior

    Science.gov (United States)

    Brambleby, J.; Goddard, P. A.; Singleton, J.; Jaime, M.; Lancaster, T.; Huang, L.; Wosnitza, J.; Topping, C. V.; Carreiro, K. E.; Tran, H. E.; Manson, Z. E.; Manson, J. L.

    2017-01-01

    We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. The data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system.

  7. Magnetic properties and magnetocaloric effect in NdxLa1-xFe11.5Al1.5 compounds

    Institute of Scientific and Technical Information of China (English)

    Wang Fang; Wang Guang-Jun; Sun Ji-Rong; Shen Bao-Gen

    2008-01-01

    Effects of Nd-doping on the magnetic properties and magnetocaloric effects (MCEs) of NdxLa1-xFe11.5Al1.5 have been investigated. Substitution of Nd leads to a weakening of the antiferromagnetic (AFM) coupling and an enhancement of the ferromagnetic (FM) coupling. This in turn results in a complex magnetic behaviour for Nd0.2La0.8Fe11.52Al1.5 characterized by the occurrence of two phase transitions at ~188 K (PM-AFM) and ~159 K (AFM-FM). As a result, a table-like MCE (9 J/kg·K) is found in a wide temperature range (160-185 K) for a field change of 0-5 T around the transition temperature, as evidenced by both the magnetic and calorimetric measurements. Based on the analysis of low-temperature heat capacity, it is found that the AFM-FM phase transition modifies the electron density significantly, and the major contribution to the entropy change comes from the electronic entropy change.

  8. Theoretical studies on polynuclear {Cu(II)5Gd(III)n} clusters (n = 4, 2): towards understanding their large magnetocaloric effect.

    Science.gov (United States)

    Rajeshkumar, Thayalan; Annadata, Harshini V; Evangelisti, Marco; Langley, Stuart K; Chilton, Nicholas F; Murray, Keith S; Rajaraman, Gopalan

    2015-02-16

    Density functional theory (DFT) studies on two polynuclear clusters, [Cu(II)5Gd(III)4O2(OMe)4(teaH)4(O2CC(CH3)3)2(NO3)4] (1) and [Cu5Gd2(OH)4(Br)2-(H2L)2(H3L)2(NO3)2(OH2)4] (2), have been carried out to probe the origin of the large magnetocaloric effect (MCE). The magnetic exchange interactions for 1 and 2 via multiple pathways are estimated using DFT calculations. While the calculated exchange parameters deviate from previous experimental estimates obtained by fitting the magnetic data, the DFT parameter set is found to offer a striking match to the magnetic data for both complexes, highlighting the problem of overparameterization. Magnetostructural correlations for {Cu-Gd} pairs have been developed where both the Cu-O-Gd angles and Cu-O-Gd-O dihedral angles are found to significantly influence the magnitude and sign of the exchange constants. The magnitude of the MCE has been examined as a function of the exchange interactions, and clues on how the effect can be enhanced are discussed.

  9. Magnetic and calorimetric studies of magnetocaloric effect in La0.7-xPrxCa0.3MnO3

    Science.gov (United States)

    Barik, S. K.; Aparnadevi, M.; Rebello, A.; Naik, V. B.; Mahendiran, R.

    2012-04-01

    We report magnetocaloric effect in La0.7-xPrxCa0.3MnO3 (x = 0, 0.2, 0.3, and 0.4). All these compounds undergo first-order paramagnetic to ferromagnetic transition upon cooling and show field-induced metamagnetic transition (FIMMT) in the paramagnetic state. The FIMMT is accompanied by a release of latent heat and change in temperature of the sample as evidenced from differential scanning calorimetry and thermal analysis data for x = 0.3. The magnetic entropy decreases (-ΔSm = 8.23, 8.1, 7, and 5.38 Jkg-1 K-1 for a field change of ΔH = 5 T, for x = 0, 0.2, 0.3, and 0.4, respectively) and refrigeration capacity (RC) increases with increasing x (RC = 197, 215, 240, and 259 J/kg for x = 0, 0.2, 0.3, and 0.4, respectively). We suggest that collapse of magnetic polarons in the paramagnetic state and magnetovolume effect are responsible for the observed FIMMT and large -ΔSm values.

  10. The unique effect of in-plane anisotropic strain in the magnetization control by electric field

    Science.gov (United States)

    Zhao, Y. Y.; Wang, J.; Hu, F. X.; Liu, Y.; Kuang, H.; Wu, R. R.; Sun, J. R.; Shen, B. G.

    2016-05-01

    The electric field control of magnetization in both (100)- and (011)-Pr0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PSMO/PMN-PT) heterostructures were investigated. It was found that the in-plane isotropic strain induced by electric field only slightly reduces the magnetization at low temperature in (100)-PSMO/PMN-PT film. On the other hand, for (011)-PSMO/PMN-PT film, the in-plane anisotropic strain results in in-plane anisotropic, nonvolatile change of magnetization at low-temperature. The magnetization, remanence and coercivity along in-plane [100] direction are suppressed by the electric field while the ones along [01-1] direction are enhanced, which is ascribed to the extra effective magnetic anisotropy induced by the electric field via anisotropic piezostrains. More interestingly, such anisotropic modulation behaviors are nonvolatile, demonstrating a memory effect.

  11. The unique effect of in-plane anisotropic strain in the magnetization control by electric field

    Directory of Open Access Journals (Sweden)

    Y. Y. Zhao

    2016-05-01

    Full Text Available The electric field control of magnetization in both (100- and (011-Pr0.7Sr0.3MnO3/Pb(Mg1/3Nb2/30.7Ti0.3O3(PSMO/PMN-PT heterostructures were investigated. It was found that the in-plane isotropic strain induced by electric field only slightly reduces the magnetization at low temperature in (100-PSMO/PMN-PT film. On the other hand, for (011-PSMO/PMN-PT film, the in-plane anisotropic strain results in in-plane anisotropic, nonvolatile change of magnetization at low-temperature. The magnetization, remanence and coercivity along in-plane [100] direction are suppressed by the electric field while the ones along [01-1] direction are enhanced, which is ascribed to the extra effective magnetic anisotropy induced by the electric field via anisotropic piezostrains. More interestingly, such anisotropic modulation behaviors are nonvolatile, demonstrating a memory effect.

  12. Large low field magnetocaloric effect in first-order phase transition compound TlFe3Te3 with low-level hysteresis

    Science.gov (United States)

    Mao, Qianhui; Yang, Jinhu; Wang, Hangdong; Khan, Rajwali; Du, Jianhua; Zhou, Yuxing; Xu, Binjie; Chen, Qin; Fang, Minghu

    2016-01-01

    Magnetic refrigeration based on the magnetocaloric effect (MCE) is an environment-friendly, high-efficiency technology. It has been believed that a large MCE can be realized in the materials with a first-order magnetic transition (FOMT). Here, we found that TlFe3Te3 is a ferromagnetic metal with a first-order magnetic transition occurring at Curie temperature TC = 220 K. The maximum values of magnetic entropy change (Δ) along the crystallographic c-axis, estimated from the magnetization data, reach to 5.9 J kg−1K−1 and 7.0 J kg−1 K−1 for the magnetic field changes, ΔH = 0–1 T and 0–2 T, respectively, which is significantly larger than that of MCE materials with a second-order magnetic transition (SOMT). Besides the large ΔSM, the low-level both thermal and field hysteresis make TlFe3Te3 compound an attractive candidate for magnetic refrigeration. Our findings should inspire the exploration of high performance new MCE materials. PMID:27681203

  13. Study of magnetocaloric effect in LaFe11.5Si1.5 alloys prepared by different cooling methods

    Indian Academy of Sciences (India)

    Xiang Chen; Yungui Chen; Yongbo Tang

    2014-06-01

    LaFe11.5Si1.5 alloys are annealed at 1503 K for 5 h and cooled down to room temperature by furnace cooling, air cooling and quenching in ice water, respectively. The main phases are 1:13 phases in those alloys. The impurity phases are -Fe and the amount of LaFeSi phase is so small that it is hard to observe in their XRD patterns. The powder X-ray diffraction patterns and SEM show that the three cooling methods have little influence on the phase relation and microstructure of those LaFe11.5Si1.5 alloys. But the lattice constant of LaFe11.5Si1.5 alloy prepared by quenching in ice water is lesser than those of the other two alloys, respectively. For studying the influence of different cooling processes on magnetic properties, the Curie temperature, thermal and magnetic hysteresis, magnetocaloric effect and relative cooling power are investigated. The result shows that the Curie temperature of LaFe11.5Si1.5 prepared by quenching in ice water is 197.6 K, about 4 K lesser than those of the other two LaFe11.5Si1.5 alloys. The maximum M (, ) of LaFe11.5Si1.5 prepared by furnace cooling and quenching in ice water is the most and the least under the field of 0–2 , respectively.

  14. Magnetocaloric effect and inhomogeneity of CdCr{sub 2}Se{sub 4} and HgCr{sub 2}Se{sub 4} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Bebenin, N.G., E-mail: bebenin@imp.uran.ru; Zainullina, R.I.; Sukhorukov, Yu P.

    2015-08-01

    Magnetocaloric effect in single crystals of spinels CdCr{sub 2}Se{sub 4} and HgCr{sub 2}Se{sub 4} is studied. The maximum value of the magnetic-field-induced change in entropy in the field of 15 kOe is about 1.4–1.5 J/(kg K). At Curie temperature the entropy change obeys the relation: −ΔS=αH^(2/3)–β. The magnetic transitions in the spinels are found to be noticeably smeared. The experimental data have been compared with the theoretical results obtained for Heisenberg model in the mean field approximation (MFA). It is found that MFA overestimates the change of entropy in a magnetic field and underestimates the influence of inhomogeneity on ΔS. - Highlights: • The maximum value of the magnetic-field-induced change in entropy in CdCr{sub 2}Se{sub 4} and HgCr{sub 2}Se{sub 4} in the field of 15 kOe is found to be about 1.4–1.5 J/(kg K). • At Curie temperature the entropy change obeys the relation: −ΔS= αH^(2/3)−β. • Heisenberg model in the mean field approximation overestimates the change of entropy in magnetic field.

  15. Magnetization process, bipartite entanglement, and enhanced magnetocaloric effect of the exactly solved spin-1/2 Ising-Heisenberg tetrahedral chain.

    Science.gov (United States)

    Strečka, Jozef; Rojas, Onofre; Verkholyak, Taras; Lyra, Marcelo L

    2014-02-01

    The frustrated spin-1/2 Ising-Heisenberg ladder with Heisenberg intra-rung and Ising inter-rung interactions is exactly solved in a longitudinal magnetic field by taking advantage of the local conservation of the total spin on each rung and the transfer-matrix method. We have rigorously calculated the ground-state phase diagram, magnetization process, magnetocaloric effect, and basic thermodynamic quantities for the model, which can be alternatively viewed as an Ising-Heisenberg tetrahedral chain. It is demonstrated that a stepwise magnetization curve with an intermediate plateau at half of the saturation magnetization is also reflected in respective stepwise changes of the concurrence serving as a measure of bipartite entanglement. The ground-state phase diagram and zero-temperature magnetization curves of the Ising-Heisenberg tetrahedral chain are contrasted with the analogous results of the purely quantum Heisenberg tetrahedral chain, which have been obtained through density-matrix renormalization group (DMRG) calculations. While both ground-state phase diagrams fully coincide in the regime of weak inter-rung interaction, the purely quantum Heisenberg tetrahedral chain develops Luttinger spin-liquid and Haldane phases for strongly coupled rungs, which are absent in the Ising-Heisenberg counterpart model.

  16. Luminescence, magnetocaloric effect and single-molecule magnet behavior in lanthanide complexes based on a tridentate ligand derived from 8-hydroxyquinoline.

    Science.gov (United States)

    Shen, Hai-Yun; Wang, Wen-Min; Bi, Yan-Xia; Gao, Hong-Ling; Liu, Shuang; Cui, Jian-Zhong

    2015-11-21

    A new family of lanthanide complexes, [Ln2(hfac)4L2] (Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6), Lu (7); hfac = hexafluoroacetylacetonate, HL = 2-(2′-benzothiazole)-8-hydroxyquinoline), was synthesized and characterized using single-crystal X-ray diffraction, elemental analysis (EA), thermal gravimetric analysis (TGA), powder X-ray diffraction (PXRD) and UV-vis spectra. X-ray crystallographic analyses reveal that 1–7 are isomorphous and crystallize in the monoclinic space group C2/c. In these dinuclear complexes, each LnШ ion is eight-coordinated with two bidentate hfac and two μ-phenol bridging L ligands. The TGA results show that the complexes have relatively high thermal stabilities. Complexes 1 and 3 show the characteristic transitions of the corresponding lanthanide ions with ligand-related emission peaks. Meanwhile, complexes 4 and 7 exhibit ligand-centered fluorescence at room temperature. Magnetic measurements were carried out on complexes 2–6. The magnetic study reveals that 2 displays a magnetocaloric effect, with a maximum −ΔSm value of 16.89 J K−1 kg−1 at 2 K for ΔH = 8 T. Dynamic magnetic studies reveal single-molecule magnet (SMM) behavior for complex 4. Fitting the dynamic magnetic data to the Arrhenius law gives an energy barrier ΔE/kB = 50.33 K and pre-exponential factor τ0 = 1.05 × 10(-8)s.

  17. Two successive magneto-structural transformations and their relation to enhanced magnetocaloric effect for Ni55.8Mn18.1Ga26.1 Heusler alloy.

    Science.gov (United States)

    Li, Zhe; Xu, Kun; Zhang, Yuanlei; Tao, Chang; Zheng, Dong; Jing, Chao

    2015-10-09

    In the present work, two successive magneto-structural transformations (MSTs) consisting of martensitic and intermartensitic transitions have been observed in polycrystalline Ni55.8Mn18.1Ga26.1 Heusler alloy. Benefiting from the additional latent heat contributed from intermediate phase, this alloy exhibits a large transition entropy change ΔStr with the value of ~27 J/kg K. Moreover, the magnetocaloric effect (MCE) has been also evaluated in terms of Maxwell relation. For a magnetic field change of 30 kOe, it was found that the calculated value of refrigeration capacity in Ni55.8Mn18.1Ga26.1 attains to ~72 J/kg around room temperature, which significantly surpasses those obtained for many Ni-Mn based Heusler alloys in the same condition. Such an enhanced MCE can be ascribed to the fact that the isothermal entropy change ΔST is spread over a relatively wide temperature interval owing to existence of two successive MSTs for studied sample.

  18. Abnormal thermal expansion, multiple transitions, magnetocaloric effect, and electronic structure of Gd{sub 6}Co{sub 4.85}

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jiliang [Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong (Hong Kong); Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716 (United States); Zheng, Zhigang [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Shan, Guangcun, E-mail: gshan2-c@my.cityu.edu.hk, E-mail: bobev@udel.edu, E-mail: apchshek@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong (Hong Kong); School of Instrumentation Science and Optoelectronics Engineering, Beihang University, Beijing 100191 (China); Bobev, Svilen, E-mail: gshan2-c@my.cityu.edu.hk, E-mail: bobev@udel.edu, E-mail: apchshek@cityu.edu.hk [Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716 (United States); Shek, Chan Hung, E-mail: gshan2-c@my.cityu.edu.hk, E-mail: bobev@udel.edu, E-mail: apchshek@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong (Hong Kong)

    2015-10-07

    The structure of known Gd{sub 4}Co{sub 3} compound is re-determined as Gd{sub 6}Co{sub 4.85}, adopting the Gd{sub 6}Co{sub 1.67}Si{sub 3} structure type, which is characterized by two disorder Co sites filling the Gd octahedral and a short Gd-Gd distance within the octahedra. The compound shows uniaxial negative thermal expansion in paramagnetic state, significant negative expansion in ferromagnetic state, and positive expansion below ca. 140 K. It also exhibits large magnetocaloric effect, with an entropy change of −6.4 J kg{sup −1} K{sup −1} at 50 kOe. In the lattice of the compound, Co atoms at different sites show different spin states. It was confirmed by the X-ray photoelectron spectra and calculation of electronic structure and shed lights on the abnormal thermal expansion. The stability of such compound and the origin of its magnetism are also discussed based on measured and calculated electronic structures.

  19. Table-like magnetocaloric effect in Gd{sub 56}Ni{sub 15}Al{sub 27}Zr{sub 2} alloy and its field independence feature

    Energy Technology Data Exchange (ETDEWEB)

    Agurgo Balfour, E.; Ma, Z.; Fu, H., E-mail: fuhao@uestc.edu.cn, E-mail: rockingsandstorm@163.com; Wang, L.; Luo, Y. [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Hadimani, R. L.; Jiles, D. C. [Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa 50011 (United States); Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011 (United States); Wang, S. F., E-mail: fuhao@uestc.edu.cn, E-mail: rockingsandstorm@163.com [North Electronic Device Research Institute, Beijing 100141 (China)

    2015-09-28

    In order to obtain “table-like” magnetocaloric effect (MCE), multiple-phase Gd{sub 56}Ni{sub 15}Al{sub 27}Zr{sub 2} alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd{sub 2}Al and GdNiAl further broadened the relatively wider magnetic entropy change (−ΔS{sub M}) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5 K to 77.5 K. The plateau feature of the MCE was found to be nearly independent of the applied magnetic field from 3 T to 5 T. The maximum −ΔS{sub M} value of the MCE platforms is 6.0 J/kg K under applied magnetic field change of 5 T. Below 3 T, the field independence of the table-like feature disappears. The relatively large constant values of −ΔS{sub M} for the respective applied magnetic fields have promising applications in magnetic refrigeration using regenerative Ericsson cycle.

  20. Low-lying magnetic excitations and magnetocaloric effect of molecular magnet K6[V15As6O42(H2O)] · 8H2O

    Science.gov (United States)

    Fu, Zhendong; Xiao, Yinguo; Su, Yixi; Zheng, Yanzhen; Kögerler, Paul; Brückel, Thomas

    2015-10-01

    Low-temperature heat capacity measurements were performed on the molecular nanomagnet \\text{K}6[\\text{V}15\\text{As}6\\text{O}42(\\text{H}2\\text{O})] \\cdot8\\text{H}2{\\text{O}} (V15). The low-lying magnetic excitations are clearly evidenced by the Schottky anomalies in the specific-heat data. The energy levels determined from the low-temperature observables agree well with the three-spin model for V15. The magnetocaloric effect of V15 is examined. The maximum entropy change of 5.31 \\text{Jkg}-1\\text{K}-1 is found for a field change of Δ H =(8-0.5) \\text{T} at ˜1.5 \\text{K} . In spite of the low ground-state spin of V15, a drastic entropy change of 4.12 \\text{Jkg}-1\\text{K}-1 is observed for a field change of Δ H = (8-0.05) \\text{T} at 0.4 K, which is comparable to the entropy change of some high-spin sub-kelvin magnetic coolers at such low temperatures. Anisotropy and consequent zero-field splitting result in this characteristic of V15 and may open new possibilities in the design of ultra-low-temperature molecular coolers.

  1. Giant magnetocaloric effect in Gd2NiMnO6 and Gd2CoMnO6 ferromagnetic insulators

    Science.gov (United States)

    Krishna Murthy, J.; Devi Chandrasekhar, K.; Mahana, Sudipta; Topwal, D.; Venimadhav, A.

    2015-09-01

    We have investigated the magnetocaloric effect in double perovskite Gd2NiMnO6 (GNMO) and Gd2CoMnO6 (GCMO) samples by magnetic and heat capacity measurements. Ferromagnetic ordering is observed at ~130 K (~ 112 K) in GNMO (GCMO), while the Gd exchange interactions seem to dominate for T  <  20 K. In GCMO, below 50 K, antiferromagnetic behaviour due to the 3d-4f negative exchange interaction is observed. A maximum entropy (-ΔS M) and adiabatic temperature change of ~35.5 J Kg-1 K-1 (~ 24 J Kg-1 K-1) and 10.5 K (6.5 K) is observed in GNMO (GCMO) for a magnetic field change of 7 T at low temperatures. Absence of magnetic and thermal hysteresis and their insulating nature make them promising for low temperature magnetic refrigeration.

  2. Two successive magneto-structural transformations and their relation to enhanced magnetocaloric effect for Ni55.8Mn18.1Ga26.1 Heusler alloy

    Science.gov (United States)

    Li, Zhe; Xu, Kun; Zhang, Yuanlei; Tao, Chang; Zheng, Dong; Jing, Chao

    2015-10-01

    In the present work, two successive magneto-structural transformations (MSTs) consisting of martensitic and intermartensitic transitions have been observed in polycrystalline Ni55.8Mn18.1Ga26.1 Heusler alloy. Benefiting from the additional latent heat contributed from intermediate phase, this alloy exhibits a large transition entropy change ΔStr with the value of ~27 J/kg K. Moreover, the magnetocaloric effect (MCE) has been also evaluated in terms of Maxwell relation. For a magnetic field change of 30 kOe, it was found that the calculated value of refrigeration capacity in Ni55.8Mn18.1Ga26.1 attains to ~72 J/kg around room temperature, which significantly surpasses those obtained for many Ni-Mn based Heusler alloys in the same condition. Such an enhanced MCE can be ascribed to the fact that the isothermal entropy change ΔST is spread over a relatively wide temperature interval owing to existence of two successive MSTs for studied sample.

  3. Two successive magneto-structural transformations and their relation to enhanced magnetocaloric effect for Ni55.8Mn18.1Ga26.1 Heusler alloy

    Science.gov (United States)

    Li, Zhe; Xu, Kun; Zhang, Yuanlei; Tao, Chang; Zheng, Dong; Jing, Chao

    2015-01-01

    In the present work, two successive magneto-structural transformations (MSTs) consisting of martensitic and intermartensitic transitions have been observed in polycrystalline Ni55.8Mn18.1Ga26.1 Heusler alloy. Benefiting from the additional latent heat contributed from intermediate phase, this alloy exhibits a large transition entropy change ΔStr with the value of ~27 J/kg K. Moreover, the magnetocaloric effect (MCE) has been also evaluated in terms of Maxwell relation. For a magnetic field change of 30 kOe, it was found that the calculated value of refrigeration capacity in Ni55.8Mn18.1Ga26.1 attains to ~72 J/kg around room temperature, which significantly surpasses those obtained for many Ni-Mn based Heusler alloys in the same condition. Such an enhanced MCE can be ascribed to the fact that the isothermal entropy change ΔST is spread over a relatively wide temperature interval owing to existence of two successive MSTs for studied sample. PMID:26450663

  4. Surface spin-glass, large surface anisotropy, and depression of magnetocaloric effect in La0.8Ca0.2MnO3 nanoparticles

    Science.gov (United States)

    Xi, S. B.; Lu, W. J.; Wu, H. Y.; Tong, P.; Sun, Y. P.

    2012-01-01

    The surface magnetic behavior of La0.8Ca0.2MnO3 nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature TF does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer. PMID:23319829

  5. Surface spin-glass, large surface anisotropy, and depression of magnetocaloric effect in La(0.8)Ca(0.2)MnO(3) nanoparticles.

    Science.gov (United States)

    Xi, S B; Lu, W J; Wu, H Y; Tong, P; Sun, Y P

    2012-12-15

    The surface magnetic behavior of La(0.8)Ca(0.2)MnO(3) nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature T(F) does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer.

  6. Martensitic transition, inverse magnetocaloric effect and shape memory characteristics in Mn48-xCuxNi42Sn10 Heusler alloys

    Science.gov (United States)

    Liu, Changqin; Li, Zhe; Zhang, Yuanlei; Liu, Yang; Sun, Junkun; Huang, Yinsheng; Kang, Baojuan; Xu, Kun; Deng, Dongmei; Jing, Chao

    2017-03-01

    In this paper, we have systematically prepared a serials of polycrystalline Mn48-xCuxNi42Sn10 alloys (x=0, 1, 3, 5, 6, 8, 10 and 12) and investigated the influence of the Cu doping on martensitic transition (MT) as well as magnetic properties. Experimental results indicate that the MT temperature and the martensite Curie temperature (TcM) shift to high temperature with increasing the substitution of Cu (from Mn rich alloy to Ni rich alloy), while the austenite Curie temperature (TcA) is almost unchanged. It was found that the structures undergo L21 and 4O with the increasing of Cu concentration near room temperature. Therefore, the magnetostructural transition can be tuned by appropriate Cu doping in these alloys. Moreover, we mainly studied the multiple functional properties for inverse magnetocaloric effect and shape memory characteristics associated with the martensitic transition. A large positive isothermal entropy change of Mn48Ni42Sn10 was obtained, and the maximum transition entropy change achieves about 48 J/kg K as x=8. In addition, a considerable temperature-induced spontaneous strain with the value of 0.16% was obtained for Mn48Ni42Sn10 alloys.

  7. Magnetic properties and magnetocaloric effect of Gd(Ni{sub 1-x}Fe{sub x}){sub 3} crystalline compound and powder

    Energy Technology Data Exchange (ETDEWEB)

    Bajorek, Anna; Chelkowska, Grazyna; Kwiecien, Marzena [August Chelkowski Institute of Physics, University of Silesia, Katowice (Poland); Haneczok, Grzegorz [Institute of Materials Science, University of Silesia, Katowice (Poland); Chrobak, Artur

    2009-04-15

    In the paper we present and discuss magnetic properties of the Gd(Ni{sub 1-x}Fe{sub x}){sub 3} crystalline compounds and their ball-milled powders in a context of the magnetocaloric effect (MCE). Moreover, based on the obtained results, powders and composites with non-magnetic (Cu) and magnetic (Fe) additions were prepared. Magnetic quantities such as the Curie temperature, the saturation magnetization and the MCE (as a magnetic entropy change) were determined for all examined samples. In the case of the bulk crystalline compounds a partial substitution of Ni by Fe atoms causes a decrease of the saturation magnetization as well as the MCE and an increase of the Curie temperature. Samples with x ranging from 0.1 to 0.15 show the best potential for room-temperature refrigeration. Pulverization of the tested compounds leads to formation of flake-like grains with thickness less than 1{mu}m. Such grinding causes a decrease of the Curie temperature (by about 10 K) as well as the MCE (by about 50%) in a comparison with the crystalline samples. In the case of the composite with magnetic addition an enhancement of the MCE was observed. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Magneto-thermal conduction and magneto-caloric effect in poly and nano crystalline forms of multiferroic GdCrO3

    Science.gov (United States)

    Uma, S.; Philip, J.

    2014-09-01

    Gadolinium chromite, GdCrO3, belongs to the family of rare earth chromites, exhibiting multiferroism with coupling between electric polarization and magnetic ordering. It is understood that the interaction between Gd3+ and Cr3+ ions is responsible for switchable polarization in this system. Below Néel temperature the spins of Cr3+ ions interact in anti-parallel through super exchange mechanism, giving rise to antiferromagnetic ordering at around 169 K in poly and nanocrystalline phases of this material. In order to understand the nature of spin-lattice coupling and magnon-phonon interaction in the intermediate temperature range (150-250 K), the magneto-thermal conduction and magneto-caloric effect in poly and nanocrystalline forms of this material are reported. These properties show anomalies around 169 K, which is described as due to spin-phonon coupling. When particle sizes are reduced to nanometer scales, thermal conductivity decreases significantly while specific heat capacity increases. The former is explained as due to reduction in phonon mean free path and phonon scattering from nanoparticle interfaces, while the latter is ascribed to contributions from Einstein oscillators at weakly bound atoms at the interfaces of nanocrystals.

  9. Large low field magnetocaloric effect in first-order phase transition compound TlFe3Te3 with low-level hysteresis

    Science.gov (United States)

    Mao, Qianhui; Yang, Jinhu; Wang, Hangdong; Khan, Rajwali; Du, Jianhua; Zhou, Yuxing; Xu, Binjie; Chen, Qin; Fang, Minghu

    2016-09-01

    Magnetic refrigeration based on the magnetocaloric effect (MCE) is an environment-friendly, high-efficiency technology. It has been believed that a large MCE can be realized in the materials with a first-order magnetic transition (FOMT). Here, we found that TlFe3Te3 is a ferromagnetic metal with a first-order magnetic transition occurring at Curie temperature TC = 220 K. The maximum values of magnetic entropy change (Δ) along the crystallographic c-axis, estimated from the magnetization data, reach to 5.9 J kg‑1K‑1 and 7.0 J kg‑1 K‑1 for the magnetic field changes, ΔH = 0–1 T and 0–2 T, respectively, which is significantly larger than that of MCE materials with a second-order magnetic transition (SOMT). Besides the large ΔSM, the low-level both thermal and field hysteresis make TlFe3Te3 compound an attractive candidate for magnetic refrigeration. Our findings should inspire the exploration of high performance new MCE materials.

  10. Magnetocaloric effects in Mn1.35Fe0.65P1-xSix compounds

    Institute of Scientific and Technical Information of China (English)

    Geng Yao-Xiang; Tegus O; Bi Li-Ge

    2012-01-01

    The structural and magnetocaloric properties of Mn1.35Fe0.s5P1-xSix compounds are investigated. The Sisubstituted compounds,Mn1.35Fe0.65P1-xSix with x =0.52,0.54,0.55,0.56,and 0.57,are prepared by high-energy ball milling and the solid-state reaction.The X-ray diffraction shows that the compounds crystallize into the Fe2P-type hexagonal structure with space group P(6)2m.The magnetic measurements show that the Curie temperature of the compound increases from 253 K for x =0.52 to 296 K for x =0.56.The isothermal magnetic-entropy change of the Mn1.35Fe0.65P1-xSix compound decreases with the Si content increasing.The maximal value of the magnetic-entropy change is about 7.0 J/kg·K in the Mn1.35Feo.65Po.48Sio.52 compound with a field change of 1.5 T.The compound quenched in water possesses a larger magnetic entropy change and a smaller thermal hysteresis than the non-quenched samples.The thermal hysteresis of the compound is less than 3.5 K.The maximum adiabatic temperature change is about 1.4 K in the Mn1.35Feo.65P0.45Si0.55 compound with a field change of 1.48 T.

  11. Magnetocaloric effect and H gradient in bulk La(Fe,Si)13Hy magnetic refrigerants obtained by HDSH

    Science.gov (United States)

    Bez, Henrique N.; Eggert, Bruno G. F.; Lozano, Jaime A.; Bahl, Christian R. H.; Barbosa, Jader R.; Teixeira, Cristiano S.; Wendhausen, Paulo A. P.

    2015-07-01

    Results are reported on the preparation of bulk parts of La(Fe,Si)13Hy via the Hydrogen-Decrepitation-Sintering-Hydrogenation (HDSH) process. Net shape parts for application in room-temperature magnetic refrigeration have been produced in only 8 h of heat treatment which is considerably faster than the conventional ingot homogenization heat treatment of 7 days. The samples produced by HDSH showed higher amounts of hydrogen than the parts hydrogenated by the conventional method of thermal homogenization (20 h at 1423 K), milling to fine powder and subsequent hydrogenation. Hydrogenation parameters play an important role for the stability of the desired La(Fe,Si)13 phase during the process. Hydrogen desorption was seen to occur at two temperature ranges as a result of internal gradients. Dissimilar amounts of α-Fe were precipitated for different hydrogenation times. As a result, parts produced via HDSH with 2 and 4 h of hydrogenation exhibited different magnetocaloric behaviours. For a hydrogenation step of 4 h, parts with a demagnetization factor of 0.49 showed an adiabatic temperature change (ΔTad) higher than 1 K for a temperature range of 40 K with a maximum value of 1.57 K for an applied magnetic field of 1.75 T. As the duration of the hydrogenation step of the HDSH process decreased to 2 h, ΔTad was larger than 1 K for a temperature range of 24 K. However the maximum value of ΔTad at 328 K was 2.2 K, which is 37.5% larger than the maximum value for a hydrogenation period of 4 h.

  12. Coupled magnetostructural transition in Ni-Mn-V-Ga Heusler alloys and its effect on the magnetocaloric and transport properties

    Science.gov (United States)

    Devarajan, U.; Kannan, M.; Thiyagarajan, R.; Manivel Raja, M.; Rama Rao, N. V.; Singh, Sanjay; Venkateshwarlu, D.; Ganesan, V.; Ohashi, M.; Arumugam, S.

    2016-02-01

    In the present work, the magnetocaloric and transport properties of Ni2.2Mn0.72-x V x Ga1.08 (x  =  0.0, 0.04, 0.08, 0.12) magnetic shape memory alloys are investigated. The alloys show a coupled magnetostructural transition from paramagnetic austenite to ferromagnetic martensite in a composition range of 0  ⩽  x  ⩽  0.08. For higher V substitution (x  =  0.12), the martensite transition is lower than the conventional ferromagnetic transition. Large magnetic entropy change values of about 12.4, 16.2 and 19 J kg-1 K-1 and corresponding refrigeration capacities of 60.6, 82.5, and 103 J kg-1 were observed for x  =  0, 0.04 and 0.08 alloys, respectively. The above two parameters linearly increase with increasing magnetic field. The indirect adiabatic temperature change calculated from the heat capacity measurement is found to be at its maximum for x  =  0.12 at H  =  8 T. The magnetoresistance is observed to increase from 0% (x  =  0.12) to 28% (x  =  0) at the maximum field of 8 T. The Sommerfeld coefficients are almost the same for the parent and a V-doped sample, which reveals a low free electron density, and the Debye coefficients decrease with an increase in V doping, confirming the phenomenon of electron-phonon scattering. The critical exponents at second order magnetic transition for x  = 0.12 are calculated as β  =  0.482, γ  =  1.056, δ  =  3.021, which agrees closely with mean field theory.

  13. The effect of beam directivity on the inspection of anisotropic materials using ultrasonic arrays

    Science.gov (United States)

    Lane, C. J. L.; Wilcox, P. D.

    2012-05-01

    The beam directivity from an ultrasonic transducer in isotropic materials is well documented. However, beam directivities in elastically anisotropic materials and their effect on ultrasonic NDE inspection has been investigated far less extensively. In this paper, analytical and numerical finite element models are developed to predict the beam directivity in a single crystal nickel-based superalloy. This material is highly anisotropic and is used widely in the gas-turbine industry. The developed models are used to investigate the effect of the crystallographic orientation on the beam directivity. In turn, the effect of beam directivity on defect detection sensitivity and characterization capability using an ultrasonic array is demonstrated. It is shown that the effect is particularly important for the accurate sizing of small defects.

  14. Gd3Al2-xSix系合金磁热效应的研究%Study on Magnetocaloric Effects of Gd3Al2-xSix Alloys

    Institute of Scientific and Technical Information of China (English)

    生利英

    2013-01-01

    采用真空高频磁悬浮炉制备出一系列Gd3Al2-xSix (x=0,0.1,0.2,0.5,0.8)合金.通过Si对Al的部分替代,研究了Si元素微量替代对Gd3Al2合金磁热效应的影响.结果表明,Gd3Al2-xSix系合金的结构与Gd3Al2相同;随着Si含量的增加,Gd3Al2-xSix系合金的居里温度和磁热效应发生了变化,这说明Si对Al的部分替代改变了GdAl2合金的磁热效应.%A series of Gd3Al2-χSiχ, (χ=0,0.1, 0.2, 0.5, 0.8) alloys were prepared in a high-frequency floating furnace. The effects of minor substitution of Al by Si on the magnetocaloric effects of Gd3Al2 alloy were investigated. The results show that the microstructure of Gd3Al2, alloy is the same with Gd2Al2 alloy. The Cure temperature and magnetocaloric effects of Gd3Al2-χSiχ alloys change with Si content increasing. The minor addition of Si can change the magnetocaloric effects of Gd3Al2-χSiχ alloy.

  15. Improvement of magnetocaloric properties of Gd-Ge-Si alloys by alloying with iron

    Directory of Open Access Journals (Sweden)

    Erenc-Sędziak T.

    2013-01-01

    Full Text Available The influence of annealing of Gd5Ge2Si2Fex alloys at 1200°C and of alloying with various amount of iron on structure as well as thermal and magnetocaloric properties is investigated. It was found that annealing for 1 to 10 hours improves the entropy change, but reduces the temperature of maximum magnetocaloric effect by up to 50 K. Prolonged annealing of the Gd5Ge2Si2 alloy results in the decrease of entropy change due to the reduction of Gd5Ge2Si2 phase content. Addition of iron to the ternary alloy enhances the magnetocaloric effect, if x = 0.4 – 0.6, especially if alloying is combined with annealing at 1200°C: the peak value of the isothermal entropy change from 0 to 2 T increases from 3.5 to 11 J/kgK. Simultaneously, the temperature of maximum magnetocaloric effect drops to 250 K. The changes in magnetocaloric properties are related to the change in phase transformation from the second order for arc molten ternary alloy to first order in the case of annealed and/or alloyed with iron. The results of this study indicate that the minor addition of iron and heat treatment to Gd-Ge-Si alloys may be useful in improving the materials’ magnetocaloric properties..

  16. The persistence of the magnetocaloric effect in (La1-x)A(x)(0.67)Ba0.33Mn1.05O3-δ

    DEFF Research Database (Denmark)

    Ancona-Torres, Carlos Eugenio; Pryds, Nini; Kuhn, Luise Theil

    2010-01-01

    temperature, TC, and the magnetocaloric properties was investigated. The prepared samples are single phase, with space group R-3c. The lattice parameters and average A-site ionic radius, rA decrease linearly with x while the size disorder, as characterized by the variance, σ2, increases from 0.014 to 0...

  17. Applicability of scaling behavior and power laws in the analysis of the magnetocaloric effect in second-order phase transition materials

    Science.gov (United States)

    Romero-Muñiz, Carlos; Tamura, Ryo; Tanaka, Shu; Franco, Victorino

    2016-10-01

    In recent years, universal scaling has gained renewed attention in the study of magnetocaloric materials. It has been applied to a wide variety of pure elements and compounds, ranging from rare-earth-based materials to transition metal alloys, from bulk crystalline samples to nanoparticles. It is therefore necessary to quantify the limits within which the scaling laws would remain applicable for magnetocaloric research. For this purpose, a threefold approach has been followed: (a) the magnetocaloric responses of a set of materials with Curie temperatures ranging from 46 to 336 K have been modeled with a mean-field Brillouin model, (b) experimental data for Gd has been analyzed, and (c) a 3D-Ising model—which is beyond the mean-field approximation—has been studied. In this way, we can demonstrate that the conclusions extracted in this work are model-independent. It is found that universal scaling remains applicable up to applied fields, which provide a magnetic energy to the system up to 8% of the thermal energy at the Curie temperature. In this range, the predicted deviations from scaling laws remain below the experimental error margin of carefully performed experiments. Therefore, for materials whose Curie temperature is close to room temperature, scaling laws at the Curie temperature would be applicable for the magnetic field range available at conventional magnetism laboratories (˜10 T), well above the fields which are usually available for magnetocaloric devices.

  18. Magnetocaloric phenomena in Mg-ferrite nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Burianova, S; Holec, P; Plocek, J [Charles University, Faculty of Science, Department of Inorganic chemistry, Prague (Czech Republic); Poltierova-Vejpravova, J, E-mail: burianovasimona@email.c, E-mail: jana@mag.mff.cuni.c

    2010-01-01

    A comparative study of magnetocaloric effect (MCE) in superparamagnetic (SPM) regime is reported in two different types of magnesium ferrite nanostructures. The samples were prepared either by microemulsion method as MgFe{sub 2}O{sub 4} nanoparticles encapsulated in amorphous SiO{sub 2}, or as matrix-less nanoparticles using hydrothermal synthesis in supercritical water conditions. The particle diameter in all prepared samples was obtained from XRD measurements and TEM analysis. All samples show a SPM behavior above the blocking temperature, T{sub B}. The entropy change, {Delta}S was finally derived from the measurements of magnetization, M(H,T) curves at defined temperature intervals. We observed, that all samples show a broad peak of {Delta}S in the temperature range that is fairly above the T{sub B}. The values of the {Delta}S also depend on the particle size, and they are of about two orders lower than those reported in the famous giant magnetocaloric materials.

  19. Unruh effect in vacua with anisotropic scaling: Applications to multilayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Katsnelson, M.I. [Radboud University Nijmegen, Institute for Molecules and Materials, Heyndaalseweg 135, NL-6525AJ Nijmegen (Netherlands); Volovik, G.E. [Low Temperature Laboratory, School of Science and Technology, Aalto University, P.O. Box 15100, FI-00076 Aalto (Finland); L. D. Landau Institute for Theoretical Physics, Kosygina 2, 119334 Moscow (Russian Federation); Zubkov, M.A., E-mail: zubkov@itep.ru [ITEP, B.Cheremushkinskaya 25, Moscow, 117259 (Russian Federation)

    2013-09-15

    We extend the calculation of the Unruh effect to the universality classes of quantum vacua obeying topologically protected invariance under anisotropic scaling r→br, t→b{sup z}t. Two situations are considered. The first one is related to the accelerated detector which detects the electron–hole pairs. The second one is related to the system in external electric field, when the electron–hole pairs are created due to the Schwinger process. As distinct from the Unruh effect in relativistic systems (where z=1) the calculated radiation is not thermal, but has properties of systems in the vicinity of quantum criticality. The vacuum obeying anisotropic scaling can be realized, in particular, in multilayer graphene with the rhombohedral stacking. Opportunities of the experimental realization of the Unruh effect in this situation are discussed. -- Highlights: •Unruh effect in the system with anisotropic scaling (multilayer graphene) is investigated. •The accelerated detector is considered which detects the electron–hole pairs. •The system in external electric field is considered as the “accelerated vacuum”. •Unruh effect in the nonrelativistic case differs from that of the relativistic case.

  20. Determination of the magnetocaloric effect associated with martensitic transition in Ni46Cu4Mn38Sn12 and Ni5oCoMn34In15 Heusler alloys

    Institute of Scientific and Technical Information of China (English)

    Li Zhe; Jing Chao; Zhang Hao-Lei; Cao Shi-Xun; Zhang Jin-Cang

    2011-01-01

    This paper presents a study of the inverse magnetocaloric effect (MCE)corresponding to martensitic transition using various experimental approaches for Ni46Cu4Mn3sSn12 and Ni50CoMn34In,5 Heusler alloy. Through heat capacity measurements, it is found that the "giant inverse MCE" upon martensitic transition evaluated by the Maxwell relation in these alloys are unphysical results. This is due to the coexistence of both martensitic and austenitic phases, as well as thermal hysteresis during martensitic transition. However, careful study indicates that the spurious results during martensitic transition can be removed using a Clausius-Clapeyron equation based on magnetization measurements.

  1. Enhanced Magnetocaloric Effect Driven by Interfacial Magnetic Coupling in Self-Assembled Mn3O4-La(0.7)Sr(0.3)MnO3 Nanocomposites.

    Science.gov (United States)

    Vandrangi, Suresh K; Yang, Jan-Chi; Zhu, Yuan-Min; Chin, Yi-Ying; Lin, Hong-Ji; Chen, Chien-Te; Zhan, Qian; He, Qing; Chen, Yi-Chun; Chu, Ying-Hao

    2015-12-09

    Magnetic refrigeration, resulting from the magnetocaloric effect of a material around the magnetic phase-transition temperature, is a topic of great interest as it is considered to be an alternate energy solution to conventional vapor-compression refrigeration. The viability of a magnetic refrigeration system for magnetic cooling can be tested by exploiting materials in various forms, from bulk to nanostrucutres. In this study, magnetocaloric properties of self-assembled Mn3O4-La(0.7)Sr(0.3)MnO3 nanocomposites, with varying doping concentrations of Mn3O4 in the form of nanocrystals embedded in the La(0.7)Sr(0.3)MnO3 matrix, are investigated. The temperatures corresponding to the paramagnetic-to-ferromagnetic transitions are higher, and the values of change in magnetic entropy under a magnetic field of 2 T show an enhancement (highest being ∼130%) for the nanocomposites with low doping concentrations of Mn3O4, compared to that of pure La(0.7)Sr(0.3)MnO3 thin films. Relative cooling power remain close to those of La(0.7)Sr(0.3)MnO3. The enhanced magnetic phase-transition temperature and magnetocaloric effect are interpreted and evidenced in the framework of interfacial coupling between Mn3O4 and La(0.7)Sr(0.3)MnO3. This work demonstrates the potentiality of self-assembled nanostructures for magnetic cooling near room temperature under low magnetic fields.

  2. Reversible magnetocaloric effect in materials with first order phase transitions in cyclic magnetic fields: Fe48Rh52 and Sm0.6Sr0.4MnO3

    Science.gov (United States)

    Aliev, A. M.; Batdalov, A. B.; Khanov, L. N.; Kamantsev, A. P.; Koledov, V. V.; Mashirov, A. V.; Shavrov, V. G.; Grechishkin, R. M.; Kaul', A. R.; Sampath, V.

    2016-11-01

    The magnetocaloric effect (MCE) in an Fe48Rh52 alloy and Sm0.6Sr0.4MnO3 manganite was studied in cyclic magnetic fields. The adiabatic temperature change in the Fe48Rh52 alloy for a magnetic field change (ΔB) of 8 T and a frequency (f) of 0.13 Hz reaches the highest value of (ΔTad) of -20.2 K at 298 K. The magnitude of the MCE in Sm0.6Sr0.4MnO3 reaches ΔTad = 6.1 K at the same magnetic field change at 143 K. The temperature regions, where a strong MCE is exhibited in an alternating magnetic field, are bounded in both compounds. In the case of the Fe48Rh52 alloy, the temperature range for this phenomenon is bounded above by the ferromagnetic to antiferromagnetic transition temperature in the zero field condition during cooling. In the case of the Sm0.6Sr0.4MnO3 manganite, the temperature range for the MCE is bounded below by the ferromagnetic-paramagnetic transition temperature in zero field during heating. The presence of these phase boundaries is a consequence of the existence of areas of irreversible magnetic-field-induced phase transitions. It is found that the effect of long-term action of thousands of cycles of magnetization/demagnetization degrades the magnetocaloric properties of the Fe48Rh52 alloy. This can be explained by the gradual decrease in the size of the ferromagnetic domains and increasing role of the domain walls due to giant magnetostriction at the ferromagnetic to antiferromagnetic transition temperature. The initial magnetocaloric properties can be restored by heating of the material above their Curie temperature.

  3. Development of Power Electronics Based Test Platform for Characterization and Testing of Magnetocaloric Materials

    Directory of Open Access Journals (Sweden)

    Deepak Elamalayil Soman

    2015-01-01

    Full Text Available Magnetocaloric effects of various materials are getting more and more interesting for the future, as they can significantly contribute towards improving the efficiency of many energy intensive applications such as refrigeration, heating, and air conditioning. Accurate characterization of magnetocaloric effects, exhibited by various materials, is an important process for further studies and development of the suitable magnetocaloric heating and cooling solutions. The conventional test facilities have plenty of limitations, as they focus only on the thermodynamic side and use magnetic machines with moving bed of magnetocaloric material or magnet. In this work an entirely new approach for characterization of the magnetocaloric materials is presented, with the main focus on a flexible and efficient power electronic based excitation and a completely static test platform. It can generate a periodically varying magnetic field using superposition of an ac and a dc magnetic field. The scale down prototype uses a customized single phase H-bridge inverter with essential protections and an electromagnet load as actuator. The preliminary simulation and experimental results show good agreement and support the usage of the power electronic test platform for characterizing magnetocaloric materials.

  4. Effects of anisotropic thermal conductivity in magnetohydrodynamics simulations of a reversed-field pinch.

    Science.gov (United States)

    Onofri, M; Malara, F; Veltri, P

    2010-11-19

    A compressible magnetohydrodynamics simulation of the reversed-field pinch is performed including anisotropic thermal conductivity. When the thermal conductivity is much larger in the direction parallel to the magnetic field than in the perpendicular direction, magnetic field lines become isothermal. As a consequence, as long as magnetic surfaces exist, a temperature distribution is observed displaying a hotter confined region, while an almost uniform temperature is produced when the magnetic field lines become chaotic. To include this effect in the numerical simulation, we use a multiple-time-scale analysis, which allows us to reproduce the effect of a large parallel thermal conductivity. The resulting temperature distribution is related to the existence of closed magnetic surfaces, as observed in experiments. The magnetic field is also affected by the presence of an anisotropic thermal conductivity.

  5. Magnetocaloric properties of rare-earth substituted DyCrO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    McDannald, A. [Material Science and Engineering Department, University of Connecticut, Storrs, Connecticut 06269 (United States); Jain, M., E-mail: menka.jain@uconn.edu [Institute of Material Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)

    2015-07-28

    Recently, there has been a focus on the need for efficient refrigeration technology without the use of expensive or harmful working fluids, especially at temperatures below 30 K. Solid state refrigeration, based on the magnetocaloric effect, provides a possible solution to this problem. The rare-earth chromites (RCrO{sub 3}), especially DyCrO{sub 3}, with its large magnetic moment dysprosium ion, are potential candidates for such an application. The Dy{sup 3+} ordering transition at low temperatures (<10 K) likely causes a large magnetocaloric response in this material. This study investigates the possibility of tuning the magnetocaloric properties through the use of rare-earth substitution. Both Y{sup 3+} and Ho{sup 3+} substitutions were found to decrease the magnetocaloric response by disrupting the R{sup 3+} ordering. Whereas Er{sup 3+} substitution was found to increase the magnetocaloric response, likely due to an increase in the R{sup 3+} ordering temperature. The large magnetocaloric entropy change of Er{sup 3+} substituted DyCrO{sub 3} (10.92 J/kg K with a relative cooling power of 237 J/kg at 40 kOe and 5 K) indicates that this material system is well suited for low temperature (<30 K) solid state refrigeration applications.

  6. Effect of Anisotropic Velocity Structure on Acoustic Emission Source Location during True-Triaxial Deformation Experiments

    Science.gov (United States)

    Ghofrani Tabari, Mehdi; Goodfellow, Sebastian; Young, R. Paul

    2016-04-01

    Although true-triaxial testing (TTT) of rocks is now more extensive worldwide, stress-induced heterogeneity due to the existence of several loading boundary effects is not usually accounted for and simplified anisotropic models are used. This study focuses on the enhanced anisotropic velocity structure to improve acoustic emission (AE) analysis for an enhanced interpretation of induced fracturing. Data from a TTT on a cubic sample of Fontainebleau sandstone is used in this study to evaluate the methodology. At different stages of the experiment the True-Triaxial Geophysical Imaging Cell (TTGIC), armed with an ultrasonic and AE monitoring system, performed several velocity surveys to image velocity structure of the sample. Going beyond a hydrostatic stress state (poro-elastic phase), the rock sample went through a non-dilatational elastic phase, a dilatational non-damaging elasto-plastic phase containing initial AE activity and finally a dilatational and damaging elasto-plastic phase up to the failure point. The experiment was divided into these phases based on the information obtained from strain, velocity and AE streaming data. Analysis of the ultrasonic velocity survey data discovered that a homogeneous anisotropic core in the center of the sample is formed with ellipsoidal symmetry under the standard polyaxial setup. Location of the transducer shots were improved by implementation of different velocity models for the sample starting from isotropic and homogeneous models going toward anisotropic and heterogeneous models. The transducer shot locations showed a major improvement after the velocity model corrections had been applied especially at the final phase of the experiment. This location improvement validated our velocity model at the final phase of the experiment consisting lower-velocity zones bearing partially saturated fractures. The ellipsoidal anisotropic velocity model was also verified at the core of the cubic rock specimen by AE event location of

  7. Effect of strain path change on limits to ductility of anisotropic metal sheets

    DEFF Research Database (Denmark)

    Kuroda, M.; Tvergaard, Viggo

    2000-01-01

    Localized necking in thin metal sheets is analyzed by using the M-K-model approach, and the effect of a number of different non-proportional strain paths prior to the occurrence flow localization are considered. The analyses account for plastic anisotropy, using four different anisotropic...... of the anisotropic plasticity models, and it is shown that elastic straining plays a large role, as the stresses quickly move from one point of the yield surface to another. When the load is removed between steps, the stress point moves in a different manner, which results in quite different flow localization...... plasticity models to fit a set of experimental data for cold-rolled steel sheet. The predicted forming limit diagrams show strong dependence on whether or not the load on the sheet is removed between two load steps on a non-proportional strain path. This dependence is investigated in detail for one...

  8. Necking of anisotropic micro-films with strain-gradient effects

    Institute of Scientific and Technical Information of China (English)

    Brian Nyvang Legarth

    2008-01-01

    Necking of stubby micro-films of aluminum is investigated numerically by considering tension of a speci-men with an initial imperfection used to onset localisation. Plastic anisotropy is represented by two different yield cri-teria and strain-gradient effects are accounted for using the visco-plastic finite strain model. Furthermore, the model is extended to isotropic anisotropic hardening (evolving aniso-tropy). For isotropic hardening plastic anisotropy affects the predicted overall nominal stress level, while the peak stress remains at an overall logarithmic strain corresponding to the hardening exponent. This holds true for both local and non-local materials. Anisotropic hardening delays the point of maximum overall nominal stress.

  9. Cyclotron Line Features from Near-Critical Fields II on the Effect of Anisotropic Radiation Fields

    CERN Document Server

    Araya-Gochez, R A; Araya-Gochez, Rafael A.; Harding, Alice K.

    2000-01-01

    We assess the impact of radiation anisotropy on the line shapes that result from relativistic magnetic Compton scattering in the low-density/high-field regime. A Monte Carlo implementation of radiation transport allows for spatial diffusion of photons in arbitrary geometries and accounts for relativistic angular redistribution. The cross section includes natural line widths and photon "spawning" from up to fourth harmonic photons. In our first paper we noted that even if the photon injection is isotropic a strongly anisotropic radiation field rapidly ensues. We now investigate the angular distribution of cyclotron spectra emerging from an internally irradiated magnetized plasma with a prescribed global geometry (either cylindrical or plane parallel) and the effects of anisotropic photon injection on the line shapes. Varying the input angular distribution permits a better understanding of the line formation process in more realistic scenarios where the radiative mechanisms are influenced by the intrinsic aniso...

  10. Saving Moore’s Law Down To 1 nm Channels With Anisotropic Effective Mass

    Science.gov (United States)

    Ilatikhameneh, Hesameddin; Ameen, Tarek; Novakovic, Bozidar; Tan, Yaohua; Klimeck, Gerhard; Rahman, Rajib

    2016-08-01

    Scaling transistors’ dimensions has been the thrust for the semiconductor industry in the last four decades. However, scaling channel lengths beyond 10 nm has become exceptionally challenging due to the direct tunneling between source and drain which degrades gate control, switching functionality, and worsens power dissipation. Fortunately, the emergence of novel classes of materials with exotic properties in recent times has opened up new avenues in device design. Here, we show that by using channel materials with an anisotropic effective mass, the channel can be scaled down to 1 nm and still provide an excellent switching performance in phosphorene nanoribbon MOSFETs. To solve power consumption challenge besides dimension scaling in conventional transistors, a novel tunnel transistor is proposed which takes advantage of anisotropic mass in both ON- and OFF-state of the operation. Full-band atomistic quantum transport simulations of phosphorene nanoribbon MOSFETs and TFETs based on the new design have been performed as a proof.

  11. Room temperature magnetocaloric effect and refrigerant capacitance in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanotube arrays

    Energy Technology Data Exchange (ETDEWEB)

    Kumaresavanji, M., E-mail: vanji.hplt@gmail.com; Sousa, C. T.; Pires, A.; Pereira, A. M.; Araujo, J. P. [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Porto (Portugal); Lopes, A. M. L. [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Porto (Portugal); CFNUL, University of Lisbon, Lisbon (Portugal)

    2014-08-25

    High aspect ratio La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanotube (NT) arrays have been synthesized using nitrates based sol-gel precursor by nanoporous anodized aluminum oxide template assisted method. Their phase purity and microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Magnetocaloric effect (MCE) of as prepared NTs was investigated by means of field dependence magnetization measurements. Significant magnetic entropy change, −△S{sub M} = 1.6 J/kg K, and the refrigerant capacitance, RC = 69 J/kg, were achieved near the transition temperature at 315 K for 5 T. For comparison, a bulk sample was also prepared using the same precursor solution which gives a value of −△S{sub M} = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △S{sub M} value, the NTs present an expanded temperature dependence of −△S{sub M} curves that spread over a broad temperature range and assured to be appropriate for active magnetic refrigeration. The diminutive MCE observed in manganite NTs is explained by the increased influence of surface sites of nanograins which affect the structural phase transition occurred by external magnetic field due to the coupling between magnetism and the lattice in manganese perovskites. Our report paves the way for further investigation in 1D manganite nanostructured materials towards applications in such magnetic refrigeration technology or even on hyperthermia/drug delivery.

  12. Magnetocaloric effect in pristine and Bi-doped Pr0.6Sr0.4MnO3 manganite

    Science.gov (United States)

    Daivajna, Mamatha D.; Rao, Ashok

    2016-11-01

    Near room temperature, magnetocaloric effect in pristine and Bi-doped Pr0.6Sr0.4MnO3 manganites has been studied using in-field heat capacity measurements. The Debye temperature (θD) for the pristine sample was estimated to be 522 K and its value increases to 530 K for the Bi-doped sample with x=0.05. The entropy associated with paramagnetic (PM) to ferromagnetic (FM) transition is found to be 2.4 J/mol K and 2.3 J/mol K for x=0 and 0.05 compositions respectively. The estimated values of adiabatic temperature ∆Tad for the samples with x=0 and x=0.05 are respectively 2.2 K and 1.9 K for 0-6 Tesla. The maximum isothermal change in entropy, ∆SM for the sample Pr0.6Sr0.4MnO3 with transition temperature 306 K is found to be 2.7 J/kg-K with application of external magnetic field of 2 T and for Bi-doped sample (with x=0.05) the isothermal change in entropy reduces to 2.0 J/kg-K. The calculated maximum values of the isothermal entropy changes, ∆SM for the pristine sample, vary in the range 1.7-3.9 J/kg-K for a magnetic field change of 1-6 T. The present results suggest that these compounds can be possible candidates as magnetic refrigerants. This results in a large relative cooling power (RCP) around 93.5 J kg-1 K for the pristine sample under an application of magnetic field of 2 T. On contrary, with Bi-doping, RCP decreases to 56 J kg-1 K at external field of 2 T.

  13. Magnetocaloric effect and magnetothermopower in the room temperature ferromagnet Pr0.6Sr0.4MnO3

    Science.gov (United States)

    Maheswar Repaka, D. V.; Tripathi, T. S.; Aparnadevi, M.; Mahendiran, R.

    2012-12-01

    We have investigated magnetization (M), magnetocaloric effect (MCE), and magnetothermopower (MTEP) in polycrystalline Pr0.6Sr0.4MnO3, which shows a second-order paramagnetic to ferromagnetic transition near room temperature (TC = 305 K). However, field-cooled M(T) within the long range ferromagnetic state shows an abrupt decrease at TS = 86 K for μ0H inverse MCE) at TS. ΔSm = -2.185 J/kg K (-3.416 J/kg K) with refrigeration capacity RC = 43.4 J/kg (103.324 J/kg) for field change of μ0ΔH = 1.5 T (3 T) at TC = 304 K is one of the largest values reported in manganites near room temperature. Thermopower (Q) is negative from 350 K to 20 K, which shows a rapid decrease at TC and a small cusp around TS in zero field. The MTEP [ΔQ/Q(0)] reaches a maximum value of 25% for μ0ΔH = 3 T around TC, which is much higher than 15% dc magnetoresistance for the same field change. A linear relation between MTEP and magnetoresistance and between ΔSm and ΔQ are found near TC. Further, ac magnetotransport in low dc magnetic fields (μ0 H ≤ 0.1 T), critical analysis of the paramagnetic to ferromagnetic transition, and scaling behavior of ΔSm versus a reduced temperature under different magnetic fields are also reported. Coexistence of large magnetic entropy change and magnetothermopower around room temperature makes this compound interesting for applications.

  14. Fluid-like elasticity induced by anisotropic effective mass density

    DEFF Research Database (Denmark)

    Ma, Guancong; Fu, Caixing; Wang, Guanghao

    medium calculation reveals that the indefinite effective mass density (positive along one spatial direction, but negative along another) is responsible to this exotic behavior. Experiments show good agreement with theoretical predictions and simulations. Our findings can see applications in many...

  15. Effect of R substitution on magnetic properties and magnetocaloric effects of La1-xRxFe11.5Si1.5 compounds with R=Ce, Pr and Nd

    Institute of Scientific and Technical Information of China (English)

    Shen Jun; Li Yang-Xian; Sun Ji-Rong; Shen Bao-Gen

    2009-01-01

    Magnetic properties and magnetocaloric effects of La1-xRxFe11.5Sil.5 (R=Pr, (0 ≤ x ≤ 0.5); R = Ce and Nd, (0 ≤ x ≤ 0.3)) compounds are investigated. Partially replacing La with R = Ce, Pr and Nd in La1-xRxFe11.5Si1.5 leads to a reduction in Curie temperature due to the lattice contraction. The substitution of R for La causes an enhancement in field-induced itinerant electron metamagnetic transition, which leads to a remarkable increase in magnetic entropy change △Sm and also in hysteresis loss. However, a high effective refrigerant capacity Rceff is still maintained in La1-xPxFe11.5Si1.5. In the present samples, a large △Sm and a high Rceff have been achieved simultaneously.

  16. Effective dielectric response of graded composite materials containing anisotropic particles

    Institute of Scientific and Technical Information of China (English)

    Sang Zhi-Fang; Li Zhen-Ya

    2005-01-01

    The effective dielectric response of granular composites, in which spheroidal particles with graded shells are randomly distributed in a host matrix, is investigated. General expressions for the effective dielectric constant of the composites and partial resonant condition are obtained in the dilute limit by use of a quasi-static approximation. In particular, spheroidal particles with a power-law gradation profile in the shells are studied in detail. We find that, by adjusting the dielectric gradient profile in the shells, the shape and structure of particles, it is possible to enhance the effective dielectric constant of the composite and to realize partial resonance. Under the partial resonant conditions,the coated spheroidal particles with graded shells within the host matrix can be regarded as equivalent homogeneous spheroids embedded in the same host. The equivalent spheroids have the same dielectric constant as the original cores and semiaxes equal to those of the original shells: i.e., the partial resonant system behaves as if the cores of the particles were enlarged and the shells were absent.

  17. Mesh locking effects in the finite volume solution of 2-D anisotropic diffusion equations

    Science.gov (United States)

    Manzini, Gianmarco; Putti, Mario

    2007-01-01

    Strongly anisotropic diffusion equations require special techniques to overcome or reduce the mesh locking phenomenon. We present a finite volume scheme that tries to approximate with the best possible accuracy the quantities that are of importance in discretizing anisotropic fluxes. In particular, we discuss the crucial role of accurate evaluations of the tangential components of the gradient acting tangentially to the control volume boundaries, that are called into play by anisotropic diffusion tensors. To obtain the sought characteristics from the proposed finite volume method, we employ a second-order accurate reconstruction scheme which is used to evaluate both normal and tangential cell-interface gradients. The experimental results on a number of different meshes show that the scheme maintains optimal convergence rates in both L2 and H1 norms except for the benchmark test considering full Neumann boundary conditions on non-uniform grids. In such a case, a severe locking effect is experienced and documented. However, within the range of practical values of the anisotropy ratio, the scheme is robust and efficient. We postulate and verify experimentally the existence of a quadratic relationship between the anisotropy ratio and the mesh size parameter that guarantees optimal and sub-optimal convergence rates.

  18. The effect of boron doping on crystal structure, magnetic properties and magnetocaloric effect of DyCo2

    Science.gov (United States)

    Wang, C. L.; Liu, J.; Mudryk, Y.; Gschneidner, K. A.; Long, Y.; Pecharsky, V. K.

    2016-05-01

    The magnetic properties and magnetic entropy changes of DyCo2Bx (x=0, 0.05, 0.1, and 0.2) alloys were investigated. The Curie temperature (TC) increases with increasing B concentration. The frequency dependence of ac magnetic susceptibility of DyCo2 caused by the narrow domain wall pinning effect is depressed by B doping, but the coercivity and the magnetic viscosity are prominently increased in the B doped alloys. The magnetic transition nature of DyCo2Bx changes from the first-order to the second-order with increasing x, which leads to the decrease of the maximum magnetic entropy change. However, the relative cooling power (RCP) of DyCo2 and the B doped alloys remains nearly constant.

  19. Brewster effect in metafilms composed of bi-anisotropic split-ring resonators

    CERN Document Server

    Tamayama, Yasuhiro

    2015-01-01

    The Brewster effect is extended to single-layer metafilms. In contrast to bulk media, the Brewster effect in metafilms can be realized by tailoring the radiation pattern of a distribution of meta-atoms rather than the effective medium parameters. A metafilm composed of bi-anisotropic split-ring resonators is designed based on the theory, and its characteristics are numerically analyzed. The simulation demonstrates that there exists a condition for which the polarization of the reflected wave becomes independent of the incident polarization at a particular angle of incidence.

  20. Simulations of the anisotropic kinetic and magnetic alpha effects

    CERN Document Server

    Brandenburg, A

    2007-01-01

    The validity of a closure called the minimal tau approximation (MTA), is tested in the context of dynamo theory, wherein triple correlations are assumed to provide relaxation of the turbulent electromotive force. Under MTA, the alpha effect in mean field dynamo theory becomes proportional to a relaxation time scale multiplied by the difference between kinetic and current helicities. It is shown that the value of the relaxation time is positive and, in units of the turnover time at the forcing wavenumber, it is of the order of unity. It is quenched by the magnetic field -- roughly independently of the magnetic Reynolds number. However, this independence becomes uncertain at large magnetic Reynolds number. Kinetic and current helicities are shown to be dominated by large scale properties of the flow.

  1. Magnetocaloric effect and temperature coefficient of resistance of La0.85Ag0.15MnO3 epitaxial thin films obtained by polymer-assisted deposition

    Directory of Open Access Journals (Sweden)

    Cobas Acosta R.

    2014-07-01

    Full Text Available We report the magnetocaloric effects and temperature coefficient of resistance (TCR of La0.85Ag0.15MnO3 epitaxial thin films grown on single-crystal substrates of LaAlO3 (001 and SrTiO3 (001 using the chemical solution approach of polymer-assisted deposition (PAD. The film thicknesses are in the range 30-35 nm. Magnetocaloric effects, with entropy changes of -2.14 J/kg.K, in the case of the LaAlO3 substrate and -2.72 J/kg.K for the SrTiO3 substrate, (corresponding to a magnetic field variation of 2T were obtained at room temperature. The refrigeration capacity at this field variation reached large values of 125 J/kg and 216 J/kg, indicating that these films prepared by PAD have the potential for microcooling applications. The temperature coefficient of resistance has been calculated from the resistivity measurements. A maximum TCR value of 3.01 % K-1 was obtained at 309 K, which shows that these films also have potential as uncooled thermometers for bolometric applications.

  2. Investigation of magnetocaloric effect in La0.45Pr0.25Ca0.3MnO3 by magnetic, differential scanning calorimetry and thermal analysis

    Science.gov (United States)

    Aparnadevi, M.; Barik, S. K.; Mahendiran, R.

    2012-10-01

    We investigated magnetocaloric effect in La0.45Pr0.25Ca0.3MnO3 by direct methods (changes in temperature and latent heat) and indirect method (magnetization isotherms). This compound undergoes a first-order paramagnetic to ferromagnetic transition with TC=200 K upon cooling. The paramagnetic phase becomes unstable and it transforms into a ferromagnetic phase under the application of magnetic field, which results in a field-induced metamagnetic transition (FIMMT). The FIMMT is accompanied by release of latent heat and temperature of the sample as evidenced from differential scanning calorimetry and thermal analysis experiments. A large magnetic entropy change of ΔSm=-7.2 J kg-1 K-1 at T=212.5 K and refrigeration capacity of 228 J kg-1 are found for a field change of ΔH=5 T. It is suggested that destruction of magnetic polarons and growth of ferromagnetic phase accompanied by a lattice volume change with increasing magnetic field is responsible for the large magnetocaloric effect in this compound.

  3. Large magnetocaloric effect in Ln{sub 0.5}Ca{sub 0.5}MnO{sub 3} (Ln=Gd, DY) compounds: Conseqence of magnetic precursor effect of rare earth ions

    Energy Technology Data Exchange (ETDEWEB)

    Das, Kalipada, E-mail: kalipada.das@saha.ac.in; Paramanik, Tapas; Das, I.

    2015-01-15

    Magnetic, specific heat and magnetocaloric studies have been performed on rare earth calcium manganites; Ln{sub 0.5}Ca{sub 0.5}MnO{sub 3} (Ln=Gd, Dy). The observed isothermal magnetic entropy change is fairly large at low temperature in the manganites family, which is attributed to the magnetic precursor effect of rare-earth ions. For Gd{sub 0.5}Ca{sub 0.5}MnO{sub 3}, the isothermal magnetic entropy change (−ΔS) at 4 K, obtained for 7 T magnetic field, is as high as 22.8 J/kg K. On the other hand, −ΔS is 8.5 J/kg K for Dy{sub 0.5}Ca{sub 0.5}MnO{sub 3}. The large value of magnetic entropy change at the cryogenic temperature range for these compounds is interesting from application point of view. - Highlights: • No long range magnetic ordering of Gd{sub 0.5}Ca{sub 0.5}MnO{sub 3} and Dy{sub 0.5}Ca{sub 0.5}MnO{sub 3} has been observed in magnetization measurement down to T=2 K still these compounds show large magnetocaloric effect. • Specific heat of the compounds in absence of magnetic field increases at low temperature (down to 3 K). • Results are analyzed considering magnetic precursor effect of rare earth ions (Gd and Dy ions)

  4. Effects of anisotropic winds on massive stars evolution

    CERN Document Server

    Cyril, Georgy; André, Maeder

    2010-01-01

    Whenever stars are rotating very fast ($\\Omega/\\Omega_\\mathrm{crit} > 0.7$, with $\\Omega_\\mathrm{crit}$ the Keplerian angular velocity of the star accounting for its deformation) radiative stellar winds are enhanced in polar regions. This theoretical prediction is now confirmed by interferometric observations of fast rotating stars.} Polar winds remove less angular momentum than spherical winds and thus allow the star to keep more angular momentum. We quantitatively assess the importance of this effect. First we use a semi-analytical approach to estimate the variation of the angular momentum loss when the rotation parameter increases. Then we compute complete 9 M$_\\odot$ stellar models at very high angular velocities (starting on the ZAMS with $\\Omega/\\Omega_\\mathrm{crit} = 0.8$ and reaching the critical velocity during the Main Sequence) with and without radiative wind anisotropies. When wind anisotropies are accounted for, the angular momentum loss rate is reduced by less than $4%$ for $\\Omega/\\Omega_\\mathr...

  5. Effect of Fe substitution on magnetocaloric effect in metamagnetic boron-carbide ErNi{sub 2−x}Fe{sub x}B{sub 2}C compounds

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yikun, E-mail: zhangyk@epm.neu.edu.cn [Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110004 (China); Yang, Baijun [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2014-10-15

    Highlights: • Magnetism and magnetocaloric effect in ErNi{sub 2−x}Fe{sub x}B{sub 2}C were studied. • Ni site Fe substitution can reduce the magnetic hysteresis of ErNi{sub 2}B{sub 2}C. • The origin of MCE and its potential application in ErNi{sub 2−x}Fe{sub x}B{sub 2}C were discussed. - Abstract: The magnetic properties and magnetocaloric effect (MCE) in ErNi{sub 2−x}Fe{sub x}B{sub 2}C have been studied. Substitution of Fe for Ni lowered the magnetic transition temperature T{sub M}, and reduced the magnetic hysteresis of ErNi{sub 2}B{sub 2}C. An inverse MCE was observed under low magnetic field and at low temperatures, which is attributed to the nature of antiferromagnetic state for the present ErNi{sub 2−x}Fe{sub x}B{sub 2}C compounds. A normal MCE was observed under higher magnetic field changes, which is related to a field-induced first order metamagnetic transition from antiferromagnetic to ferromagnetic state. The maximum values of magnetic entropy change −ΔS{sub M}{sup max} are 14.5, 12.7, and 10.6 J/kg K with a magnetic field change of 0–70 kOe for x = 0, 0.1, and 0.2 in ErNi{sub 2−x}Fe{sub x}B{sub 2}C, respectively.

  6. A giant magnetocaloric effect with a tunable temperature transition close to room temperature in Na-deficient La0.8Na0.2-x□xMnO3 manganites.

    Science.gov (United States)

    Wali, M; Skini, R; Khlifi, M; Dhahri, E; Hlil, E K

    2015-07-28

    A giant magnetocaloric effect induced by sodium-deficiency in a La0.8Na0.2-x□xMnO3 (0.00 ≤ x ≤ 0.15) polycrystalline sample is reported in the present research work. The ability to tune the temperature transition close to room temperature is revealed to be possible by changing the sodium-deficiency content as well. All samples were synthesized using solid-solid reaction. X-ray diffraction and magnetization measurements were performed to investigate their crystallographic structure and magnetocaloric properties. A rhombohedral structure with the R3[combining macron]c space group is deduced from pattern diffraction refinement of all samples. A second-order magnetic phase transition from the ferromagnetic to the paramagnetic state at the Curie temperature (Tc) is observed. Such a Tc decreased from 335 to 260 K when the sodium deficiency rate increased. Besides, the magnetic entropy change and the related Relative Cooling Power (RCP) values, sensitive to sodium-deficiency, were estimated. The magnetic entropy change ranges increased from 2.38 J kg(-1) K(-1) to 3.48 J kg(-1) K(-1) under a magnetic field of 2 T, whereas the RCP varied from 210 to 235 J kg(-1) under an applied magnetic field of 5 T, when x increased from 0.00 to 0.15. The comparison of the values reported in the reference Gd material underlines that the proposed oxide material has substantial advantages for magnetic refrigeration.

  7. Effect of trivalent rare earth doping on magnetic and magnetocaloric properties of Pr0.5(Ce,Eu,Y)0.1Sr0.4MnO3 manganites

    Science.gov (United States)

    Sakka, A.; M'nassri, R.; Chniba-Boudjada, N.; Ommezzine, M.; Cheikhrouhou, A.

    2016-06-01

    Experimental studies of the structural, magnetic and magnetocaloric properties of the three compounds Pr0.5X0.1Sr0.4MnO3 (X = Ce, Eu and Y) are reported. Our samples were synthesized using the Pechini sol-gel method. X-ray powder diffraction at room temperature indicates that our materials crystallize in the orthorhombic structure with Pbnm space group. The compounds undergo a second-order magnetic transition from paramagnetic to ferromagnetic state around their own Curie temperatures T C ~ 310, 270 and 230 K for X = Ce, Eu and Y, respectively. A considerable magnetocaloric effect (MCE) is observed around room temperature. The maximum values of magnetic entropy change ∆ S max are 3.54, 3.81 and 2.99 J/kgK for the samples with X = Ce, Eu and Y, respectively, when a magnetic field of 5 T was applied. The relative cooling power (RCP) values for the corresponding materials are 246.60, 261.66 and 298 J/kg. It is shown that for Pr0.5X0.1Sr0.4MnO3 the exponent n and the magnetic entropy change follow a master curve behavior. With the universal scaling curve, the experimental ∆ S at several temperatures and fields can be extrapolated.

  8. Quantum signatures of a molecular nanomagnet in direct magnetocaloric measurements.

    Science.gov (United States)

    Sharples, Joseph W; Collison, David; McInnes, Eric J L; Schnack, Jürgen; Palacios, Elias; Evangelisti, Marco

    2014-10-22

    Geometric spin frustration in low-dimensional materials, such as the two-dimensional kagome or triangular antiferromagnetic nets, can significantly enhance the change of the magnetic entropy and adiabatic temperature following a change in the applied magnetic field, that is, the magnetocaloric effect. In principle, an equivalent outcome should also be observable in certain high-symmetry zero-dimensional, that is, molecular, structures with frustrated topologies. Here we report experimental realization of this in a heptametallic gadolinium molecule. Adiabatic demagnetization experiments reach ~200 mK, the first sub-Kelvin cooling with any molecular nanomagnet, and reveal isentropes (the constant entropy paths followed in the temperature-field plane) with a rich structure. The latter is shown to be a direct manifestation of the trigonal antiferromagnetic net structure, allowing study of frustration-enhanced magnetocaloric effects in a finite system.

  9. In-plane anisotropic converse magnetoelectric coupling effect in FeGa/polyvinylidene fluoride heterostructure films

    Science.gov (United States)

    Zuo, Zhenghu; Zhan, Qingfeng; Dai, Guohong; Chen, Bin; Zhang, Xiaoshan; Yang, Huali; Liu, Yiwei; Li, Run-Wei

    2013-05-01

    We investigated the converse magnetoelectric (CME) effect in the Fe81Ga19/polyvinylidene fluoride (PVDF) heterostructure films. A weak in-plane uniaxial magnetic anisotropy was observed in the as-deposited magnetostrictive FeGa films. When a positive (negative) electric field is applied on the ferroelectric PVDF substrates, both the coercivity and the squareness of magnetic hysteresis loops of FeGa films for the magnetic field parallel to the easy axis become larger (smaller), but for the magnetic field parallel to the hard axis the coercivity and the remanence get smaller (larger), indicating an anisotropic CME effect in FeGa/PVDF heterostructure films.

  10. Extrinsic spin Hall effect from anisotropic Rashba spin-orbit coupling in graphene

    Science.gov (United States)

    Yang, H.-Y.; Huang, Chunli; Ochoa, H.; Cazalilla, M. A.

    2016-02-01

    We study the effect of anisotropy of the Rashba coupling on the extrinsic spin Hall effect due to spin-orbit active adatoms on graphene. In addition to the intrinsic spin-orbit coupling, a generalized anisotropic Rashba coupling arising from the breakdown of both mirror and hexagonal symmetries of pristine graphene is considered. We find that Rashba anisotropy can strongly modify the dependence of the spin Hall angle on carrier concentration. Our model provides a simple and general description of the skew scattering mechanism due to the spin-orbit coupling that is induced by proximity to large adatom clusters.

  11. Interface crack growth for anisotropic plasticity with non-normality effects

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Legarth, Brian Nyvang

    2007-01-01

    elastic–viscoplastic material model is applied, using an anisotropic yield criterion, and in each case analyzed the effect of non-normality is compared with results for the standard normality flow rule. Due to the mismatch of elastic properties across the interface the corresponding elastic solution has...... an oscillating stress singularity, and with conditions of small scale yielding this solution is applied as boundary conditions on the outer edge of the region analyzed. Crack growth resistance curves are calculated numerically, and the effect of the near-tip mode mixity on the steady-state fracture toughness...

  12. Orientation dependent size effects in single crystalline anisotropic nanoplates with regard to surface energy

    Energy Technology Data Exchange (ETDEWEB)

    Assadi, Abbas, E-mail: assadi@aut.ac.ir; Salehi, Manouchehr, E-mail: msalehi@aut.ac.ir; Akhlaghi, Mehdi, E-mail: makhlagi@aut.ac.ir

    2015-07-17

    In this work, size dependent behavior of single crystalline normal and auxetic anisotropic nanoplates is discussed with consideration of material surface stresses via a generalized model. Bending of pressurized nanoplates and their fundamental resonant frequency are discussed for different crystallographic directions and anisotropy degrees. It is explained that the orientation effects are considerable when the nanoplates' edges are pinned but for clamped nanoplates, the anisotropy effect may be ignored. The size effects are the highest when the simply supported nanoplates are parallel to [110] direction but as the anisotropy gets higher, the size effects are reduced. The orientation effect is also discussed for possibility of self-instability occurrence in nanoplates. The results in simpler cases are compared with previous experiments for nanowires but with a correction factor. There are still some open questions for future studies. - Highlights: • Size effects in single crystalline anisotropic nanoplates are discussed. • A generalized model is established containing some physical assumptions. • Orientation dependent size effects due to material anisotropy are explained. • Bending, instability and frequencies are studied at normal/auxetic domain.

  13. Anisotropic Magnetoresistance Effect in Amorphous and Nanocrystalline Fe(Cu,Nb)-Si-B Alloys

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The magnetoresistance effect and magnetic properties in amorphous and nanocrystalline Fe(Cu, Nb)-Si-B ribbons have been investigated. It was observed that the anisotropic magnetoresistance (AMR) of nanocrystalline alloy is much smaller than that of amorphous alloy, indicating that the anisotropy of nanocrystalline alloy becomes smaller after crystallizing, and the smallest AMR is coincident with the excellent soft magnetic characteristics. It is believed that the smaller magnetic crystalline anisotropy is the origin of the excellent soft magnetic characteristics of nanocrystalline alloy.

  14. Effect of Quantum Fluctuation on Two-Dimensional Spatially Anisotropic Heisenberg Antiferromagnet with Integer Spin

    Institute of Scientific and Technical Information of China (English)

    JI An-Chun; TIAN Guang-Shan

    2006-01-01

    In the present paper, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuation in a two-dimensional spatially anisotropic Heisenberg antiferromagnet with integer spin S. Previously, someauthors computed this quantity by the mean-field theory based on the Schwinger boson representation of spin operators.However, for S = 1, their result is much less than the one derived by numerical calculations. By taking the effect ofquantum spin fluctuation into consideration, we are able to produce a greatly improved result.

  15. Investigation of the Effects of Anisotropic Flow of Pore Water and Multilayered Soils on Three-Dimensional Consolidation Characteristics

    Directory of Open Access Journals (Sweden)

    Arpan Laskar

    2017-01-01

    Full Text Available Many practical engineering problems are seriously different from the assumptions which are considered for one-dimensional consolidation test and need to concentrate on three-dimensional consolidation of soil under different boundary conditions. In this study three-dimensional consolidation tests are performed with four different anisotropic flow conditions of pore water and fifteen different combinations of horizontal layered soils. Twelve different three-dimensional consolidation tests are also performed with different soils, surrounded by anisotropic vertical soil layers on two opposite sides. From these studies, it is observed that the anisotropic flow of pore water does not have any effect on initial and final surface settlement of soil but has a significant effect during the consolidation process. The anisotropic flow of pore water during the consolidation process has an immense effect on the coefficient of consolidation. Horizontal layered soil has a great effect on both surface settlement and the rate of settlement. Vertical soil layers on two opposite sides of consolidative soil have an immense effect on the horizontal movements of consolidating soil, finally affecting the resultant vertical settlement of soil. Vertical anisotropic surrounding soil layers also have an effect on the rate of consolidation settlement.

  16. Thermodynamic and magnetocaloric properties of geometrically frustrated Ising nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Žukovič, M., E-mail: milan.zukovic@upjs.sk

    2015-01-15

    Thermodynamic and magnetocaloric properties of geometrically frustrated Ising spin clusters of selected shapes and sizes are studied by exact enumeration. In the ground state the magnetization and the entropy show step-wise variations with an applied magnetic field. The number of steps, their widths and heights depend on the cluster shape and size. While the character of the magnetization plateau heights is always increasing, the entropy is not necessarily decreasing function of the field, as one would expect. For selected clusters showing some interesting ground-state properties, the calculations are extended to finite temperatures by exact enumeration of densities of states in the energy-magnetization space. In zero field the focus is laid on a peculiar behavior of some thermodynamic quantities, such as the entropy, the specific heat and the magnetic susceptibility. In finite fields various thermodynamic functions are studied in the temperature-field parameter plane and particular attention is paid to the cases showing an enhanced magnetocaloric effect. The exact results on the finite clusters are compared with the thermodynamic limit behavior obtained from Monte Carlo simulations. - Highlights: • We study frustrated spin clusters of various shapes and sizes on a triangular lattice. • Ground-state magnetizations and entropies in a field are exactly determined. • Peculiar behavior of some quantities is studied in zero field and finite temperatures. • Enhanced magnetocaloric effect is observed at relatively low temperatures and fields. • Thermodynamic limit behavior is estimated by Monte Carlo simulations.

  17. Magnetocaloric pump. [for cryogenic fluids

    Science.gov (United States)

    Brown, G. V. (Inventor)

    1974-01-01

    A vessel having inlet and outlet valves is disposed in a container with a fluid to be pumped which may be evolved from a liquid in the container below the vessel. A magnetocaloric substance is disposed in the vessel and causes fluid vapor in the vessel to expand and be expelled through the outlet valve. Vapor is drawn in through the inlet valve as the substance cools. The inlet valves may be one-way check valves or may be solenoid valves energized at appropriate times by timing circutis. A timer controlled heating element may also be disposed in the vessel to operate in conjunction with the magnetic field.

  18. Dufour and Soret effects on MHD flow of Williamson fluid over an infinite rotating disk with anisotropic slip

    CERN Document Server

    Khan, Najeeb Alam

    2016-01-01

    This study deals with the investigation of MHD flow of Williamson fluid over an infinite rotating disk with the effects of Soret, Dufour, and anisotropic slip. The anisotropic slip and the Soret and Dufour effects are the primary features of this study, which greatly influence the flow, heat and mass transport properties. In simultaneous appearance of heat and mass transfer in a moving fluid, the mass flux generated by temperature gradients is known as the thermal-diffusion or Soret effect and the energy flux created by a composition gradient is called the diffusion-thermo or Dufour effect, however, difference in slip lengths in streamwise and spanwise directions is named as anisotropic slip. The system of nonlinear partial differential equations (PDEs), which governs the flow, heat and mass transfer characteristics, is transformed into ordinary differential equations (ODEs) with the help of von K\\'arm\\'an similarity transformation. A numerical solution of the complicated ODEs is carried out by a MATLAB routi...

  19. Effects of anisotropic thermal conduction on wind properties in hot accretion flow

    CERN Document Server

    Bu, De-Fu; Yuan, Ye-Fei

    2016-01-01

    Previous works have clearly shown the existence of winds from black hole hot accretion flow and investigated their detailed properties. In extremely low accretion rate systems, the collisional mean-free path of electrons is large compared with the length-scale of the system, thus thermal conduction is dynamically important. When the magnetic field is present, the thermal conduction is anisotropic and energy transport is along magnetic field lines. In this paper, we study the effects of anisotropic thermal conduction on the wind production in hot accretion flows by performing two-dimensional magnetohydrodynamic simulations. We find that thermal conduction has only moderate effects on the mass flux of wind. But the energy flux of wind can be increased by a factor of $\\sim 10$ due to the increase of wind velocity when thermal conduction is included. The increase of wind velocity is because of the increase of driving forces (e.g. gas pressure gradient force and centrifugal force) when thermal conduction is includ...

  20. Magnetic anisotropic effects and electronic correlations in MnBi ferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Antropov, VP; Antonov, VN; Bekenov, LV; Kutepov, A; Kotliar, G

    2014-08-07

    The electronic structure and numerous magnetic properties of MnBi magnetic systems are investigated using local spin density approximation (LSDA) with on-cite Coulomb correlations (LSDA+U) included. We show that the inclusion of Coulomb correlations provides a much better description of equilibrium magnetic moments on Mn atoms as well as the magnetic anisotropy energy behavior with temperature and magneto-optical effects. We found that the inversion of the anisotropic pairwise exchange interaction between Bi atoms is responsible for the observed spin reorientation transition at 90 K. This interaction appears as a result of strong spin orbit coupling on Bi atoms, large magnetic moments on Mn atoms, significant p-d hybridization between Mn and Bi atoms, and it depends strongly on lattice constants (anisotropic Bi-Bi exchange striction). A better agreement with the magneto-optical Kerr measurements at higher energies is obtained. We also present the detailed investigation of the Fermi surface, the de Haas-van Alphen effect, and the x-ray magnetic circular dichroism in MnBi.

  1. Magnetic anisotropic effects and electronic correlations in MnBi ferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Antropov, V P [Ames Laboratory; Antonov, V N [Ames Laboratory; Bekenov, L V [Institute of metal Physics; Kutepov, A [Ames Laboratory; Kotliar, G [Rutgers University

    2014-08-01

    The electronic structure and numerous magnetic properties of MnBi magnetic systems are investigated using local spin density approximation (LSDA) with on-cite Coulomb correlations (LSDA+U) included. We show that the inclusion of Coulomb correlations provides a much better description of equilibrium magnetic moments on Mn atoms as well as the magnetic anisotropy energy behavior with temperature and magneto-optical effects. We found that the inversion of the anisotropic pairwise exchange interaction between Bi atoms is responsible for the observed spin reorientation transition at 90 K. This interaction appears as a result of strong spin orbit coupling on Bi atoms, large magnetic moments on Mn atoms, significant p-d hybridization between Mn and Bi atoms, and it depends strongly on lattice constants (anisotropic Bi-Bi exchange striction). A better agreement with the magneto-optical Kerr measurements at higher energies is obtained. We also present the detailed investigation of the Fermi surface, the de Haas–van Alphen effect, and the x-ray magnetic circular dichroism in MnBi.

  2. Effect of initial stress on reflection at the free surface of anisotropic elastic medium

    Indian Academy of Sciences (India)

    M D Sharma

    2007-12-01

    The propagation of plane waves is considered in a general anisotropic elastic medium in the presence of initial stress. The Christoffel equations are solved into a polynomial of degree six. The roots of this polynomial represent the vertical slowness values for the six quasi-waves resulting from the presence of a discontinuity in the medium. Three of these six values are identified with the three quasi-waves traveling in the medium but away from its boundary. Reflection at the free plane surface is studied for partition of energy among the three reflected waves. For post-critical incidence, the reflected waves are inhomogeneous (evanescent) waves. Numerical examples are considered to exhibit the effects of initial stress on the phase direction, attenuation and reflection coefficients of the reflected waves. The phase velocities and energy shares of the reflected waves change significantly with initial stress as well as anisotropic symmetry. The presence of initial stress, however, has a negligible effect on the phase directions of reflected waves.

  3. Study of the magnetocaloric properties of the antiferromagnetic compounds RGa2 (R = Ce, Pr, Nd, Dy, Ho and Er).

    Science.gov (United States)

    dos Reis, R D; da Silva, L M; dos Santos, A O; Medina, A M N; Cardoso, L P; Gandra, F G

    2010-12-08

    Magnetocaloric properties of antiferromagnetic RGa(2) (R = Ce, Pr, Nd, Dy, Ho and Er) compounds have been reported. These systems present an antiferromagnetic transition below 15 K and a field induced metamagnetic transition from the antiferromagnetic to ferromagnetic state. Our results show that the character of the magnetic field induced transition along the series affects the magnetocaloric properties. For the compounds with R = Ho, Dy and Er both negative and positive magnetocaloric effect (MCE) were observed above μ(0)ΔH = 2 T where the rate between negative and positive MCE contributions depends on how the magnetic transitions occur in these compounds. The evaluated values of maximum magnetocaloric properties of RGa(2) compounds are similar to other potential magnetic refrigerant materials reported in the literature.

  4. High performance magnetocaloric perovskites for magnetic refrigeration

    OpenAIRE

    Velázquez, David

    2012-01-01

    We have applied mixed valance manganite perovskites as magnetocaloric materials in a magnetic refrigeration device. Relying on exact control of the composition and a technique to process the materials into single adjoined pieces, we have observed temperature spans above 9 K with two materials. Reasonable correspondence is found between experiments and a 2D numerical model, using the measured magnetocaloric properties of the two materials as input. © 2012 American Institute of Physics.

  5. Magnetocaloric properties and critical behavior of high relative cooling power FeNiB nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhary, V. [Interdisciplinary Graduate School, Nanyang Technological University, Singapore 639798 (Singapore); Energy Research Institute @NTU, Nanyang Technological University, Singapore 637553 (Singapore); School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Maheswar Repaka, D. V.; Chaturvedi, A.; Ramanujan, R. V., E-mail: ramanujan@ntu.edu.sg [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Sridhar, I. [School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798 (Singapore)

    2014-10-28

    Low cost magnetocaloric nanomaterials have attracted considerable attention for energy efficient applications. We report a very high relative cooling power (RCP) in a study of the magnetocaloric effect in quenched FeNiB nanoparticles. RCP increases from 89.8 to 640 J kg{sup −1} for a field change of 1 and 5 T, respectively, these values are the largest for rare earth free iron based magnetocaloric nanomaterials. To investigate the magnetocaloric behavior around the Curie temperature (T{sub C}), the critical behavior of these quenched nanoparticles was studied. Detailed analysis of the magnetic phase transition using the modified Arrott plot, Kouvel-Fisher method, and critical isotherm plots yields critical exponents of β = 0.364, γ = 1.319, δ = 4.623, and α = −0.055, which are close to the theoretical exponents obtained from the 3D-Heisenberg model. Our results indicate that these FeNiB nanoparticles are potential candidates for magnetocaloric fluid based heat pumps and low grade waste heat recovery.

  6. Magnetocaloric properties and critical behavior of high relative cooling power FeNiB nanoparticles

    Science.gov (United States)

    Chaudhary, V.; Maheswar Repaka, D. V.; Chaturvedi, A.; Sridhar, I.; Ramanujan, R. V.

    2014-10-01

    Low cost magnetocaloric nanomaterials have attracted considerable attention for energy efficient applications. We report a very high relative cooling power (RCP) in a study of the magnetocaloric effect in quenched FeNiB nanoparticles. RCP increases from 89.8 to 640 J kg-1 for a field change of 1 and 5 T, respectively, these values are the largest for rare earth free iron based magnetocaloric nanomaterials. To investigate the magnetocaloric behavior around the Curie temperature (TC), the critical behavior of these quenched nanoparticles was studied. Detailed analysis of the magnetic phase transition using the modified Arrott plot, Kouvel-Fisher method, and critical isotherm plots yields critical exponents of β = 0.364, γ = 1.319, δ = 4.623, and α = -0.055, which are close to the theoretical exponents obtained from the 3D-Heisenberg model. Our results indicate that these FeNiB nanoparticles are potential candidates for magnetocaloric fluid based heat pumps and low grade waste heat recovery.

  7. Simulation of field-temperature effects in magnetic media using anisotropic Preisach models

    Energy Technology Data Exchange (ETDEWEB)

    Adly, A.A. [Cairo Univ., Giza (Egypt); Mayergoyz, I.D. [Univ. of Maryland, College Park, MD (United States). Electrical Engineering Dept.

    1998-07-01

    Prediction of temperature effects on magnetic properties has always been a topic of wide interest. Studying these effects may be particularly crucial for estimating the reliability of magnetic recording media and/or proper electrical machine core designs when significant working temperature variations are expected. In this paper, simulation of field-temperature effects in magnetic media is proposed by using a 2-D anisotropic Preisach-type hysteresis model. A technique for solving the identification problem of this model is developed. Experimental testing of the proposed model has been carried out on two different thin film hard disk samples. Comparison between measured and computed values indicate that the suggested model can lead to good qualitative, as well as quantitative, simulation results.

  8. Tailoring Effective Media by Mie Resonances of Radially-Anisotropic Cylinders

    Directory of Open Access Journals (Sweden)

    Henrik Kettunen

    2015-05-01

    Full Text Available This paper studies constructing advanced effective materials using arrays of circular radially-anisotropic (RA cylinders. Homogenization of such cylinders is considered in an electrodynamic case based on Mie scattering theory. The homogenization procedure consists of two steps. First, we present an effectively isotropic model for individual cylinders, and second, we discuss the modeling of a lattice of RA cylinders. Radial anisotropy brings us extra parameters, which makes it possible to adjust the desired effective response for a fixed frequency. The analysis still remains simple enough, enabling a derivation of analytical design equations. The considered applications include generating artificial magnetism using all-dielectric cylinders, which is currently a very sought-after phenomenon in optical frequencies. We also study how negative refraction is achieved using magnetodielectric RA cylinders.

  9. Phase transition and magnetocaloric effect of Ni{sub 50}Mn{sub 29}Ga{sub 21−x}Tb{sub x} (0 ⩽ x ⩽ 1) alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Yuye; Wang, Jingmin, E-mail: jingmin@buaa.edu.cn; Hua, Hui; Jiang, Chengbao; Xu, Huibin

    2015-05-25

    Highlights: • Effect of Tb addition on phase transition temperatures of Ni{sub 50}Mn{sub 29}Ga{sub 21} were clarified. • Coupled magneto-structural transition were observed in Ni{sub 50}Mn{sub 29}Ga{sub 21}Tb{sub 0.2} alloy. • Large magnetocaloric effect was monitored from the magneto-structural transition. - Abstract: Ni{sub 50}Mn{sub 29}Ga{sub 21−x}Tb{sub x} (0 ⩽ x ⩽ 1) alloys were studied with the microstructure, phase transition, and magnetocaloric effect. Dual-phase microstructure containing the martensite matrix and Tb-rich precipitations were formed. The martensitic transformation was observed over the whole composition range, with the transformation temperature T{sub M} significantly increased by the addition of terbium. The magnetic transition temperatures of the austenite and martensite, i.e. T{sub C}{sup A} and T{sub C}{sup M}, were monitored for 0 ⩽ x ⩽ 0.16 and 0.27 ⩽ x ⩽ 1, respectively. Both T{sub C}{sup A} and T{sub C}{sup M} were slightly decreased by the addition of terbium. For 0.16 ⩽ x ⩽ 0.27 the martensitic transformation was coincided with the magnetic transition in case of T{sub M} = T{sub C}, giving rise to the coupled magneto-structural transition from ferromagnetic martensite to paramagnetic austenite. Sizable magnetic entropy change was induced by magnetic field in the vicinity of the coupled magneto-structural transition.

  10. Field- and temperature-induced evolution of the magnetocaloric effect in Ba0.3Sr1.7Co2Fe12O22 single crystals with heliconical magnetism.

    Science.gov (United States)

    Yan, Li-Qin; Chun, Sae Hwan; Sun, Young; Shin, Kwang Woo; Jeon, Byung-Gu; Shen, Shi Peng; Kim, Kee Hoon

    2013-06-26

    The magnetocaloric effect (MCE) associated with the spin transitions of alternating longitudinal conical (ALC)-mixed conical (MC) and MC-ferrimagnetic (FIM) states in a Ba0.3Sr1.7Co2Fe12O22 single crystal has been investigated. For magnetic field directions applied along either the [120] or [001] directions, the crystal is found to exhibit the conventional and inverse MCE near the ALC-MC (T(N1) = 235 K) and MC-FIM (T(N2) = 348 K) states, respectively. The dependence of the magnetic entropy on the magnetic field also exhibits such sign change behaviors in the MCE, which is attributed to the magnetic field induced gradual collapse of heliconical magnetic order.

  11. Stability of standing spin wave in permalloy thin film studied by anisotropic magnetoresistance effect

    Energy Technology Data Exchange (ETDEWEB)

    Yamanoi, K.; Yokotani, Y. [Department of Physics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan); Cui, X. [Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395 (Japan); Yakata, S. [Department of Information Electronics, Fukuoka Institute of Technology, 3-30-1 Wajiro-higashi, Higashi-ku, Fukuoka 811-0295 (Japan); Kimura, T., E-mail: t-kimu@phys.kyushu-u.ac.jp [Department of Physics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan); Research Center for Quantum Nano-Spin Sciences, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan)

    2015-12-21

    We have investigated the stability for the resonant spin precession under the strong microwave magnetic field by a specially developed detection method using the anisotropic magnetoresistance effect. The electrically separated excitation and detection circuits enable us to investigate the influence of the heating effect and the nonuniform spin dynamics independently. The large detecting current is found to induce the field shift of the resonant spectra because of the Joule heating. From the microwave power dependence, we found that the linear response regime for the standing spin wave is larger than that for the ferromagnetic resonance. This robust characteristic of the standing spin wave is an important advantage for the high power operation of the spin-wave device.

  12. The effect of Dy doped on structural, magnetic and magnetocaloric properties of La0.67-xDyxPb0.33MnO3 (x=0.00, 0.15 and 0.20) compounds

    Science.gov (United States)

    Zaidi, N.; Mnefgui, S.; Dhahri, A.; Dhahri, J.; Hlil, E. K.

    2014-10-01

    La0.67-xDyxPb0.33MnO3 (x=0.00, 0.15 and 0.20) compounds were prepared using solid-state reaction. X-ray diffraction and magnetic measurements were used to investigate the effects of Dy doping on the physical properties of La0.67-xDyxPb0.33MnO3. XRD data have been analyzed by Rietveld refinement technique. Results have shown that all obtained perovskite manganites were a single phase. Moreover they crystallized in a rhombohedric structure with R3barc space group. Magnetization as a function of temperature has shown that these compounds exhibit a transition from a ferromagnetic to paramagnetic phase with increasing temperature. A magnetocaloric effect in the obtained samples has been deduced by two methods: Classical Maxwell relation and Landau theory. The maximum of magnetic entropy change |ΔSMmax| in a magnetic field change of 5 T is found to be 4.26 J kg-1 K-1 at 360 K, 3.51 J kg-1 K-1 at 290 K and 2.3 J kg-1 K-1 at 277 K for x=0.00, 0.15 and 0.20, respectively. At this value of magnetic field, the relative cooling power (RCP) is found to be 292, 246 and 215 J kg-1 for x=0.00, 0.15 and 0.20, respectively. Our result on magnetocaloric properties suggests that La0.67-xDyxPb0.33MnO3 (x=0.00, 0.15 and 0.2) compounds are attractive as possible refrigerants for near room temperature magnetic refrigeration.

  13. 基于Maxwell关系分析制冷工质磁热效应的研究%Study on the Magnetocaloric Effect of Magnetic Refrigerant Based on Maxwell Relations

    Institute of Scientific and Technical Information of China (English)

    包立夫

    2016-01-01

    Magnetocaloric effect ( MCE ) refers to heating or cooling phenomenon of magnetic materials in the magnetization and demagnetization. The nature of MCE is the changing of magnetic ordering degree ( entropy change) in the materials, which can cause heating or cooling behavior of behavior. Magnetic refrigerant with magnetocaloric effect has potential application in refrigeration industry. The isothermal entropy change is one of the important parameters to measure the performance of magnetic refrigerant. The principle of using Maxwell relations was illustrated to analyze the performance of refrigerant. According to the magnetization curve of refrigerant, it was pointed out that method of using Maxwell relations to analyze the performance of specific refrigerant, which provided reference for related researchers.%磁热效应是指对磁性材料进行磁化或退磁时所产生放热或吸热的现象,其本质是材料内部的磁有序度发生改变(熵的改变),引起材料本身的吸热放热行为。具有磁热效应的磁性制冷工质在制冷工业中有着潜在的应用。等温熵变是衡量磁性制冷工质性能大小的重要参数之一。本文介绍了利用Maxwell关系分析制冷工质性能的原理。针对制冷工质的磁化曲线,阐述了利用Maxwell关系分析具体制冷工质性能的思路和方法,为相关研究人员提供了参考。

  14. Investigation of magnetocaloric effect in La{sub 0.45}Pr{sub 0.25}Ca{sub 0.3}MnO{sub 3} by magnetic, differential scanning calorimetry and thermal analysis

    Energy Technology Data Exchange (ETDEWEB)

    Aparnadevi, M.; Barik, S.K. [Department of Physics, 2 Science Drive 3, National University of Singapore, Lower Kent Ridge Road, Singapore-117 452 (Singapore); Mahendiran, R., E-mail: phyrm@nus.edu.sg [Department of Physics, 2 Science Drive 3, National University of Singapore, Lower Kent Ridge Road, Singapore-117 452 (Singapore)

    2012-10-15

    We investigated magnetocaloric effect in La{sub 0.45}Pr{sub 0.25}Ca{sub 0.3}MnO{sub 3} by direct methods (changes in temperature and latent heat) and indirect method (magnetization isotherms). This compound undergoes a first-order paramagnetic to ferromagnetic transition with T{sub C}=200 K upon cooling. The paramagnetic phase becomes unstable and it transforms into a ferromagnetic phase under the application of magnetic field, which results in a field-induced metamagnetic transition (FIMMT). The FIMMT is accompanied by release of latent heat and temperature of the sample as evidenced from differential scanning calorimetry and thermal analysis experiments. A large magnetic entropy change of {Delta}S{sub m}=-7.2 J kg{sup -1} K{sup -1} at T=212.5 K and refrigeration capacity of 228 J kg{sup -1} are found for a field change of {Delta}H=5 T. It is suggested that destruction of magnetic polarons and growth of ferromagnetic phase accompanied by a lattice volume change with increasing magnetic field is responsible for the large magnetocaloric effect in this compound. - Highlights: Black-Right-Pointing-Pointer We report magnetic entropy change measured by indirect and direct methods in La{sub 0.45}Pr{sub 0.25}Ca{sub 0.3}MnO{sub 3.} Black-Right-Pointing-Pointer Anomalous field-induced induced metamagnetic transition is found in the paramagnetic state. Black-Right-Pointing-Pointer A large reversible magnetic entropy change ({Delta}S{sub m}=7.2 J kg{sup -1} K{sup -1} for {Delta}H=5 T). Black-Right-Pointing-Pointer A large refrigeration capacity (RC=228 J kg{sup -1}). Black-Right-Pointing-Pointer Collapse of magnetic polarons is suggested as possible origin of the large MCE.

  15. Effects of manganese doping on magnetocaloric effect in Ge-rich Gd5Ge2.05Si1.95 alloy

    Institute of Scientific and Technical Information of China (English)

    E.Yüzüak; I.Dincer; Y.Elerman

    2012-01-01

    The structure,magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy,X-ray powder diffraction,differential scanning calorimeter (DSC) and magnetization measurements.The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired.DSC measurements were performed to determine the transformation temperatures for each alloy.Both alloys exhibited the first order phase transition around room temperature.The alloys showed an anti-ferromagnetic transition around 60 K.The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation.The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T,respectively.

  16. Pressure-tuned magnetocaloric effect in Mn0.93Cr0.07CoGe

    NARCIS (Netherlands)

    Caron, L.; Trung, N.T.; Brück, E.

    2011-01-01

    Effects of physical and chemical pressures in the Mn1−xCrxCoGe series of compounds are studied. Cr substitution and hydrostatic pressure play similar roles in displacing TC to lower temperatures and coupling or decoupling magnetic and crystallographic transitions. In this work the similarities and d

  17. Simulated magnetocaloric properties of MnCr2O4 spinel

    Directory of Open Access Journals (Sweden)

    Mahmoud A. Hamad

    2016-03-01

    Full Text Available The magnetocaloric properties of MnCr2O4 spinel have been simulated based on a phenomenological model. The simulation of magnetization as function of temperature is used to explore magnetocaloric properties such as magnetic entropy change, heat capacity change, and relative cooling power. The results imply the prospective application of MnCr2O4 spinel to achieve magnetocaloric effect at cryogenic temperatures (20–60 K near Curie temperatures (38–44 K. According to the obtained results it is recommended that MnCr2O4 spinel can be used as a promising practical material in the active magnetic regenerator cycle that cools hydrogen gas.

  18. Development of a new magnetocaloric material used in a magnetic refrigeration device

    Directory of Open Access Journals (Sweden)

    Hardy V.

    2012-06-01

    Full Text Available Testing directly a magnetocaloric material in a magnetic refrigeration (MR system is the best way to judge of its applicative potentialities. In this spirit, an oxide expected to show promising magnetocaloric properties around room temperature (Pr0.65Sr0.35MnO3 was produced in large scale and shaped in order to build a regenerator. Magnetization, heat capacity, resistivity, thermal conductivity and a direct test in a MR device were carried out on this manganite. The results were compared to those observed in the reference material which is Gadolinium. The two main conclusions of these preliminary results are: (i the Pr0.65Sr0.35MnO3 actually displays not only a significant magnetocaloric effect but also a real refrigeration capability at room temperature; (ii the temperature spans reached in these first experiments are even found to well compare with those obtained with Gd.

  19. A multicaloric material as a link between electrocaloric and magnetocaloric refrigeration.

    Science.gov (United States)

    Ursic, Hana; Bobnar, Vid; Malic, Barbara; Filipic, Cene; Vrabelj, Marko; Drnovsek, Silvo; Jo, Younghun; Wencka, Magdalena; Kutnjak, Zdravko

    2016-05-25

    The existence and feasibility of the multicaloric, polycrystalline material 0.8Pb(Fe1/2Nb1/2)O3-0.2Pb(Mg1/2W1/2)O3, exhibiting magnetocaloric and electrocaloric properties, are demonstrated. Both the electrocaloric and magnetocaloric effects are observed over a broad temperature range below room temperature. The maximum magnetocaloric temperature change of ~0.26 K is obtained with a magnetic-field amplitude of 70 kOe at a temperature of 5 K, while the maximum electrocaloric temperature change of ~0.25 K is obtained with an electric-field amplitude of 60 kV/cm at a temperature of 180 K. The material allows a multicaloric cooling mode or a separate caloric-modes operation depending on the origin of the external field and the temperature at which the field is applied.

  20. Effect of Fe substitution on magnetocaloric effect in La{sub 0.7}Sr{sub 0.3}Mn{sub 1-x}Fe{sub x}O{sub 3} (0.05{<=}x{<=}0.20)

    Energy Technology Data Exchange (ETDEWEB)

    Barik, S.K.; Krishnamoorthi, C. [Department of Physics and NUS Nanoscience and Nanotechnology Initiative, 2 Science Drive 3, National University of Singapore, Singapore 117542, Singapore. (Singapore); Mahendiran, R., E-mail: phyrm@nus.edu.s [Department of Physics and NUS Nanoscience and Nanotechnology Initiative, 2 Science Drive 3, National University of Singapore, Singapore 117542, Singapore. (Singapore)

    2011-04-15

    We have studied the effect of Fe substitution on magnetic and magnetocaloric properties in La{sub 0.7}Sr{sub 0.3}Mn{sub 1-x}Fe{sub x}O{sub 3} (x=0.05, 0.07, 0.10, 0.15, and 0.20) over a wide temperature range (T=10-400 K). It is shown that substitution by Fe gradually decreases the ferromagnetic Curie temperature (T{sub C}) and saturation magnetization up to x=0.15 but a dramatic change occurs for x=0.2. The x=0.2 sample can be considered as a phase separated compound in which both short-range ordered ferromagnetic and antiferromagnetic phases coexist. The magnetic entropy change (-{Delta}S{sub m}) was estimated from isothermal magnetization curves and it decreases with increase of Fe content from 4.4 J kg{sup -1} K{sup -1} at 343 K (x=0.05) to 1.3 J kg{sup -1} K{sup -1} at 105 K (x=0.2), under {Delta}H=5 T. The La{sub 0.7}Sr{sub 0.3}Mn{sub 0.93}Fe{sub 0.07}O{sub 3} sample shows negligible hysteresis loss, operating temperature range over 60 K around room temperature with refrigerant capacity of 225 J kg{sup -1}, and magnetic entropy of 4 J kg{sup -1} K{sup -1} which will be an interesting compound for application in room temperature refrigeration. - Research highlights: > We report magnetocaloric effect in La{sub 0.7}Sr{sub 0.3}Mn{sub 1-x}Fe{sub x}O{sub 3} (x=0-0.2). > Magnetic entropy change ({Delta}S{sub m}) decreases with increasing x. > A large {Delta}S{sub m} and refrigeration capacity are found around 300 K in x=0.07.

  1. Effect of Bi doping on magnetic and magnetocaloric properties of La0.7-xBixSr0.3MnO3 (0<=x<=0.4)

    Science.gov (United States)

    Barik, S. K.; Mahendiran, R.

    2010-05-01

    We investigated the effect of Bi doping on magnetic and magnetocaloric properties of La0.7-xBixSr0.3MnO3 (x=0.0-0.4). It is shown that the low temperature ground state changes from a ferromagnet (x=0) to a charge-ordered antiferromagnet for x=0.4. While the paramagnetic-ferromagnetic (PM-FM) transition is second-order in x≤0.25, it changes into first-order for x=0.3 which is at the magnetic phase boundary. The changes in the magnetic ground state affect magnetic entropy. The magnitude of the isothermal magnetic entropy (|ΔSM|) at the FM Curie temperature increases from 4.56 J/kg K for x=0 to a maximum value of 5.02 J/kg K for x=0.05 and then decreases to nearly zero for x=0.4 at the charge order transition. In contrast to x≤0.25, the ΔSM of x=0.3 is magnetic history dependent and its temperature dependence exhibits a clear step at TCO=260 K followed by a plateau between 240 and 185 K. Although |ΔSM|=3.1 J/kg K of x=0.3 is small compared to other compositions, it has a high relative cooling power (325 J/kg) which is desirable for magnetic refrigeration over a wide temperature. The unusual magnetic and magnetocaloric properties of x=0.3 are attributed to the existence of short-range charge-orbital (CO) correlations in the PM state. It is suggested that harnessing competition between FM spin ordering and CO correlations may provide a strategy to enhance magnetic refrigeration capacity over a wide temperature range.

  2. Effective Heat and Mass Transport Properties of Anisotropic Porous Ceria for Solar Thermochemical Fuel Generation

    Directory of Open Access Journals (Sweden)

    Sophia Haussener

    2012-01-01

    Full Text Available High-resolution X-ray computed tomography is employed to obtain the exact 3D geometrical configuration of porous anisotropic ceria applied in solar-driven thermochemical cycles for splitting H2O and CO2. The tomography data are, in turn, used in direct pore-level numerical simulations for determining the morphological and effective heat/mass transport properties of porous ceria, namely: porosity, specific surface area, pore size distribution, extinction coefficient, thermal conductivity, convective heat transfer coefficient, permeability, Dupuit-Forchheimer coefficient, and tortuosity and residence time distributions. Tailored foam designs for enhanced transport properties are examined by means of adjusting morphologies of artificial ceria samples composed of bimodal distributed overlapping transparent spheres in an opaque medium.

  3. The Effect of Anisotropic Viscosity on Cold Fronts in Galaxy Clusters

    CERN Document Server

    ZuHone, J A; Markevitch, M; Stone, J M; Biffi, V

    2014-01-01

    Cold fronts--contact discontinuities in the intracluster medium (ICM) of galaxy clusters--should be disrupted by Kelvin-Helmholtz (K-H) instabilities due to the associated shear velocity. However, many observed cold fronts appear stable. This opens the possibility to place constraints on microphysical mechanisms that stabilize them, such as the ICM viscosity and/or magnetic fields. We performed exploratory high-resolution simulations of cold fronts arising from subsonic gas sloshing in cluster cores using the grid-based Athena MHD code, comparing the effects of isotropic Spitzer and anisotropic Braginskii viscosity (expected in a magnetized plasma). Magnetized simulations with full Braginskii viscosity or isotropic Spitzer viscosity reduced by a factor f ~ 0.1 are both in qualitative agreement with observations in terms of suppressing K-H instabilities. The RMS velocity and turbulence within the sloshing region is only modestly reduced by Braginskii viscosity. We also performed unmagnetized simulations with a...

  4. Anisotropic surroundings effects on photo absorption of partially embedded Au nanospheroids in silica glass substrate

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Xuan; Shibayama, Tamaki, E-mail: shiba@qe.eng.hokudai.ac.jp; Watanabe, Seiichi [Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060–8628 (Japan); Yu, Ruixuan; Ishioka, Junya [Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido 060–8628 (Japan)

    2015-02-15

    The influence of a directly adjacent or an anisotropic surrounding medium alters the plasmonic properties of a nanoparticle because it provides a mechanism for symmetry breaking of the scattering. Given the success of ion irradiation induced embedment of rigid metallic nanospheroids into amorphous substrate, it is possible to examine the effect of the silica glass substrate on the plasmonic properties of these embedded nanospheroids. In this work presented here, discrete dipole approximation (DDA) calculations for the Au nanospheroids’ optical properties were performed based on 3–dimensional (3D) configuration extracted from planar SEM micrographs and cross–sectional TEM micrographs of the Au nanospheroids partially embedded in the silica glass, and the well–matched simulations with respect to the experimental measurements could demonstrate the dielectric constant at the near surface of silica glass decreased after Ar–ion irradiation.

  5. Anisotropic media effect on the dipole moment of some coumarin dyes.

    Science.gov (United States)

    Zakerhamidi, M S; Ghanadzadeh, A; Moghadam, M; Tajalli, H

    2010-11-01

    The ground state (μ(g)) and the excited state (μ(e)) dipole moments of two coumarin laser dyes, C500 and C503, were studied at room temperature in various solvents, viz., aprotic solvents, alcohols and liquid crystals at 298 K. We report dipole moment of laser dyes in different anisotropic (liquid crystals) and isotropic environments. The dipole moments values in different media help to investigate environment effects on the molecular dipole moment and provide a straightforward method for comparing their properties. Ground and excited state dipole moments of coumarin dyes were evaluated by means of solvatochromic shift method. It was observed that dipole moment values of excited states (μ(e)) were higher than corresponding ground state values (μ(g)), indicating a substantial redistribution of the π-electron densities in a more polar excited state for the dyes investigated.

  6. Effect of anisotropic and isotropic solvent on the dipole moment of coumarin dyes.

    Science.gov (United States)

    Zakerhamidi, M S; Ghanadzadeh, A; Moghadam, M

    2011-03-01

    The ground state (μ(g)) and the excited state (μ(e)) dipole moments of two coumarin laser dyes, coumarin 440 and 460, were studied at room temperature in various solvents, viz., general solvents, alcohols and liquid crystals at 298 K. In this work, we report dipole moment of laser dyes in different anisotropic (liquid crystal) and isotropic environments for understanding the effects of environments on the molecular dipole moment and comparing them. Ground and excited state dipole moments of coumarin dyes were evaluated by means of solvatochromic shift method. It was observed that dipole moment values of excited states (μ(e)) were higher than the corresponding ground state values (μ(g)) in all media.

  7. Twist angle effect on anisotropic mobility of hexagonal dislocation networks in {110} of alpha-iron

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jinbo [ORNL; Osetskiy, Yury N [ORNL; Stoller, Roger E [ORNL

    2012-01-01

    Atomistic studies of anisotropic mobility of hexagonal dislocation networks (HDNs) in a series of twist boundaries (1 -1 0) has been performed in alpha-iron. In contrast with previous work that neglected the twist angle effect, we find when the twist angle approaches to 0, the resistance to the HDN motion could become much lower than Peierls stress of edge dislocations <1 1 1>/2 when the HDN moves along [0 0 1], but beyond Peierls stress of screw dislocations <1 1 1>/2 when the HDN moves along other directions. Vector form of Orowan equation and differential displacement map of dislocation core are used to analyse the behaviour of these boundary dislocations. This work seems favourable for understanding the absence of anomalous slip in alpha-iron.

  8. A family of Fe(3+) based double-stranded helicates showing a magnetocaloric effect, and Rhodamine B dye and DNA binding activities.

    Science.gov (United States)

    Adhikary, Amit; Jena, Himanshu Sekhar; Konar, Sanjit

    2015-09-21

    Herein, the synthesis, structural characterization, magnetic properties and guest binding activities of four Fe(3+) based double-stranded helicates namely; [Fe2(L)2](ClO4)(Cl)·4(CH3OH)·2(H2O) (), [Fe2(L)2](BF4)2·2(H2O) (), [Fe2(L)2](NO3)2·3(CH3OH)·2(H2O) (), and [Fe2(L)2](Cl)2·2(CH3OH)·4(H2O) () are reported. Complexes have been synthesized using the hydrazide-based ligand H2L (H2L = N'1,N'4-bis(2-hydroxybenzylidene)succinohydrazide) and the corresponding Fe(2+) salts. Each of the independent cationic complexes [Fe2(L)2](2+) shows double-stranded helicates from the self-assembly of the ligand and metal ions in a 2 : 2 ratio, where the individual Fe(3+) centre is lying on a C2-axis and the ligand strands wrap around it. In , ligand L adopts "pseudo-C" conformations and forms a double-stranded dinuclear helicate with a small cage in between them. Moreover, in , each of the independent cationic complexes [Fe2L2](2+) is inherently chiral and possesses P for right-hand and M for left-hand helicity and as a consequence is a racemic solid. Detailed magnetic studies of all the complexes reveal that the Fe(3+) centres are magnetically isolated and isotropic in nature. Estimation of the Magnetocaloric Effect (MCE) from magnetization data unveils a moderate MCE at a temperature of 3 K with magnetic entropy changes (-ΔSm) of 22.9, 27.7, 24.1, 26.5 J kg(-1) K(-1) at a magnetic field of 7 T for complexes , respectively. Also, the variation of the -ΔSm values was justified by considering the parameter of magnetization per unit mass. Stability of all the complexes in solution phase was confirmed by ESI-mass spectrometric analysis and liquid phase FT-IR spectroscopy. Further, the interaction of the complexes with Rhodamine B dye was examined by UV-vis and fluorescence spectroscopic study. The observed blue-shift in the fluorescence study and hyperchromicity and hypochromicity with the appearance of two isosbestic points in the UV-vis study ascertain the interactions of

  9. Anisotropic turbulence and zonal jets in rotating flows with a β-effect

    Directory of Open Access Journals (Sweden)

    B. Galperin

    2006-01-01

    Full Text Available Numerical studies of small-scale forced, two-dimensional turbulent flows on the surface of a rotating sphere have revealed strong large-scale anisotropization that culminates in the emergence of quasi-steady sets of alternating zonal jets, or zonation. The kinetic energy spectrum of such flows also becomes strongly anisotropic. For the zonal modes, a steep spectral distribution, E(n=CZ (Ω/R2 n-5, is established, where CZ=O(1 is a non-dimensional coefficient, Ω is the angular velocity, and R is the radius of the sphere, respectively. For other, non-zonal modes, the classical, Kolmogorov-Batchelor-Kraichnan, spectral law is preserved. This flow regime, referred to as a zonostrophic regime, appears to have wide applicability to large-scale planetary and terrestrial circulations as long as those are characterized by strong rotation, vertically stable stratification and small Burger numbers. The well-known manifestations of this regime are the banded disks of the outer planets of our Solar System. Relatively less known examples are systems of narrow, subsurface, alternating zonal jets throughout all major oceans discovered in state-of-the-art, eddy-permitting simulations of the general oceanic circulation. Furthermore, laboratory experiments recently conducted using the Coriolis turntable have basically confirmed that the lateral gradient of ''planetary vorticity'' (emulated via the topographic β-effect is the primary cause of the zonation and that the latter is entwined with the development of the strongly anisotropic kinetic energy spectrum that tends to attain the same zonal and non-zonal distributions, −5 and , respectively, in both the slope and the magnitude, as the corresponding spectra in other environmental conditions. The non-dimensional coefficient CZ in the −5 spectral law appears to be invariant, , in a variety of simulated and natural flows. This paper provides a brief review of the zonostrophic regime. The review includes the

  10. Magnetic, thermal and magnetocaloric properties of non-stoichiometric TbMn{sub 0.33}Ge{sub 2} compound

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Sachin; Suresh, K.G., E-mail: suresh@phy.iitb.ac.in

    2014-09-01

    Magnetic, heat capacity and magnetocaloric properties of non-stoichiometric TbMn{sub 0.33}Ge{sub 2} compound have been studied. Different measurements show that it undergoes three magnetic transitions at T{sub N}, T{sub 1} and T{sub 2}. The magnetocaloric effect has been estimated from magnetization data using Maxwell's relation. The existence of collinear and sine wave modulated components makes the magnetic structure complex at low temperatures. It is also found that this compound shows normal and inverse magnetocaloric effects in different temperature regimes.

  11. The expected low field magnetocaloric effect of La0.7Ba0.3MnO3 manganite at room temperature

    Science.gov (United States)

    Mohamed, Abd El-Moez A.; Hernando, B.

    2016-04-01

    La0.7Ba0.3MnO3 manganite oxide was prepared by the sol-gel method. X-ray diffraction has shown the high homogeneity of the compound and Reitveld refinement has proved the R-3C rhombohedral structure. The temperature dependence of magnetization at different applied magnetic fields of 50 Oe, 100 Oe and 200 Oe shows a magnetic phase transition at room temperature around 302 K. The magnetocaloric properties and the related parameters have been calculated theoretically based on a phenomenological model. The results include the magnetic field dependence of magnetic entropy change, relative cooling power and specific heat. The constructed universal curve of the magnetic entropy change has proved the second order nature of magnetic phase transition in the studied compound.

  12. Latent heat contribution to the direct magnetocaloric effect in Ni-Mn-Ga shape memory alloys with coupled martensitic and magnetic transformations

    Science.gov (United States)

    Caballero-Flores, R.; Sánchez-Alarcos, V.; Recarte, V.; Pérez-Landazábal, J. I.; Gómez-Polo, C.

    2016-05-01

    We report the direct magnetocaloric response of materials that present a second-order phase transition in the temperature range where a first-order structural transition also occurs. In particular, the influence of the latent heat on the field-induced adiabatic temperature change has been analyzed in a Ni-Mn-Ga alloy with coupled martensitic and magnetic transformations. It is found that discrepancies around 20% arise depending on whether the latent heat is taken into account or not. From the observed results, a general expression for the indirect determination of the adiabatic temperature change, that takes into account the contributions of both the martensitic and magnetic transformations, is proposed and experimentally confirmed. The observed key role of the latent heat allows us to understand why materials with first-order transformations do not present adiabatic temperature changes as higher as those which would correspond to materials undergoing second-order transformations with similar isothermal entropy change.

  13. Effect of Fe substitution on magnetocaloric effect in La 0.7Sr 0.3Mn 1- xFe xO 3 (0.05≤ x≤0.20)

    Science.gov (United States)

    Barik, S. K.; Krishnamoorthi, C.; Mahendiran, R.

    2011-04-01

    We have studied the effect of Fe substitution on magnetic and magnetocaloric properties in La0.7Sr0.3Mn1-xFexO3 (x=0.05, 0.07, 0.10, 0.15, and 0.20) over a wide temperature range (T=10-400 K). It is shown that substitution by Fe gradually decreases the ferromagnetic Curie temperature (TC) and saturation magnetization up to x=0.15 but a dramatic change occurs for x=0.2. The x=0.2 sample can be considered as a phase separated compound in which both short-range ordered ferromagnetic and antiferromagnetic phases coexist. The magnetic entropy change (-ΔSm) was estimated from isothermal magnetization curves and it decreases with increase of Fe content from 4.4 J kg-1 K-1 at 343 K (x=0.05) to 1.3 J kg-1 K-1 at 105 K (x=0.2), under ΔH=5 T. The La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating temperature range over 60 K around room temperature with refrigerant capacity of 225 J kg-1, and magnetic entropy of 4 J kg-1 K-1 which will be an interesting compound for application in room temperature refrigeration.

  14. Synthesizing metamaterials with angularly independent effective medium properties based on an anisotropic parameter retrieval technique coupled with a genetic algorithm

    Science.gov (United States)

    Jiang, Zhi Hao; Bossard, Jeremy A.; Wang, Xiande; Werner, Douglas H.

    2011-01-01

    In this paper, we present a method to retrieve the effective electromagnetic parameters of a slab of anisotropic metamaterial from reflection and transmission coefficients (or scattering parameters). In this retrieval method, calculated or measured scattering parameters are employed for plane waves incident obliquely on a metamaterial slab at different angles. Useful analytical expressions are derived for extracting the homogeneous anisotropic medium parameters of a metamaterial. To validate the method, the effective permittivity and permeability tensor parameters for a composite split-ring resonator-wire array are retrieved and shown to be consistent with observations previously reported in the literature. This retrieval method is further incorporated into a genetic algorithm (GA) to synthesize an infrared zero-index-metamaterial with a wide field-of-view, demonstrating the utility of the new design approach. The anisotropic parameter retrieval algorithm, when combined with a robust optimizer such as GA, can provide a powerful design tool for exploiting the anisotropic properties in metamaterials to achieve specific angle dependant or independent responses.

  15. Magnetocaloric materials and first order phase transitions

    DEFF Research Database (Denmark)

    Neves Bez, Henrique

    of the properties of such materials.The experimental characterization of these materials is done through various different methods, such as X-ray diffraction, magnetometry, calorimetry, direct measurements of entropy change, capacitance dilatometry, scanning electron microscopy,energy-dispersive X-ray spectrometry......This thesis studies the first order phase transitions of the magnetocaloric materials La0.67Ca0.33MnO3 and La(Fe,Mn,Si)13Hz trying to overcome challenges that these materials face when applied in active magnetic regenerators. The study is done through experimental characterization and modelling...... and magnetocaloric regenerative tests. The magnetic, thermal and structural properties obtained from such measurements are then evaluated through different models, i.e. the Curie-Weiss law, the Bean-Rodbell model, the free electron model and the Debye model.The measured magnetocaloric properties of La0.67Ca0.33MnO3...

  16. Non—Darcian and Anisotropic Effects on Natural Convection in Horizontal Porous Media Enclosure

    Institute of Scientific and Technical Information of China (English)

    ZhangJingzhou; SunRenqia

    1996-01-01

    Natural convection heat transfer in a horizontal enclosure filled with anisotropic porous media,being isothermally heated at bettom and cooled at top while the vertical walls being adiabatic,is numerically studied by applying the Brinkman model-a modified form of Darcy model giving consideratioin to the viscous effect.The results show that:(1)a larger permeability ratio(K*) causes a lower flow intensity in the enclosure and a smaller Nusselt number,all Nusselt numbers approach unity in the limit of K*→∞;a larger thermal conductivity ratio(λ*) causes a stranger distortion of isotherms in the enclosure and a higher flow velocity near the walls,all the Nusselt numbers approach unity in the limit of λ*-→0,the permeability and thermal conductivity ratios generally have opposing effects on the Nusselt number.(2) an increasing Darcy number decreases the flow intensity and heat tansfer rates,which is more significant at a lower permeability ratio.In particular,with K*≤0.25,the Nusselt number for Da=10-3 would differ from that of Darcy flow up to an amount of 30%,an analysis neglecting the non-Darican effect will inevitably be of considerable error.

  17. Modelling and simulation of regenerators with complex flow arrangements for active magnetocaloric refrigeration

    DEFF Research Database (Denmark)

    Lei, Tian; Nielsen, Kaspar Kirstein; Engelbrecht, Kurt

    2014-01-01

    Compared to a conventional vapor compression refrigera-tion system, a magnetocaloric refrigerator has many advantages, such as potentially high efficiency, low vibration and avoidance of refrigerants that deplete the ozone layer and cause the green-house effect. As a main component of the active...

  18. Magnetic structure and phase formation of magnetocaloric Mn-Fe-P-X compounds

    NARCIS (Netherlands)

    Ou, Z.Q.

    2013-01-01

    This thesis presents a study of the crystal and magnetic structure, the magnetocaloric effect and related physical properties in Mn-Fe-P-X compounds. The influences of boron addition in (Mn,Fe)2(P,As) compounds have been studied. It is found that boron atoms occupy interstitial sites within the basa

  19. Magnetocaloric and magnetoresistive properties of La0.67Ca0.33-xSrxMnO3

    DEFF Research Database (Denmark)

    Dinesen, Anders Reves

    This thesis presents results of an experimental investigation of magneto-caloric and magnetoresistive properties of a series of polycrystalline Ca- and Sr-doped lanthanum manganites, La0.67Ca0.33-xSrxMnO3 (0=x=0.33 ), with the perovskite structure. The samples consisted of sintered oxide powders...... a magnetocaloric effect in the vicinity of TC. A model for the mag-netocaloric effect based on Weiss mean field theory and classical theories for heat capacities was developed. The model provided reasonable predictions of the magne-tocaloric properties of the samples. The compounds with low Sr content showed...... a magnetocaloric effect comparable to that of Gadolinium, the prototypical working material for magnetic refrigeration at room temperature. A less comprehensive part of the investigation regarded the magnetoresistive properties of the La0.67Ca0.33-xSrxMnO3 system. It was found that the polycrystalline nature...

  20. Multiphase flow simulation with gravity effect in anisotropic porous media using multipoint flux approximation

    KAUST Repository

    Negara, Ardiansyah

    2015-03-04

    Numerical investigations of two-phase flows in anisotropic porous media have been conducted. In the flow model, the permeability has been considered as a full tensor and is implemented in the numerical scheme using the multipoint flux approximation within the framework of finite difference method. In addition, the experimenting pressure field approach is used to obtain the solution of the pressure field, which makes the matrix of coefficient of the global system easily constructed. A number of numerical experiments on the flow of two-phase system in two-dimensional porous medium domain are presented. In this work, the gravity is included in the model to capture the possible buoyancy-driven effects due to density differences between the two phases. Different anisotropy scenarios have been considered. From the numerical results, interesting patterns of the flow, pressure, and saturation fields emerge, which are significantly influenced by the anisotropy of the absolute permeability field. It is found that the two-phase system moves along the principal direction of anisotropy. Furthermore, the effects of anisotropy orientation on the flow rates and the cross flow index are also discussed in the paper.

  1. Thermofluid Analysis of Magnetocaloric Refrigeration

    Energy Technology Data Exchange (ETDEWEB)

    Abdelaziz, Omar [ORNL; Gluesenkamp, Kyle R [ORNL; Vineyard, Edward Allan [ORNL; Benedict, Michael [GE Appliances

    2014-01-01

    While there have been extensive studies on thermofluid characteristics of different magnetocaloric refrigeration systems, a conclusive optimization study using non-dimensional parameters which can be applied to a generic system has not been reported yet. In this study, a numerical model has been developed for optimization of active magnetic refrigerator (AMR). This model is computationally efficient and robust, making it appropriate for running the thousands of simulations required for parametric study and optimization. The governing equations have been non-dimensionalized and numerically solved using finite difference method. A parametric study on a wide range of non-dimensional numbers has been performed. While the goal of AMR systems is to improve the performance of competitive parameters including COP, cooling capacity and temperature span, new parameters called AMR performance index-1 have been introduced in order to perform multi objective optimization and simultaneously exploit all these parameters. The multi-objective optimization is carried out for a wide range of the non-dimensional parameters. The results of this study will provide general guidelines for designing high performance AMR systems.

  2. Molecular anisotropic magnetoresistance

    Science.gov (United States)

    Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy

    2015-12-01

    Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3 d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.

  3. Mixture of Anisotropic Fluids

    Science.gov (United States)

    Florkowski, W.; Maj, R.

    The recently introduced approach describing coupled quark and gluon anisotropic fluids is generalized to include explicitly the transitions between quarks and gluons. We study the effects of such processes on the thermalization rate of anisotropic systems. We find that the quark-gluon transitions may enhance the overall thermalization rate in the cases where the initial momentum anisotropies correspond to mixed oblate-prolate or prolate configurations. On the other hand, no effect on the thermalization rate is found in the case of oblate configurations. The observed regularities are connected with the late-time behavior of the analyzed systems which is described either by the exponential decay or the power law.

  4. Mixture of anisotropic fluids

    CERN Document Server

    Florkowski, Wojciech

    2013-01-01

    The recently introduced approach describing coupled quark and gluon anisotropic fluids is generalized to include explicitly the transitions between quarks and gluons. We study the effects of such processes on the thermalization rate of anisotropic systems. We find that the quark-gluon transitions may enhance the overall thermalization rate in the cases where the initial momentum anisotropies correspond to mixed oblate-prolate or prolate configurations. On the other hand, no effect on the thermalization rate is found in the case of oblate configurations. The observed regularities are connected with the late-time behavior of the analyzed systems which is described either by the exponential decay or the power law.

  5. DEM Simulation of Biaxial Compression Experiments of Inherently Anisotropic Granular Materials and the Boundary Effects

    Directory of Open Access Journals (Sweden)

    Zhao-Xia Tong

    2013-01-01

    Full Text Available The reliability of discrete element method (DEM numerical simulations is significantly dependent on the particle-scale parameters and boundary conditions. To verify the DEM models, two series of biaxial compression tests on ellipse-shaped steel rods are used. The comparisons on the stress-strain relationship, strength, and deformation pattern of experiments and simulations indicate that the DEM models are able to capture the key macro- and micromechanical behavior of inherently anisotropic granular materials with high fidelity. By using the validated DEM models, the boundary effects on the macrodeformation, strain localization, and nonuniformity of stress distribution inside the specimens are investigated using two rigid boundaries and one flexible boundary. The results demonstrate that the boundary condition plays a significant role on the stress-strain relationship and strength of granular materials with inherent fabric anisotropy if the stresses are calculated by the force applied on the wall. However, the responses of the particle assembly measured inside the specimens are almost the same with little influence from the boundary conditions. The peak friction angle obtained from the compression tests with flexible boundary represents the real friction angle of particle assembly. Due to the weak lateral constraints, the degree of stress nonuniformity under flexible boundary is higher than that under rigid boundary.

  6. Transverse anisotropic magnetoresistance effects in pseudo-single-crystal γ'-Fe4N thin films

    Science.gov (United States)

    Kabara, Kazuki; Tsunoda, Masakiyo; Kokado, Satoshi

    2016-05-01

    Transverse anisotropic magnetoresistance (AMR) effects, for which magnetization is rotated in an orthogonal plane to the current direction, were investigated at various temperatures, in order to clarify the structural transformation from a cubic to a tetragonal symmetry in a pseudo-single-crystal Fe4N film, which is predicted from the usual in-plane AMR measurements by the theory taking into account the spin-orbit interaction and crystal field splitting of 3d bands. According to a phenomenological theory of AMR, which derives only from the crystal symmetry, a cos 2θ component ( C2 tr ) exists in transverse AMR curves for a tetragonal system but does not for a cubic system. In the Fe4N film, the C2 tr shows a positive small value (0.12%) from 300 K to 50 K. However, the C2 t r increases to negative value below 50 K and reaches to -2% at 5 K. The drastic increasing of the C2 tr demonstrates the structural transformation from a cubic to a tetragonal symmetry below 50 K in the Fe4N film. In addition, the out-of-plane and in-plane lattice constants (c and a) were precisely determined with X-ray diffraction at room temperature using the Nelson-Riely function. As a result, the positive small C2 t r above 50 K is attributed to a slightly distorted Fe4N lattice (c/a = 1.002).

  7. Magnetocaloric effect and the influence of pressure on magnetic properties of La-excess pseudo-binary alloys La1+δ(Fe0.85Si0.15)13

    Science.gov (United States)

    Vuong, Van Hiep; Do Thi, Kim Anh; Thuan Nguyen, Khac; Le, Van Hong; Nhat Hoang, Nam

    2016-10-01

    The La-excess alloys La1+δ(Fe0.85Si0.15)13 (δ = 0.06 and 0.09) exhibit large magnetocaloric effect which has been attributed to the occurrence of itinerant-electron metamagnetic transition near the Curie temperature TC. The maximum entropy change -ΔSm was shown to be from 4.5 to 11.5 J/kg K for the applied field variation ΔH from 20 to 70 kOe, respectively. The estimated relative cooling power for ΔH = 70 kOe was 418 J/kg. The alloys show a typical NaZn13-type cubic structure, featuring a doping-induced magnetovolume effect with the increase in TC. Under the applied pressure up to 2 GPa, the TC as deduced from resistance measurements decreased linearly, ΔTC = 113 (for δ = 0.06) and 111 K (for δ = 0.09), together with a corresponding decrease of resistivity, Δρ = 6.1 μΩ m at room temperature for both samples. At a low pressure, the effect of spontaneous magnetostriction on TC caused by applying the pressure appeared to have a similar magnitude to that of the negative magnetovolume effect caused by La-excess doping. In comparison with other stoichiometric La(Fe1-xSix)13 compounds, the pressure in our case was shown to have a smaller influence on TC.

  8. Developing a Magnetocaloric Domestic Heat Pump

    DEFF Research Database (Denmark)

    Bahl, Christian R.H.

    2014-01-01

    beverage coolers, A/Cs for cars and electronics cooling. Devices for heating have not been extensively demonstrated. Here we consider a promising application of magnetocaloric heat pumps for domestic heating. The task of designing and building such a device is a multidisciplinary one encompassing materials...

  9. High performance magnetocaloric perovskites for magnetic refrigeration

    DEFF Research Database (Denmark)

    Bahl, Christian R. H.; Velazquez, David; Nielsen, Kaspar K.

    2012-01-01

    We have applied mixed valance manganite perovskites as magnetocaloric materials in a magnetic refrigeration device. Relying on exact control of the composition and a technique to process the materials into single adjoined pieces, we have observed temperature spans above 9 K with two materials. Re...

  10. Evaluating the Poroelastic Effect on Anisotropic, Organic-Rich, Mudstone Systems

    Science.gov (United States)

    Suarez-Rivera, Roberto; Fjær, Erling

    2013-05-01

    Understanding the poroelastic effect on anisotropic organic-rich mudstones is of high interest and value for evaluating coupled effects of rock deformation and pore pressure, during drilling, completion and production operations in the oilfield. These applications include modeling and prevention of time-dependent wellbore failure, improved predictions of fracture initiation during hydraulic fracturing operations (Suarez-Rivera et al. Presented at the Canadian Unconventional Resources Conference held in Calgary, Alberta, Canada, 15-17 November 2011. CSUG/SPE 146998 2011), improved understanding of the evolution of pore pressure during basin development, including subsidence and uplift, and the equilibrated effective in situ stress (Charlez, Rock mechanics, vol 2 1997; Katahara and Corrigan, Pressure regimes in sedimentary basins and their prediction: AAPG Memoir, vol 76, pp 73-78 2002; Fjær et al. Petroleum related rock mechanics. 2nd edn 2008). In isotropic rocks, the coupled poro-elastic deformations of the solid framework and the pore fluids are controlled by the Biot and Skempton coefficients. These are the two fundamental properties that relate the rock framework and fluid compressibility and define the magnitude of the poroelastic effect. In transversely isotropic rocks, one desires to understand the variability of these coefficients along the directions parallel and longitudinal to the principal directions of material symmetry (usually the direction of bedding). These types of measurements are complex and uncommon in low-porosity rocks, and particularly problematic and scarce in tight shales. In this paper, we discuss a methodology for evaluating the Biot's coefficient, its variability along the directions parallel and perpendicular to bedding as a function of stress, and the homogenized Skempton coefficient, also as a function of stress. We also predict the pore pressure change that results during undrained compression. Most importantly, we provide values

  11. Influence of Tb substitution on low-field magnetocaloric effect in Gd5Si1.72Ge2.28 alloy

    Institute of Scientific and Technical Information of China (English)

    DENG Jian-qiu; ZHUANG Ying-hong; WANG Ri-chu; YANG Zhen; XU Bin

    2008-01-01

    The lattice parameters, magnetic phase transition, Curie temperature and magnetocaloric properties for (Gd1-xTbx)5Si1.72-Ge2.28 alloys with x = 0, 0.15, 0.20 and 0.25 were investigated by X-ray powder diffractometry and magnetization measurements. The results show that suitable partial substitution of Tb in Gd5Si1.72Ge2.28 compound remains the first-order magnetic-crystallographic transition and enhances the magnetic entropy change, although Tb substitution decreases the Curie temperature (Tc) of the compounds. The magnetic entropy change of (Gd1-xTbx)5Si1.72Ge2.28 alloys retains a large value in the low magnetic field of 1.0 T.The maximum magnetic entropy change for (Gd0.80Tb0.20)5Si1.72Ge2.28 alloy in the magnetic field from 0 to 1.0 T reaches 8.7 J/(kg·K),which is nearly 4 times as large as that of (Gd0.3Dy0.7)5Si4 compound (|△Smax| = 2.24 J/(kg·K), TC = 198 K).

  12. Quantitative separation of the anisotropic magnetothermopower and planar Nernst effect by the rotation of an in-plane thermal gradient.

    Science.gov (United States)

    Reimer, Oliver; Meier, Daniel; Bovender, Michel; Helmich, Lars; Dreessen, Jan-Oliver; Krieft, Jan; Shestakov, Anatoly S; Back, Christian H; Schmalhorst, Jan-Michael; Hütten, Andreas; Reiss, Günter; Kuschel, Timo

    2017-01-17

    A thermal gradient as the driving force for spin currents plays a key role in spin caloritronics. In this field the spin Seebeck effect (SSE) is of major interest and was investigated in terms of in-plane thermal gradients inducing perpendicular spin currents (transverse SSE) and out-of-plane thermal gradients generating parallel spin currents (longitudinal SSE). Up to now all spincaloric experiments employ a spatially fixed thermal gradient. Thus, anisotropic measurements with respect to well defined crystallographic directions were not possible. Here we introduce a new experiment that allows not only the in-plane rotation of the external magnetic field, but also the rotation of an in-plane thermal gradient controlled by optical temperature detection. As a consequence, the anisotropic magnetothermopower and the planar Nernst effect in a permalloy thin film can be measured simultaneously. Thus, the angular dependence of the magnetothermopower with respect to the magnetization direction reveals a phase shift, that allows the quantitative separation of the thermopower, the anisotropic magnetothermopower and the planar Nernst effect.

  13. Quasiparticle anisotropic hydrodynamics

    CERN Document Server

    Alqahtani, Mubarak

    2016-01-01

    We study an azimuthally-symmetric boost-invariant quark-gluon plasma using quasiparticle anisotropic hydrodynamics including the effects of both shear and bulk viscosities. We compare results obtained using the quasiparticle method with the standard anisotropic hydrodynamics and viscous hydrodynamics. We consider the predictions of the three methods for the differential particle spectra and mean transverse momentum. We find that the three methods agree for small shear viscosity to entropy density ratio, $\\eta/s$, but show differences at large $\\eta/s$. Additionally, we find that the standard anisotropic hydrodynamics method shows suppressed production at low transverse-momentum compared to the other two methods, and the bulk-viscous correction can drive the primordial particle spectra negative at large $p_T$ in viscous hydrodynamics.

  14. Using COMSOL Multiphysics Software to Model Anisotropic Dielectric and Metamaterial Effects in Folded-Waveguide Traveling-Wave Tube Slow-Wave Circuits

    Science.gov (United States)

    Starinshak, David P.; Smith, Nathan D.; Wilson, Jeffrey D.

    2008-01-01

    The electromagnetic effects of conventional dielectrics, anisotropic dielectrics, and metamaterials were modeled in a terahertz-frequency folded-waveguide slow-wave circuit. Results of attempts to utilize these materials to increase efficiency are presented.

  15. Magnetic properties and low-temperature large magnetocaloric effect in the antiferromagnetic HoCu{sub 0.33}Ge{sub 2} and ErCu{sub 0.25}Ge{sub 2} compounds

    Energy Technology Data Exchange (ETDEWEB)

    Gao, R.L. [School of Metallurgy and Materials Engineering, Chongqing University of Science and Technology, Chongqing 401331 (China); Xu, Z.Y., E-mail: zhyxu@nim.ac.cn [National Institute of Metrology, Beijing 100029 (China); Wang, L.C. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Dong, Q.Y.; Zhang, Y. [Department of Physics, Capital Normal University, Beijing 100048 (China); Liu, F.H. [National Space Science Center, Beijing 100190 (China); Mo, Z.J. [School of material Science and Engineering, Hebei University of Technology, Tianjin 300401 (China); Niu, E. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Fu, C.L.; Cai, W.; Chen, G.; Deng, X.L. [School of Metallurgy and Materials Engineering, Chongqing University of Science and Technology, Chongqing 401331 (China)

    2015-05-15

    Highlights: • Antiferromagnetic material RCu{sub x}Ge{sub 2} of high purity was prepared. • Large MCE as −10.2 J/kg K and −10.5 J/kg K for RCu{sub x}Ge{sub 2} (Ho, Er) was obtained for field change of 0–50 kOe. • The RCu{sub x}Ge{sub 2} compounds with variable x had different transition temperature which made them suitable for ‘table-like’ magnetocaloric refrigerant. - Abstract: Magnetic properties and magnetocaloric effect (MCE) of HoCu{sub 0.33}Ge{sub 2} and ErCu{sub 0.25}Ge{sub 2} compounds have been investigated. The compounds were determined to be antiferromagnetic with the Néel temperatures T{sub N} = 9 K and 3.9 K, respectively. The critical transition magnetic fields for the metamagnetic transition from antiferromagnetic to ferromagnetic state below T{sub N} were determined to be 10 kOe for HoCu{sub 0.33}Ge{sub 2} at 5 K and 6 kOe for ErCu{sub 0.25}Ge{sub 2} at 2 K. Large MCE with the maximal values of magnetic entropy changes (ΔS{sub M}) as −10.2 J/kg K at 10.5 K were found in HoCu{sub 0.33}Ge{sub 2} for field changes of 0–70 kOe and −10.5 J/kg K at 5.5 K in ErCu{sub 0.25}Ge{sub 2} for field changes of 0–50 kOe, respectively. The large ΔS{sub M} around T{sub N} as well as no hysteresis loss made RCu{sub x}Ge{sub 2} competitive candidates as low temperature magnetic refrigerant.

  16. Measurement of the anisotropic thermal conductivity of molybdenum disulfide by the time-resolved magneto-optic Kerr effect

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jun, E-mail: junliu@illinois.edu; Choi, Gyung-Min; Cahill, David G. [Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States)

    2014-12-21

    We use pump-probe metrology based on the magneto-optic Kerr effect to measure the anisotropic thermal conductivity of (001)-oriented MoS{sub 2} crystals. A ≈20 nm thick CoPt multilayer with perpendicular magnetization serves as the heater and thermometer in the experiment. The low thermal conductivity and small thickness of the CoPt transducer improve the sensitivity of the measurement to lateral heat flow in the MoS{sub 2} crystal. The thermal conductivity of MoS{sub 2} is highly anisotropic with basal-plane thermal conductivity varying between 85–110 W m{sup -1} K{sup -1} as a function of laser spot size. The basal-plane thermal conductivity is a factor of ≈50 larger than the c-axis thermal conductivity, 2.0±0.3 W m{sup -1} K{sup -1}.

  17. Magnetocaloric effect in as-cast Gd{sub 1−x}Y{sub x} alloys with x = 0.0, 0.1, 0.2, 0.3, 0.4

    Energy Technology Data Exchange (ETDEWEB)

    Lara Pérez, E. S.; Hernández Paz, J. F.; Elizalde Galindo, J. T., E-mail: jose.elizalde@uacj.mx [Instituto de Ingeniería y Tecnología, Universidad Autónoma de Ciudad Juárez, Ave. Del Charro 450 norte, 32310 Ciudad Juárez, Chihuahua (Mexico); Betancourt, I. [Departamento de Materiales Metálicos y Cerámicos, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, México D.F. 04510 (Mexico); Matutes Aquino, J. A. [Centro de Investigación en Materiales Avanzados, S.C., Miguel de Cervantes 120, 31109 Chihuahua (Mexico)

    2014-05-07

    In this report, we present the magnetocaloric effect of Gd{sub 1−x}Y{sub x} alloys (0.0 ≤ × ≤ 0.4) prepared by arc-melting from high purity Gd and Y precursors in inert atmosphere. The formation of Gd{sub 1−x}Y{sub x} solid solutions was verified by means of X-ray diffraction analysis across the compositional series; also, residual secondary phases Gd and Y were present. Magnetic characterization performed by Vibrating Sample Magnetometry at a maximum applied field of 3.0 T showed a drastic reduction of the magnetization saturation (from 233 emu/g for x = 0.0 to 183 emu/g for x = 0.4), due to a dilution effect of the Y alloying, together with a marked Curie temperature decrease from 296 K to 196 K between x = 0.0 and x = 0.4. The second-order character of the magnetic transition was established by Arrot plots for all the cases. On the other hand, the magnetic entropy variation, determined from numerical integration of Maxwell relation displayed excellent values above 5.30 J/kg K for alloys with x < 0.3 due to the steep transition of the thermomagnetic curves.

  18. Study of multi-layer active magnetic regenerators using magnetocaloric materials with first and second order phase transition

    Science.gov (United States)

    Lei, T.; Engelbrecht, K.; Nielsen, K. K.; Neves Bez, H.; Bahl, C. R. H.

    2016-09-01

    Magnetocaloric materials (MCM) with a first order phase transition (FOPT) usually exhibit a large, although sharp, isothermal entropy change near their Curie temperature, compared to materials with a second order phase transition (SOPT). Experimental results of applying FOPT materials in recent magnetocaloric refrigerators (MCR) demonstrated the great potential for these materials, but a thorough study on the impact of the moderate adiabatic temperature change and strong temperature dependence of the magnetocaloric effect (MCE) is lacking. Besides, comparing active magnetic regenerators (AMR) using FOPT and SOPT materials is also of fundamental interest. We present modeling results of multi-layer AMRs using FOPT and SOPT materials based on a 1D numerical model. First the impact of isothermal entropy change, adiabatic temperature change and shape factor describing the temperature dependence of the MCE are quantified and analyzed by using artificially built magnetocaloric properties. Then, based on measured magnetocaloric properties of La(Fe,Mn,Si)13H y and Gd, an investigation on how to layer typical FOPT and SOPT materials with different temperature spans is carried out. Moreover, the sensitivity of variation in Curie temperature distribution for both groups of AMRs is investigated. Finally, a concept of mixing FOPT and SOPT materials is studied for improving the stability of layered AMRs with existing materials.

  19. Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

    Directory of Open Access Journals (Sweden)

    R. Niemann

    2016-06-01

    Full Text Available Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.

  20. Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

    Science.gov (United States)

    Niemann, R.; Hahn, S.; Diestel, A.; Backen, A.; Schultz, L.; Nielsch, K.; Wagner, M. F.-X.; Fähler, S.

    2016-06-01

    Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.