Magnetocaloric effect in ferrite nanoparticles
Poddar, P.; Gass, J.; Rebar, D. J.; Srinath, S.; Srikanth, H.; Morrison, S. A.; Carpenter, E. E.
2006-12-01
A comparative study of the magnetocaloric effect (MCE) is reported in two different types of chemically synthesized magnetic nanoparticle systems—cobalt ferrite and manganese zinc ferrite with mean size around 5 and 15 nm, respectively. While CoFe 2O 4 nanoparticles were synthesized using co-precipitation, the Mn 0.68Zn 0.25Fe 2.07O 4 (MZFO) nanoparticles were prepared by reverse micelle technique using AOT as surfactant. Our results indicate that the change in entropy with the change in applied magnetic field (d S/d H) is reasonably large for this class of nanoparticles and has a wide distribution over a broad temperature range covering the region above and below the blocking temperature. The maximum entropy change is influenced by the particle size, overall distribution in anisotropy and magnetic moments.
Evaluating the effect of magnetocaloric properties on magnetic refrigeration performance
DEFF Research Database (Denmark)
Engelbrecht, Kurt; Bahl, Christian Robert Haffenden
2010-01-01
Active magnetic regenerator (AMR) refrigerators represent an alternative to vapor compression technology that relies on the magnetocaloric effect in a solid refrigerant. Magnetocaloric materials are in development and properties are reported regularly. Recently, there has been an emphasis on...
Magnetic Refrigeration and the Magnetocaloric Effect
DEFF Research Database (Denmark)
Petersen, Thomas Frank; Pryds, Nini; Smith, Anders;
2006-01-01
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...... 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...
Magnetocaloric effect: Overcoming the magnetic limit
Energy Technology Data Exchange (ETDEWEB)
Plaza, E.J.R. [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, Unicamp, Zeferino Vaz s/n, 13083-970 Campinas, SP (Brazil); Instituto de Fisica, Universidade do Estado do Rio de Janeiro-UERJ, Rua Sao Francisco Xavier, 524, 20550-013 RJ (Brazil)], E-mail: plaza@ifi.unicamp.br; Campoy, J.C.P. [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, Unicamp, Zeferino Vaz s/n, 13083-970 Campinas, SP (Brazil)
2009-03-15
We have studied anomalous peaks observed in magnetocaloric -{delta}S(T) curves for systems that undergo first-order magnetostructural transitions. The origin of those peaks, which can exceed the conventional magnetic limit, R ln(2J+1), is discussed on thermodynamic bases by introducing an additional-exchange contribution (due to exchange constant variation arising from magnetostructural transition). We also applied a semiphenomenological model to include this additional-exchange contribution in Gd{sub 5}Si{sub 2}Ge{sub 2}- and MnAs-based systems, obtaining excellent results for the observed magnetocaloric effect.
Magnetocaloric effect: Overcoming the magnetic limit
Plaza, E. J. R.; Campoy, J. C. P.
2009-03-01
We have studied anomalous peaks observed in magnetocaloric -Δ S( T) curves for systems that undergo first-order magnetostructural transitions. The origin of those peaks, which can exceed the conventional magnetic limit, R ln(2 J+1), is discussed on thermodynamic bases by introducing an additional-exchange contribution (due to exchange constant variation arising from magnetostructural transition). We also applied a semiphenomenological model to include this additional-exchange contribution in Gd 5Si 2Ge 2- and MnAs-based systems, obtaining excellent results for the observed magnetocaloric effect.
Magnetocaloric Studies of the Peak Effect in Nb
Daniilidis, N. D.; Dimitrov, I. K.; Mitrovic, V F; Elbaum, C.; Ling, X. S.
2006-01-01
We report a magnetocaloric study of the peak effect and Bragg glass transition in a Nb single crystal. The thermomagnetic effects due to vortex flow into and out of the sample are measured. The magnetocaloric signature of the peak effect anomaly is identified. It is found that the peak effect disappears in magnetocaloric measurements at fields significantly higher than those reported in previous ac-susceptometry measurements. Investigation of the superconducting to normal transition reveals t...
Evaluating the effect of magnetocaloric properties on magnetic refrigeration performance
Engelbrecht, Kurt; Bahl, Christian Robert Haffenden
2010-01-01
Active magnetic regenerator (AMR) refrigerators represent an alternative to vapor compression technology that relies on the magnetocaloric effect in a solid refrigerant. Magnetocaloric materials are in development and properties are reported regularly. Recently, there has been an emphasis 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...
Theoretical investigations on the magnetocaloric and barocaloric effects in TbyGd(1−y)Al2 series
International Nuclear Information System (INIS)
Highlights: ► Anisotropic magnetocaloric effect in in Tb0.4Gd0.6Al2. ► Prediction of barocaloric effect in Tb0.4Gd0.6Al2. ►An optimal hybrid magnetocaloric material using TbyGd(1-y)Al2 compounds. -- Abstract: We report the calculations on the magnetocaloric and barocaloric effects in ferromagnetic series TbyGd(1−y)Al2. Our model includes the crystalline electrical field interaction, exchange interactions among Tb–Tb, Gd–Gd and Tb–Gd magnetic ions and the Zeeman effect for an anisotropic system. The lattice and electronic entropies were included in adiabatic processes. The magnetocaloric effect calculated for magnetic field changes along the easy magnetic direction 〈1 1 1〉 is in good agreement with the experimental data. Calculation along the hard magnetization direction 〈0 0 1〉 predicts anomalous magnetocaloric effect, which was ascribed to the spin reorientation processes. From the available experimental data of Curie temperature dependence on pressure, the exchange model parameters were scaled and the barocaloric effect was calculated
Investigation on the magnetocaloric effect in TbN compound
International Nuclear Information System (INIS)
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
Magnetocaloric effect in ferroelectric Ising chain magnet
Qi, Yan; Liu, Jia; Yu, Nai-sen; Du, An
2016-05-01
We investigate the magnetocaloric effect (MCE) in multiferroic chain system by adopting the elastic Ising-chain model. Based on the transfer-matrix method, the magnetothermal quantities of characterizing MCE behaviors including the entropy, entropy change and adiabatic cooling rate are rigorously determined. Combined with analysis of ground-state, we mainly discuss results in an antiferromagnetic regime associated with ferroelectric transition. Our results show that the entropy change is greatly enhanced near the saturation field as frustration parameter varies in this regime, and accompanied with remarkable inverse MCE, indicating the enormous potential of multiferroic system in low-temperature refrigeration. Meanwhile we also observe a prominent temperature variation in the isoentropy curves close to zero-temperature ferroelectric transition, but this enhancing MCE signal is very sensitive to the thermal fluctuations, and can be strongly suppressed even under a small temperature.
Tunable magnetocaloric effect in transition metal alloys
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.
The magnetocaloric effect: The role of magnetic anisotropy
Energy Technology Data Exchange (ETDEWEB)
Bennett, L.H.; McMichael, R.D.; Shull, R.D.; Swartzendruber, L.J. (NIST, Gaithersburg, Maryland 20899 (United States)); Watson, R.E. (Brookhaven National Laboratory, Upton, New York 11973 (United States))
1993-05-15
In a ferromagnet, the magnetic entropy change induced by the application of a magnetic field is greatest in the temperature regime near the Curie point. In the paramagnetic temperature regime, the magnitude of the magnetocaloric effect is expected to rise monotonically with the size of the individual moments that make up the material. The magnetic properties of such materials are relevant to devices employing magnetic refrigeration. One aspect of the problem, namely the impact of uniaxial magnetic anisotropy on the magnetocaloric effect, is explored. The results of Monte Carlo simulations for classical Heisenberg ferromagnets on a fcc lattice with anisotropy are presented.
The magnetocaloric effect: The role of magnetic anisotropy
International Nuclear Information System (INIS)
In a ferromagnet, the magnetic entropy change induced by the application of a magnetic field is greatest in the temperature regime near the Curie point. In the paramagnetic temperature regime, the magnitude of the magnetocaloric effect is expected to rise monotonically with the size of the individual moments that make up the material. The magnetic properties of such materials are relevant to devices employing magnetic refrigeration. One aspect of the problem, namely the impact of uniaxial magnetic anisotropy on the magnetocaloric effect, is explored. The results of Monte Carlo simulations for classical Heisenberg ferromagnets on a fcc lattice with anisotropy are presented
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 of...... gadolinium. The adiabatic temperature change DeltaTad of gadolinium sheets upon application of a magnetic field has been measured at a range of applied magnetic fields and sample orientations. A significant dependence of DeltaTad on the sample orientation is observed. This can be accounted for by the...
Thermodynamic model of the magnetocaloric effect near the first-order magnetic phase transitions
Energy Technology Data Exchange (ETDEWEB)
Spichkin, Y.I. [Advanced Magnetic Technologies and Consulting, Ltd., Moscow 115114 (Russian Federation)]. E-mail: spichkin@ndfeb.ru; Tishin, A.M. [Physics Faculty of M.V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation)
2005-04-15
Magnetocaloric effect (MCE) arising in the materials with the first-order magnetic phase transitions (such as heavy rare earth metals, FeRh and GdSiGe alloys, lanthanides) has been considered in the framework of thermodynamic approach. The exchange, magnetoelastic, anisotropic and magnetic energy contributions to the MCE and their temperature dependences were calculated in the vicinity of the first-order transition. It was shown that the model adequately describes the MCE and gives the values of the adiabatic temperature change and isothermal magnetic entropy change, which are in accord with direct experimental measurements. Possible mechanisms of the MCE near the first-order transitions are discussed.
Barocaloric and Magnetocaloric Effects in Fe49Rh51
Stern-Taulats, E.; Planes, Antoni; Lloveras Muntané, Pol Marcel; Barrio Casado, María del; Tamarit Mur, José Luis; Pramanick, Sabyasachi; Majumdar, Subham; Frontera, Carlos; Mañosa, Lluís
2014-01-01
We report on calorimetry under applied hydrostatic pressure and magnetic field at the antiferromagnetic (AFM)-ferromagnetic (FM) transition of Fe$_{49}$Rh$_{51}$. Results demonstrate the existence of a giant barocaloric effect in this alloy, a new functional property that adds to the magnetocaloric and elastocaloric effects previously reported for this alloy. All caloric effects originate from the AFM/FM transition which encompasses changes in volume, magnetization and entropy. The strong sen...
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...... and without a direct measurement of the sample temperature, one can determine an appropriate sweep-rate of the magnetic field....
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.
International Nuclear Information System (INIS)
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
Inconvenient magnetocaloric effect in ferromagnetic shape memory alloys
International Nuclear Information System (INIS)
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
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.
DEFF Research Database (Denmark)
Lipsø, Hans Kasper Wigh; Nielsen, Kaspar Kirstein; Christensen, Dennis; Bahl, Christian Robert Haffenden; Engelbrecht, Kurt; Kuhn, Luise Theil; Smith, Anders
2011-01-01
The effect of demagnetization in a stack of gadolinium plates is determined experimentally by using spatially resolved measurements of the adiabatic temperature change due to the magnetocaloric effect. The number of plates in the stack, the spacing between them and the position of the plate on...
Simulation of the magnetocaloric effect in Tb nanofilms
International Nuclear Information System (INIS)
Rare-earth (RE) metals have different magnetic structures resulting from the competition between the crystal-field and exchange interactions. When a magnetic field is applied it creates a third interaction and the magnetic structures are more complicated. In thin films, it is expected that even the magnetic arrangement itself can be strongly modified. Rare-earth helimagnets such as Terbium (Tb), Holmium (Ho) and Dysprosium (Dy) represent the best candidates to evidence such finite-size effects. This finite-size effect is caused by the reduced number of atoms in the direction perpendicular to the film plane that leads to a decrease of the total magnetic exchange energy. We report this contribution to the investigation of magnetocaloric effect (MCE) of thin Terbium films in the helimagnetic temperature range, from TC = 219 K to TN = 231 K, for external fields of the order of 1 kOe. We find that for strong fields, H = 50 kOe, the adiabatic temperature change ΔT near the Néel temperature is around 15 K for any thickness of Tb films. However large thickness effects are found for small values of the magnetic field. For field strength of the order of a few kOe, the thermocaloric efficiency increases significantly for ultrathin (nanomagnetic) films
Colossal magnetocaloric effect in magneto-auxetic systems
Dudek, M. R.; Wojciechowski, K. W.; Grima, J. N.; Caruana-Gauci, R.; Dudek, K. K.
2015-08-01
We show that a mechanically driven magnetocaloric effect (MCE) in magneto-auxetic systems (MASs) in the vicinity of room temperature is possible and the effect can be colossal. Even at zero external magnetic field, the magnetic entropy change in this reversible process can be a few times larger in magnitude than in the case of the giant MCE discovered by Pecharsky and Gschneidner in Gd5(Si2Ge2). MAS represent a novel class of metamaterials having magnetic insertions embedded within a non-magnetic matrix which exhibits a negative Poisson’s ratio. The auxetic behaviour of the non-magnetic matrix may either enhance the magnetic ordering process or it may result in a transition to the disordered phase. In the MAS under consideration, a spin 1/2 system is chosen for the magnetic component and the well-known Onsager solution for the two-dimensional square lattice Ising model at zero external magnetic field is used to show that the isothermal change in magnetic entropy accompanying the auxetic behaviour can take a large value at room temperature. The practical importance of our findings is that MCE materials used in present engineering applications may be further enhanced by changing their geometry such that they exhibit auxetic behaviour.
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.
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.
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.
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.
Anisotropy of the magnetocaloric effect in DyNiAl
Czech Academy of Sciences Publication Activity Database
Kaštil, J.; Javorský, P.; Andreev, Alexander V.
2009-01-01
Roč. 321, č. 15 (2009), s. 2318-2321. ISSN 0304-8853 Institutional research plan: CEZ:AV0Z10100520 Keywords : magnetocaloric effec * DyNiAl * magnetism * anisotropy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.204, year: 2009
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.
International Nuclear Information System (INIS)
Highlights: • Ni51Cu4Mn20Ga25 alloy exhibits normal elastocaloric and magnetocaloric effects. • L21 atomic order of the alloy is increased after annealing at 773 K for 10 h. • Increasing L21 atomic order improves its elastocaloric and magnetocaloric effects. • Atomic ordering modifies the magnetic and martensitic transitions of the system. - Abstract: The coexisting elastocaloric and magnetocaloric effects in ferromagnetic shape memory alloys have attracted much attention for the potential application in solid state refrigeration. Previous studies show that the L21 atomic ordering of Heusler ferromagnetic shape memory alloys plays important role on their magnetocaloric effect. However, no research work investigates the effect of atomic ordering on their elastocaloric effect yet. In this study, we investigated the influence of atomic ordering on the elastocaloric and magnetocaloric effects of a Ni51Cu4Mn20Ga25 ferromagnetic shape memory alloy. The alloy exhibits normal elastocaloric effect and normal magnetocaloric effect near room temperature. Moreover, we found that the enhancement of atomic order in this alloy can greatly increase the entropy change and refrigeration capacity of its elastocaloric and magnetocaloric effects. This is attributed to that the atomic ordering modifies the magnetic and martensitic transitions of the system
Energy Technology Data Exchange (ETDEWEB)
Huang, Chonghui [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Wang, Yu, E-mail: yuwang@mail.xjtu.edu.cn [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China); Multi-disciplinary Materials Research Center, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an 710049 (China); Tang, Zhao; Liao, Xiaoqi; Yang, Sen; Song, Xiaoping [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049 (China)
2015-05-05
Highlights: • Ni{sub 51}Cu{sub 4}Mn{sub 20}Ga{sub 25} alloy exhibits normal elastocaloric and magnetocaloric effects. • L2{sub 1} atomic order of the alloy is increased after annealing at 773 K for 10 h. • Increasing L2{sub 1} atomic order improves its elastocaloric and magnetocaloric effects. • Atomic ordering modifies the magnetic and martensitic transitions of the system. - Abstract: The coexisting elastocaloric and magnetocaloric effects in ferromagnetic shape memory alloys have attracted much attention for the potential application in solid state refrigeration. Previous studies show that the L2{sub 1} atomic ordering of Heusler ferromagnetic shape memory alloys plays important role on their magnetocaloric effect. However, no research work investigates the effect of atomic ordering on their elastocaloric effect yet. In this study, we investigated the influence of atomic ordering on the elastocaloric and magnetocaloric effects of a Ni{sub 51}Cu{sub 4}Mn{sub 20}Ga{sub 25} ferromagnetic shape memory alloy. The alloy exhibits normal elastocaloric effect and normal magnetocaloric effect near room temperature. Moreover, we found that the enhancement of atomic order in this alloy can greatly increase the entropy change and refrigeration capacity of its elastocaloric and magnetocaloric effects. This is attributed to that the atomic ordering modifies the magnetic and martensitic transitions of the system.
Barocaloric effect in the magnetocaloric prototype Gd5Si2Ge2
Energy Technology Data Exchange (ETDEWEB)
Yuce, Suheyla; Barrio, Maria; Emre, Baris; Stern-Taulats, Enric; Planes, Antoni; Tamarit, Josep-Lluis; Mudryk, Yaroslav; Gschneidner, Karl A.; Pecharsky, Vitalij K.; Manosa, Lluis
2012-08-16
We report on calorimetric measurements under hydrostatic pressure that enabled us to determine the barocaloric effect in Gd5Si2Ge2. The values for the entropy change for moderate pressures compare favourably to those corresponding to the magnetocaloric effect in this compound. Entropy data are complemented with direct measurements of the adiabatic pressure-induced temperature change.
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
International Nuclear Information System (INIS)
The effect of demagnetization in a stack of gadolinium plates is determined experimentally by using spatially resolved measurements of the adiabatic temperature change due to the magnetocaloric effect. The number of plates in the stack, the spacing between them and the position of the plate 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. - Highlights: → The magnetocaloric effect is used as an indirect measure of the internal magnetic field. → To our knowledge nobody has published experimental determination of demagnetizing field in stack configurations of plates of magnetic material. → We present good agreement between the experimental results and an established numerical model. → This serves to show that the model may be used further to predict, e.g., optimal configurations.
Study of Suitable Arrangement of Magnetic Circuits for Realization of Magnetocaloric Effect
Czech Academy of Sciences Publication Activity Database
Doležel, Ivo; Ota, J.; Ulrych, B.
Pilsen : University of West Bohemia, 2009, s. 1-5. ISBN 978-80-7043-821-3. [Advanced Methods of the Theory of Electrical Engineering - AMTEE 09. Cheb (CZ), 07.09.2009-09.09.2009] Institutional research plan: CEZ:AV0Z20570509 Keywords : magnetocaloric effect * magnetic field * permanent magnets Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering http://amtee.zcu.cz
DEFF Research Database (Denmark)
Jeppesen, Stinus; Linderoth, Søren; Pryds, Nini; Kuhn, Luise Theil; Jensen, Jesper Buch
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...
Czech Academy of Sciences Publication Activity Database
Burkhanov, G.S.; Kolchugina, N.B.; Tereshina, Evgeniya; Tereshina, I. S.; Politova, G.A.; Chzhan, V.B.; Badurski, D.; Chistyakov, O.D.; Paukov, M.; Drulis, H.; Havela, L.
2014-01-01
Roč. 104, č. 24 (2014), "242402-1"-"242402-5". ISSN 0003-6951 R&D Projects: GA ČR GAP204/12/0150 Institutional support: RVO:68378271 Keywords : high-purity rare-earth metals * gadolinium * magnetocaloric effect * hydrogenation * structural studies Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.302, year: 2014
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.
International Nuclear Information System (INIS)
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
Giant magnetocaloric effect in antiferromagnetic DyVO4 compound
Midya, A.; Khan, N.; Bhoi, D.; Mandal, P.
2014-09-01
We have investigated the magnetic and magnetocaloric properties of DyVO4 by magnetization and heat capacity measurements. χ(T) shows antiferromagnetic to paramagnetic transition at TNDy~3.5 K. The compound undergoes a metamagnetic transition and exhibits a huge entropy change. The maximum values of magnetic entropy change (ΔSM), adiabatic temperature change (ΔTad) and refrigerant capacity (RC) reach 26 J kg-1 K-1, 17 K, and 526 J kg-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.
Magnetocaloric effect in (TbcR1-c)Co2 (R=Er and Ho)
International Nuclear Information System (INIS)
Highlights: • Microscopical description of the chemical disorder in rare earth based compounds. • Magnetocaloric effect in compounds with first order phase transition. • Effect of impurities on the nature of the magnetic phase transition. - Abstract: In this paper we theoretically discuss the magnetocaloric effect in (TbcR1-c)Co2 (R = Er and Ho). To this end, we use a model Hamiltonian in which are included the 4f electrons from rare earth ions and the 3d electrons from Co ions. In the model is also included an extra term to account for the crystal electric field, which plays an important role in the magnetic and caloric properties of these compounds
MnFe(PGe) compounds: Preparation, structural evolution, and magnetocaloric effects
International Nuclear Information System (INIS)
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. (paper)
Wada, H.; Takahara, T.; Katagiri, K.; Ohnishi, T.; Soejima, K.; Yamashita, K.
2015-05-01
Magnetocaloric and related properties of Ru and Ni substituted (MnFe)2(PSi) are presented. It is found that Ru and Ni are effective doping elements to reduce the thermal hysteresis of (MnFe)2(PSi). The origin of the thermal hysteresis is discussed on the basis of a thermodynamic model. It is shown that the elastic energy is responsible for the thermal hysteresis. We also show recent developments of the production process of Mn compounds in an industrial scale.
Staunton, J. B.; Banerjee, R.; dos Santos Dias, Manuel; Deak, A.; Szunyogh, L.
2014-01-01
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 $T_t =$ 495K and a maximum isothermal entropy change in 2 Tesla of $|\\Delta S|= 21.1$ J~K$^{-1}$~kg$^{-1}$. A...
Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy
Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.
2016-01-01
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.
International Nuclear Information System (INIS)
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. (paper)
Szałowski, Karol; Balcerzak, Tadeusz
2014-09-01
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.
Elasticity and magnetocaloric effect in MnFe4Si3
Herlitschke, M.; Klobes, B.; Sergueev, I.; Hering, P.; Perßon, J.; Hermann, R. P.
2016-03-01
The room temperature magnetocaloric material MnFe4Si3 was investigated with nuclear inelastic scattering (NIS) and resonant ultrasound spectroscopy (RUS) at different temperatures and applied magnetic fields in order to assess the influence of the magnetic transition and the magnetocaloric effect on lattice dynamics. The NIS data give access to phonons with energies above 3 meV, whereas RUS probes the elasticity of the material in the MHz frequency range and thus low-energy, ˜ neV, phonon modes. A significant influence of the magnetic transition on the lattice dynamics is observed only in the low-energy, long-wavelength limit. MnFe4Si3 and other compounds in the Mn5 -xFexSi3 series were also investigated with vibrating sample magnetometry, resistivity measurements, and Mössbauer spectroscopy in order to study the magnetic transitions and to complement the results obtained on the lattice dynamics.
Magnetocaloric effect in (Tb,Dy,R)(Co,Fe){sub 2} (R = Ho, Er) multicomponent compounds
Energy Technology Data Exchange (ETDEWEB)
Tereshina, I S; Politova, G A; Burkhanov, G S; Chistyakov, O D [Baikov Institute of Metallurgy and Material Sciences RAS, Moscow 119991 (Russian Federation); Tereshina, E A [Institute of Physics ASCR, Prague 18221 (Czech Republic); Nikitin, S A, E-mail: teresh@imet.ac.ru [Lomonosov Moscow State University, Moscow 119991 (Russian Federation)
2011-01-01
The magnetic, magnetocaloric, and magnetoelastic properties of Tb{sub x}Dy{sub y}R{sub z}(Co,Fe){sub 2} (R = Ho, Er; x + y + z = 1) single-phase alloys prepared by arc melting were investigated. The high-purity samples with various compositions were used for the study, and a comprehensive investigation of the properties was performed. The measurements of the magnetocaloric effect (MCE) were carried out by a direct method; and the magnetostriction was determined using the strain-gauge technique. In the vicinity of the magnetic phase transition, an abrupt change of the magnetization, a large MCE, and the maxima of volume magnetostriction were observed for the compounds studied. Obtained results of MCE in (Tb,Dy)Co{sub 2} agree well with available theoretical calculations.
Magnetic properties and magnetocaloric effect in Tb3Al2 compound
International Nuclear Information System (INIS)
Highlights: • Domain-wall-freezing effect may occur at low temperature due to magnetocrystalline anisotropy. • The ΔTad for Tb3Al2 is 9.0 K under 50 kOe, comparable to that of La(Fe0.88Si0.12)13 compound. • The full width at half-maximum value of ΔTad peak is much larger than that for La(Fe0.88Si0.12)13. - Abstract: Magnetic properties of intermetallic Tb3Al2 compound have been investigated systematically by magnetization and heat capacity measurements. Tb3Al2 compound undergoes a ferromagnetic–paramagnetic transition at Curie temperature TC = 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. Tb3Al2 compound shows large magnetocaloric effect without hysteresis loss around TC, 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 ΔTad peak for Tb3Al2 at 50 kOe is 55 K, more than three times of that (17 K) for typical magnetocaloric material La(Fe0.88Si0.12)13
Field-induced reversible magnetocaloric effect in CoCl2
International Nuclear Information System (INIS)
Research highlights: The electronic structure and magnetic properties of CoCl2 have been investigated by several groups, but the magnetocaloric effect was not reported. In this paper, we study the magnetic and magnetocaloric properties of the antiferromagnet CoCl2 at low temperatures. A large negative magnetic-entropy change and a large cooling power are found together with a field-induced MCE conversion (the MCE changes its sign in the applied magnetic field). - Abstract: A sign change of the magnetocaloric effect is induced by a magnetic field, which is related to a field-induced transition from the antiferromagnetic to the ferromagnetic state below the Neel temperature of CoCl2 nanoparticles. The reversible magnetic-entropy change -ΔSm (4.1 and 11.5 J kg-1 K-1 at 27 K for a field change of 3 and 7 T, respectively) almost without hysteresis and the large cooling power (83.4 and 148 J kg-1, correspondingly) indicates that CoCl2 is a potential candidate for application in magnetic refrigeration in the low-temperature range.
Metamagnetic transition and magnetocaloric effect in ErCo2
International Nuclear Information System (INIS)
The magnetization MH(T) and the specific heat capacity cP,H(T) of the ErCo2 intermetallic compound were measured in the temperature range 5-100 K and in 0, 7 or 14 T applied field, respectively. A clear first-order phase transition is found at the magnetic ordering of the Er sublattice. While for order-disorder transitions in simple ferromagnets there is a good agreement between magnetocaloric performance predicted on the basis of magnetization measurements compared to calorimetric measurements, it is necessary to investigate whether the agreement is still present for materials with more complex transitions (e.g. order-order, metamagnetic, first order etc). From the magnetization data the magnetic entropy change at the transition was calculated using the Maxwell relations. From the cP,H(T) measurements both the magnetic entropy change and the adiabatic temperature change were calculated and compared to values obtained from MH(T) and to the values calculated by the usual approximative expressions. The agreement is less good than in the case of second-order phase transitions. The discrepancy is interpreted in terms of the theory of first-order/metamagnetic transitions showing that the boundary conditions used in the derivation of the approximative formulae for simple ferromagnetic materials are not appropriate for more complex transitions as in ErCo2. (author)
International Nuclear Information System (INIS)
Magnetocaloric studies have been performed on a two-dimensional (2D) quantum system Cu(en)(H2O)2SO4 (en=ethylendiamine=C2N2H8) in the temperature range from 0.6 K to 4 K in magnetic fields up to 2 T by adiabatic magnetization and demagnetization measurements. The title compound has been previously identified as a potential realization of the quasi-two dimensional spatially anisotropic triangular Heisenberg antiferromagnet with spin 1/2 and effective intralayer exchange coupling, J/kB= −1.4 K. A phase transition to the magnetically ordered state has been observed in zero magnetic field at TN = 0.91 K. The normal magnetocaloric effect (MCE) was observed in the temperature range from 0.6 K to 0.98 K. In contrast, at temperatures near the phase transition the character of MCE changes to inverse and above the temperature 2 K the normal MCE was observed again. This change can be ascribed to the onset of short-range magnetic correlations previously observed in specific heat and susceptibility studies.
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.
History dependence of directly observed magnetocaloric effects in (Mn, Fe)As
Bratko, Milan; Morrison, Kelly; de Campos, Ariana; Gama, Sergio; Lesley F. Cohen; Sandeman, Karl G.
2012-01-01
We use a calorimetric technique operating in sweeping magnetic field to study the thermomagnetic history- dependence of the magnetocaloric effect (MCE) in Mn0.985Fe0.015As. We study the magnetization history for which a "colossal" MCE has been reported when inferred indirectly via a Maxwell relation. We observe no colossal effect in the direct calorimetric measurement. We further examine the impact of mixed-phase state on the MCE and show that the first order contribution scales linearly with...
Modeling and Characterization of the Magnetocaloric Effect in Ni2MnGa Materials
Energy Technology Data Exchange (ETDEWEB)
Nicholson, Don M [ORNL; Odbadrakh, Khorgolkhuu [ORNL; Shassere, Benjamin [ORNL; Rios, Orlando [ORNL; Hodges, Jason P [ORNL; Ludtka, Gerard Michael [ORNL; Porter, Wallace D [ORNL; Safa-Sefat, Athena [ORNL; Rusanu, Aurelian [ORNL; Brown, Greg [ORNL; Evans III, Boyd Mccutchen [ORNL
2014-01-01
Magnetic shape memory alloys have great promise as magneto-caloric effect refrigerant materials due to their combined magnetic and structural transitions. Computational and experimental research is reported on the Ni2MnGa material system. The magnetic states of this system are explored using the Wang-Landau statistical approach in conjunction with the Locally Self-consistent Multiple-Scattering method. The effects of alloying agents on the transition temperatures of the Ni2MnGa alloy are investigated using differential scanning calorimetry and superconducting quantum interference device. Experiments are performed at the Spallation Neutron Source at Oak Ridge National Laboratory to observe the structural and magnetic phase transformations.
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.
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.
International Nuclear Information System (INIS)
The magnetocaloric effect is the isothermal change of magnetic entropy and the adiabatic temperature change induced in a magnetic material when an external magnetic field is applied. In this work, we present an experimental setup to study this effect in metamagnetic transitions, using the differential thermal analysis technique, which consists in measuring simultaneously the temperatures of the sample of interest and a reference one while an external magnetic field ramp is applied. We have tested our system to measure the magnetocaloric effect in La0.305Pr0.32Ca0.375MnO3, which presents phase separation effects at low temperatures (T<200 K). We obtain ΔT vs H curves, and analyze how the effect varies by changing the rate of the magnetic field ramp. Our results show that the intensity of the effect increases with the magnetic field change rate. We also have obtained the effective heat capacity of the system without the sample by performing calorimetric measurements using a pulse heat method, fitting the temperature change with a two tau description. With this analysis, we are able to describe the influence of the environment and subtract it to calculate the adiabatic temperature change of the sample.
Energy Technology Data Exchange (ETDEWEB)
Bennett, L.H.; McMichael, R.D.; Swartzendruber, L.J.; Shull, R.D. (National Inst. of Standards and Technology, Gaithersburg, MD (USA)); Watson, R.E. (Brookhaven National Lab., Upton, NY (USA))
1991-01-01
The magnetic entropy change of a ferromagnet induced by an application of a magnetic field is greatest in the temperature region near the Curie point, and the magnitude of the effect is expected to rise monotonically with the size of individual moments which make up the material. We explore the case of nanocomposite materials with ferromagnetically interacting clusters having large cluster magnetic moments as a function of cluster size. As cluster size increases, both Monte Carlo and mean field calculations show a decrease in the entropy change at {Tc} for a given applied field and constant total magnetic moment, and an increase in the entropy change well over {Tc}. In addition, for the first time, we present a comparison of the results of mean field and Monte Carlo calculations of the magnetocaloric effect in classical Heisenberg ferromagnets. Previous calculations of the magnetocaloric effect have taken the mean field approach, which is known to underestimate the spontaneous magnetization below {Tc}. These issues are relevant to devices employing magnetic refrigeration. 11 refs., 2 figs.
Analysis of the Magnetocaloric Effect in Powder Samples Obtained by Ball Milling
Blázquez, J. S.; Ipus, J. J.; Moreno-Ramírez, L. M.; Borrego, J. M.; Lozano-Pérez, S.; Franco, V.; Conde, C. F.; Conde, A.
2015-06-01
Since the discovery of the giant magnetocaloric effect (MCE) close to room temperature in FeRh and particularly in Gd5Si2Ge2 compounds, the study of this phenomenon has experienced an exponential growth. Among the different techniques used to produce magnetocaloric materials, ball milling has been shown as a very versatile one and presents several advantages over other preparation techniques ( e.g., easy scale-up to industrial production). Although a general decrease of the peak value of the magnetic entropy change is observed for milled samples, it can be compensated by the large broadening of the MCE peak, leading to an increase of the refrigeration capacity. In this short review, several aspects inherent to powder samples affecting MCE will be discussed, such as the relevant effect of the demagnetizing field, the possible multiphase character, and the presence of Curie temperature distributions. In mechanically alloyed samples, the two latter factors are typically affected by the degree of integration of the different starting constituents.
Specific heat and magnetocaloric effect in RMnO3 (R=Gd and Tb) multiferroics
International Nuclear Information System (INIS)
Multiferroic RMnO3 (R= Gd and Tb) samples were prepared through sol gel method. After characterizing the sample structurally, a systematic investigation of specific heat was performed over the temperature range 4-70 K under 0T, 2T and 5T magnetic fields to study the magnetocaloric effect. The samples are found to exhibit three transitions near 40 K, 25 K and below 10 K. The hump at 10 K broadens under magnetic fields of 2T and 5T, indicating the shift in entropy to higher temperature. The magnetocaloric effect (MCE) of the samples in terms of isothermal entropy change (ΔS) and adiabatic temperature change (ΔTad) was evaluated from these specific heat measurements under 2T and 5T magnetic fields. From the systematic analysis it has been observed that the samples can be used as magnetic refrigerant that induces an adiabatic cooling of about ΔTad ≈ 2.4 K on application of 5T magnetic fields in the temperature range 4-30 K
Czech Academy of Sciences Publication Activity Database
Tereshina, I.; Cwik, J.; Tereshina, Evgeniya; Politova, G.; Burkhanov, G.; Chzhan, V.; Ilyushin, A.; Miller, M.; Zaleski, A.; Nenkov, K.; Schultz, L.
2014-01-01
Roč. 50, č. 11 (2014), s. 2504604. ISSN 0018-9464 Institutional support: RVO:68378271 Keywords : giant magnetostriction * Laves phase structure * magnetic anisotropy * magnetocaloric effect * rare- earth intermetallic Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2014
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...
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.
Pressure effect on phase transitions and magnetocaloric effect in Gd.sub.5./sub.Ge.sub.4./sub..
Czech Academy of Sciences Publication Activity Database
Arnold, Zdeněk; Skorokhod, Yuriy; Kamarád, Jiří; Magen, C.; Algarabel, P.A.
2009-01-01
Roč. 105, č. 3 (2009), 07A934/1-07A934/3. ISSN 0021-8979 R&D Projects: GA ČR(CZ) GA106/06/0368 Institutional research plan: CEZ:AV0Z10100521 Keywords : Curie temperature * ferromagnetic materials * ferromagnetic-antiferromagnetic transitions * gadolinium compounds * magnetocaloric effect Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.072, year: 2009
Effective medium theory for anisotropic metamaterials
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.
Experimental investigation of small-scale magnetocaloric refrigerator
Czech Academy of Sciences Publication Activity Database
Kaštil, Jiří; Tětek, J.; Tuček, A.
2013-01-01
Roč. 124, č. 4 (2013), s. 740-744. ISSN 0587-4246 Institutional support: RVO:68378271 Keywords : magnetocaloric refrigerator * magnetocaloric effect Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.604, year: 2013
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.
Low-field magnetocaloric effect in (Gd1-xDyx)3Al2 alloys
International Nuclear Information System (INIS)
The effects of Dy substitution on the magnetic properties and magnetocaloric effect of (Gd1-xDyx)3Al2 (x = 0-0.5) alloys have been investigated by X-ray diffraction and magnetization measurements. It was found that Dy substitution decreased the cell volume as well as the magnetic transition temperature. The maximum magnetic entropy change for a magnetic field change from 0 to 1 T almost keep constant with values of -2.2 to -2.5 J/kg K, while the refrigerant capacity (RC) decreases with Dy addition. The adjustable Curie temperature, moderate magnetic entropy change, and large RC make these alloys potential candidates as magnetic refrigerant.
Giant magnetocaloric effect, magnetization plateaux and jumps of the regular Ising polyhedra
International Nuclear Information System (INIS)
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
Large rotating magnetocaloric effect in the orthorhombic DyMnO3 single crystal
Balli, M.; Mansouri, S.; Jandl, S.; Fournier, P.; Dimitrov, D. Z.
2016-07-01
A large magnetocaloric effect can be obtained around TN, Dy ̴8 K simply by spinning the orthorhombic DyMnO3 single crystal within the cb-plane in a constant magnetic field, instead of the standard magnetization-demagnetization process. Under 7 T, the maximum rotating entropy change (-ΔSR, cb) and the associated adiabatic temperature change (ΔTad, cb) are 16.3 J/kg K and 11 K, respectively. The corresponding refrigerant capacity is 440 J/kg, with no thermal and field hysteresis losses. Our findings show that the orthorhombic DyMnO3 could be used as a good refrigerant in more compact and efficient cryomagnetocaloric refrigerators.
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.
Magnetic properties and magnetocaloric effect of the compound NdSi
International Nuclear Information System (INIS)
The magnetic properties and magnetocaloric effect (MCE) of the compound NdSi have been studied. The magnetic ground state of this compound is determined to be ferromagnetic and a second-order phase transition occurs at the Curie temperature TC=46 K. Large magnetic-entropy changes (ΔS) with no hysteresis loss are found with field variation. Maximum values of ΔS −6.8 J/kg K and −12.4 J/kg K are found for field changes of 0–20 kOe and 0–50 kOe, respectively. With the merits of the large ΔS and without hysteresis loss, NdSi can be considered as a competitive candidate magnetic refrigerant
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.
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.
International Nuclear Information System (INIS)
A ternary Ho–Al–Co system with high glass-forming ability (GFA) was developed and fully glassy rods with diameters up to 1 cm can be produced for the best glass former of Ho55Al27.5Co17.5 alloy. The thermal stability and low-temperature magnetic properties of the Ho55Al27.5Co17.5 bulk metallic glass (BMG) were studied. The magnetic transition temperature of this alloy is ∼14 K as determined by the thermomagnetic measurement. Two indicators, i.e. isothermal magnetic entropy change (ΔSM) and the relative cooling power (RCP), were adopted to evaluate the magnetocaloric effect (MCE) of the alloy under a low magnetic field up to 2 T, which can be generated by permanent magnets. The values of |ΔSM| and RCP are 7.98 J kg−1 K−1 and 191.5 J kg−1, respectively. The Ho55Al27.5Co17.5 BMG with good MCE and high GFA provides an attractive candidate for magnetic refrigeration applications, like hydrogen liquefaction and storage. - Highlights: ► A ternary Ho–Al–Co BMG system with high glass-forming ability was developed. ► Fully glassy rods of Ho55Al27.5Co17.5 alloy were produced up to 1 cm in diameter. ► The thermal stability and magnetic properties of the BMG were evaluated. ► The BMG exhibits good magnetocaloric effect under a low magnetic field up to 2 T.
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.
International Nuclear Information System (INIS)
A facile hydrothermal strategy is proposed to synthesize flower-like β- Co(OH)2 hierarchical microspherical superstructures with a diameter of 0.5-1.5 µm, which are self-assembled by β - Co(OH)2 nano sheets with the average thickness ranging between 20 and 40 nm. The magnetocaloric effect associated with magnetic phase transitions in Co(OH)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 –ΔSm (13.4 J/kg K at 15 K for a field change of 5 T) indicates that flower-like Co(OH)2 superstructures is a potential candidate for application in magnetic refrigeration in the low-temperature range. (author)
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.
From direct to inverse giant magnetocaloric effect in Co-doped NiMnGa multifunctional alloys
Czech Academy of Sciences Publication Activity Database
Fabbrici, S.; Kamarád, Jiří; Arnold, Zdeněk; Casoli, F.; Paoluzi, A.; Bolzoni, F.; Cabassi, R.; Solzi, C.; Porcari, G.; Pernechele, C.; Albertini, F.
2011-01-01
Roč. 59, č. 1 (2011), s. 412-419. ISSN 1359-6454 R&D Projects: GA ČR GA202/09/0030 Institutional research plan: CEZ:AV0Z10100521 Keywords : Ni–Mn–Ga–Co * ferromagnetic shape memory alloys * magnetostructural transformations * magnetic properties * inverse magnetocaloric effect Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.755, year: 2011 www.elsevier.com/locate/actamat
Tereshina, I. S.; Chzhan, V. B.; Tereshina, E. A.; Khmelevskyi, S.; Burkhanov, G. S.; Ilyushin, A. S.; Paukov, M. A.; Havela, L.; Karpenkov, A. Yu.; Cwik, J.; Koshkid'ko, Yu. S.; Miller, M.; Nenkov, K.; Schultz, L.
2016-07-01
The influence of simultaneous substitution within the rare earth (R) and Co sublattices on the structural, magnetic, and magnetocaloric properties of the Laves phase RCo2-type compounds is studied. Main attention is devoted to the studies of the magnetostructural phase transitions and the transition types with respect to the alloy composition. Multicomponent alloys Tbx(Dy0.5Ho0.5)1-xCo2 and Tbx(Dy0.5Ho0.5)1-xCo1.75Al0.25 were prepared with the use of high purity metals. Majority of the Tbx(Dy0.5Ho0.5)1-xCo2 alloys exhibit magnetic transitions of the first-order type and a large magnetocaloric effect. The substitution of Al for Co in Tbx(Dy0.5Ho0.5)1-xCo2 increases the Curie temperature (TC) but changes the transition type from first-to the second-order. The discussion of the physical mechanisms behind the observed phenomena is given on the basis of the first principles electronic-structure calculations taking into account both the atomic disorder and the magnetic disorder effects at finite temperatures. The advantage of Al-containing materials is that sufficiently high magnetocaloric effect values are preserved at T > TC.
Magnetism and magnetocaloric effect study of CaFe0.7Co0.3O3
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.
Practical system for the direct measurement of magneto-caloric effect by micro-thermocouples.
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. PMID:22938309
International Nuclear Information System (INIS)
High-purity Gd prepared by distillation is a structurally inhomogeneous system consisting of needle-shaped crystals of cross section 0.5–2.5 μm with near-c-axis orientation embedded in a matrix of nanosized (30–100 nm) grains. By measuring the magnetocaloric effect (MCE) directly, we find that the MCE values differ markedly for the plate-shaped samples cut out of a distillate along and perpendicular to the crystals. The effect of small controlled amounts of impurity (hydrogen) on the properties of distilled Gd is further studied. We observe opposite trends in the MCE response to hydrogen charging with respect to the crystal's orientation within the samples and discuss mechanisms interrelating the unique structural morphology with the impurity behavior. As an overall assessment, the Curie temperatures of α-GdHx solid solutions increase from 291 K up to 294 K when increasing hydrogen concentration x from 0 to 0.15. Hydrogenation is found to broaden the ferromagnetic-to-paramagnetic phase transition. Hydrogen-containing specimens demonstrate reversibility of MCE at these temperatures.
The influence of Co substitution on the magnetocaloric effect of Gd(Al,Fe)2
International Nuclear Information System (INIS)
The magnetocaloric effect (MCE) in samples GdAl1.7(Fe1-xCox)0.3 with x= 0, 0.1, 0.2, 0.3 and 0.4 were investigated by x-ray diffraction (XRD) and magnetization measurements. It was found that five samples crystallize well in the MgCu2-type structure. The lattice parameter and the values of Curie temperature decrease with increasing Co content, whereas the magnetic-entropy change and cooling capacity increase. In the magnetic-field change of 2.0 T the maximum of the magnetic-entropy change and refrigerant capacity in sample GdAl1.7Fe0.7Co0.3 reach 4.8 J kg-1 K-1 and 88.3 J kg-1, respectively. The maximum of the magnetic-entropy change is comparable to that of Gd metal (3.8 J kg-1 K-1 in Δ B=1.5 T)
Influence of fabrication conditions on giant magnetocaloric effect of Ni–Mn–Sn ribbons
International Nuclear Information System (INIS)
The magnetocaloric effect of Ni50Mn50−xSnx ribbons (x = 11–15) prepared by using melt-spinning and subsequent annealing has been investigated. The x-ray diffraction data of specimens show that all the samples are partially crystallized with Ni2MnSn phase. The magnetic transitions of these ribbons strongly depend on Sn-concentration and annealing process. Particularly, the antiferromagnetic–ferromagnetic transition is just observed at a narrow range of the Sn-concentration (x = 12–14). The positive magnetic entropy changes occurring at the transition temperature of the antiferromagnetic phase are quite large, |ΔSm|max = 5.7 J kg−1 K−1 (for x = 13) with external magnetic field change ΔH = 12 kOe. Besides that, the negative magnetic entropy changes take place near Curie temperature and their magnitude is also large, |ΔSm|max = 1.9 J kg−1 K−1 (for x = 13). The obtained results indicate that Ni50Mn50−xSnx ribbons are good candidates for magnetic refrigeration application at room temperature. (paper)
Room temperature table-like magnetocaloric effect in amorphous Gd50Co45Fe5 ribbon
Liu, G. L.; Zhao, D. Q.; Bai, H. Y.; Wang, W. H.; Pan, M. X.
2016-02-01
Gd50Co45Fe5 amorphous alloy ribbon with a table-like magnetocaloric effect (MCE) suitable for the ideal Ericsson cycle at room temperature has been developed. In addition to a high magnetic transition temperature of 289 K very close to that of Gd (294 K), a relatively large value of refrigerant capacity (~521 J kg-1) has been achieved under a field change of 5 T. This value of refrigerant capacity (RC) is about 27% and 70% larger than those of Gd (~410 J kg-1) and Gd5Si2Ge2 (~306 J kg-1). More importantly, the peak value of magnetic entropy change (-Δ S\\text{M}\\max ) approaches a nearly constant value of ~3.8 J ṡ kg-1 ṡ K-1 under an applied field change of 0~5 T in a wide temperature span over 40 K around room temperature, which could be used as the candidate working material in the Ericsson-cycle magnetic regenerative refrigerator around room temperature.
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.
Magnetocaloric effect and critical behavior in Mn2-imidazole-[Nb(CN)8] molecular magnetic sponge
Fitta, Magdalena; Pełka, Robert; Gajewski, Marcin; Mihalik, Marian; Zentkova, Maria; Pinkowicz, Dawid; Sieklucka, Barbara; Bałanda, Maria
2015-12-01
A comprehensive study of magnetocaloric effect (MCE) and critical behavior in the {Mn2(imH)2(H2O)4[Nb(CN)8]·4H2O}n molecular magnet is reported. The compound is an example of a magnetic sponge, where structural changes provoked by dehydration process lead to the increase of Tc critical temperature from 25 K for the as-synthesized sample (1) up to 60 K for the anhydrous one (2). MCE and critical behavior were investigated by magnetization measurements. The maximum value of magnetic entropy change ΔS, determined by the magnetization measurements for 1 is 6.70 J mol-1 K-1 (8.95 J kg-1 K-1) at μ0ΔH=5 T, while for 2 it is equal to 4.02 J mol-1 K-1 (7.73 J kg-1 K-1) at the same magnetic field change. The field dependence of MCE at Tc for 1 and 2 was consistent with critical exponents, which allowed to classify both phases to 3D Heisenberg universality class. The Tc-2/3 dependence of the maximum entropy change has been tested using data of 1 and 2 together with MCE data previously reported for other members of the ferrimagnetic Mn2-L-[Nb(CN)8] (L=imidazole, pyridazine and pyrazole) series. Experimental MCE results have been compared with the spin contribution to the magnetic entropy change estimated using a molecular field approximation.
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.
Magnetocaloric effect and magnetoresistance correlation in Ge-doped Mn2Sb
International Nuclear Information System (INIS)
Magnetocaloric effect (MCE) and magnetoresistance (MR) in Ge-doped Mn2Sb systems with near-room-temperature, first-order antiferromagnetic (AFM) to ferrimagnetic (FRI) transitions have been studied. They show an inverse MCE with a 3.2 J/kg-K isothermal change in entropy (ΔS), and a refrigeration capacity that varies linearly up to 130 J kg−1 for a 13 Tesla magnetic field change. MR (dominated by change in electronic structure) and ΔS (dominated by change in magnetic entropy) are shown to have similar temperature dependence but with opposite signs due to coupled electronic and magnetic changes across the transition. The ratio of the peak values of MR (%) and ΔS is found to be −5.6 (J/kg-K)−1, which remains nearly constant for the studied range of magnetic field change. Existing data of MR and MCE in other Mn2Sb systems (with substitution elements other than Ge) with nearby transition temperatures also show nearly same value for this ratio. Therefore, this ratio can be related to coupling between magnetic and electronic changes and will be an useful parameter for systems with such transitions. (paper)
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.
Magnetism in Complex Oxides Probed by Magnetocaloric Effect and Transverse Susceptibility
Bingham, Nicholas S.
Magnetic oxides exhibit rich complexity in their fundamental physical properties determined by the intricate interplay between structural, electronic and magnetic degrees of freedom. The common themes that are often present in these systems are the phase coexistence, strong magnetostructural coupling, and possible spin frustration induced by lattice geometry. While a complete understanding of the ground state magnetic properties and cooperative phenomena in this class of compounds is key to manipulating their functionality for applications, it remains among the most challenging problems facing condensed-matter physics today. To address these outstanding issues, it is essential to employ experimental methods that allow for detailed investigations of the temperature and magnetic field response of the different phases. In this PhD dissertation, I will demonstrate the relatively unconventional experimental methods of magnetocaloric effect (MCE) and radio-frequency transverse susceptibility (TS) as powerful probes of multiple magnetic transitions, glassy phenomena, and ground state magnetic properties in a large class of complex magnetic oxides, including La0.7Ca0.3- xSrxMnO3 (x = 0, 0.05, 0.1, 0.2 and 0.25), Pr0.5Sr0.5MnO3, Pr1-xSrxCoO 3 (x = 0.3, 0.35, 0.4 and 0.5), La5/8- xPrxCa3/8MnO3 (x = 0.275 and 0.375), and Ca3Co2O 6. First, the influences of strain and grain boundaries, via chemical substitution and reduced dimensionality, were studied via MCE in La0.7Ca 0.3-xSrxMnO 3. Polycrystalline, single crystalline, and thin-film La0.7Ca 0.3-xSrxMnO 3 samples show a paramagnetic to ferromagnetic transition at a wide variety of temperatures as well as an observed change in the fundamental nature of the transition (i.e. first-order magnetic transition to second order magnetic transition) that is dependent on the chemical concentration and dimensionality. Systematic TS and MCE experiments on Pr0.5Sr0.5MnO 3 and Pr0.5Sr0.5CoO3 have uncovered the different nature of low
The influence of hysteresis on the determination of the magnetocaloric effect in Gd_{5}Si_{2}Ge_{2}
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...... modelling magnetocaloric materials. It is shown that the model reproduces the magnetization data, directly measured adiabatic temperature changes and provides a good description of the material behavior under application conditions. We find that the material settles in an area of metastability under...... 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....
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.
Cugini, F.; Porcari, G.; Viappiani, C.; Caron, L.; dos Santos, A. O.; Cardoso, L. P.; Passamani, E. C.; Proveti, J. R. C.; Gama, S.; Brück, E.; Solzi, M.
2016-01-01
We present direct measurements of the magnetocaloric effect on a Fe2P-based compound induced by a milliseconds pulsed magnetic field of 1 T to test their possible use in high frequency (up to 100 Hz) thermomagnetic cycles. The reported measurements were performed with an innovative and versatile non-contact set up based on the mirage effect. The adiabatic temperature change of a MnFeP0.45As0.55 sample is presented and compared with measurements performed varying the same magnetic field in a time interval of 1 s and 100 ms. These results demonstrate the absence of kinetic constraints in the first-order phase transition of this sample induced on the milliseconds time scale. The study of the materials' response to millisecond magnetic field pulses represents a fundamental test for the development of more powerful and efficient magnetic refrigerators.
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.
Pressure effects on the magnetocaloric properties of Ni-rich and Mn-rich Ni.sub.2./sub.MnGa alloys
Czech Academy of Sciences Publication Activity Database
Albertini, F.; Kamarád, Jiří; Arnold, Zdeněk; Pareti, L.; Villa, E.; Righi, L.
2007-01-01
Roč. 316, - (2007), s. 364-367. ISSN 0304-8853 R&D Projects: GA ČR(CZ) GA106/06/0368 Institutional research plan: CEZ:AV0Z10100521 Keywords : magnetocaloric effect * magnetoelastic property * pressure effect * Heusler alloy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.704, year: 2007
Observable effects of anisotropic bubble nucleation
Blanco-Pillado, Jose J
2010-01-01
Our universe may have formed via bubble nucleation in an eternally-inflating background. Furthermore, the background may have a compact dimension--the modulus of which tunnels out of a metastable minimum during bubble nucleation--which subsequently grows to become one of our three large spatial dimensions. Then the reduced symmetry of the background is equivalent to anisotropic initial conditions in our bubble universe. We compute the inflationary spectrum in such a scenario and, as a first step toward understanding the effects of anisotropy, project it onto spherical harmonics. The resulting spectrum exhibits anomalous multipole correlations, their relative amplitude set by the present curvature parameter, which extend to arbitrarily large multipole moments. This raises the possibility of future detection, if slow-roll inflation does not last too long within our bubble. A full understanding of the observational signal must account for the effects of background anisotropy on photon free streaming, and is left...
Effective orthorhombic anisotropic models for wavefield extrapolation
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.
Magnetocaloric Materials and the Optimization of Cooling Power Density
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.
Investigation on the magnetocaloric effect in RNi2 (R: Dy, tb) melt-spun ribbon
de Souza, M. V.
2016-08-01
We report a theoretical and experimental investigation on the magnetocaloric properties of the rare earth RNi2 (R=Dy,Tb) in melt-spun ribbon and bulk form. The theoretical calculations were performed using a Hamiltonian model including the Zeeman-exchange interactions and the crystalline electrical field. Thus the magnetocaloric potential was calculated in the easy magnetic axes, in order an average over all of the possible directions. The isothermal entropy-change dependence on temperature calculated was compared with available experimental data for melt-spun ribbon and bulk material. We also investigated, theoretically and experimentally, the behavior of a DyNi2 and TbNi2 composite with optimized molar proportions and discussed this in the context of the optimum regeneration Ericsson cycle.
International Nuclear Information System (INIS)
The intermetallic compound MnFe4Si3 has been studied by high-resolution Time of Flight (TOF) neutron powder diffraction. MnFe4Si3 crystallizes in the hexagonal space group P63/mcm with lattice constants of a=b=6.8043(4) Å and c=4.7254(2) Å at 310 K. Magnetic susceptibility measurements show clearly the magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. Magnetic structure refinements based on neutron powder diffraction data with and without external magnetic field reveal strong evidence on the origin of the large magnetocaloric effect (MCE) in this material as a partial reordering of the spins between ∼270 K and 300 K. In addition, electronic structure calculations using the self-consistent, spin-polarized Tight Binding-Linear MuffinTin Orbital (TB-LMTO) method were also accomplished to address the “coloring problem” (Mn/Fe site preference) as well as the unique ferromagnetic behavior of this intermetallic compound. - Graphical abstract: Theoretical and experimental reinvestigation of the magnetic structure of MnFe4Si3 for a better understanding of its large magnetocaloric effect (MCE). - Highlights: • Strong magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. • MCE associated to a partial reordering of the spins between ∼270 K and 300 K. • DFT calculations show strong relation between MCE and spintronic materials
Assessment of the magnetocaloric effect in La,Pr(Fe,Si) under cycling
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.
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).
New rare earth-based magnetocaloric materials for magnetic refrigeration
Mayer, Charlotte
2011-01-01
The studies presented in this manuscript deal with the synthesis and characterization of new rare-earth based magnetocaloric materials for magnetic refrigeration applications. The first chapter is an introduction to the concepts of magnetocaloric effect and magnetic refrigeration and establishes a review of the magnetocaloric materials existing today. Two research axes were explored in order to obtain materials with a high refrigeration capacity (RC) and to identify strategies for improving t...
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.
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.
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.
Magnetocaloric effect in La(Fe0.89Si0.11)13 irradiated by protons
International Nuclear Information System (INIS)
The magnetic properties and the magnetic entropy change of La(Fe0.89Si0.11)13 compounds under proton irradiation were investigated. With increasing proton fluence, the atomic displacement increased, which gave rise to increase of the lattice constant and Curie temperature. The magnetic entropy change slightly decreased with increasing proton fluence, but still remained large. Among the demonstrated attractive features of the materials, the maximum hysteresis loss almost disappeared and the relative cooling power increased slightly under proton irradiation. - Research highlights: → La(Fe0.89Si0.11)13 is well known as a giant magnetocaloric effect (MCE). → To improve its MCE, the proton was irradiated. → Tc increased to 5%. → Magnetic refrigeration efficiency was considerably improved by proton irradiation.
Pandey, Sudip; Quetz, Abdiel; Aryal, Anil; Dubenko, Igor; Samanta, Tapas; Mazumdar, Dipanjan; Stadler, Shane; Ali, Naushad
2016-05-01
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.
Large magnetocaloric effect in single crystal Pr0.63Sr0.37MnO3
Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho
2005-05-01
This article reports the magnetocaloric effect in a single crystal Pr0.63Sr0.37MnO3, which undergoes a very sharp ferromagnetic-to-paramagnetic phase transition at ˜300K. A large magnetic entropy change of 8.52J/kgK and a large adiabatic temperature change of 5.65K for an applied field change of 50kOe were observed around 300K; this allows water to be used as a heat transfer fluid in the room-temperature magnetic refrigeration regime. The distribution of entropy change (ΔSM) was found to be very uniform and which is desirable for an Ericson-cycle magnetic refrigerator. The large magnetic entropy change induced by a relatively low magnetic field change is beneficial for household application.
International Nuclear Information System (INIS)
We report temperature and field dependent lattice structure, magnetic properties and magnetocaloric effect in epitaxial Fe50Rh50 thin films with (001) texture. Temperature-dependent XRD measurements reveal an irreversible first-order phase transition with 0.66% lattice change upon heating/cooling. First-principle calculation shows a state change of Rh from non-magnetic (0 μB) for antiferromagnetic phase to magnetic (0.93 μB) state for ferromagnetic phase. A jump of magnetization at temperature of 305 K and field more than 5 T indicates a field-assisted magnetic state change of Ru that contributes to the jump. Giant positive magnetic entropy change was confirmed by isothermal magnetization measurements and an in-situ temperature rise of 15 K. The magnetic state change of Rh between antiferromagnetic and ferromagnetic states is the main origin of giant magnetic entropy change and large thermal hysteresis observed.
Zhou, Tiejun; Cher, M. K.; Shen, L.; Hu, J. F.; Yuan, Z. M.
2013-12-01
We report temperature and field dependent lattice structure, magnetic properties and magnetocaloric effect in epitaxial Fe50Rh50 thin films with (001) texture. Temperature-dependent XRD measurements reveal an irreversible first-order phase transition with 0.66% lattice change upon heating/cooling. First-principle calculation shows a state change of Rh from non-magnetic (0 μB) for antiferromagnetic phase to magnetic (0.93 μB) state for ferromagnetic phase. A jump of magnetization at temperature of 305 K and field more than 5 T indicates a field-assisted magnetic state change of Ru that contributes to the jump. Giant positive magnetic entropy change was confirmed by isothermal magnetization measurements and an in-situ temperature rise of 15 K. The magnetic state change of Rh between antiferromagnetic and ferromagnetic states is the main origin of giant magnetic entropy change and large thermal hysteresis observed.
Energy Technology Data Exchange (ETDEWEB)
Zhou, Tiejun, E-mail: Zhou_Tiejun@dsi.a-star.edu.sg [Data Storage Institute, A*STAR (Agency for Science Technology and Research), 5 Engineering Drive 1, Singapore 117608 (Singapore); Cher, M.K. [Data Storage Institute, A*STAR (Agency for Science Technology and Research), 5 Engineering Drive 1, Singapore 117608 (Singapore); Shen, L. [Department of Physics, 2 Science Drive 3, National University of Singapore, Singapore 117542 (Singapore); Hu, J.F.; Yuan, Z.M. [Data Storage Institute, A*STAR (Agency for Science Technology and Research), 5 Engineering Drive 1, Singapore 117608 (Singapore)
2013-12-06
We report temperature and field dependent lattice structure, magnetic properties and magnetocaloric effect in epitaxial Fe{sub 50}Rh{sub 50} thin films with (001) texture. Temperature-dependent XRD measurements reveal an irreversible first-order phase transition with 0.66% lattice change upon heating/cooling. First-principle calculation shows a state change of Rh from non-magnetic (0 μ{sub B}) for antiferromagnetic phase to magnetic (0.93 μ{sub B}) state for ferromagnetic phase. A jump of magnetization at temperature of 305 K and field more than 5 T indicates a field-assisted magnetic state change of Ru that contributes to the jump. Giant positive magnetic entropy change was confirmed by isothermal magnetization measurements and an in-situ temperature rise of 15 K. The magnetic state change of Rh between antiferromagnetic and ferromagnetic states is the main origin of giant magnetic entropy change and large thermal hysteresis observed.
A novel Ho 36Dy 20Al 24Co 20 bulk metallic glass with large magnetocaloric effect
Liang, L.; Hui, X.; Zhang, C. M.; Lu, Z. P.; Chen, G. L.
2008-04-01
A new heavy rare-earth-based Ho 36Dy 20Al 24Co 20 bulk metallic glass (BMG) has been prepared by a copper mold casting. A maximum magnetic entropy change of 11.77 J/kg K has been measured in Ho 36Dy 20Al 24Co 20 bulk metallic glass under a magnetic field of 5 Tesla, which is larger than that of the early reported Ho-based bulk metallic glass Ho 30Y 26Al 24Co 20. The half-maximum temperature range of the entropy change peak is as large as 40 K, leading to a superior refrigerant capacity to those of the Gd 5Si 2Ge 2 and Gd 5Si 2Ge 1.9Fe 0.1 crystalline compounds. The excellent magnetocaloric effect together with the unique properties of metallic glass makes this alloy a promising candidate for a magnetic refrigerant in the temperature range below 50 K.
Hysteresis in Magnetocaloric Materials
DEFF Research Database (Denmark)
von Moos, Lars
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...... the low field heating and high field cooling entropy curves, which can reduce the MCE estimate significantly. The experimental data obtained through the material characterization is used as a foundation for Preisach type models. This type of model is suited to handle the non-equilibrium nature of first...... set points, which is demonstrated to induce partial hysteresis loop behavior that will generally underestimate thermal hysteresis. Furthermore it is shown that care should be taken in non-isofield type experiments, as is the case for direct MCE experiments. Measuring the temperature dependence...
Table-like magnetocaloric effect of Fe88-xNdxCr8B4 composite materials
Lai, J. W.; Zheng, Z. G.; Zhong, X. C.; Franco, V.; Montemayor, R.; Liu, Z. W.; Zeng, D. C.
2015-09-01
The narrow working temperature range due to the sharp magnetic entropy change |ΔSM| 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 Fe88-xNdxCr8B4 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 (TC) ranged from 322 K to 350 K and the peak value of |ΔSM| 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 |ΔSM| 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 |ΔSM| value was much larger than the previous reported Fe-based amorphous composite Fe78-xCexSi4Nb5B12Cu1. This composite can be used as the working material in the Ericsson-cycle magnetic regenerative refrigerator around room temperature.
Impact of silicon doping on the magnetocaloric effect of MnFeP0.35As0.65 powder
Wlodarczyk, P.; Hawelek, L.; Kowalczyk, M.; Kaminska, M.; Zackiewicz, P.; Polak, M.; Hreczka, M.; Kolano-Burian, A.
2016-06-01
The magnetocaloric effect in the MnFeP0.35As0.65-xSix intermetallic compounds, prepared via solid-state sintering was studied. Adiabatic temperature and magnetic entropy changes were obtained in order to characterize these compounds. The substitution of silicon for arsenic leads to a significant enhancement of the magnetocaloric effect for silicon amount x = 0.11. The adiabatic temperature change increased from 2.3 to 3.3 K for the magnetic field change from 0 to 1.7 T. This improvement has been correlated with the increase of crystalline cell volume and change of lattice constants. Additionally, the structure of pure MnFeP0.33As0.67 has been modeled in order to check the spin alignment within the framework of ferromagnetic collinear model.
Anisotropic fluid from nonlocal tidal effects
Culetu, Hristu
2014-01-01
The Shiromizu et al. \\cite{SMS} covariant decomposition formalism is used to find out the brane properties rooted from the 5-dimensional Witten bubble spacetime. The non-local tensor $E_{ab}$ generated by the 5-dimensional Weyl tensor gives rise at an anisotropic energy-momentum tensor on the brane with negative energy density and $p = \\rho/3$ as equation of state. The tidal acceleration is towards the brane and that is in accordance with the negative energy density on the brane. The anisotropic fluid has vanishing "bulk" viscosity but the shear viscosity coefficient is $r$- and $t$- dependent. The brane is endowed with an apparent horizon which is exactly the radial null geodesic.
Analyzing and Predicting Anisotropic Effects of BRDFs
Czech Academy of Sciences Publication Activity Database
Filip, Jiří
New York: ACM, 2015, s. 25-32. ISBN 978-1-4503-3812-7. [ACM SIGGRAPH Symposium on Applied Perception. Tubingen (DE), 13.09.2015-14.09.2015] R&D Projects: GA ČR(CZ) GA14-10911S; GA ČR(CZ) GA14-02652S Institutional support: RVO:67985556 Keywords : BRDF * anisotropic * shape * illumination * measure Subject RIV: BD - Theory of Information http://library.utia.cas.cz/separaty/2015/RO/filip-0448393.pdf
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.
Hu, Zhang; Bao-Gen, Shen
2015-01-01
The ternary intermetallic RTX compounds (R = rare earth, T = transitional metal, X = p-block metal) have been investigated extensively in the past few decades due to their interesting physical properties. Recently, much attention has been paid to the magnetocaloric effect (MCE) of these RTX compounds, especially the ones with heavy rare-earth, for their potential application in low temperature magnetic refrigeration. In this paper, we review the MCE of RTSi and RTAl systems with R = Gd~Tm, T ...
Giant low-field magnetocaloric effect in single-crystalline EuTi0.85Nb0.15O3
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.
Giant low-field magnetocaloric effect in single-crystalline EuTi0.85Nb0.15O3
International Nuclear Information System (INIS)
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
Effective Acquisition of Dense Anisotropic BRDF
Czech Academy of Sciences Publication Activity Database
Filip, Jiří; Vávra, Radomír; Havlíček, Michal
Stockholm : IEEE Computer Society, 2014, s. 2047-2052. ISBN 978-1-4799-5208-3. ISSN 1051-4651. [ICPR 2014 - The 22nd International Conference on Pattern Recognition. Stockholm (SE), 24.08.2014-28.08.2014] R&D Projects: GA ČR(CZ) GA14-10911S; GA ČR(CZ) GA14-02652S; GA ČR GAP103/11/0335 Institutional support: RVO:67985556 Keywords : BRDF * measurement * anisotropic * goniometer Subject RIV: BD - Theory of Information http://library.utia.cas.cz/separaty/2014/RO/filip-0431132.pdf
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...
Table-like magnetocaloric effect of Fe88−xNdxCr8B4 composite materials
International Nuclear Information System (INIS)
The narrow working temperature range due to the sharp magnetic entropy change |ΔSM| 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 Fe88−xNdxCr8B4 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 (TC) ranged from 322 K to 350 K and the peak value of |ΔSM| 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 |ΔSM| 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 |ΔSM| value was much larger than the previous reported Fe-based amorphous composite Fe78−xCexSi4Nb5B12Cu1. This composite can be used as the working material in the Ericsson-cycle magnetic regenerative refrigerator around room temperature. - Highlights: • The TC ranges from 322 K to 350 K when increasing Nd substitution from 5 to 15 at%. • |ΔSM| 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 ,|ΔSM| ~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
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)
Effects of nonuniform acceptance in anisotropic flow measurements
International Nuclear Information System (INIS)
The applicability of anisotropic flow measurement techniques and their extension for detectors with nonuniform azimuthal acceptance are discussed. Considering anisotropic flow measurements with two and three (mixed harmonic) azimuthal correlations we introduce a set of observables based on the x and y components of the event flow vector. These observables provide independent measures of anisotropic flow and can be used to test the self-consistency of the analysis. Based on these observables we propose a technique that explicitly takes into account the effects of nonuniform detector acceptance. Within this approach the acceptance corrections, as well as parameters that define the method applicability, can be determined directly from experimental data. For practical purposes a brief summary of the method is provided at the end
Specular nonlinear anisotropic polarization effect along fourfold crystal symmetry axes
Bungay, A.R.; Popov, S. V.; N. I. Zheludev; Svirko, Y.P.
1995-01-01
We present what is to our knowledge the first experimental observation of the specular nonlinear anisotropic polarization effect of a pump-induced polarization-plane rotation for normal-incidence reflection from the (001) surface of a cubic crystal. In GaAs, azimuth rotation of the order of 9 × 10^-6 rad is seen for a pump intensity of 75 MW/cm^-2 at 750 nm, from which the anisotropic component of the cubic nonlinearity |Re(?xxxx ? 2?xxyy ? ?xyyx)| = 5 × 10^-9 esu is found.
International Nuclear Information System (INIS)
The structure of known Gd4Co3 compound is re-determined as Gd6Co4.85, adopting the Gd6Co1.67Si3 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−1 K−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
Table-like magnetocaloric effect in Gd56Ni15Al27Zr2 alloy and its field independence feature
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.
Table-like magnetocaloric effect in Gd56Ni15Al27Zr2 alloy and its field independence feature
International Nuclear Information System (INIS)
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
de Paula, V. G.; da Silva, L. M.; dos Santos, A. O.; Lang, R.; Otubo, L.; Coelho, A. A.; Cardoso, L. P.
2016-03-01
The correlation between structural and magnetic properties of GdA l2 , focusing on the role played by the disorder in magnetic ordering and how it influences the magnetocaloric effect (MCE) are discussed. Micrometric-sized particles, consisting of nanocrystallites embedded in an amorphous matrix, were prepared by a mechanical milling technique and characterized by means of x-ray diffraction, scanning and high-resolution transmission electron microscopy as well as magnetic measurements as a function of an applied external magnetic field and temperature. The results show that the average particle size is just slightly diminished (≈7%) with the milling time (between 3 and 13 h), whereas the average crystallite size undergoes an expressive reduction (≈43%). For long milling times, structural disorders mostly associated with crystallite size singularly affect the magnetic properties, leading to a large tablelike MCE in the temperature range between 30 and 165 K. Below 30 K, nanocrystallites with dimensions below a given critical size cause an enhancement in the magnetic entropy change related to superparamagnetic behavior. In contrast, for low milling times, relative cooling power values are improved. These striking features along with the small magnetic hysteresis observed make the milled GdA l2 a promising material for application in the magnetic refrigeration technology. Finally, a discussion in an attempt to elucidate the origin of the spin-glass states previously reported in the literature for mechanically milled GdA l2 samples for very long times (400 and 1000 h) is presented.
Microstructure and magnetocaloric effects in partially amorphous Gd55Co15Al30-xSix alloys
International Nuclear Information System (INIS)
Highlights: → The primary crystalline phase of the metallic glasses is identified to be Gd2Al. → Phase separation is observed in the system with negative heat of mixing. → Relationship between the microstructure and MCE of Gd-based BMG composite. - Abstract: In order to clarify the phase components and further improve the glass-forming ability of Gd55Co15Al30 alloy, substitution of Al with Si was adopted. Although the X-ray powder diffraction experiment indicated an amorphous structure of the Gd55Co15Al30-xSix (x = 1, 2, 3) alloys, precipitation of crystalline Gd2Al phase was evident from the energy-dispersive spectroscopy, selected-area diffraction, and magnetization measurements. The magnetocaloric effect of Si substituted alloys is lower than that of Gd52.5Co16.5Al31 alloy with a similar composition and full amorphous structure, which is ascribed to the presence of antiferromagnetic Gd2Al phase whose magnetic entropy change is lower.
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 the...
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.
Effective wavefield extrapolation in anisotropic media: Accounting for resolvable anisotropy
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.
Generalized method for retrieving effective parameters of anisotropic metamaterials.
Castanié, A; Mercier, J-F; Félix, S; Maurel, A
2014-12-01
Electromagnetic or acoustic metamaterials can be described in terms of equivalent effective, in general anisotropic, media and several techniques exist to determine the effective permeability and permittivity (or effective mass density and bulk modulus in the context of acoustics). Among these techniques, retrieval methods use the measured reflection and transmission coefficients (or scattering coefficients) for waves incident on a metamaterial slab containing few unit cells. Until now, anisotropic effective slabs have been considered in the literature but they are limited to the case where one of the axes of anisotropy is aligned with the slab interface. We propose an extension to arbitrary orientations of the principal axes of anisotropy and oblique incidence. The retrieval method is illustrated in the electromagnetic case for layered media, and in the acoustic case for array of tilted elliptical particles. PMID:25606924
Zverev, V. I.; Saletskij, A. M.; Gimaev, R. R.; Tishin, A. M.; Miyanaga, T.; Staunton, J. B.
2016-01-01
The large magnetocaloric effect (MCE), which accompanies the first order ferromagnetic/anti-ferromagnetic transition in CsCl-ordered Fe-Rh alloys, has been investigated by measurements in slowly cycled magnetic fields of up to 2 T in magnitude for a range of temperatures, 300K < T < 350K. A bulk sample with composition Fe(50.4)Rh(49.6) was used and the results were compared with those produced by the ab-initio density functional theory-based disordered local moment (DLM) theory of the MCE. Th...
Efficient anisotropic wavefield extrapolation using effective isotropic models
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.
Effect of neutron anisotropic scattering in fast reactor analysis
International Nuclear Information System (INIS)
Numerical tests were performed about an effect of a neutron anisotropic scattering on criticality in the Sn transport calculation. The simplest approximation, the consistent P approximation and the extended transport approximation were compared with each other in one-dimensional slab fast reactor models. JAERI fast set which has been used for fast reactor analyses is inadequate to evaluate the effect because it doesn't include the scattering matrices and the self-shielding factors to calculate the group-averaged cross sections weighted by the higher-order moment of angular flux. In the present study, the sub-group method was used to evaluate the group-averaged cross sections. Results showed that the simplest approximation is inadequate and the transport approximation is effective for evaluating the anisotropic scattering. (author)
Properties of magnetocaloric materials with a distribution of Curie temperatures
International Nuclear Information System (INIS)
The magnetocaloric properties of inhomogeneous ferromagnets that contain distributions of Curie temperatures are considered as a function of the width of such a distribution. Assuming a normal distribution of the Curie temperature, the average adiabatic temperature change, ΔTad, the isothermal magnetic entropy change, Δs, and the heat capacity, cp, in zero magnetic field and an applied magnetic field of μ0H=1T, have been calculated using the mean field model of ferromagnetism. Interestingly, both the peak position and amplitude of each of these parameters vary differently with the width of the distribution, explaining the observed mismatch of peak temperatures reported in experiments. Also, the field dependence of ΔTad and Δs is found to depend on the width of the distribution. - Highlights: → Modeled distributions of Curie temperatures affect the measured magnetocaloric effect. → The magnetocaloric physical properties are affected differently. → A distribution affects the field dependence of the magnetocaloric effect.
Strain modulated large magnetocaloric effect in Sm0.55Sr0.45MnO3 epitaxial films
Giri, S. K.; Dasgupta, Papri; Poddar, A.; Sahoo, R. C.; Paladhi, D.; Nath, T. K.
2015-01-01
Epitaxial Sm0.55Sr0.45MnO3 thin films were deposited on LAO (001), LSAT (001), and STO (001) single crystalline substrates by pulsed laser deposition technique to investigate the correlation between the substrate induced film lattice strain and magnetocaloric effect (MCE). The film on LAO substrate (S_LAO), which is under compressive strain, undergoes ferromagnetic → paramagnetic transition at TC ˜ 165 K. The films on STO (S_STO) and LSAT (S_LSAT) substrates are under tensile strain and have TC ˜ 120 K and 130 K, respectively. At T LSAT films, hysteresis is also observed between field cooled cooling and warming cycle in magnetization versus temperature measurement at low magnetic field similar to first order-like magnetic phase transition. No signature of first order magnetic phase transition has been observed in the case of S_LAO film. Most interestingly, both normal (i.e., negative ΔSM) and inverse (i.e., positive ΔSM) MCE around TC and above Tp, respectively, for S_STO and S_LSAT films have been observed with maximum value of MCE ˜ 10 J kg-1 K-1. The S_STO film also exhibits a large relative cooling power of 142 J/kg for a magnetic field change of 1 T. Our findings of substrate-induced strain modulated large MCE in epitaxial Sm0.55Sr0.45MnO3 films have been well explained through the substrate induced film lattice strain, and it may be useful for active magnetic refrigerant materials.
Magnetic properties and magnetocaloric effect at room temperature of Ni50-xAgxMn37Sn13 alloys
International Nuclear Information System (INIS)
In this work, we present a detailed study of the magnetic properties and the magnetocaloric effect at room temperature of Ni50-xAgxMn37Sn13 alloys with x = 1, 2, and 4, which were prepared by using an arc-melting method. Experimental results reveal that a partial replacement of Ag for Ni leads to a decrease in the anti-FM phase in the alloys. In addition, the martensitic-austenitic phase transition shifts towards lower temperature and is broaded. The Curie temperature (TAC ) for the austenitic phase also shifts toward to lower temperature, but not by much. The Curie temperature was found to be 308, 305, and 298 K for x = 1, 2, and 4, respectively. The magnetic entropy change (ΔSm) of the samples was calculated by using isothermal magnetization data. Under an applied magnetic field change of 10 kOe, the maximum value of ΔSm (|ΔSmax|) was achieved at around room temperature and did not change much (∼0.8 J·kg-1·K-1) with increasing Ag-doping concentration. Particularly, the M2 vs. H/M curves prove that all the samples exhibited a secondorder magnetic phase transition. Based on Landau's phase-transition theory and careful analyses of the magnetic data around the TAC , we have determined the critical parameters β, γ, δ, and TC . The results show that the β values are located between those expected for the 3D-Heisenberg model (β = 0.365) and mean-field theory (β = 0.5). Such a result proves the coexistence of short-range and long-range ferromagnetic interactions in Ni50-xAgxMn37Sn13 alloys. The nature of the changes in the critical parameters and the |ΔSmax| is thoroughly discussed by means of structural analyses.
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.
Czech Academy of Sciences Publication Activity Database
Sun, Y.; Kamarád, Jiří; Arnold, Zdeněk; Kou, Z..; Cheng, Z.
2006-01-01
Roč. 88, č. 10 (2006), 102505/1-102505/3. ISSN 0003-6951 R&D Projects: GA ČR(CZ) GA106/06/0368 Institutional research plan: CEZ:AV0Z10100521 Keywords : magnetocaloric effect * pressure effect * manganites * single crystal Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.977, year: 2006
Effective Elliptic Models for Efficient Wavefield Extrapolation in Anisotropic Media
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.
Anisotropic Paramagnetic Meissner Effect by Spin-Orbit Coupling
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.
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)
Energy Technology Data Exchange (ETDEWEB)
Gourdon, Olivier, E-mail: gourdono@lanl.gov [Los Alamos Neutron Scattering Center, National Laboratory, Los Alamos, NM 87545 (United States); Gottschlich, Michael; Persson, Joerg [Jülich Center for Neutron Science JCNS-2 and Peter Grünberg Institut PGI-4, JARA-FIT, Forschungszentrum Jülich 52425 Jülich (Germany); Cruz, Clarina de la [Quantum Condensed Matter Division, Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Petricek, Vaclav [Institute of Physics ASCR v.v.i., Na Slovance 2, 182 21 Prague (Czech Republic); McGuire, Michael A. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Brückel, Thomas [Jülich Center for Neutron Science JCNS-2 and Peter Grünberg Institut PGI-4, JARA-FIT, Forschungszentrum Jülich 52425 Jülich (Germany)
2014-08-15
The intermetallic compound MnFe{sub 4}Si{sub 3} has been studied by high-resolution Time of Flight (TOF) neutron powder diffraction. MnFe{sub 4}Si{sub 3} crystallizes in the hexagonal space group P6{sub 3}/mcm with lattice constants of a=b=6.8043(4) Å and c=4.7254(2) Å at 310 K. Magnetic susceptibility measurements show clearly the magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. Magnetic structure refinements based on neutron powder diffraction data with and without external magnetic field reveal strong evidence on the origin of the large magnetocaloric effect (MCE) in this material as a partial reordering of the spins between ∼270 K and 300 K. In addition, electronic structure calculations using the self-consistent, spin-polarized Tight Binding-Linear MuffinTin Orbital (TB-LMTO) method were also accomplished to address the “coloring problem” (Mn/Fe site preference) as well as the unique ferromagnetic behavior of this intermetallic compound. - Graphical abstract: Theoretical and experimental reinvestigation of the magnetic structure of MnFe{sub 4}Si{sub 3} for a better understanding of its large magnetocaloric effect (MCE). - Highlights: • Strong magnetic transition from paramagnetism to ferromagnetism at about 302(2) K. • MCE associated to a partial reordering of the spins between ∼270 K and 300 K. • DFT calculations show strong relation between MCE and spintronic materials.
International Nuclear Information System (INIS)
The glass formation ability, the structure and the magnetocaloric effect of the bulk metallic glassy Gd55Co20Fe5Al20 alloy were investigated. Bulk metallic glassy (BMGs) alloys were prepared by a copper-mold casting method. The glass forming ability and their structure were studied by using X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The XRD analysis revealed that the as-cast cylinder of Gd55Co20Fe5Al20 alloy showed fully amorphous structure in 2 mm diameter. The DSC revealed that the bulk cylinder of the Gd55Co20Fe5Al20 alloy showed a distinct glass transition temperature and a relatively wide supercooled liquid region before crystallization. SQUID investigated the magnetic properties and the entropy changes. The Curie temperature of Gd55Co20Fe5Al20 BMGs alloy was about 130 K, but the maximum magnetic entropy changes(-ΔSM) showed at about 125 K, a little lower than the Curie temperature 130 K. The reason could probably be due to the presence of a little amount of nanocrystalline particles between amorphous phases. The BMG alloy has the characteristic of second-order transition (SOT) on Arrott plots. The results showed that the amorphous sample had a relatively improved magnetocaloric effect, indicating that the amorphous alloy could be considered as a candidate for magnetic refrigeration applications in the temperature interval range of 100-200 K
Czech Academy of Sciences Publication Activity Database
Tereshina, I.; Politova, G.; Tereshina, Evgeniya; Nikitin, S.; Burkhanov, G.; Chistyakov, O.; Karpenkov, A.
2010-01-01
Roč. 200, č. 9 (2010), "092012-1"-"092012-4". ISSN 1742-6588. [International Conference on Magnetism - ICM 2009. Karlsruhe , 26.07.2009-31.07.2009] Institutional research plan: CEZ:AV0Z10100520 Keywords : terfenol-D * rare-earth Intermetallics * magnetostriction * magnetocaloric effect Subject RIV: BM - Solid Matter Physics ; Magnetism
Vortex induced strain effects in anisotropic superconductors
International Nuclear Information System (INIS)
Strain in a superconductor, produced by the normal vortex core, can affect both static and dynamic properties of vortices. It causes an additional vortex-vortex interaction which is long-ranged (∼ 1/r2) as compared with finite but much stronger London interaction in the fields far below Hc2. The energy of this magneto-elastic interaction is calculated within London model. The role of strain effects in forming vortex lattice structure is demonstrated for YBa2Cu3O7
Effect of different potentials on anisotropic flow
International Nuclear Information System (INIS)
During the last two decades heavy ion collision (HIC) has became the most intensively developing field of nuclear physics to study the nuclear properties. One of the observable used to understand this kind of behavior is collective flow. At low energies, due to the dominance of attractive mean field collective flow becomes negative, which changes to some positive value with the increase in incident energy. The value of intermediate incident energy at which the flow vanishes and attains a zero is called the balance energy (Ebal). In the past few years collective flow and its disappearance has been studied widely. In the present paper, the effect of different potentials on Ebal is studied by using IQMD model, where the total interaction potential of a HIC is combination of Skyrme potential, Yukawa potential, Coulomb potential, momentum dependent potential and density dependent symmetry potential
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.
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.
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)
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)
Estimation of effective hydrogeological parameters in heterogeneous and anisotropic aquifers
Lin, Hsien-Tsung; Tan, Yih-Chi; Chen, Chu-Hui; Yu, Hwa-Lung; Wu, Shih-Ching; Ke, Kai-Yuan
2010-07-01
SummaryObtaining reasonable hydrological input parameters is a key challenge in groundwater modeling. Analysis of temporal evolution during pump-induced drawdown is one common approach used to estimate the effective transmissivity and storage coefficients in a heterogeneous aquifer. In this study, we propose a Modified Tabu search Method (MTM), an improvement drawn from an alliance between the Tabu Search (TS) and the Adjoint State Method (ASM) developed by Tan et al. (2008). The latter is employed to estimate effective parameters for anisotropic, heterogeneous aquifers. MTM is validated by several numerical pumping tests. Comparisons are made to other well-known techniques, such as the type-curve method (TCM) and the straight-line method (SLM), to provide insight into the challenge of determining the most effective parameter for an anisotropic, heterogeneous aquifer. The results reveal that MTM can efficiently obtain the best representative and effective aquifer parameters in terms of the least mean square errors of the drawdown estimations. The use of MTM may involve less artificial errors than occur with TCM and SLM, and lead to better solutions. Therefore, effective transmissivity is more likely to be comprised of the geometric mean of all transmissivities within the cone of depression based on a precise estimation of MTM. Further investigation into the applicability of MTM shows that a higher level of heterogeneity in an aquifer can induce an uncertainty in estimations, while the changes in correlation length will affect the accuracy of MTM only once the degree of heterogeneity has also risen.
Anisotropic hydrodynamics, holography and the chiral magnetic effect
International Nuclear Information System (INIS)
We discuss a possible dependence of the chiral magnetic effect (CME) on the elliptic flow coefficient υ2. 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 υ2. 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.)
Spin Hall effect of a light beam in anisotropic metamaterials
International Nuclear Information System (INIS)
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. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Strain dependent magnetocaloric effect in La0.67Sr0.33MnO3 thin-films
Suresh Kumar, V.; Rami Chukka; Zuhuang Chen; Ping Yang; Lang Chen
2013-01-01
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 rela...
Gottschall, T.; Skokov, K. P.; Scheibel, F.; Acet, M.; Zavareh, M. Ghorbani; Skourski, Y.; Wosnitza, J.; Farle, M.; Gutfleisch, O.
2016-02-01
Large magnetocaloric effects can be obtained in Ni-Mn-based Heusler alloys due to the magnetostructural transition between martensite and austenite. This phase transformation proceeds via nucleation and growth. By direct measurements of the adiabatic temperature change Δ Tad using different magnetic-field-sweeping rates from 0.01 up to 1500 T s-1 , we study the dynamic behavior of the two Heusler compounds Ni50 Mn35 In15 and Ni45 Mn37 In13 Co5 transforming near room temperature. From these experiments, we conclude that the nucleation process is rather slow in contrast to the relatively fast movement of the phase boundary between martensite and austenite. This is a limiting factor for cooling concepts operating at frequencies beyond 100 Hz. However, the dynamic effects of the transition are negligible in field rates typically used in magnetic refrigeration. These findings are essential considering the suitability of Heusler compounds for energy-efficient solid-state cooling.
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.
International Nuclear Information System (INIS)
The effects of Al substitution on the phase transitions and magnetocaloric effect of Ni43Mn46Sn11-xAlx (x=0-2) ferromagnetic shape memory alloys were investigated by X-ray diffraction and magnetization measurements. With the increase of Al content, the cell volume decreases due to the smaller radius of Al, and the martensitic transformation temperature increases rapidly, while the Curie temperature of austenitic phase shows a small increase. A large positive and a negative magnetic entropy change were observed near the first-order martensitic transition and the second-order magnetic transition, respectively. The magnetic entropy changes, hysteresis behavior, and refrigerant capacity near the two transitions are compared.
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
Fracture of anisotropic materials with plastic strain-gradient effects
DEFF Research Database (Denmark)
Legarth, Brian Nyvang
2013-01-01
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...... 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 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...
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.
Giant magnetocaloric effect in magnetically frustrated EuHo2O4 and EuDy2O4 compounds
Midya, A.; Khan, N.; Bhoi, D.; Mandal, P.
2012-09-01
We have investigated the magnetic and magnetocaloric properties of EuHo2O4 and EuDy2O4 by magnetization and heat capacity measurements down to 2 K. These compounds undergo a field-induced antiferromagnetic to ferromagnetic transition and exhibit a huge entropy change. For a field change of 0-8 T, the maximum magnetic entropy and adiabatic temperature changes are 30 (25) J kg-1 K-1 and 12.7 (16) K, respectively, and the corresponding value of refrigerant capacity is 540 (415) J kg-1 for EuHo2O4 (EuDy2O4). These magnetocaloric parameters also remain large down to lowest temperature measured and are even larger than that for some of the potential magnetic refrigerants reported in the same temperature range. Moreover, these materials are highly insulating and exhibit no thermal and field hysteresis, fulfilling the necessary conditions for a good magnetic refrigerant in the low-temperature region.
Magnetocaloric effect in La(Fe{sub 0.89}Si{sub 0.11}){sub 13} irradiated by protons
Energy Technology Data Exchange (ETDEWEB)
Kim, Sol Ji [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Lee, Kyu Jun; Jung, Myung Hwa [Department of Physics, Sogang University, Seoul 121-742 (Korea, Republic of); Oh, Hyun Jin [Department of Ophthalmic Optics, Masan University, Chanwon 630-729 (Korea, Republic of); Kwon, Yong Seung, E-mail: yskwon@skku.ac.k [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)
2011-04-15
The magnetic properties and the magnetic entropy change of La(Fe{sub 0.89}Si{sub 0.11}){sub 13} compounds under proton irradiation were investigated. With increasing proton fluence, the atomic displacement increased, which gave rise to increase of the lattice constant and Curie temperature. The magnetic entropy change slightly decreased with increasing proton fluence, but still remained large. Among the demonstrated attractive features of the materials, the maximum hysteresis loss almost disappeared and the relative cooling power increased slightly under proton irradiation. - Research highlights: > La(Fe{sub 0.89}Si{sub 0.11}){sub 13} is well known as a giant magnetocaloric effect (MCE). > To improve its MCE, the proton was irradiated. > T{sub c} increased to 5%. > Magnetic refrigeration efficiency was considerably improved by proton irradiation.
Ulyanov, A. N.; Kang, Y. M.; Yoo, S. I.
2008-04-01
Metamagnetic transition was observed in low magnetic field for La0.7Ca0.3MnO3-δ lanthanum manganite prepared by solid-state technology. Magnetization shape causes giant low field magnetocaloric effect at Curie temperature TC=242K. Magnetic entropy changes ΔSm, deduced with isothermal magnetization curves, are equal to 7.0 and 8.0J /kgK in the field change from 0 to 1.0 and 2.0T, respectively. The obtained ΔSm are essentially higher than that reported before for lanthanum manganites with similar TC. The observation shows the way for the construction the magnetic refrigerants, working in the field of permanent magnets, which is beneficial for household and automotive applications.
Magnetocaloric effect in gadolinium-oxalate framework Gd2(C2O4)3(H2O)6⋅(0⋅6H2O)
International Nuclear Information System (INIS)
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(C2O4)3(H2O)6⋅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)
Low-temperature large reversible “table-like” magnetocaloric effect in HoNi0.9Cu0.1Al compound
International Nuclear Information System (INIS)
Magnetic properties and magnetocaloric effect (MCE) of HoNi0.9Cu0.1Al have been investigated. The compound experienced two phase transitions at about 5.7 K and 11.8 K which was assumed as the combination and competence between the ferromagnetic and antiferromagnetic ordering components. “Table-like” magnetic entropy changes were found under low field changes. The maximum values of ΔS were –10.3 and –23.5 J/kg K with corresponding RC as 98 J/kg and 330 J/kg for field changes of 0–20 kOe and 0–50 kOe, respectively. The “table-like” ΔS, large RC, low ordering temperatures and no hysteresis loss enabled it a potential material for commercial utilization in the future
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.
Effect of Interplanetary Transients on Cosmic Ray Anisotropic Variations
Institute of Scientific and Technical Information of China (English)
无
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.
International Nuclear Information System (INIS)
The influence of Cr substituted for Fe in Fe78-xCrxSi4Nb5B12Ag1 ribbons on the crystallization and magnetic properties including the magnetocaloric effect have been investigated. DSC measurements showed that the crystallization temperature and the crystallization activation energy increased with Cr content. Thermomagnetic curves measured in low applied field indicated that there is a sharp ferromagnetic-paramagnetic phase transition at Curie temperature, TC, of the amorphous phase. In addition, substitution of Cr for Fe led to approximate linear decrease of TC with Cr content, namely from 450K to 280K for x = 0 and x = 8, respectively. From a series of the isothermal magnetization curves M(H) measured at different temperatures, magnetic entropy change ΔSm was determined at magnetic field variations of 13.5, 10.0 and 5.0 kOe. Maximum value of ΔSm (occurred near TC) decreased with increasing Cr content and these values established are quite large at low field variation. Namely, at moderate low magnetic field variation of 5.0 kOe, |ΔSm|max is of 4.4 and 1.9 J/kg.K for x = 0 and x = 8, respectively. Our studied alloys system could be considered as the best magnetocaloric material candidates for magnetic refrigeration because of colossal magnetic entropy change at low field variation and working temperature could be controlled in large region by substitution effect. The anti-corrosion ability of alloys was also examined.
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...
Practical system for the direct measurement of magneto-caloric effect by micro-thermocouples
Czech Academy of Sciences Publication Activity Database
Kamarád, Jiří; Kaštil, J.; Arnold, Zdeněk
2012-01-01
Roč. 83, č. 8 (2012), "083902-1"-"083902-7". ISSN 0034-6748 R&D Projects: GA ČR GAP204/12/0692 Institutional research plan: CEZ:AV0Z10100521 Keywords : copper * cryostats * magnetic transition * magnetic variables measurement * magneto caloric effects * microsensors * permanent magnets * refrigeration Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.602, year: 2012
Anomalous Skin Effect for Anisotropic Electron Velocity Distribution Function
Energy Technology Data Exchange (ETDEWEB)
Igor Kaganovich; Edward Startsev; Gennady Shvets
2004-02-19
The anomalous skin effect in a plasma with a highly anisotropic electron velocity distribution function (EVDF) is very different from skin effect in a plasma with the isotropic EVDF. An analytical solution was derived for the electric field penetrated into plasma with the EVDF described as a Maxwellian with two temperatures Tx >> Tz, where x is the direction along the plasma boundary and z is the direction perpendicular to the plasma boundary. The skin layer was found to consist of two distinctive regions of width of order nTx/w and nTz/w, where nTx,z/w = (Tx,z/m)1/2 is the thermal electron velocity and w is the incident wave frequency.
Imaging the anisotropic nonlinear Meissner effect in unconventional superconductors
International Nuclear Information System (INIS)
We present measurements on the anisotropic nonlinear Meissner effect (aNLME). Using a laser scanning microscope we have directly imaged this effect in a self-resonant spiral patterned from a thin film of the dx2-y2 superconductor YBa2Cu3O7-δ. The spiral is excited at one of its resonant frequencies while a focused laser spot is scanned across its surface. The local illumination by the laser gives rise to a detectable change in the resonant properties. At low temperatures, the aNLME causes a direction dependent contribution to the critical current density. This makes it possible to image the directions of nodes and anti-nodes of the superconducting order parameter and the contribution of Andreev bound states associated with them. These two contributions to the photoresponse can be distinguished by their temperature dependence, which is consistent with theoretical predictions.
Effective Orthorhombic Anisotropic Models for Wave field Extrapolation
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
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.
Superlensing effect of an anisotropic metamaterial slab with near-zero dynamic mass
Zhou, Xiaoming; Hu, Gengkai
2011-01-01
A metamaterial slab of anisotropic mass with one diagonal component being infinity and the other being zero is demonstrated to behave as a superlens for acoustic imaging beyond the diffraction limit. The underlying mechanism for extraordinary transmission of evanescent waves is attributed to the zero mass effect. Microstructure design for such anisotropic lens is also presented. In contrast to the anisotropic superlens based on Fabry-P\\'erot resonant mechanism, the proposed lens operates with...
Emre, Baris; Bruno, Nickolaus M.; Yuce Emre, Suheyla; Karaman, Ibrahim
2014-12-01
The effect of Nb substitution for Ni in Ni45Co5Mn40Sn10 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. Ni45Co5Mn40Sn10 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 Ni45Co5Mn40Sn10 alloys potential candidates for solid state refrigeration near room temperature.
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.)
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.
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.
Strain dependent magnetocaloric effect in La0.67Sr0.33MnO3 thin-films
Kumar, V. Suresh; Chukka, Rami; Chen, Zuhuang; Yang, Ping; Chen, Lang
2013-05-01
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.
DEFF Research Database (Denmark)
Lei, Tian; Engelbrecht, Kurt; Nielsen, Kaspar Kirstein;
2016-01-01
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...... 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...
Effective Dirac Hamiltonian for anisotropic honeycomb lattices: Optical properties
Oliva-Leyva, M.; Naumis, Gerardo G.
2016-01-01
We derive the low-energy Hamiltonian for a honeycomb lattice with anisotropy in the hopping parameters. Taking the reported Dirac Hamiltonian for the anisotropic honeycomb lattice, we obtain its optical conductivity tensor and its transmittance for normal incidence of linearly polarized light. Also, we characterize its dichroic character due to the anisotropic optical absorption. As an application of our general findings, which reproduce the previous case of uniformly strained graphene, we study the optical properties of graphene under a nonmechanical distortion.
Aeroelastic modal dynamics of wind turbines including anisotropic effects
Skjoldan, Peter Fisker; Hansen, Morten Hartvig; Rubak, Rune; Thomsen, Kenneth
2011-01-01
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...
Anisotropic Effects on Constitutive Model Parameters of Aluminum Alloys
Brar, Nachhatter; Joshi, Vasant
2011-06-01
Simulation of low velocity impact on structures or high velocity penetration in armor materials heavily rely on constitutive material models. The model constants are required input to computer codes (LS-DYNA, DYNA3D or SPH) to accurately simulate fragment impact on structural components made of high strength 7075-T651 aluminum alloys. Johnson-Cook model constants determined for Al7075-T651 alloy bar material failed to simulate correctly the penetration into 1' thick Al-7075-T651plates. When simulations go well beyond minor parameter tweaking and experimental results are drastically different it is important to determine constitutive parameters from the actual material used in impact/penetration experiments. To investigate anisotropic effects on the yield/flow stress of this alloy we performed quasi-static and high strain rate tensile tests on specimens fabricated in the longitudinal, transverse, and thickness directions of 1' thick Al7075-T651 plate. Flow stresses at a strain rate of ~1100/s in the longitudinal and transverse direction are similar around 670MPa and decreases to 620 MPa in the thickness direction. These data are lower than the flow stress of 760 MPa measured in Al7075-T651 bar stock.
Madiligama, A. S. B.; Ari-Gur, P.; Shavrov, V. G.; Koledov, V. V.; Calder, S.; Mashirov, A. V.; Kamantsev, A. P.; Dilmieva, E. T.; Gonzalez-Legarreta, L.; Grande, B. H.; Vega, V. V.; Kayani, A.
2016-08-01
Magnetic cooling is a green cooling technology, which is more energy efficient than existing fluid-compression cooling machines. Ni41Mn39In12Co8 alloy, which demonstrates promising magnetocaloric performances, was investigated using neutron diffraction and thermomagnetic measurements. The austenite structure is cubic L21 (Fm\\bar{3}m), while that of the martensite is a mix of 8 and 6 M modulated monoclinic structures (P\\quad 1\\quad 2/m\\quad 1). The austenitic site occupancy refinements reveal that all substituting Co atoms occupy Ni-sites. Most Mn atoms (65%) are in the Mn-sites and the rest go to In-sites (about 35%) and Ni-sites (less than 5%). This disorder of the magnetic atoms (Mn, Ni and Co) in the austenitic phase remains unchanged during the martensitic transition. The distortions of the interatomic distances due to the modulation of the martensitic structures further enhance the disorder in the magnetic interactions. Thermomagnetic measurements indicate that the austenitic phase is ferromagnetic. Cooling to below 250 K, where the alloy loses its ferromagnetic nature, and down to 50 K, the lack of any antiferromagnetic Bragg peaks suggests no antiferromagnetic ordering in the martensitic phase. At very low temperatures in the martensitic phase, spin glass magnetic nature is identified by magnetic measurements, and the spin-glass transition temperature is ∼19 K.
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...... 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 (ΔTadΔTad) higher than 1 K for a temperature range of 40 K with a maximum value of 1.57 K for...
Magnetocaloric Pumping of Liquid Oxygen
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.
Simulated magnetocaloric properties of MnCr2O4 spinel
Mahmoud A. Hamad
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...
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.
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
Das, Kalipada; Das, I.
2016-03-01
Magnetocaloric effect (MCE) is the change in temperature or entropy of a material due to the application of external magnetic field. The temperature dependence of MCE shows maximum value near the ferromagnetic transition of the material. Material with large MCE near room temperature will make revolutionary change in cooling technology and will have large impact in human society. We have transformed antiferromagnetic bulk manganite material La0.48Ca0.52MnO3 to ferromagnetic material by the reduction of the particle size in nanometer scale. MCE, as well as the Relative cooling power (RCP) of the material at room temperature (RT) systematically increase with the reduction of the particle sizes. The RCP value for the 45 nm particle size sample at RT is about 400% larger compared with the bulk counterpart. Our detail study on the nano form of the compound highlights an effective way to enhance the MCE. It opens up a vast possibility of achieving giant enhancement of MCE of several already known materials just by the reduction of the particle size in nanometer scale.
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.
DEFF Research Database (Denmark)
Han, Li; Hegelund Spangsdorf, Steeven; Van Nong, Ngo;
2016-01-01
-rate) using spark plasma sintering (SPS). The effects of SPS conditions on the anisotropic thermoelectric properties and microstructure evolutions were systematically investigated. The change of sintering temperature showed stronger influence than other sintering parameters to the resulting thermoelectric...
Thermal diffusivity and anisotropic effects in transparent polymers using colinear mirage detection
Pandey, G.; Boué, C.; D. Fournier; Boccara, A.
1994-01-01
Colinear mirage detection was found to be simple and efficient to solve the problem of thermal diffusivity measurements in transparent polymer foils. Both reliable values have been obtained and anisotropic effects revealed.
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.
Energy Technology Data Exchange (ETDEWEB)
Balli, M., E-mail: mohamed.balli@usherbrooke.ca; Jandl, S. [Regroupement québécois sur les matériaux de pointe, Département de physique, Université de Sherbrooke, Quebec J1K 2R1 (Canada); Fournier, P. [Regroupement québécois sur les matériaux de pointe, Département de physique, Université de Sherbrooke, Quebec J1K 2R1 (Canada); Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8 (Canada); Gospodinov, M. M. [Institute of Solid State Physics, Bulgarian Academy of Science, Sofia 1184 (Bulgaria)
2014-05-07
Magnetic and magnetocaloric properties of single crystal double perovskite La{sub 2}MnNiO{sub 6} have been investigated in details. Its ordered phase with a high Curie temperature (T{sub C} = 280 K) exhibits a significant refrigerant capacity around room temperature. A model based on the mean field theory approximation has been used in order to quantify the magnetic and magnetocaloric properties in the ordered La{sub 2}MnNiO{sub 6}. The magnetization and entropy changes were satisfactorily simulated as a function of temperature and magnetic field. On the other hand, the presence of cationic disorder in La{sub 2}MnNiO{sub 6} phases allows to shift the Curie point to low temperature without a significant change in the magnetocaloric performance.
International Nuclear Information System (INIS)
Magnetic, specific heat and magnetocaloric studies have been performed on rare earth calcium manganites; Ln0.5Ca0.5MnO3 (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 Gd0.5Ca0.5MnO3, 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 Dy0.5Ca0.5MnO3. 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 Gd0.5Ca0.5MnO3 and Dy0.5Ca0.5MnO3 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)
Superlensing effect of an anisotropic metamaterial slab with near-zero dynamic mass
Zhou, Xiaoming; Hu, Gengkai
2011-06-01
A metamaterial slab of anisotropic mass with one diagonal component being infinity and the other being zero is demonstrated to behave as a superlens for acoustic imaging beyond the diffraction limit. The underlying mechanism for extraordinary transmission of evanescent waves is attributed to the zero mass effect. Microstructure design for such anisotropic lens is also presented. In contrast to the anisotropic superlens based on Fabry-Pérot resonant mechanism, the proposed lens operates without the limitation on lens thickness, thus more flexible in practical applications. Numerical modeling is performed to validate the proposed ideas.
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.
International Nuclear Information System (INIS)
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. (paper)
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.
The existence of giant magnetocaloric effect and laminar structure in Fe73.5-x Cr x Si13.5B9Nb3Cu1
International Nuclear Information System (INIS)
Amorphous soft magnetic ribbons Fe73.5-x Cr x Si13.5B9Nb3Cu1 (x=1-5) have been fabricated by rapid quenching on a single copper wheel. The differential scanning calorimetry (DSC) patterns showed that the crystallization temperature of α-Fe(Si) phase is ranging from 542 to 569 deg. C, a little higher than that of pure Finemet (x=0). With the same annealing regime, the crystallization volume fraction as well as the particle size of α-Fe(Si) crystallites decreased with increasing Cr amount substituted for Fe in studied samples. Especially, the interesting fact is that the laminar structure of heat-treated ribbons on the surface contacted to copper wheel in the fabricating process has been firstly discovered and explained to be related to the existence of Cr in studied samples. The hysteresis loop measurement indicated that there is the pinning of displacement of domain walls. The giant magnetocaloric effect (GMCE) has been found in amorphous state of the samples. After annealing, the soft magnetic properties of investigated nanocomposite materials are desirably improved
Zverev, V. I.; Saletsky, A. M.; Gimaev, R. R.; Tishin, A. M.; Miyanaga, T.; Staunton, J. B.
2016-05-01
The large magnetocaloric effect (MCE), which accompanies the first order ferromagnetic/anti-ferromagnetic transition in CsCl-ordered Fe-Rh alloys, has been investigated by measurements in slowly cycled magnetic fields of up to 2 T in magnitude for a range of temperatures, 300 K return to its initial value following several cycles of the magnetic field. These observations were explained in the framework of the ab-initio theory for the first order transition in which the consequences of the incomplete long range compositional order and small compositional inhomogeneities of the sample were included. The mean value of the long range order parameter S used in the theoretical work was 0.985, close to the value obtained experimentally from XRD measurements. The sample inhomogeneities were modeled by regions in the sample having a distribution of S values with narrow half-width 0.004 about the mean value. The influence of such compositional disorder on both the transition temperature (323.5 K) and MCE adiabatic temperature change (ΔT = 7.5 K) was also studied.
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.
Effects of Staggered Magnetic Field on Entanglement in the Anisotropic XY Model
Institute of Scientific and Technical Information of China (English)
SUN Zhe; WANG Xiao-Guang
2006-01-01
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.
Ishikawa, K; Maeda, N.
2001-01-01
Physical properties of anisotropic compressible quantum Hall states and their implications to integer quantum Hall effect are studied based on a mean field theory on the von Neumann lattice. It is found that the Hall gas has unusual thermodynamic properties such as negative pressure and negative compressibility and unusual transport properties. Transport properties and density profile of Hall gas states at half fillings agree with those of anisotropic states discovered experimentally in highe...
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.
International Nuclear Information System (INIS)
This paper considers the effect of the anisotropic surface tension on the morphological stability of the planar interface during directional solidification. When the expression exhibiting the four-fold symmetry is included, the modified absolute stability criterion is obtained by employing the multi-variable expansion method. The linear stability analysis reveals that for the given temperature gradient, as the anisotropic surface tension parameter increases, the stability zone tends to decrease. (cross-disciplinary physics and related areas of science and technology)
Czech Academy of Sciences Publication Activity Database
Shull, R. D.; Provenzano, V.; Shapiro, A. J.; Fu, A.; Lufaso, M. W.; Karapetrova, J.; Kletetschka, Günther; Mikula, V.
2006-01-01
Roč. 99, č. 8 (2006), s. 8-8. ISSN 0021-8979 Institutional research plan: CEZ:AV0Z30130516 Keywords : magnetocaloric * (Co, Cu, Ga, Mn, Al, Bi, Sn) additions * Cryogenic properties Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.316, year: 2006
DEFF Research Database (Denmark)
Engelbrecht, Kurt; Bahl, Christian Robert Haffenden; Nielsen, Kaspar Kirstein
2011-01-01
refrigeration device for near room temperature applications, and it is driven by the magnetocaloric effect in the regenerator material. Several magnetocaloric materials with potential magnetic refrigeration applications have recently been developed and characterized; however, few of them have been tested in an...... experimental device. This paper compares the performance of three magnetocaloric material candidates for AMRs, La(Fe,Co,Si)13, (La,Ca,Sr)MnO3 and Gd, in an experimental active magnetic regenerator with a parallel plate geometry. The performance of single-material regenerators of each magnetocaloric material...... family were compared. In an attempt to improve system performance, graded two-material regenerators were made from two different combinations of La(Fe,Co,Si)13 compounds having different magnetic transition temperatures. One combination of the La(Fe,Co,Si)13 materials yielded a higher performance, while...
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.
Room temperature magnetocaloric effect and refrigerant capacitance in La0.7Sr0.3MnO3 nanotube arrays
International Nuclear Information System (INIS)
High aspect ratio La0.7Sr0.3MnO3 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, −△SM = 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 −△SM = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △SM value, the NTs present an expanded temperature dependence of −△SM 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.
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. PMID:26466301
Energy Technology Data Exchange (ETDEWEB)
Mo, Zhao Jun, E-mail: mozhaojun@iphy.ac.cn [School of Material Science and Engineering, Tianjin University of Technology, Tianjin (China); Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China); Shen, Jun, E-mail: jshen@mail.ipc.ac.cn [Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China); Gao, Xin Qiang [Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China); Liu, Yao [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter, Physics and Institute of Physics, Chinese Academy of Sciences, Beijing (China); Tang, Cheng Chun [School of Material Science and Engineering, Hebei University of Technology, Tianjin (China); Wu, Jian Feng [Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China); Hu, Feng Xia; Sun, Ji Rong; Shen, Bao Gen [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter, Physics and Institute of Physics, Chinese Academy of Sciences, Beijing (China)
2015-03-25
Highlights: • Er{sub 2}PdSi{sub 3} compound exhibits a giant reversible MCE. • Er{sub 2}PdSi{sub 3} compound’s MCEs show no thermal and magnetic hysteresis. • Under field changes of 2 T, the value of -ΔS{sub M}{sup max} is 14.5 J/kg K and the RC is 111 J/kg, respectively. - Abstract: The magnetic properties and magnetocaloric effect in R{sub 2}PdSi{sub 3} (R = Dy, Dy and Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Néel temperatures. And, it is found that the Dy{sub 2}PdSi{sub 3} and Er{sub 2}PdSi{sub 3} compounds undergo a spin-glass behavior below Néel temperature. Under the magnetic field change of 5 T, the values of -ΔS{sub M}{sup max} reach 11.8 J/kg K for Gd{sub 2}PdSi{sub 3}, 16.6 J/kg K for Dy{sub 2}PdSi{sub 3} and 22 J/kg K for Er{sub 2}PdSi{sub 3}, respectively. Especially, the values of -ΔS{sub M}{sup max} in the Er{sub 2}PdSi{sub 3} compound are 8 and 14.5 J/kg K for field change of 1 and 2 T, which is attributed to a field-induced metamagnetic transition from AFM to FM states. The large reversible -ΔS{sub M} and large RC together with the absence of thermal and field hysteresis indicate that Er{sub 2}PdSi{sub 3} compound could be a promising candidate for magnetic refrigeration at low temperatures.
Magnetocaloric properties of rare-earth substituted DyCrO3
International Nuclear Information System (INIS)
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 (RCrO3), especially DyCrO3, with its large magnetic moment dysprosium ion, are potential candidates for such an application. The Dy3+ 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 Y3+ and Ho3+ substitutions were found to decrease the magnetocaloric response by disrupting the R3+ ordering. Whereas Er3+ substitution was found to increase the magnetocaloric response, likely due to an increase in the R3+ ordering temperature. The large magnetocaloric entropy change of Er3+ substituted DyCrO3 (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
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.
Experimental study of the anisotropic magneto-Seebeck effect in (Ga,Mn)As thin films
International Nuclear Information System (INIS)
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.
International Nuclear Information System (INIS)
The surface effects on the anisotropic phase separation in photopolymerization induced phase separation of liquid crystal and polymer composites have been studied. It was found that the surface interaction between the substrate and the prepolymer and/or liquid crystal plays a crucial role in anisotropic phase separation. A theoretical model is suggested to describe the surface effects by adapting a phenomenological free energy approach. The formation of polymer layer in the presence of surface effects can be understood as competition between entropic flow and surface directed flow of polymer and liquid crystal
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.
Jet quenching effects on the anisotropic flow at RHIC
Energy Technology Data Exchange (ETDEWEB)
Andrade, R.P.G. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, SP, 09210-170 (Brazil); Noronha, J. [Instituto de Física, Universidade de São Paulo, C.P. 66318, 05315-970 São Paulo, SP (Brazil); Denicol, Gabriel S. [Department of Physics, McGill University, 3600 University Street, Montreal, Quebec, H3A 2T8 (Canada)
2014-12-15
In this article we investigate how the energy and momentum deposited by partonic dijets in the quark–gluon plasma may perturb the geometry-induced hydrodynamic expansion of the bulk nuclear matter created in heavy ion collisions at the RHIC. The coupling between the jets and the medium is done through a source term in the energy–momentum conservation equations for ideal hydrodynamics. We concentrate our attention at mid-rapidity and solve the equations event-by-event imposing boost-invariance. For p{sub T}≳1 GeV the anisotropic flow is found to be considerably enhanced, if the dijets deposit on average more than 12 GeV in the medium (or equivalently 6 GeV for each jet of the pair), which corresponds, in our model, to an average suppression greater than 65% of the initial jet transverse energy.
Jet quenching effects on the anisotropic flow at RHIC
International Nuclear Information System (INIS)
In this article we investigate how the energy and momentum deposited by partonic dijets in the quark–gluon plasma may perturb the geometry-induced hydrodynamic expansion of the bulk nuclear matter created in heavy ion collisions at the RHIC. The coupling between the jets and the medium is done through a source term in the energy–momentum conservation equations for ideal hydrodynamics. We concentrate our attention at mid-rapidity and solve the equations event-by-event imposing boost-invariance. For pT≳1 GeV the anisotropic flow is found to be considerably enhanced, if the dijets deposit on average more than 12 GeV in the medium (or equivalently 6 GeV for each jet of the pair), which corresponds, in our model, to an average suppression greater than 65% of the initial jet transverse energy
Han, Jingjia; Wu, Qingling; Xia, Younan; Wagner, Mary B; Xu, Chunhui
2016-05-01
Enhancing the maturation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) will facilitate their applications in disease modeling and drug discovery. Previous studies suggest that cell alignment could enhance hPSC-CM maturation; however, the robustness of this approach has not been well investigated. To this end, we examined if the anisotropic orientation of hPSC-CMs imposed by the underlying aligned fibers within a 3D microenvironment could improve the maturation of hPSC-CMs. Enriched hPSC-CMs were cultured for two weeks on Matrigel-coated anisotropic (aligned) and isotropic (random) polycaprolactone (PCL) fibrous scaffolds, as well as tissue culture polystyrenes (TCPs) as a control. As expected, hPSC-CMs grown on the two types of fibrous scaffolds exhibited anisotropic and isotropic orientations, respectively. Similar to cells on TCPs, hPSC-CMs cultured on these scaffolds expressed CM-associated proteins and were pharmacologically responsive to adrenergic receptor agonists, a muscarinic agonist, and a gap junction uncoupler in a dose-dependent manner. Although hPSC-CMs grown on anisotropic fibrous scaffolds displayed the highest expression of genes encoding a number of sarcomere proteins, calcium handling proteins and ion channels, their calcium transient kinetics were slower than cells grown on TCPs. These results suggest that electrospun anisotropic fibrous scaffolds, as a single method, have limited effect on improving the maturation of hPSC-CMs. PMID:27131761
Directory of Open Access Journals (Sweden)
Jingjia Han
2016-05-01
Full Text Available Enhancing the maturation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs will facilitate their applications in disease modeling and drug discovery. Previous studies suggest that cell alignment could enhance hPSC-CM maturation; however, the robustness of this approach has not been well investigated. To this end, we examined if the anisotropic orientation of hPSC-CMs imposed by the underlying aligned fibers within a 3D microenvironment could improve the maturation of hPSC-CMs. Enriched hPSC-CMs were cultured for two weeks on Matrigel-coated anisotropic (aligned and isotropic (random polycaprolactone (PCL fibrous scaffolds, as well as tissue culture polystyrenes (TCPs as a control. As expected, hPSC-CMs grown on the two types of fibrous scaffolds exhibited anisotropic and isotropic orientations, respectively. Similar to cells on TCPs, hPSC-CMs cultured on these scaffolds expressed CM-associated proteins and were pharmacologically responsive to adrenergic receptor agonists, a muscarinic agonist, and a gap junction uncoupler in a dose-dependent manner. Although hPSC-CMs grown on anisotropic fibrous scaffolds displayed the highest expression of genes encoding a number of sarcomere proteins, calcium handling proteins and ion channels, their calcium transient kinetics were slower than cells grown on TCPs. These results suggest that electrospun anisotropic fibrous scaffolds, as a single method, have limited effect on improving the maturation of hPSC-CMs.
Han, Jingjia; Wu, Qingling; Xia, Younan; Wagner, Mary B; Xu, Chunhui
2016-01-01
Enhancing the maturation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) will facilitate their applications in disease modeling and drug discovery. Previous studies suggest that cell alignment could enhance hPSC-CM maturation; however, the robustness of this approach has not been well investigated. To this end, we examined if the anisotropic orientation of hPSC-CMs imposed by the underlying aligned fibers within a 3D microenvironment could improve the maturation of hPSC-CMs. Enriched hPSC-CMs were cultured for two weeks on Matrigel-coated anisotropic (aligned) and isotropic (random) polycaprolactone (PCL) fibrous scaffolds, as well as tissue culture polystyrenes (TCPs) as a control. As expected, hPSC-CMs grown on the two types of fibrous scaffolds exhibited anisotropic and isotropic orientations, respectively. Similar to cells on TCPs, hPSC-CMs cultured on these scaffolds expressed CM-associated proteins and were pharmacologically responsive to adrenergic receptor agonists, a muscarinic agonist, and a gap junction uncoupler in a dose-dependent manner. Although hPSC-CMs grown on anisotropic fibrous scaffolds displayed the highest expression of genes encoding a number of sarcomere proteins, calcium handling proteins and ion channels, their calcium transient kinetics were slower than cells grown on TCPs. These results suggest that electrospun anisotropic fibrous scaffolds, as a single method, have limited effect on improving the maturation of hPSC-CMs. PMID:27131761
Korotana, R. K.; Mallia, G.; Fortunato, N. M.; Amaral, J. S.; Gercsi, Z.; Harrison, N. M.
2016-07-01
Manganites with the formula La1‑x Ca x MnO3 for 0.2 electronic structure. An isotropic expansion of the La0.75Ca0.25MnO3 cell at the phase transition has been observed experimentally. It is expected that there will be a large entropy change at the transition due to its first order nature. Doped lanthanum manganite (LMO) is therefore of interest as the active component in a magnetocaloric cooling device. However, the maximum obtained value for the entropy change in Ca-doped manganites merely reaches a moderate value in the field of a permanent magnet. The present theoretical work aims to shed light on this discrepancy. A combination of finite temperature statistical mechanics and first principles theory is applied to determine individual contributions to the total entropy change of the system by treating the electronic, lattice and magnetic components independently. Hybrid-exchange density functional (B3LYP) calculations and Monte Carlo simulations are performed for La0.75Ca0.25MnO3. Through the analysis of individual entropy contributions, it is found that the electronic and lattice entropy changes oppose the magnetic entropy change. The results highlighted in the present work demonstrate how the electronic and vibrational entropy contributions can have a deleterious effect on the total entropy change and thus the potential cooling power of doped LMO in a magnetocaloric device.
Effects of the Biot and the squirt-flow coupling interaction on anisotropic elastic waves
Institute of Scientific and Technical Information of China (English)
无
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.
International Nuclear Information System (INIS)
Highlights: • The Curie temperature of alloy series of Co50−xNixCr25Al25 decreases with increasing x. • The critical exponents behavior and scaling relation of the alloy series have been investigated. • Using M–H data, employing Modified Arrott plot and Kouvel–Fisher plot exponents are estimated. • The estimated critical exponent values match very well with the mean field theory. • Under a magnetic field maximum up to 5 T, normal magnetocaloric effect has been observed. - Abstract: This work reports the investigation of critical behavior of Co50−xNixCr25Al25 (x = 0 and 5) and magneto caloric effect (MCE) of bulk Co2CrAl full Heusler alloy system. The alloy series of Co50−xNixCr25Al25 (x = 0, 1, 2, 3, 4 and 5) have been prepared using arc melting technique. The magnetic properties of all the samples have been studied in the temperature range of 5–300 K. The value of Curie temperature (TC) is found to decrease with increasing doping concentration of the Ni (substitution of Ni at Co site). The critical exponents behavior and scaling relation have been investigated using magnetic isotherms in Co50−xNixCr25Al25 (x = 0 and 5) alloys. The critical exponents are estimated by various techniques such as, Modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. The value of critical exponents vicinity to the second order magnetic phase transition of Co50Cr25Al25 were found to be β = 0.488 (7), γ = 1.144 (16) and δ = 3.336 (5) with TC = 328.64 (5) K whereas for Co50Ni5Cr25Al25 the values are β = 0.522 (13), γ = 1.014 (6) and δ = 3.043 (7) with TC = 285.71 (11). The critical exponent values for both the samples are almost similar to the value as predicted by mean field theory. This has been best explained by long range mean field like ferromagnetic interaction in the entire Co50−xNixCr25Al25 (x = 0, 5) highly spin polarized full Heusler alloy system. Under an external magnetic field maximum up to 5 T, normal magneto caloric
Magnetocaloric-transport properties correlation in doped manganites
Mohamed, Abd El-Moez A.; Hernando, B.; Ahmed, A. M.
2016-05-01
This investigation is interested in studying the relation between magnetocaloric effect and transport properties in La0.7Ba0.3MnO3 manganite compound. The resistivity shows a metal-semiconductor transition at Tms temperature near to its reported Curie temperature (Tc). Magnetic field application decreases resistivity and increases Tms towards higher temperatures. The magnetoresistance shows a peak around Tc and increases in value with the applied magnetic field. A similar behavior has been observed between magnetic entropy change (ΔS), resistivity and magnetoresistance around Tc, this is attributed to the spin order/disorder feature that plays a main role in the magnetocaloric-transport correlation. In spite of this similarity, the correspondence among the experimental ΔS and ΔS based resistivity calculations is missing because of lattice polarons effect on resistivity as a result of the electron-phonon interaction. The magnetocaloric-magnetoresistance relation is also studied and results show the contribution of additional factors in the magnetoresistance mechanism other than spin disorder suppression as Jahn-Teller effect and electronic phase separation.
Energy Technology Data Exchange (ETDEWEB)
Thanh, Tran Dang [Chungbuk National University, Cheongju (Korea, Republic of); Vietnam Academy of Science and Technology, Hanoi (Viet Nam); Mai, Nguyen Thi [VNU University of Science, Hanoi (Viet Nam); Dan, Nguyen Huy [Vietnam Academy of Science and Technology, Hanoi (Viet Nam); Phan, The Long; Yu, Seong Cho [Chungbuk National University, Cheongju (Korea, Republic of)
2014-11-15
In this work, we present a detailed study of the magnetic properties and the magnetocaloric effect at room temperature of Ni{sub 50-x}Ag{sub x}Mn{sub 37}Sn{sub 13} alloys with x = 1, 2, and 4, which were prepared by using an arc-melting method. Experimental results reveal that a partial replacement of Ag for Ni leads to a decrease in the anti-FM phase in the alloys. In addition, the martensitic-austenitic phase transition shifts towards lower temperature and is broaded. The Curie temperature (T{sup A}{sub C} ) for the austenitic phase also shifts toward to lower temperature, but not by much. The Curie temperature was found to be 308, 305, and 298 K for x = 1, 2, and 4, respectively. The magnetic entropy change (ΔS{sub m}) of the samples was calculated by using isothermal magnetization data. Under an applied magnetic field change of 10 kOe, the maximum value of ΔS{sub m} (|ΔS{sub max}|) was achieved at around room temperature and did not change much (∼0.8 J·kg{sup -1}·K{sup -1}) with increasing Ag-doping concentration. Particularly, the M{sup 2} vs. H/M curves prove that all the samples exhibited a secondorder magnetic phase transition. Based on Landau's phase-transition theory and careful analyses of the magnetic data around the T{sup A}{sub C} , we have determined the critical parameters β, γ, δ, and T{sub C} . The results show that the β values are located between those expected for the 3D-Heisenberg model (β = 0.365) and mean-field theory (β = 0.5). Such a result proves the coexistence of short-range and long-range ferromagnetic interactions in Ni{sub 50-x}Ag{sub x}Mn{sub 37}Sn{sub 13} alloys. The nature of the changes in the critical parameters and the |ΔS{sub max}| is thoroughly discussed by means of structural analyses.
Sahoo, Roshnee; Nayak, Ajaya K.; Suresh, K. G.; Nigam, A K
2012-01-01
The effect of Ge substitution on the magnetic, magnetocaloric and transport properties of Ni45Co5Mn38Sb12-xGex (x=0-3) has been investigated. The decrease in the exchange interaction brought by Ge substitution can be seen from the reduction in the magnetization of austenite phase and the increase in the martensitic transition temperature. Large magnetocaloric effect and magnetoresistance have been observed at room temperature, making it a potential material system for various applications.
The unique effect of in-plane anisotropic strain in the magnetization control by electric field
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.
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.
High performance magnetocaloric perovskites for magnetic refrigeration
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.
Tailoring Effective Media by Mie Resonances of Radially-Anisotropic Cylinders
Henrik Kettunen; Henrik Wallén; Ari Sihvola
2015-01-01
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 adj...
Magnetocaloric properties and critical behavior of high relative cooling power FeNiB nanoparticles
International Nuclear Information System (INIS)
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.
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.
International Nuclear Information System (INIS)
The earliest high-Tc oxide superconductors were generally studied in the form of porous polycrystalline pellets. As material preparation technology improved, resulting in samples with orientational order and a smaller concentration of impurity phases, the effects of granular behaviour did not disappear. In both the cases of disordered and partially-ordered structures, an important question arises as to how to interpret measured low-field resistivities in terms of the underlying anisotropic single-crystal values. This paper provides the answer to this question within the context of an effective-medium theory. The authors version of the effective-medium approximation attempts to describe the electrical properties of an inhomogeneous medium, consisting of a mixture of several types of anisotropic polycrystals with different degrees of orientational order. (author)
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.
Czech Academy of Sciences Publication Activity Database
Niemann, R.; Heczko, Oleg; Schultz, L.; Fähler, S.
2014-01-01
Roč. 37, SI (2014), 281-288. ISSN 0140-7007 R&D Projects: GA ČR(CZ) GAP107/11/0391 Institutional support: RVO:68378271 Keywords : magnetocaloric * shape memory alloy s * multiferroic * Ni-Mn-Ga * Maxwell relation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.241, year: 2014
Midya, A.; Khan, N.; Bhoi, D.; Mandal, P.
2013-08-01
We have investigated the influence of 3d-4f spin interaction on magnetic and magnetocaloric properties of DyCrO4 and HoCrO4 compounds by magnetization and heat capacity measurements. Both the compounds exhibit complicated magnetic properties and huge magnetic entropy change around the ferromagnetic transition due to the strong competition between ferromagnetic and antiferromagnetic superexchange interactions. For a field change of 8 T, the maximum values of magnetic entropy change (ΔSMmax), adiabatic temperature change (ΔTad), and refrigerant capacity (RC) reach 29 J kg-1 K-1, 8 K, and 583 J kg-1, respectively, for DyCrO4 whereas the corresponding values for HoCrO4 are 31 J kg-1 K-1, 12 K, and 622 J kg-1. ΔSMmax, ΔTad, and RC are also quite large for a moderate field change. The large values of magnetocaloric parameters suggest that the zircon-type DyCrO4 and HoCrO4 could be the potential magnetic refrigerant materials for liquefaction of hydrogen.
Asoubar, Daniel; Zhang, Site; Wyrowski, Frank
2015-06-01
Birefringence effects can have a significant influence on the polarization state as well as on the transversal mode structure of laser resonators. This work introduces a flexible, fast and fully vectorial algorithm for the analysis of resonators containing homogeneous, anisotropic optical components. It is based on a generalization of the Fox and Li algorithm by field tracing, enabling the calculation of the dominant transversal resonator eigenmode. For the simulation of light propagation through the anisotropic media, a fast Fourier Transformation (FFT) based angular spectrum of plane waves approach is introduced. Besides birefringence effects, this technique includes intra-crystal diffraction and interface refraction at crystal surfaces. The combination with numerically efficient eigenvalue solvers, namely vector extrapolation methods, ensures the fast convergence of the method. Furthermore a numerical example is presented which is in good agreement to experimental measurements. PMID:26072756
Optical analogue of the Aharonov-Bohm effect using anisotropic media
International Nuclear Information System (INIS)
We show that in the context of paraxial optics, which can be analyzed through a wave equation similar to the non-relativistic Schroedinger equation of quantum mechanics but replacing time t by spatial coordinate z, the existence of a vector potential A-perpendicular mimicking the magnetic vector potential in quantum mechanics is allowed by specific gauge symmetries of the optical field in a medium with anisotropic refractive index. In this way, we use Feynman's path integral to demonstrate an optical analogue of the quantum-mechanical Aharonov-Bohm effect, encouraging the search for another optical systems with analogies with more complex quantum field theories. -- Highlights: → The optical analogue of the Aharonov-Bohm effect is demonstrated using anisotropic media. → It follows from the gauge principle applied to the optical field in the paraxial regime. → Feynman's path integral formalism is used to obtain the main result, leading directly from geometric to physical optics.
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. PMID:21231314
Sophia Haussener; Aldo Steinfeld
2012-01-01
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, conv...
Dani, I.; Tahiri, N.; Ez-Zahraouy, H.; Benyoussef, A.
2016-08-01
In this paper we study, using mean field theory (MFT), the effect of the anisotropic Dzyaloshinskii-Moriya (DM) interaction on the phase diagrams of the spin-half Ashkin-Teller model on hypercubic lattice. Different new phase diagrams are found by varying the anisotropy of DM interaction. The multicritical behavior is studied as a function of four-spin interaction coefficient J4 /J1 and for two fixed values of spin interaction coefficient J2 /J1.
Critical behavior and magnetocaloric effect of Pr{sub 1−x}Ca{sub x}MnO{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Ho, T. A.; Phan, The-Long; Yu, S. C., E-mail: scyu@chungbuk.ac.kr [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Thanh, T. D. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Institute of Materials Science, Vietnam Academy of Science and Technology, 18-Hoang Quoc Viet, Hanoi (Viet Nam); Yu, Yikyung; Tartakovsky, D. M. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, California 92093-0411 (United States); Ho, T. O. [Institute of Chemistry, Vietnam Academy of Science and Technology, 18-Hoang Quoc Viet, Hanoi (Viet Nam); Thang, P. D. [Faculty of Engineering Physics and Nanotechnology, VNU University of Engineering and Technology, 144 Xuan Thuy, Cau Giay, Hanoi (Viet Nam); Le, Anh-Tuan [Department of Nanoscience and Nanotechnology, Advanced Institute for Science and Technology, Hanoi University of Science and Technology, 01 Dai Co Viet, Hai Ba Trung, Hanoi (Viet Nam)
2015-05-07
The critical behavior of Pr{sub 1−x}Ca{sub x}MnO{sub 3} samples with x = 0.25, 0.27, and 0.29 has been investigated. Detailed analyses of magnetic-field dependences of magnetization at temperatures around the paramagnetic-ferromagnetic transition, M(H, T), reveal that the samples undergo a second-order magnetic phase transition. The Arrott plot method predicts the values of critical parameters to be T{sub C} ≈ 118 K, β = 0.351 ± 0.003, γ = 1.372 ± 0.002, and δ = 4.90 ± 0.02 for x = 0.25; T{sub C} ≈ 116 K, β = 0.362 ± 0.002, γ = 1.132 ± 0.004, and δ = 4.09 ± 0.03 for x = 0.27; and T{sub C} ≈ 110 K, β = 0.521 ± 0.002, γ = 0.912 ± 0.005, and δ = 2.71 ± 0.02 for x = 0.29. The values of β = 0.351 (for x = 0.25) and β = 0.362 (for x = 0.27) are close to the value β = 0.365 expected for the 3D Heisenberg model, proving an existence of short-range ferromagnetic interactions in these samples. A slight increase in Ca-doping content (x = 0.29) leads to the shift of the β value (=0.521) towards that of the mean-field theory (with β = 0.5) characteristic of long-range ferromagnetic interactions. The samples also exhibit a magnetocaloric effect: around T{sub C} of Pr{sub 1−x}Ca{sub x}MnO{sub 3} compounds, magnetic-entropy change reaches the maximum values of about 5.0, 4.1, and 2.5 J kg{sup −1} K{sup −1} for x = 0.25, 0.27, and 0.29, respectively, under an applied-field change of 50 kOe. Magnetic-field dependences of the maximum magnetic-entropy change (ΔS{sub max}) obey a power law |ΔS{sub max}(H)| ∝ H{sup n}, where exponent values n = 0.68–0.74 are close to those obtained from the theoretical relation n = 1 + (β − 1)/(β + γ)
Magnetocaloric properties of rare-earth substituted DyCrO3
McDannald, A.; Jain, M.
2015-07-01
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 (RCrO3), especially DyCrO3, with its large magnetic moment dysprosium ion, are potential candidates for such an application. The Dy3+ ordering transition at low temperatures (disrupting the R3+ ordering. Whereas Er3+ substitution was found to increase the magnetocaloric response, likely due to an increase in the R3+ ordering temperature. The large magnetocaloric entropy change of Er3+ substituted DyCrO3 (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.
A multicaloric material as a link between electrocaloric and magnetocaloric refrigeration
Ursic, Hana; Bobnar, Vid; Malic, Barbara; Filipic, Cene; Vrabelj, Marko; Drnovsek, Silvo; Jo, Younghun; Wencka, Magdalena; Kutnjak, Zdravko
2016-05-01
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.
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...... 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 of the...
Magnetic, magnetocaloric properties and phenomenological model in amorphous Fe60Ru20B20 alloy
Boutahar, A.; Lassri, H.; Hlil, E. K.
2015-11-01
Magnetic, magnetocaloric properties and phenomenological model of amorphous Fe60Ru20B20 alloy are investigated in detail. The amorphous alloy has been synthesized using melt spinning method. The magnetic transition nature undergoes a second-order magnetic phase transition from ferromagnetic to paramagnetic states with a Curie temperature of 254 K. Basis on the thermodynamic Maxwell's relation, magnetic entropy change (-ΔSM) is calculated. Further, we also report a theoretical investigation of the magnetocaloric effect using a phenomenological model. The best model parameters and their variation with temperature and the magnetic field were determined. The theoretical predictions are found to agree closely with experimental measurements.
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.
Simulations of the anisotropic kinetic and magnetic alpha effects
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.
Energy Technology Data Exchange (ETDEWEB)
Dhahri, Ja. [Laboratory of Physical Chemistry of Materials, Faculty of Sciences of Monastir, University of Monastir (Tunisia); Dhahri, A., E-mail: abdessalem_dhahri@yahoo.fr [Laboratory of Physical Chemistry of Materials, Faculty of Sciences of Monastir, University of Monastir (Tunisia); Center for Scientific Research, Department of Physics, Al-Qunfudah University College, Umm Al-Qura University (Saudi Arabia); Oummezzine, M. [Laboratory of Physical Chemistry of Materials, Faculty of Sciences of Monastir, University of Monastir (Tunisia); Hlil, E.K. [Institut Ne´el, CNRS–Université J. Fourier, BP166, 38042 Grenoble (France)
2015-03-15
We have studied the structural, magnetic and magnetocaloric properties of La{sub 0.6}Nd{sub 0.1}Sr{sub 0.15}Ca{sub 0.15}Mn{sub 1−x}Fe{sub x}O{sub 3} (LNSCMFe{sub x}) perovskite samples. The samples were synthesized using the solid-state reaction at high temperature and were analyzed by XRD data based on the Rietveld refinement technique. LNSCMFe{sub x} samples crystallized in orthorhombic symmetry with Pnma space group. Besides, the curves of magnetization reveals that all samples exhibit a magnetic transition from the paramagnetic to ferromagnetic phase at the Curie temperature T{sub C}, which decreases from 327 K to 296 K with the increase of the Fe doping level from x=0 to x=0.1. The thermal evolution of magnetization in the ferromagnetic phase at low temperature varies as T{sup 3/2} in accordance with Bloch's law. The magnitude of the isothermal magnetic entropy, (−ΔS{sub M}{sup max}), at the FM Curie temperature increases from 3.79 J/kg K for x=0 composition to 5.8 J/kg K for x=0.1, under a magnetic field of 5 T. For an applied magnetic field of 5 T, the relative cooling power (RCP) values are found to vary between 173.66 and 231.76 J/kg. These results suggest that these materials could be used as an active magnetic refrigerant around room temperature. - Highlights: • La{sub 0.6}Nd{sub 0.1}Sr{sub 0.15}Ca{sub 0.15}Mn{sub 1−x}Fe{sub x}O{sub 3} samples were prepared using solid-state reaction. • The manganite phase crystallizes in an orthorhombic (Pnma) structure. • The samples exhibit a second order PM–FM phase transition at T{sub C}. • LNSCMFe{sub 0.05} and LNSCMFe{sub 0.1} are potential candidates for room-temperature magnetic refrigeration.
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.
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...
Magnetic structure and phase formation of magnetocaloric Mn-Fe-P-X compounds
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
Effective dielectric response of anisotropic grains of close-packed structure
Czech Academy of Sciences Publication Activity Database
Klíč, Antonín; Rychetský, Ivan
New Jersey : IEEE - Institute of Electrical and Electronics Engineers, 2012, s. 510-512. ISBN 978-1-4673-2668-1. - (IEEE Conference Publications). [ISAF-ECAPD-PFM 2012. Aveiro (PT), 09.07.2012-13.07.2012] R&D Projects: GA ČR GAP204/12/0232 Institutional research plan: CEZ:AV0Z10100520 Keywords : anisotropic poplycrysta * spectral representation * effective permittivity * 2-component system Subject RIV: BM - Solid Matter Physics ; Magnetism http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6279558
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.
On the Newtonian anisotropic configurations
Energy Technology Data Exchange (ETDEWEB)
Shojai, F. [University of Tehran, Department of Physics, Tehran (Iran, Islamic Republic of); Institute for Research in Fundamental Sciences (IPM), Foundations of Physics Group, School of Physics, Tehran (Iran, Islamic Republic of); Fazel, M.R.; Stepanian, A. [University of Tehran, Department of Physics, Tehran (Iran, Islamic Republic of); Kohandel, M. [Alzahra University, Department of Sciences, Tehran (Iran, Islamic Republic of)
2015-06-15
In this paper we are concerned with the effects of an anisotropic pressure on the boundary conditions of the anisotropic Lane-Emden equation and the homology theorem. Some new exact solutions of this equation are derived. Then some of the theorems governing the Newtonian perfect fluid star are extended, taking the anisotropic pressure into account. (orig.)
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...
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...
International Nuclear Information System (INIS)
We carried out three-dimensional magnetohydrodynamic simulations to study the effects of plasma viscosity on the formation of sharp discontinuities of density and temperature distributions, cold fronts, in clusters of galaxies. By fixing the gravitational potential that confines the cool, dense plasma in a moving subcluster, we simulated its interaction with the hot, lower density plasma around the subcluster. At the initial state, the intracluster medium (ICM) is assumed to be threaded by uniform magnetic fields. The enhancement of plasma viscosity along the direction of magnetic fields is incorporated as anisotropic viscosity depending on the direction of magnetic fields. We found that the Kelvin-Helmholtz instability at the surface of the subcluster grows even in models with anisotropic viscosity, because its effects on the velocity shear across the magnetic field lines are suppressed. We also found that magnetic fields around the interface between the subcluster and ICM are amplified even in the presence of viscosity, while magnetic fields behind the subcluster are amplified up to β–1 ∼ 0.01 in models with viscosity, whereas they are amplified up to β–1 ∼ 0.1 in models without viscosity, where β is the ratio of gas pressure to magnetic pressure.
Effects of anisotropic thermal conduction on wind properties in hot accretion flow
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...
Horgan, C. O.; Simmonds, J. G.
1994-12-01
Many useful thin-walled structures of interest to the U.S. Army, such as rifle barrels, automotive parts, rocket casings, helicopter blades, driveshafts, and containment vessels, are often constructed of layers of anisotropic, filament or fiber-reinforced materials. While many of these structures are subject to severe mechanical, inertial, or thermal loads, they often must be designed to remain elastic. This means that it is particularly important to be able to compute accurately global characteristics, such as buckling loads and natural frequencies, as well as local information such as stresses near holes or edges. Two important, complementary regions of such structures, have been studied, namely, the interior where there are no steep stress gradients, and the edge zone(s) where stress gradients are high. For both regions, simplified, cost-effective asymptotic methods have been developed. These considerations are particularly important in layered, anisotropic structures because many investigators have (1) claimed that higher-order (and hence computationally expensive) beam, plate, or shell theories are needed for such structures and (2) not paid sufficient attention to the particularly severe end effects (breakdown of Saint-Venant's principle) such structures engender.
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.
Effects of anisotropic thermal conduction on wind properties in hot accretion flow
Bu, De-Fu; Wu, Mao-Chun; Yuan, Ye-Fei
2016-06-01
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 ˜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 included. This result demonstrates that thermal conduction plays an important role in determining the properties of wind.
Energy Technology Data Exchange (ETDEWEB)
Triki, M., E-mail: mtriki_fss@yahoo.fr [Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, B. P. 1171, 3000 Sfax (Tunisia); Dhahri, R. [Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, B. P. 1171, 3000 Sfax (Tunisia); Bekri, M. [Physics Department, Rabigh College of Science and Art, King Abdulaziz University, P.O. Box 344, Rabigh 21911 (Saudi Arabia); Dhahri, E. [Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, B. P. 1171, 3000 Sfax (Tunisia); Valente, M.A. [Physics Department (I3N), Aveiro University, Campus Universita rio de Santiago, 3800-193 Aveiro (Portugal)
2011-09-29
Highlights: > Study of magnetocaloric effect on magnetoelectric composites Pr{sub 0.6}Sr{sub 0.4}MnO{sub 3}/BaTiO{sub 3}. > Maximum magnetic entropy and RCP values are not affected for the low BTO content. > A typical second order magnetic transition near T{sub c}. > The calculated magnetic entropy shows a good agreement with experiment results. - Abstract: We have prepared composite materials composed of ferromagnetic and ferroelectric compounds having the general formula (1 - x)(Pr{sub 0.6}Sr{sub 0.4}MnO{sub 3})/x(BaTiO{sub 3}), with x is the molar ratio (x = 0.0, 0.03, 0.05, 0.10 and 0.30) using conventional ceramic double sintering process. We report the structural, magnetic and magnetocaloric properties of all samples. The presence of the two phases of Pr{sub 0.6}Sr{sub 0.4}MnO{sub 3} (PSMO) and BaTiO{sub 3} (BTO) was confirmed by X-ray diffraction (XRD) technique and the structural analysis. Magnetic measurements of magnetization versus temperature and magnetic applied field were performed. The temperature dependence of magnetization reveals that the composite samples show paramagnetic to ferromagnetic phase transition (PM-FM) when the temperature decreases. These samples have the same Curie temperature as the parent PSMO compound (T{sub c} {approx} 273 K). The magnetic entropy change |{Delta}S{sub M}| was deduced from the M(H) data by the Maxwell relation. Close to T{sub c}, a large change in magnetic entropy has been observed in all samples. The maximum value of the magnetic entropy |{Delta}S{sub M}{sup max}| decreases from 2.88 J kg{sup -1} K{sup -1} for x = 0-1.86 J kg{sup -1} K{sup -1} for x = 0.3 for an applied magnetic field of 2 T. At this value of magnetic field the relative cooling power (RCP) decreases equally from 63 J kg{sup -1} for the parent sample to 38.3 J kg{sup -1} for x = 0.3. The temperature dependence of the Landau coefficients has been deduced using the Landau expansion of the magnetic free energy, indicating the second order nature of
Ho, T. A.; Phan, M. H.; Phuc, N. X.; Lam, V. D.; Phan, T. L.; Yu, S. C.
2016-05-01
The Ti-substitution influence on the magnetic and magnetocaloric properties of La0.7Ba0.3Mn1- x Ti x O3 ( x = 0.05 and 0.1) was investigated. Based on Banerjee's criteria and Franco's universal curves, we proved the existence of a second-order magnetic phase transition in the samples. Using the modified Arrott plot method, we determined the critical parameters T C ≈ 245 K, β = 0.374 ± 0.013, γ = 1.228 ± 0.045, and δ = 4.26 ± 0.03 for x = 0.05, and T C ≈ 169 K, β = 0.339 ± 0.001, γ = 1.307 ± 0.003, and δ = 4.78 ± 0.02 for x = 0.1. With these critical values, the predictable scaling behavior of the M( H) data above and below T C proves that the calculated exponents are unambiguous and intrinsic. The values β = 0.374 for x = 0.05 and β = 0.339 for x = 0.1 suggest that the magnetic phase transition of the samples falls into the three-dimensional (3D) Heisenberg and 3D Ising universality classes, respectively, corresponding to short-range ferromagnetic (FM) order due to FM clusters in a wide temperature range even above T C, as confirmed by electron spin resonance studies. In reference to the magnetocaloric effect around T C, the magnetic entropy change reaches maximum values (|ΔSmax|) of about 4 and 3 J kg-1 K-1 for x = 0.05 and 0.1, respectively, for a magnetic field change 50 kOe. Magnetic field dependencies of |ΔSmax| obey a power function |ΔSmax( H)| ∝ H n , where exponent values n = 0.59 and 0.61 for x = 0.05 and 0.1, respectively, were determined from the relation n = 1 + ( β-1)/( β + γ). The difference between the experimental n values and the theoretical value n = 2/3 of the mean field model is due to the presence of short-range FM order in the samples.
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.
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.
Magnetocaloric and magnetic properties of SmFe0.5Mn0.5O3 complex perovskite
Silva-Santana, M. C.; daSilva, C. A.; Barrozo, P.; Plaza, E. J. R.; de los Santos Valladares, L.; Moreno, N. O.
2016-03-01
In this paper, we have investigated the physical properties of SmFe0.5Mn0.5O3 complex perovskite samples, synthesized by means of combustion reaction method. X-ray powder diffraction indicates the formation of single phase perovskite with orthorhombic structure. Low magnetic field measurements show remarkable transition at 234 K related to spin reorientation. The magnetocaloric effect shows two peaks related to magnetic behavior changes, at 18 K and at 234 K. The transition about 234 K presents inverse magnetocaloric effect. The entropy variation from magnetocaloric effect shows power law as function of applied magnetic field with maximum entropy change 5.6 J/kg K with field variation of 70 kOe. Critical exponents extracted from ΔS vs. H presents a remarkable sharp peak near antiferromagnetic to weak ferromagnetic transition temperature.
Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation
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.
International Nuclear Information System (INIS)
We study the thermomagnetic history effects arising due to phase coexistence and metastability across the first order antiferromagnetic to ferromagnetic transition in the giant magnetocaloric Fe-Rh alloy near room temperature. Magnetic force microscopy is used to visualize the phase coexistence across this magneto structural transition at sub-micrometer length scales. These local measurements provide direct evidence of strong coupling between the elastic and electronic degrees of freedom, which is thought to give rise to phase coexistence at micrometer scales. Phase coexistence and the associated history effects are shown to influence the functional properties of Fe-Rh like giant magnetocaloric effect at room temperature. (author)
Mode-coupling effects in anisotropic flow in heavy-ion collisions
Qian, Jing; Liu, Jia
2016-01-01
Higher-order anisotropic flows in heavy-ion collisions are affected by nonlinear mode coupling effects. It has been suggested that the associated nonlinear hydrodynamic response coefficients probe the transport properties and are largely insensitive to the spectrum of initial density fluctuations of the medium created in these collisions. To test this suggestion, we explore nonlinear mode coupling effects in event-by-event viscous fluid dynamics, using two different models for the fluctuating initial density profiles, and compare the nonlinear coupling coefficients between the initial eccentricity vectors before hydrodynamic expansion and the final flow vectors after the expansion. We find significant sensitivity of the mode coupling coefficients to the initial fluctuation spectrum, strong sensitivity to the specific shear viscosity at freeze-out, but only weak dependence on the shear viscosity during hydrodynamic evolution.
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.
Mode-coupling effects in anisotropic flow in heavy-ion collisions
Qian, Jing; Heinz, Ulrich; Liu, Jia
2016-06-01
Higher-order anisotropic flows in heavy-ion collisions are affected by nonlinear mode coupling effects. It has been suggested that the associated nonlinear hydrodynamic response coefficients probe the transport properties and are largely insensitive to the spectrum of initial density fluctuations of the medium created in these collisions. To test this suggestion, we explore nonlinear mode coupling effects in event-by-event viscous fluid dynamics, using two different models for the fluctuating initial density profiles, and compare the nonlinear coupling coefficients between the initial eccentricity vectors before hydrodynamic expansion and the final flow vectors after the expansion. For several mode coupling coefficients we find significant sensitivity to the initial fluctuation spectrum. They all exhibit strong sensitivity to the specific shear viscosity at freeze-out, but only weak dependence on the shear viscosity during hydrodynamic evolution.
Magneto volume effects and anisotropic properties of the new R3 (Fe Ti)29 intermetallic compounds
International Nuclear Information System (INIS)
In this work we present a review of the magneto volume and anisotropic properties of the R3 (Fe Ti)29 series of alloys characterized by measuring linear thermal expansion (LTE), a.c. initial susceptibility under hydrostatic pressure and anisotropy field using the SPD technique. We can summarize the main results obtained as follows: Large Invar-like magneto volume effects have been observed in the LTE measurements, suggesting large volume effects on TC. A large decrease of TC under hydrostatic pressure for all the studied compounds has been found. A spin reorientation process takes place in the Nd3 (Fe Ti)29 compound. Two anisotropy fields have been detected in the 3:29 compounds associated with the saturation along the two hard magnetic directions of the monoclinic structure. A first-order magnetization process takes place at low temperature for the Nd and Tb compounds. (author)
Reyes, E.; Krokhin, A. A.; Roberts, J.
2005-01-01
We calculate the static dielectric tensor of a periodic system of aligned anisotropic dielectric cylinders. Exact analytical formulas for the effective dielectric constants for the E- and H- eigenmodes are obtained for arbitrary 2D Bravais lattice and arbitrary cross-section of anisotropic cylinders. It is shown that depending on the symmetry of the unit cell photonic crystal of anisotropic cylinders behaves in the low-frequency limit like uniaxial or biaxial natural crystal. The developed th...
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.
International Nuclear Information System (INIS)
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
Buoyant Bubbles in Intracluster Gas: Effects of Magnetic Fields and Anisotropic Viscosity
Dong, Ruobing
2009-01-01
Recent observations by Chandra and XMM-Newton indicate there are complex structures at the cores of galaxy clusters, such as cavities and filaments. One plausible model for the formation of such structures is the interaction of radio jets with the intracluster medium (ICM). To investigate this idea, we use three-dimensional magnetohydrodynamic simulations including anisotropic (Braginskii) viscosity to study the effect of magnetic fields on the evolution and morphology of buoyant bubbles in the ICM. We investigate a range of different initial magnetic field geometries and strengths, and study the resulting x-ray surface brightness distribution for comparison to observed clusters. Magnetic tension forces and viscous transport along field lines tend to suppress instabilities parallel, but not perpendicular, to field lines. Thus, the evolution of the bubble depends strongly on the initial field geometry. We find toroidal field loops initially confined to the interior of the bubble are best able reproduce the obs...
Geminate ion recombination in anisotropic media. Effects of initial distribution and external field
International Nuclear Information System (INIS)
Recently we presented [Chem. Phys. Lett. 142, 385 (1987)] a method for calculating the diffusion-controlled geminate escape probability of an ion pair in an anisotropic medium. The escape probability depends on both the length and the direction of the initial interion vector, and is reducible to a function of two dimensionless variables describing the overall anisotropy of the medium. In this paper the treatment is extended to include an initial distribution of interion distances and an external field. Inclusion of a field increases the number of independently variable parameters to five: two to describe the anisotropy of the medium and three to describe the intensity and direction of the applied field. It is shown that the effects of including anisotropy are not negligible for the typical case of anthracene and that the slope-to-intercept ratio of the field-dependent escape probability for a spherically averaged distribution depends on the direction of the applied field
Qian, Jing
2016-01-01
We investigate the collective excitation effect in a scheme where three identical Rydberg atoms are arranged in an equilateral triangular lattice. By using a static electric field polarizing the atomic dipoles, the dipole-dipole interactions between two Rydberg atoms are essentially anisotropic and can even disappear in the several special resonance cases. For that fact, we observe collectively enhanced excitation probability of single Rydberg atom in resonant areas in the case of strong blockade, and that of double or triple Rydberg atoms in the case of partial blockade. To give more evidences for this collective excitation enhancement, we study the two-body quantum correlation between three Rydberg atoms, as well as the dependence of the blockade radius on the length of triangle sides, which present a good agreement with the excitation properties.
Anisotropic pressure effects on the charge order transition of (TMTTF){sub 2}X
Energy Technology Data Exchange (ETDEWEB)
Nagasawa, M., E-mail: nagasawa@chiba.dendai.ac.j [Department of Physics, Tokyo Denki University (Japan); Department of Green and Sustainable Chemistry, Tokyo Denki University (Japan); Nagasawa, T. [Department of Green and Sustainable Chemistry, Tokyo Denki University (Japan); Ichimura, K. [Division of Applied Physics, Hokkaido University (Japan); Nomura, K. [Division of Physics, Hokkaido University (Japan)
2010-06-01
We measured the conductivity along the a-direction {sigma}{sub a}(T) of the quasi one-dimensional organic conductor (TMTTF){sub 2}SbF{sub 6} under several anisotropic pressures of uniaxial strains which are parallel and perpendicular to the a-direction. The uniaxial strains were generated by so-called 'Frozen oil method'. It was found that the tendencies of the uniaxial strain dependence of the conductivity and the charge order (CO) transition temperature T{sub CO} are different. According to T{sub CO}, it decreases strongly with increasing uniaxial strain parallel to the a-direction; however, it is almost constant for that perpendicular to the a-direction. We discuss the effects of compressive uniaxial strains on the conductivity and the CO transition of (TMTTF){sub 2}SbF{sub 6}.
THE EFFECT OF ANISOTROPIC VISCOSITY ON COLD FRONTS IN GALAXY CLUSTERS
Energy Technology Data Exchange (ETDEWEB)
ZuHone, J. A.; Markevitch, M. [Astrophysics Science Division, Laboratory for High Energy Astrophysics, Code 662, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Kunz, M. W.; Stone, J. M. [Department of Astrophysical Sciences, 4 Ivy Lane, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States); Biffi, V. [SISSA-Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste (Italy)
2015-01-10
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 of placing 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 of turbulence within the sloshing region is only modestly reduced by Braginskii viscosity. We also performed unmagnetized simulations with and without viscosity and find that magnetic fields have a substantial effect on the appearance of the cold fronts, even if the initial field is weak and the viscosity is the same. This suggests that determining the dominant suppression mechanism of a given cold front from X-ray observations (e.g., viscosity or magnetic fields) by comparison with simulations is not straightforward. Finally, we performed simulations including anisotropic thermal conduction, and find that including Braginskii viscosity in these simulations does not significantly affect the evolution of cold fronts; they are rapidly smeared out by thermal conduction, as in the inviscid case.
THE EFFECT OF ANISOTROPIC VISCOSITY ON COLD FRONTS IN GALAXY CLUSTERS
International Nuclear Information System (INIS)
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 of placing 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 of turbulence within the sloshing region is only modestly reduced by Braginskii viscosity. We also performed unmagnetized simulations with and without viscosity and find that magnetic fields have a substantial effect on the appearance of the cold fronts, even if the initial field is weak and the viscosity is the same. This suggests that determining the dominant suppression mechanism of a given cold front from X-ray observations (e.g., viscosity or magnetic fields) by comparison with simulations is not straightforward. Finally, we performed simulations including anisotropic thermal conduction, and find that including Braginskii viscosity in these simulations does not significantly affect the evolution of cold fronts; they are rapidly smeared out by thermal conduction, as in the inviscid case
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
Czech Academy of Sciences Publication Activity Database
Tereshina, I.; Politova, G.; Tereshina, Evgeniya; Nikitin, S.; Burkhanov, G.; Chistyakov, O.; Karpenkov, A.
2010-01-01
Roč. 200, č. 9 (2010), 092012/1-092012/5. ISSN 1742-6588. [International Conference on Magnetism - ICM 2009. Karlsruhe , 26.07.2009-31.07.2009] Institutional research plan: CEZ:AV0Z10100520 Keywords : Laves phases * magnetocalorics * magnetostriction Subject RIV: BM - Solid Matter Physics ; Magnetism
(Magneto)caloric refrigeration: is there light at the end of the tunnel?
Pecharsky, Vitalij K; Cui, Jun; Johnson, Duane D
2016-08-13
Caloric cooling and heat pumping rely on reversible thermal effects triggered in solids by magnetic, electric or stress fields. In the recent past, there have been several successful demonstrations of using first-order phase transition materials in laboratory cooling devices based on both the giant magnetocaloric and elastocaloric effects. All such materials exhibit non-equilibrium behaviours when driven through phase transformations by corresponding fields. Common wisdom is that non-equilibrium states should be avoided; yet, as we show using a model material exhibiting a giant magnetocaloric effect, non-equilibrium phase-separated states offer a unique opportunity to achieve uncommonly large caloric effects by very small perturbations of the driving field(s).This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'. PMID:27402923
Energy Technology Data Exchange (ETDEWEB)
Mo, Zhao-Jun [School of Material Science and Engineering, Hebei University of Technology, Tianjin (China); Key laboratory of cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China); Shen, Jun, E-mail: jshen@mail.ipc.ac.cn, E-mail: tangcc@hebut.edu.cn; Wu, Jian-Feng [Key laboratory of cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China); Yan, Li-Qin; Wang, Li-Chen; Sun, Ji-rong; Shen, Bao-Gen [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter, Physics and Institute of Physics, Chinese Academy of Sciences, Beijing (China); Gao, Xin-Qiang; Tang, Cheng-Chun, E-mail: jshen@mail.ipc.ac.cn, E-mail: tangcc@hebut.edu.cn [School of Material Science and Engineering, Hebei University of Technology, Tianjin (China)
2014-02-21
The magnetic properties and magnetocaloric effect (MCE) in RCu{sub 2}Si{sub 2} and RCu{sub 2}Ge{sub 2} (R = Ho, Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Neel temperatures. The RCu{sub 2}Si{sub 2} compounds undergo spin-glassy behavior above Neel temperature. Furthermore, a field-induced metamagnetic transition from AFM to ferromagnetic (FM) states is observed in these compounds. The calculated magnetic entropy changes show that all RCu{sub 2}Si{sub 2} and RCu{sub 2}Ge{sub 2} (R = Ho, Er) compounds, especially, ErCu{sub 2}Si{sub 2} exhibits large MCEs with no thermal hysteresis and magnetic hysteresis loss. The value of −ΔS{sub M}{sup max} reaches 22.8 J/Kg K for magnetic field changes from 0 to 5 T. In particular, for field changes of 1 and 2 T, the giant reversible magnetic entropy changes −ΔS{sub M}{sup max} are 8.3 and 15.8 J/kg K at 2.5 K, which is lower than the boiling point of helium. The low-field giant magnetic entropy change, together with ignorable thermal hysteresis and field hysteresis loss of ErCu{sub 2}Si{sub 2} compound is expected to have effective applications in low temperature magnetic refrigeration.
On Peculiarities of the Anisotropic Diffusion during Forbush Effects of Galactic Cosmic Rays
International Nuclear Information System (INIS)
Experimental data of neutron super monitors, solar wind velocity and components of the interplanetary magnetic field (IMF) have been used to study a relationship between the temporal changes of the energy spectrum of the Forbush effects of galactic cosmic rays (GCR) and the power spectral density (PSD) of the IMF's strength fluctuations. Based on the energy spectrum of the Forbush effects of GCR a structure of the IMF's fluctuations is determined in the disturbed vicinity of the interplanetary space when the direct (in situ) measurements of the IMF are absent. In order to study anisotropic diffusion propagation of GCR a second order four dimensional Fokker-Plank's type partial differential equation has been numerically solved. Diffusion, convection, drift due to the regular component of the IMF and adiabatic energy changes of the GCR particles because of the interaction with the diverged solar wind inhomogeneities are included in the transport equation. The spatial distributions of the density, radial, heliolatitudinal and heliolongitudinal gradients during the Forbush effect of GCR intensity have been found for the positive (qA > 0) period of solar magnetic cycle. It is shown that a stationary diffusion-convection-drift approximation of GCR transport is an acceptable model for describing the recurrent Forbush effects of GCR associated with the established corotating disturbances in the inner heliosphere. (author)
The effect of rotation on the onset of convection in a horizontal anisotropic porous layer
Energy Technology Data Exchange (ETDEWEB)
Malashetty, M.S.; Swamy, Mahantesh [Department of Mathematics, Gulbarga University, Jnana Ganga, Gulbarga 585 106 (India)
2007-10-15
The effect of rotation and anisotropy on the onset of convection in a horizontal porous layer is investigated using a linear theory and a weak nonlinear theory. The linear theory is based on the usual normal mode technique and the nonlinear theory on the truncated Fourier series analysis. Darcy model extended to include time derivative and Coriolis terms with anisotropic permeability is used to describe the flow through porous media. A modified energy equation including the thermal anisotropy is used. The effect of rotation, mechanical and thermal anisotropy parameters and the Prandtl number on the stationary and overstable convection is discussed. It is found that the effect of mechanical anisotropy is to allow the onset of oscillatory convection instead of stationary. It is also found that the existence of overstable motions in case of rotating porous medium is not restricted to a particular range of Prandtl number as compared to the pure viscous fluid case. The steady finite amplitude analysis is performed using truncated Fourier series to find the Nusselt number. The effect of various parameters on heat transfer is investigated. (author)
International Nuclear Information System (INIS)
Although transport calculations are often formulated in terms of mass-based isotropic distribution coefficients, it is the abundance of reactive surface areas of subsurface materials that controls contaminant adsorption. In water-saturated homogeneous systems devoid of advective fluxes (e.g., batch experiments), the available reactive surface area is similar to the total surface area (as measured by conventional methods such as BET gas adsorption). However, in physically and chemically heterogeneous systems with advective fluxes, the effective reactive surface area (i.e., the surface area that a packet of advecting water interacts with) is smaller than the laboratory measured surface area and is a complex function of advective velocity and the correlation structures of the physical and chemical heterogeneities. Theoretical derivations for an important but simple type of heterogeneity (fine-scale horizontal layering) suggest that the effective reactive surface area is an anisotropic property of the medium and is inversely correlated with the anisotropy in hydraulic conductivity. The implications of reactive transport anisotropy include the concept that the retardation factor should be treated as a directional property rather than being treated as a constant. Furthermore, because of the inverse relationship between effective reactive surface area and hydraulic conductivity, batch adsorption experiments tend to overestimate the retention of contaminants relative to intact natural materials
Shawish, Samir El; CIZELJ Leon; SIMONOVSKI IGOR
2012-01-01
In this work we propose an anisotropic elasto-plastic finite element model to account for various observations in the tensile test experiments on stainless steel specimen. Using Voronoi construction for the grains, grain boundaries and anisotropic Hill’s plastic potential function, we find a clear correlation between the computed average misorientation angle, measuring the change of local crystal orientations, and the applied plastic strain, in agreement with the electron backscatter diffract...
Energy Technology Data Exchange (ETDEWEB)
Giri, S.K. [Department of Physics, Indian Institute of Technology, Kharagpur, West Bengal 721302 (India); Dasgupta, Papri; Poddar, A. [Experimental Condensed Matter Physics Division, Saha Institute of Nuclear Physics, West Bengal (India); Nath, T.K., E-mail: tnath@phy.iitkgp.ernet.in [Department of Physics, Indian Institute of Technology, Kharagpur, West Bengal 721302 (India)
2015-05-15
Graphical abstract: ΔS{sub M} vs. T plots of nano (left) and bulk (right) samples at different magnetic fields. - Highlights: • Bulk to nano show first order FM → PM phase transition at low magnetic field. • Bulk sample exhibits normal and inverse MCE around T{sub C} and after T{sub g}, respectively. • The value of ΔS{sub M} at T{sub C} is almost three times larger than at T{sub g}. • The value of ΔS{sub M} also decreases with reduction of particles sizes. • The bulk sample also exhibits a large RCP of 43.5 J/kg for a magnetic field of 1 T. - Abstract: Magnetic and magnetocaloric properties of Sm{sub 0.35}Pr{sub 0.15}Sr{sub 0.5}MnO{sub 3} polycrystalline manganite (bulk and nanometric samples) are investigated in detail. It has been observed that all the particle sizes (bulk to nano) show first order ferromagnetic → paramagnetic phase transition at low magnetic field. Ferromagnetic transition temperature also decreases with decreasing the particle size. This suggests that ferromagnetism is weakened and the first order magnetic phase transition is softened. We have investigated the magnetocaloric effect (MCE) of both bulk and nanometric samples around their spin glass-like transition temperature, T{sub g} and Curie temperature, T{sub C}. It has been found that bulk sample exhibits both normal (i.e., negative ΔS{sub M}) and inverse (i.e., positive ΔS{sub M}) MCE around T{sub C} and after T{sub g}, respectively. The value of ΔS{sub M} (+3.17 J kg{sup −1} K{sup −1}) at T{sub C} is almost three times larger than at T{sub g} (ΔS{sub M} = −0.52 J kg{sup −1} K{sup −1}) for a magnetic field change of 7 T. The bulk sample also exhibits a large relative cooling power (RCP) of 43.5 J/kg for a magnetic field of 1 T. The corresponding adiabatic temperature change of bulk sample is observed to be ∼1.5 K for a magnetic field change of 3 T. The value of ΔS{sub M} also decreases with reduction of particles sizes. The temperature width of ΔS{sub M
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.
Model anisotropic quantum Hall states
Qiu, R. -Z.; Haldane, F.D.M.; Wan, Xin; Yang, Kun; Yi, Su
2012-01-01
Model quantum Hall states including Laughlin, Moore-Read and Read-Rezayi states are generalized into appropriate anisotropic form. The generalized states are exact zero-energy eigenstates of corresponding anisotropic two- or multi-body Hamiltonians, and explicitly illustrate the existence of geometric degrees of in the fractional quantum Hall effect. These generalized model quantum Hall states can provide a good description of the quantum Hall system with anisotropic interactions. Some numeri...
Comparison of magnetocaloric properties from magnetic and thermal measurements
International Nuclear Information System (INIS)
The isothermal change of the magnetic entropy of a magnetically ordered material upon application of external magnetic field can be calculated from the temperature and field dependence of the magnetization or of the specific heat. The adiabatic temperature change, i.e., the magnetocaloric effect (MCE) can be measured directly or can be calculated via different methods using the field-dependent specific heat values, or a combination of data obtained via magnetization and thermal measurements. In the present study, magnetic and thermal measurements were carried out on Gd75Y25(TC=232 K) and Gd48Y52(TC=161 K) samples, for applied fields ranging between 0 and 7 T. From both datasets, the magnetic entropy change and MCE values were calculated and compared, in order to assess the mutual reliability of the methods applied. The magnetically or thermally deduced specific heat discontinuities show a reasonable agreement within experimental error. Similar comparison of the calculated magnetic entropy changes reveals that the measured transition temperature and the shape of the curve do not depend on the method selected. It is demonstrated that the choice of an integration constant during entropy calculation has a significant impact on the adiabatic temperature change deduced from the field and temperature dependence of the entropies. For the MCE, a better approximation can be obtained using the magnetically acquired magnetic entropy change and the field-dependent specific heat. The results prove that magnetic measurements carried out in high enough magnetic fields provide reliable information on the isothermal magnetic entropy change and, when combined with field-dependent specific heat measurements, on the magnetocaloric effect as well. copyright 1997 American Institute of Physics
Preliminary Analysis of a Fully Solid State Magnetocaloric Refrigeration
Energy Technology Data Exchange (ETDEWEB)
Abdelaziz, Omar [ORNL
2016-01-01
Magnetocaloric refrigeration is an alternative refrigeration technology with significant potential energy savings compared to conventional vapor compression refrigeration technology. Most of the reported active magnetic regenerator (AMR) systems that operate based on the magnetocaloric effect use heat transfer fluid to exchange heat, which results in complicated mechanical subsystems and components such as rotating valves and hydraulic pumps. In this paper, we propose an alternative mechanism for heat transfer between the AMR and the heat source/sink. High-conductivity moving rods/sheets (e.g. copper, brass, iron, graphite, aluminum or composite structures from these) are utilized instead of heat transfer fluid significantly enhancing the heat transfer rate hence cooling/heating capacity. A one-dimensional model is developed to study the solid state AMR. In this model, the heat exchange between the solid-solid interfaces is modeled via a contact conductance, which depends on the interface apparent pressure, material hardness, thermal conductivity, surface roughness, surface slope between the interfaces, and material filled in the gap between the interfaces. Due to the tremendous impact of the heat exchange on the AMR cycle performance, a sensitivity analysis is conducted employing a response surface method, in which the apparent pressure, effective surface roughness and grease thermal conductivity are the uncertainty factors. COP and refrigeration capacity are presented as the response in the sensitivity analysis to reveal the important factors influencing the fully solid state AMR and optimize the solid state AMR efficiency. The performances of fully solid state AMR and traditional AMR are also compared and discussed in present work. The results of this study will provide general guidelines for designing high performance solid state AMR systems.
Czech Academy of Sciences Publication Activity Database
Fabbrici, S.; Porcari, G.; Cugini, F.; Solzi, M.; Kamarád, Jiří; Arnold, Zdeněk; Cabassi, R.; Albertini, F.
2014-01-01
Roč. 16, č. 4 (2014), s. 2204-2222. ISSN 1099-4300 Institutional support: RVO:68378271 Keywords : magnetic shape memory materials * magnetocaloric effect * multifunctional Heusler alloys Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.502, year: 2014
Magnetic refrigeration at room temperature - from magnetocaloric materials to a prototype
DEFF Research Database (Denmark)
Kuhn, Luise Theil; Pryds, Nini; Bahl, Christian Robert Haffenden; Smith, Anders
2011-01-01
materials, their shaping and graded composition for technological use. Modelling the performance of a permanent magnet with optimum use of the flux and relatively low weight, and designing and constructing a prototype continuous magnetic refrigeration device have also been major tasks in the project......Based on the magnetocaloric effect, magnetic refrigeration at room temperature has for the past decade been a promising, environmentally friendly new energy technology predicted to have a significantly higher efficiency than the present conventional methods. However, so far only a few prototype...... refrigeration machines have been presented worldwide and there are still many scientific and technological challenges to be overcome. We report here on the MagCool project, which spans all the way from basic materials studies to the construction of a prototype. Emphasis has been on ceramic magnetocaloric...
Structural, magnetic and magnetocaloric properties of (Mn, Co)2(Si, P) compounds
International Nuclear Information System (INIS)
Highlights: • Mn1.2Co0.8Si0.2P0.8 shows an antiferro–ferromagnetic transition at 235 K. • Addition of B leads to an increase of the transition temperature TN. • A modest inverse magnetocaloric effect is observed at TN. - Abstract: We report on various approaches to control the antiferro–ferromagnetic transition temperature of Mn1.2Co0.8Si0.2P0.8 and related materials for magnetocaloric applications. The effects of the Si substitution, Mn/Co ratio and B addition/substitution on MnCoP have been characterized by X-ray diffraction and magnetic measurements. In each case, these parameters have a great influence on the structural and magnetic properties. Silicon and boron turn out to be the elements suitable to substitute the phosphorous and bring TN closer to room temperature. The study thus paves the way for future tuning of the working temperature and adjustment of the magnetic properties. With entropy change of about 1.4 J kg−1 K−1 for 5 T, the inverse magnetocaloric effect of Mn1.2Co0.8Si0.2P0.8 is modest, but might present some interest for applications other than magnetic cooling
International Nuclear Information System (INIS)
Full text: In this paper, is a study of the transport properties in anisotropic polycrystalline superconducting. The presence of certain order of orientation of grains in polycrystalline superconducting (Bi,Pb)2 Sr2 Ca2 Cu3 O10+delta, is modeled by introducing a probability of orientation, gamma factor. In addition, is included in the model the concentration c, which characterize the contribution of porosity to the decrease in the conductivity of the Crystal, transparent. Assumes that pores and pimples are ellipsoid flattened with similar dimensions and takes into account the values of conductivity of beads in each direction. The calculation is based on the application of a generalization of the approximation of the effective way to the study of heterogeneous media, which is called coherent potential approximation (APC). The results are compared with an empirical model developed recently for samples of YBa2 Cu3 O7-delta (YBCO) which enriches its employment and applied to ceramic superconducting in general. (author)
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.
Transverse anisotropic magnetoresistance effects in pseudo-single-crystal γ'-Fe4N thin films
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).
Effect of additives on the anisotropic etching of silicon by using a TMAH based solution
Jun, Ki-Hwa; Kim, Bum-Joon; Kim, Jung-Sik
2015-09-01
In this study, the anisotropic etching properties of single crystal silicon were examined using a tetramethyl ammonium hydroxide (TMAH). The variations in the Si etching rate and surface morphology at different etching temperatures and TMAH concentrations were evaluated. The effects of different additives were also examined. As the THAM concentration (10-25 wt. %) decreased, the etching rate increased from 10 μm/h to 70 μm/h at temperatures between 70°C and 90°C. On the other hand, the etched surface roughness became degraded as the hillock density and corner undercut ratio increased. To solve these problems, four additives, pyrazine, ammonium persulfate (AP), ammonium hydrogen sulfate (AHS), and isopropyl alcohol (IPA), were added to the TMAH solution. The experimental results showed that these additives play an important role in increasing the etching rate up to 10-20%. The etched surface was also improved significantly by the decreased hillock density on the surface. The addition of IPA to the TMAH solution showed excellent results in improving the etched surface flatness and the undercutting compensation. On the other hand, one of the characteristics of IPA is the decrease in etching rate with increasing amount of IPA. [Figure not available: see fulltext.
International Nuclear Information System (INIS)
The high-level radioactive waste is to be disposed into a deep underground repository. Safe long-term isolation of high-level waste relies largely on stability and water-tightness of host rocks of repository. True triaxial compression tests of rocks have been carried out to investigate fracturing of rocks under anisotropic compression, water-driven fracturing and permeability change by effective and differential stresses. (author)
International Nuclear Information System (INIS)
The anisotropic mobility of hexagonal dislocation networks (HDNs) in a series of (1 1¯ 0) twist boundaries under applied shear stress has been studied at the atomic scale in α-iron. A strong angular effect on the HDN mobility is found to be correlated with the dislocation core structure. The vector form of the Orowan equation and differential displacement maps of dislocation cores are used to account for the HDN behavior under loading.
Averaging anisotropic cosmologies
International Nuclear Information System (INIS)
We examine the effects of spatial inhomogeneities on irrotational anisotropic cosmologies by looking at the average properties of anisotropic pressure-free models. Adopting the Buchert scheme, we recast the averaged scalar equations in Bianchi-type form and close the standard system by introducing a propagation formula for the average shear magnitude. We then investigate the evolution of anisotropic average vacuum models and those filled with pressureless matter. In the latter case we show that the backreaction effects can modify the familiar Kasner-like singularity and potentially remove Mixmaster-type oscillations. The presence of nonzero average shear in our equations also allows us to examine the constraints that a phase of backreaction-driven accelerated expansion might put on the anisotropy of the averaged domain. We close by assessing the status of these and other attempts to define and calculate 'average' spacetime behaviour in general relativity
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.
International Nuclear Information System (INIS)
In this presentation authors deals with determination of effective dose in anisotropic gamma radiation fields. It was conclude that: - Straightforward application of Hp(10) as surrogate for E may not work under certain conditions; - Partial data on behavior of E and Hp(10) for different dosimeters allow to estimate E/Hp(10) conversion coefficients for any particular composite source; - In practical situations, anisotropy of workplace fields may be measured by six- collimator device assessing contribution to a dose from six orthogonal directions; - Reasonably conservative conversion coefficients may be assessed for given energy spectrum and degree of anisotropy of workplace fields; - For strongly anisotropic fields multiple dosimetry approach gives the best estimate of E comparing to plain Hp(10) readouts or integral conversion coefficients
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}.
Liu, Jun; Choi, Gyung-Min; Cahill, David G.
2014-12-01
We use pump-probe metrology based on the magneto-optic Kerr effect to measure the anisotropic thermal conductivity of (001)-oriented MoS2 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 MoS2 crystal. The thermal conductivity of MoS2 is highly anisotropic with basal-plane thermal conductivity varying between 85-110 Wm -1K -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 .3W m -1K -1 .
International Nuclear Information System (INIS)
We use pump-probe metrology based on the magneto-optic Kerr effect to measure the anisotropic thermal conductivity of (001)-oriented MoS2 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 MoS2 crystal. The thermal conductivity of MoS2 is highly anisotropic with basal-plane thermal conductivity varying between 85–110 W m-1 K-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-1 K-1
Magnetocaloric Properties Response in High-Speed Melt-Spun La-Ce-Fe-Si Ribbons
Hou, Xueling; Han, Ning; Xue, Yun; Lu, Qianqian; Wang, Xiaochen; Phan, Manh-Huong
2016-06-01
The structure and magnetocaloric properties of La-Ce-Fe-Si alloys have been studied. The samples were prepared by melt spinning, the surface speed of the Cu wheel being 55 m/s. The as-spun ribbons were subsequently annealed at 1273 K for different times (10 min-1 h) and then quenched to room temperature. When the annealing time was 20 min, on a 1.5-T applied magnetic field, the maximum magnetic entropy change (ΔS M) of the ribbons reached values of 33.8 J/kg K at the Curie temperature of T C ˜ 182 K. When the annealing time was longer than 20 min, the maximum magnetic entropy change (|ΔS M,Max|) tended to decrease while the T C remained almost unchanged. In the annealing process, La/Ce located at grain boundaries was easily oxidized on the ribbon surface. The presence of large grain sizes and La2O3 or LaO were shown to degrade the magnetocaloric properties. On the other hand, the substitution of Ce for La improved the magnetocaloric effect of La-Fe-Si compounds, which is of practical importance for magnetic refrigeration.
International Nuclear Information System (INIS)
Earth-abundant, low-cost, and rare earth free magnetocaloric nanomaterials have attracted considerable attention for affordable, ‘green’, energy-efficient thermal management applications. Hence, we investigated the magnetocaloric properties and critical behavior of (Fe70Ni30)92Mn8 alloy nanoparticles. A near room temperature magnetocaloric effect, with a high relative cooling power (RCP), was obtained by alloying FeNi with Mn and fcc (γ) phase stabilization. The Curie temperature (T C) of the γ- phase was 40 K less than that of the T C of the bcc (α) phase. For a field change of 5 T, the RCP for the α- and γ- phase was found to be 507 J kg−1 and 466 J kg−1, respectively; these values are higher than those for Gd nanoparticles. The RCP exhibited a power law relationship with magnetic field H. Critical exponents values of δ = 4.71, β = 0.319 and γ = 1.195 were obtained, close to those obtained from the short range order 3D-Heisenberg model. Our results demonstrate the feasibility of developing high RCP, low-cost, rare earth free magnetocaloric nanoparticles for near room temperature applications. (paper)
International Nuclear Information System (INIS)
Highlights: • The Pr0.6Ca0.1Sr0.3Mn1−xFexO3 (x = 0, 0.025, 0.05, 0.075) compounds were synthesized using the Pechini sol–gel method. • Large magnetocaloric effect is reported based on second order phase transition. • Noticeable |ΔSM| at low field makes the system useful for magnetic refrigeration. - Abstract: The effects of partial substitution of manganese by iron on the physical properties of Pr0.6Ca0.1Sr0.3Mn1−xFexO3 (0 ⩽ x ⩽ 0.075) were investigated experimentally. Our samples were synthesized using the Pechini sol–gel method. X-ray diffraction analysis shows that our compounds crystallize in the orthorhombic structure with the Pbnm space group. Magnetic measurements show that all our materials exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The M(T) curves at μ0H = 0.05 T indicate a monotonic drop in the Curie temperature (TC) from 270 K for x = 0.0–112 K for x = 0.075 as the Fe concentration is increased. The results of electrical resistivity versus temperature measurements show that all our samples exhibit a metallic behavior at low temperature. For higher values of temperature, metal–insulator transition is seen at temperature Tp. From isothermal magnetization versus magnetic applied field, we deduced the magnetic entropy change ΔSM. The maximum values of the magnetic entropy change (-ΔSMmax) at 5 T applied change in the magnetic field are 3.64 and 3.12 J/kg K for x = 0 and x = 0.075 samples respectively. Under an applied magnetic field of 5 T, the relative cooling power (RCP) values are found between 243 and 256 J/kg for undoped sample and x = 0.075 respectively. Our results are interesting enough and suggest that these materials may be suitable candidates as working substances in magnetic refrigeration
Energy Technology Data Exchange (ETDEWEB)
Phan, The-Long; Jung, C. U.; Lee, B. W., E-mail: bwlee@hufs.ac.kr [Department of Physics and Oxide Research Center, Hankuk University of Foreign Studies, Yongin 449-791 (Korea, Republic of); Ho, T. A.; Manh, T. V. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Dang, N. T. [Institute of Research and Development, Duy Tan University, Da Nang (Viet Nam); Thanh, T. D. [Institute of Materials Science, Vietnam Academy of Science and Technology, Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam)
2015-10-14
We prepared orthorhombic La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} samples (x = 0, 0.04, 0.06, and 0.08) by conventional solid-state reaction and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field measurements, M(T, H). The experimental results revealed that an x increase in La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} reduced the ferromagnetic-paramagnetic transition temperature (T{sub C}) from 260 K (for x = 0) to ∼126 K (for x = 0.08). Around the T{sub C}, maximum magnetic-entropy changes for a magnetic-field variation interval H = 50 kOe are about 10.7, 8.5, 7.4, and 5.8 J·kg{sup −1}·K{sup −1} for x = 0, 0.04, 0.06, and 0.08, respectively, corresponding to refrigerant capacities RC = 250–280 J·kg{sup −1}. These values are comparable to those of some conventional MC materials, revealing the applicability of La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} in magnetic refrigeration. Using the Arrott method and scaling hypothesis as analyzing high-field M(H, T) data, and the universal-curve construction of the magnetic entropy change, we found a magnetic-phase separation. While the samples x = 0−0.06 exhibit a first-order magnetic phase transition, x = 0.08 exhibits the crossover of the first-to-second-order phase transformation (with its critical-exponent values close to those expected for the tricritical mean-field theory) and has the presence of ferromagnetic clusters even above the T{sub C}. Such the variations in the magnetism and MC effect are related to the changes in structural parameters caused by the Y substitution for La because Y doping does not change the concentration ratio of Mn{sup 3+}/Mn{sup 4+}.
International Nuclear Information System (INIS)
We prepared orthorhombic La0.7−xYxCa0.3MnO3 samples (x = 0, 0.04, 0.06, and 0.08) by conventional solid-state reaction and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field measurements, M(T, H). The experimental results revealed that an x increase in La0.7−xYxCa0.3MnO3 reduced the ferromagnetic-paramagnetic transition temperature (TC) from 260 K (for x = 0) to ∼126 K (for x = 0.08). Around the TC, maximum magnetic-entropy changes for a magnetic-field variation interval H = 50 kOe are about 10.7, 8.5, 7.4, and 5.8 J·kg−1·K−1 for x = 0, 0.04, 0.06, and 0.08, respectively, corresponding to refrigerant capacities RC = 250–280 J·kg−1. These values are comparable to those of some conventional MC materials, revealing the applicability of La0.7−xYxCa0.3MnO3 in magnetic refrigeration. Using the Arrott method and scaling hypothesis as analyzing high-field M(H, T) data, and the universal-curve construction of the magnetic entropy change, we found a magnetic-phase separation. While the samples x = 0−0.06 exhibit a first-order magnetic phase transition, x = 0.08 exhibits the crossover of the first-to-second-order phase transformation (with its critical-exponent values close to those expected for the tricritical mean-field theory) and has the presence of ferromagnetic clusters even above the TC. Such the variations in the magnetism and MC effect are related to the changes in structural parameters caused by the Y substitution for La because Y doping does not change the concentration ratio of Mn3+/Mn4+
Effects of geometrical anisotropy on failure in a plastically anisotropic metal
DEFF Research Database (Denmark)
Legarth, Brian Nyvang
2005-01-01
Failure by debonding of rigid inclusions in a metal-matrix is numerically analyzed within a unit cell approach. Finite strain analyses are conducted under plane strain conditions assuming a plastically anisotropic matrix material. Focus is given to geometrical anisotropy induced by different aspect...
Energy Technology Data Exchange (ETDEWEB)
Phan, The-Long; Ho, T.A. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Thang, P.D. [Faculty of Engineering Physics and Nanotechnology, VNU-University of Engineering and Technology, Xuan Thuy, Cau Giay, Hanoi (Viet Nam); Tran, Q.T. [Center for Science and Technology Communication, Ministry of Science and Technology, 113 Tran Duy Hung, Hanoi (Viet Nam); Thanh, T.D.; Phuc, N.X. [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Phan, M.H. [Department of Physics, University of South Florida, Tampa, FL 33620 (United States); Huy, B.T. [Department of Chemistry, Changwon National University, Changwon 641-773 (Korea, Republic of); Yu, S.C., E-mail: scyu@chungbuk.ac.kr [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of)
2014-12-05
Highlights: • Tricritical point in Y-doped Nd{sub 0.7}Sr{sub 0.3}MnO{sub 3} manganites. • A large magnetic-entropy change. • Magnetic inhomogeneity and phase separation. - Abstract: We have determined the values of critical exponents of two polycrystalline samples (Nd{sub 1−x}Y{sub x}){sub 0.7}Sr{sub 0.3}MnO{sub 3} (x = 0 and 0.07) from the magnetization data versus temperature and magnetic field, M(H, T), to learn about their magnetic and magnetocaloric (MC) properties. The results reveal the samples exhibiting the crossover of first-order and second-order phase transitions, where the exponent values β = 0.271 and γ = 0.922 for x = 0, and β = 0.234–0.236 and γ = 1.044–1.063 for x = 0.07 determined by using modified Arrott plots and static-scaling hypothesis are close to those expected for the tricritical mean-field theory (β = 0.25 and γ = 1.0). Particularly, the T{sub C} of x = 0 and 0.07 can be any value in the temperature ranges of 240–255 K and 170–278 K, respectively, depending on the magnitude of applied magnetic field and determination techniques. Around the T{sub C}, studying the MC effect of the samples has revealed a large magnetic-entropy change (ΔS{sub m}) up to ∼8 J/kg K for the applied field interval ΔH = 50 kOe, corresponding to refrigerant capacity values of 200–245 J/kg. These phenomena are related to the crossover nature and the persisting of FM/anti-FM interactions even above the T{sub C}, as further confirmed by electron-spin-resonance data, Curie–Weiss law-based analyses, and an exponential parameter characteristic of magnetic order n = dLn|ΔS{sub m}|/dLnH.
Performance-oriented Analysis of a Hybrid magnetic Assembly for a Heat-pump Magnetocaloric Device
DEFF Research Database (Denmark)
Insinga, Andrea Roberto; Smith, Anders; Bahl, Christian R.H.; Bjørk, Rasmus
2014-01-01
Conventional active-regenerator magnetocaloric devices include moving parts, with the purpose of generating an oscillating magnetic field in the magneto-caloric material, placed inside the regenerator. In this work a different design is analyzed, for application in a magnetocaloric heat pump. In...
International Nuclear Information System (INIS)
In this paper, the properties of the right circular polarized (RCP) waves in the three-dimensional (3D) dispersive photonic crystals (PCs) consisting of the magnetized plasma and uniaxial material with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, which the homogeneous anisotropic dielectric spheres (the uniaxial material) immersed in the magnetized plasma background, as the Faraday effects of magnetized plasma are considered (the incidence electromagnetic wave vector is parallel to the external magnetic field at any time). The equations for calculating the anisotropic photonic band gaps (PBGs) for the RCP waves in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, anisotropic dielectric filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the properties of first two anisotropic PBGs for the RCP waves are investigated in detail, respectively. The numerical results show that the anisotropy can open partial band gaps in fcc lattices at U and W points, and the complete PBGs for the RCP waves can be achieved compared to the conventional 3D dispersive PCs composed of the magnetized plasma and isotropic material. It is also shown that the first two anisotropic PBGs can be tuned by those parameters as mentioned above. Those PBGs can be enlarged by introducing the uniaxial material into such 3D PCs as the Faraday effects are considered
Energy Technology Data Exchange (ETDEWEB)
Zhang, Hai-Feng, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing Univ. Aeronaut. Astronaut.), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu, Shao-Bin, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn; Tang, Yi-Jun [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing Univ. Aeronaut. Astronaut.), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Zhen, Jian-Ping [Nanjing Artillery Academy, Nanjing 211132 (China)
2014-03-15
In this paper, the properties of the right circular polarized (RCP) waves in the three-dimensional (3D) dispersive photonic crystals (PCs) consisting of the magnetized plasma and uniaxial material with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, which the homogeneous anisotropic dielectric spheres (the uniaxial material) immersed in the magnetized plasma background, as the Faraday effects of magnetized plasma are considered (the incidence electromagnetic wave vector is parallel to the external magnetic field at any time). The equations for calculating the anisotropic photonic band gaps (PBGs) for the RCP waves in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, anisotropic dielectric filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the properties of first two anisotropic PBGs for the RCP waves are investigated in detail, respectively. The numerical results show that the anisotropy can open partial band gaps in fcc lattices at U and W points, and the complete PBGs for the RCP waves can be achieved compared to the conventional 3D dispersive PCs composed of the magnetized plasma and isotropic material. It is also shown that the first two anisotropic PBGs can be tuned by those parameters as mentioned above. Those PBGs can be enlarged by introducing the uniaxial material into such 3D PCs as the Faraday effects are considered.
International Nuclear Information System (INIS)
The behaviour of concrete, considered as isotropic for a sound material, becomes anisotropic and unilateral as soon as microcracks are initiated. Concrete also shows a different behaviour in tension than in compression. However, isotropic models, which are more simple and time costless, are still widely used for industrial applications. An anisotropic and unilateral model, with few parameters, is thus proposed in the present work, which enhances the accuracy of the description of concrete's behaviour, while remaining suitable for industrial studies. The validation of the model is based on experimental results. Numerical simulations of structures are also proposed, among which one concerns a representative volume of a confinement vessel. Finally, a non local theory is investigated to overcome the problems induced by strain localisation. (author)
New effect of ionizing irradiation: anisotropic expansion of a peptide crystal
Energy Technology Data Exchange (ETDEWEB)
Kuroda, S.; Kurita, Y.; Miyagawa, I.
1985-10-01
Expansion of crystals resulting from X irradiation was studied in the case of a peptide, N-acetyl-D, L-alanine. This expansion was discovered by examining several irradiated organic solids for possible expansion, which was suggested by the recent observation of crystal imperfections in another peptide. The expansion, which occurred anisotropically along the c axis, was found to depend on dose, the maximum being as large as 20% when assisted by heat treatment.
Coulomb Blockade Anisotropic Magnetoresistance Effect in a (Ga,Mn)As Single-Electron Transistor
Czech Academy of Sciences Publication Activity Database
Wunderlich, J.; Jungwirth, Tomáš; Kaestner, B.; Irvine, A.C.; Shick, Alexander; Stone, N.; Wang, K. Y.; Rana, U.; Giddings, A.D.; Foxon, C. T.; Campion, R. P.; Williams, D.A.; Gallagher, B. L.
2006-01-01
Roč. 97, č. 7 (2006), 077201/1-077201/4. ISSN 0031-9007 R&D Projects: GA ČR GA202/05/0575; GA MŠk LC510 Grant ostatní: EPSRC(GB) GR/S81407/01 Institutional research plan: CEZ:AV0Z10100521 Keywords : anisotropic magnetoresistance * Coulomb blockade * single electron transistor Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.072, year: 2006
Directory of Open Access Journals (Sweden)
S. Patel
2011-08-01
Full Text Available Using the general loss-cone distribution function electromagnetic ion cyclotron (EMIC instability affected by up going ion beam has been studied by investigating the trajectories of charged particles. The plasma consisting of resonant and non-resonant particles has been considered. It is assumed that the resonant particles participate in energy exchange with the wave, whereas non-resonant particles support the oscillatory motion of the wave. The effect of ion beam velocity on the dispersion relation, growth rate, parallel and perpendicular resonant energy of the EMIC wave with general loss-cone distribution function in hot anisotropic plasma is described by particle aspect approach. The effect of beam anisotropy and beam density on electromagnetic ion cyclotron instabilities is investigated. Growth length is derived for EMIC waves in hot anisotropic plasma. It is found that the effect of the ion beam is to reduce the energy of transversely heated ions, whereas the thermal anisotropy of the background plasma acts as a source of free energy for the EMIC wave and enhances the growth rate. It is observed that ion beam velocity opposite to the wave propagation and its density reduces the growth rate and enhance the reduction in perpendicularly heated ions energy. The effect of ion beam anisotropy on EMIC wave is also discussed. These results are determined for auroral acceleration region. It is also found that the EMIC wave emissions occur by extracting energy of perpendicularly heated ions in the presence of an up flowing ion beam.
Li, Ye; Zhang, Yixin; Zhu, Yun; Chen, Minyu
2016-07-01
Based on the spatial power spectrum of the refractive index of anisotropic turbulence, the average polarizability of the Gaussian Schell-model quantized beams and lateral coherence length of the spherical wave propagating through the ocean water channel are derived. Numerical results show that, in strong temperature fluctuation, the depolarization effects of anisotropic turbulence are inferior to isotropic turbulence, as the other parameters of two links are the same. The depolarization effects of salinity fluctuation are less than the effects of the temperature fluctuation; the average polarizability of beams increases when increasing the inner scale of turbulence and the source's transverse size; and the larger rate of dissipation of kinetic energy per unit mass of fluid enhances the average polarizability of beams. The region of the receiving radius is smaller than the characteristic radius and the average polarizability of beams in isotropy turbulence is smaller than that of beams in anisotropy turbulence. However, the receiving radius region is larger than a characteristic radius and the average polarizability of beams in isotropy turbulence is larger than that of beams in anisotropy turbulence. PMID:27409215
Molecular anisotropic magnetoresistance
Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy
2015-01-01
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 $3d$ transition-metal wires. We show that the gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symm...
Anisotropic inflation in a 5D standing wave braneworld and effective dimensional reduction
International Nuclear Information System (INIS)
We investigate a cosmological solution within the framework of a 5D standing wave braneworld model generated by gravity coupled to a massless scalar phantom-like field. By obtaining a full exact solution of the model we found a novel dynamical mechanism in which the anisotropic nature of the primordial metric gives rise to (i) inflation along certain spatial dimensions, and (ii) deflation and a shrinking reduction of the number of spatial dimensions along other directions. This dynamical mechanism can be relevant for dimensional reduction in string and other higher-dimensional theories in the attempt of getting a 4D isotropic expanding space–time
Edge states in a honeycomb lattice: effects of anisotropic hopping and mixed edges
Dahal, Hari P.; Hu, Zi-Xiang; Sinitsyn, N. A.; YANG Kun; Balatsky, A. V.
2009-01-01
We study the edge states in graphene in the presence of a magnetic field perpendicular to the plane of the lattice. Most of the works done so far discuss the edge states in either zigzag or armchair edge graphene considering an isotropic electron hopping. In practice, graphene can have mixture of armchair and zigzag edges and the electron hopping can be anisotropic, which is the subject of this article. We predict that the mixed edges smear the enhanced local density of states (LDOS) at E=0 o...
Energy Technology Data Exchange (ETDEWEB)
Panda, J.; Saha, S.N.; Nath, T.K., E-mail: tnath@phy.iitkgp.ernet.in
2015-09-25
Highlights: • The Curie temperature of alloy series of Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} decreases with increasing x. • The critical exponents behavior and scaling relation of the alloy series have been investigated. • Using M–H data, employing Modified Arrott plot and Kouvel–Fisher plot exponents are estimated. • The estimated critical exponent values match very well with the mean field theory. • Under a magnetic field maximum up to 5 T, normal magnetocaloric effect has been observed. - Abstract: This work reports the investigation of critical behavior of Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} (x = 0 and 5) and magneto caloric effect (MCE) of bulk Co{sub 2}CrAl full Heusler alloy system. The alloy series of Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} (x = 0, 1, 2, 3, 4 and 5) have been prepared using arc melting technique. The magnetic properties of all the samples have been studied in the temperature range of 5–300 K. The value of Curie temperature (T{sub C}) is found to decrease with increasing doping concentration of the Ni (substitution of Ni at Co site). The critical exponents behavior and scaling relation have been investigated using magnetic isotherms in Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} (x = 0 and 5) alloys. The critical exponents are estimated by various techniques such as, Modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. The value of critical exponents vicinity to the second order magnetic phase transition of Co{sub 50}Cr{sub 25}Al{sub 25} were found to be β = 0.488 (7), γ = 1.144 (16) and δ = 3.336 (5) with T{sub C} = 328.64 (5) K whereas for Co{sub 50}Ni{sub 5}Cr{sub 25}Al{sub 25} the values are β = 0.522 (13), γ = 1.014 (6) and δ = 3.043 (7) with T{sub C} = 285.71 (11). The critical exponent values for both the samples are almost similar to the value as predicted by mean field theory. This has been best explained by long range mean field like ferromagnetic interaction in the
Czech Academy of Sciences Publication Activity Database
Gourdon, O.; Gottschlich, G.; Persson, J.; de la Cruz, C.; Petříček, Václav; McGuire, M.A.; Bruckel, T.
2014-01-01
Roč. 216, AUG (2014), s. 56-64. ISSN 0022-4596 Grant ostatní: AV ČR(CZ) Praemium Academiae Institutional support: RVO:68378271 Keywords : magneto caloric effect materials * intermetallic * silicide * magnetism * neutron diffraction * density functional theory Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.133, year: 2014
Anisotropic Inflation with General Potentials
Shi, Jiaming; Qiu, Taotao
2015-01-01
Anomalies in recent observational data indicate that there might be some "anisotropic hair" generated in an inflation period. To obtain general information about the effects of this anisotropic hair to inflation models, we studied anisotropic inflation models that involve one vector and one scalar using several types of potentials. We determined the general relationship between the degree of anisotropy and the fraction of the vector and scalar fields, and concluded that the anisotropies behave independently of the potentials. We also generalized our study to the case of multi-directional anisotropies.
Phase diagram and magnetocaloric effect in Mn2Ni1.64−xCoxSn0.36 alloys
International Nuclear Information System (INIS)
The effect of Co substitution for Ni in Mn-rich Mn2Ni1.64−xCoxSn0.36 ferromagnetic shape memory alloys has been studied. With increasing Co content, the martensitic transformation temperatures decrease due to the decrease in valence electron concentration. The great enhancements of magnetization and Curie temperature by Co doping could be attributed to the strong Co–Mn interaction, changing Mn–Mn coupling from antiferromagnetic to ferromagnetic. In the composition range of 0.08⩽x⩽0.24, large magnetization changes and large magnetic entropy changes are observed with martensitic transformation.
Effects of the excess iron on phase and magnetocaloric property of LaFe11.6*xSi1.4 alloys
Institute of Scientific and Technical Information of China (English)
陈湘; 陈云贵; 唐永柏; 肖定全
2015-01-01
The effect of Fe on microstructure and magnetic thermal performance of LaFe11.6*xSi1.4 alloys were studied by X-ray dif-fraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and vibrating-sample magnetometer (VSM), respectively. The results showed that the excess Fe would make the 1:13 phase reduce in proportion and the easy corrosion phase LaFeSi phase disappear in LaFe11.6*xSi1.4 alloys. The LaFe11.6*xSi1.4 alloys kept the first order magnetic phase transition, and the maximum isothermal magnetic entropy changed and the relative cooling power reached the maximum in LaFe11.6*xSi1.4 alloys with x=1.05 and 1.1, respectively.
International Nuclear Information System (INIS)
The magnetic properties and mgnetocaloric effect (MCE) of the Gd65Al15Co20-xFex(x = 0 - 20) and Gd65-yLREyAl15Fe20 (LRE La, Ce, Pr, Nd; y = 0 - 20) glassy ribbons have been investigated. The Curie temperature (Tc) of the Gd-based Gd65Al15Co20-xFex glassy ribbons can be greatly increased by moderate Fe substitution. Furthermore, it is found that Ce atom among the other light-rare-earth elements is more prefer one for adjusting the Tc of the Gd65-yLREyAl15Fe20 glassy ribbons. The low materials cost, improved MCE properties make Gd65-yCeyAl15Fe20 glassy ribbons attractive candidates for magnetic refrigeration application in the intermediate temperatures of 80-220 K.
Energy Technology Data Exchange (ETDEWEB)
Fang, Y K; Lai, C H; Hsieh, C C; Chang, W C [Department of Physics, National Chung Cheng University, Ming Hsiung, Chia-Yi, 62102 Taiwan (China); Zhao, X G [Shenyang National Laboratory for Materials Science, Institute of Metal Research, and International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China); Chang, H W [Department of Physics, Tunghai University, Taichung, Taiwan (China); Li, W, E-mail: ykfang@126.com, E-mail: phywcc@ccu.edu.tw [Division of Functional Materials Research, Central Iron and Steel Research Institute, Beijing, 100081 (China)
2011-01-01
The magnetic properties and mgnetocaloric effect (MCE) of the Gd{sub 65}Al{sub 15}Co{sub 20-x}Fe{sub x}(x = 0 - 20) and Gd{sub 65-y}LRE{sub y}Al{sub 15}Fe{sub 20} (LRE La, Ce, Pr, Nd; y = 0 - 20) glassy ribbons have been investigated. The Curie temperature (T{sub c}) of the Gd-based Gd{sub 65}Al{sub 15}Co{sub 20-x}Fe{sub x} glassy ribbons can be greatly increased by moderate Fe substitution. Furthermore, it is found that Ce atom among the other light-rare-earth elements is more prefer one for adjusting the T{sub c} of the Gd{sub 65-y}LRE{sub y}Al{sub 15}Fe{sub 20} glassy ribbons. The low materials cost, improved MCE properties make Gd{sub 65-y}Ce{sub y}Al{sub 15}Fe{sub 20} glassy ribbons attractive candidates for magnetic refrigeration application in the intermediate temperatures of 80-220 K.
Universal behavior of magnetocaloric effect in a layered perovskite La1.2Sr1.8Mn2O7 single crystal
Thanh, Tran Dang; Manh, T. V.; Ho, T. A.; Telegin, Andrey; Phan, T. L.; Yu, S. C.
2016-04-01
In this paper, we present a detailed analysis on temperature and magnetic field dependences of the magnetic entropy change (ΔSm) near the ferromagnetic (FM)-paramagnetic (PM) phase transition of a La1.2Sr1.8Mn2O7 single crystal. Experimental results reveal the material exhibiting a FM-PM phase transition at TC=85 K, and belongs to a second-order phase transition (SOPT). Around TC, -ΔSm reaches the maximum value (|ΔSmax|), which increases with increasing an applied magnetic field change, ΔH. The |ΔSmax| values found are about 0.93, 1.73, 2.38, 2.91, and 3.33 J kg-1 K-1 for ΔH=10, 20, 30, 40, and 50 kOe, respectively. However, the peak position of the -ΔSm(T) curves is effectively shifted to higher temperatures when ΔH increases. Additionally, the ΔSm(T) curves measured at different ΔH values do not collapse into a universal curve when they are normalized to their respective ΔSmax value, and Prod. Type: rescaled the temperature axis with θ1=(T-TC)/(Tr-TC) for a reference temperature Tr>TC or TrTC.
Energy Technology Data Exchange (ETDEWEB)
Gálisová, Lucia, E-mail: galisova.lucia@gmail.com [Department of Applied Mathematics and Informatics, Faculty of Mechanical Engineering, Technical University, Letná 9, 042 00 Košice (Slovakia); Strečka, Jozef, E-mail: jozef.strecka@upjs.sk [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia)
2015-10-16
Magnetocaloric effect in a double-tetrahedral chain, in which nodal lattice sites occupied by the localized Ising spins regularly alternate with three equivalent lattice sites available for mobile electrons, is exactly investigated by considering the one-third electron filling and the ferromagnetic Ising exchange interaction between the mobile electrons and their nearest Ising neighbours. The entropy and the magnetic Grüneisen parameter, which closely relate to the magnetocaloric effect, are exactly calculated in order to investigate the relation between the ground-state degeneracy and the cooling efficiency of the hybrid spin–electron system during the adiabatic demagnetization. - Highlights: • A double-tetrahedral chain of mobile electrons and localized Ising spins is studied. • Magnetic Grüneisen parameter for the system is exactly derived. • Macroscopically degenerate phases FRU and FM constitute the ground state. • MCE is three times higher nearby FRU–FM transition than in FRU phase at small fields.
Magnetic and magnetocaloric properties of martensitic Ni2Mn1.4Sn0.6 Heusler alloy
International Nuclear Information System (INIS)
The evolutions of magnetic properties at low temperatures and the influence of magnetic field on the temperature dependence of specific heat in martensitic Ni2Mn1.4Sn0.6 Heusler alloy are studied. The frequency-dependent blocking temperature and considerable exchange bias below it are measured in the martensitic phase. From the analysis of the specific heat curves under magnetic field, a large inverse magnetocaloric effect manifested as the magnetic field induced rise of isothermal magnetic entropy and/or magnetic field induced adiabatic temperature decrease in the vicinity of the reverse magnetostructural transformation and a significant value of the conventional magnetocaloric effect at the Curie temperature are obtained. The Debye temperature and electronic coefficient equal to ΘD=310±2 K and γ= 16.6±0.3 mJ/K2mol, respectively, do not depend on the magnetic field.
Rotation and Anisotropic Molecular Orbital Effect in a Single H2TPP Molecule Transistor
Sakata, Shuichi; Yoshida, Kenji; Kitagawa, Yuichi; Ishii, Kazuyuki; Hirakawa, Kazuhiko
2013-12-01
Electron transport through a single molecule is determined not only by the intrinsic properties of the molecule but also by the configuration of the molecule with respect to the lead electrodes. Here, we show how electron transport through a single H2TPP molecule is modulated by changes in the configuration. The Coulomb stability diagram of a single H2TPP molecule transistor exhibited a few different patterns in different measurement scans. Furthermore, the sample exhibited negative differential resistance, the magnitude of which changed with the pattern in the Coulomb stability diagram. Such behavior can be explained by the rotation of the molecule with anisotropic molecular orbitals in the gap electrodes induced by electrical stress. Moreover, we find that the energy separations between molecular orbitals are also affected by the rotation, confirming that the metal-molecule interface configuration renormalizes the electronic levels in the molecule.
Effects of anisotropic diffusion and finite island sizes in homoepitaxial growth Pt on Pt(100)-hex
DEFF Research Database (Denmark)
Mortensen, Jens Jørgen; Linderoth, T.R.; Jacobsen, Karsten Wedel; Lægsgaard, E.; Stensgaard, I.; Besenbacher, F.
exhibits a height modulation caused by the misfit between the topmost quasi-hexagonal layer and the quadratic substrate. resulting in a highly anisotropic large scale surface morphology with six-atom wide channels running along the [1(1) over bar0$] direction. From an autocorrelation analysis of the......The diffusion, nucleation, and growth of Pt on the hexagonally reconstructed Pt(100)-hex surface are investigated. By means of Scanning Tunneling Microscopy (STM), the positions, sizes, and number densities of monoatomically high, rectangular. reconstructed Pt islands, formed in the submonolayer...... coverage regime. have been determined for substrate temperatures in the range T = 318-497 K and adatom deposition rates from R=4 x 10(-5) to 7 x 10(-3) site(-1) s(-1). The measurements are compared to the results of kinetic Monte Carlo (KMC) simulations and rate equation theory. The Pt(100)-hex surface...
Hills, M E; Olsen, A L; Nichols, L W
1968-08-01
Cary model 14 spectrophotometers like other prism and grating instruments have polarization characteristics that affect the transmittance values of anisotropic or dichroic materials. In the uv, the degree of polarization is fairly constant from 3000 A to 4000 A, whereas in the visible, it shows some variation with wavelength. In the near ir, the variation of the degree of polarization with wavelength is large, showing sharply defined maxima at approximately 0.77 micro, 0.97 micro, and 1.27 micro. The spectral transmittance of optical quality sapphire, a uniaxial crystal, cut at 45 degrees , 60 degrees , and 90 degrees to the c axis, showed undulations for certain orientations of the privileged directions. PMID:20068821
Energy Technology Data Exchange (ETDEWEB)
Jin, Dong-Dong [Key Laboratory of Semiconductor Materials Science, and Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Department of Physics, Tsinghua University, Beijing 100084 (China); Wang, Lian-shan, E-mail: ls-wang@semi.ac.cn; Yang, Shao-Yan, E-mail: sh-yyang@semi.ac.cn; Li, Hui-jie; Zhang, Heng; Wang, Jian-xia; Xiang, Ruo-fei; Wei, Hong-yuan; Jiao, Chun-mei; Liu, Xiang-Lin; Zhu, Qin-Sheng, E-mail: qszhu@semi.ac.cn; Wang, Zhan-Guo [Key Laboratory of Semiconductor Materials Science, and Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhang, Liu-Wan [Department of Physics, Tsinghua University, Beijing 100084 (China)
2014-01-28
In this paper, a theory is developed to study the anisotropic scattering effect of the inclined misfit dislocation on the two-dimensional electron gas in Al(In)GaN/GaN heterostructures. The inclined misfit dislocation, which differs from the well-known vertical threading dislocation, has a remarkable tilt angle from the vertical. The predicted electron mobility shows a remarkable anisotropy. It has a maximum mobility value along the direction perpendicular to the projection of the inclined dislocation line, and a minimum mobility value along the direction parallel to the projection. The degree of the anisotropic scattering effect will be even greater with the increase of the tilt angle.
Sundqvist, Jon O.; Owocki, Stanley P.; Cohen, David H.; Leutenegger, Maurice A.; Townsend, Richard H. D.
2011-01-01
We present a generalised formalism for treating the porosity-associated reduction in continuum opacity that occurs when individual clumps in a stochastic medium become optically thick. We consider geometries resulting in either isotropic or anisotropic effective opacity, and, in addition to an idealised model in which all clumps have the same local overdensity and scale, we also treat an ensemble of clumps with optical depths set by Markovian statistics. This formalism is then applied to the ...
Direct measurements of the magnetocaloric effect
DEFF Research Database (Denmark)
Nielsen, Kaspar Kirstein; Bahl, Christian R.H.; Neves Bez, Henrique;
2014-01-01
We present an experimental setup recently developed at DTU Energy Conversion for measuring specific heat and direct isothermal entropy change in a varying magnetic field (DSC device) using calorimetry. The device operates in high vacuum (~1e-6 mbar) and measurements are fully automated with respect...... magnetic field scans under isothermal conditions (direct isothermal entropy change measurements)....
International Nuclear Information System (INIS)
Employing the reductive perturbation technique, Zakharov–Kuznetzov (ZK) equation is derived for dust acoustic (DA) solitary waves in a magnetized plasma which consists the effects of dust anisotropic pressure, arbitrary charged dust particles, Boltzmann distributed ions, and Kappa distributed superthermal electrons. The ZK solitary wave solution is obtained. Using the small-k expansion method, the stability analysis for DA solitary waves is also discussed. The effects of the dust pressure anisotropy and the electron superthermality on the basic characteristics of DA waves as well as on the three-dimensional instability criterion are highlighted. It is found that the DA solitary wave is rarefactive (compressive) for negative (positive) dust. In addition, the growth rate of instability increases rapidly as the superthermal spectral index of electrons increases with either positive or negative dust grains. A brief discussion for possible applications is included
International Nuclear Information System (INIS)
Low field magnetic and magnetocaloric properties of the compound LaMn1.9Fe0.1Si2 have been investigated. Using the M-H data measured at various temperatures, we have derived the magnetic entropy change |ΔS| as a function of temperature and magnetic field, by using the Maxwell relation. The temperature dependence of the Landau coefficient has been derived by fitting the magnetization, using the Landau expansion of magnetic free energy and Arrott plots. The results show that LaMn1.9Fe0.1Si2 is ferromagnetically ordered around room temperature (285 K) and the nature of the phase transition at this temperature is found to be second order.
Fractures in anisotropic media
Shao, Siyi
theory and experimental results in this report demonstrate that the presence of fractures in anisotropic material can be unambiguously interpreted if experimental measurements are made as a function of stress, which eliminates many fracture-generated discrete modes (e.g., interface waves, and leaky guided-modes). Orthogonal fracture networks that are often encountered in field exploration bring in additional challenges for seismic/acoustic data interpretation. An innovative wavefront imaging system with a bi-axial load frame was designed and implemented on orthogonally-fractured samples to determine the effect of fracture networks on elastic wave propagation. The effects of central wave guiding and extra time delays along a fracture intersection were observed in experiments and was analyzed. Interpreting data from media with intersecting fracture sets must account for fracture intersections and the non-uniformity of fracture properties caused by local tectonic conditions or other physical process such as non-uniform fluid distributions within a network and/or chemical alterations.
Phase control studies in Gd5Si2Ge2 giant magnetocaloric compound
International Nuclear Information System (INIS)
Highlights: ► Study of time dependence of O(I) to M phase. ► Determination of the optimal annealing time. ► New method for phase amount estimation (O(I) and M). ► Effect of annealing on the MCE. ► Analysis of the nature of the magnetic transition through the Arrot plot representation. - Abstract: A systematic set of annealings on arc-melted synthesized Gd5Si2Ge2 sample was performed. Through powder X-ray diffraction (XRD) and magnetometry measurements we monitored the effect of varying the annealing time with constant temperature (T = 1473 K) on the formation of the monoclinic (M) crystallographic phase fraction, which is the one responsible for the giant magnetocaloric effect (GMCE) in this compound. The conversion of the orthorhombic O(I) crystallographic phase into M was achieved, resulting in a significant increase of the M mass fraction. Such conversion led to a change in the magnetic transition nature, evolving from a second to a first order transition for the as-cast and annealed samples, respectively. An optimal annealing time range for the M phase conversion was identified to be within 80–120 min at T = 1473 K followed by a rapid quenching to liquid N2. Furthermore, an increase up to ∼50% of the magnetocaloric effect was obtained for the sample annealed during 120 min.
International Nuclear Information System (INIS)
The two-dimensional adiabatic ratchet dynamics of Abrikosov vortices in a symmetric periodic pinning potential is considered in the presence of a dc and ac transport currents and anisotropy of the viscous vortex motion at zero temperature. Exact analytical expressions for two anisotropic nonlinear current-voltage responses along and across the transport current direction are derived and analyzed in the framework of the washboard pinning potential model. The physical origin of these voltages that are odd with respect to the current direction reversal is caused by the interplay between the vortex guiding effect, which is even with respect to the magnetic field reversal, and the ratchet asymmetry owing to the tilt of the pinning potential by the dc component of the transport current.
Extremely Anisotropic Scintillations
Walker, Mark; Bignall, Hayley
2008-01-01
A small number of quasars exhibit interstellar scintillation on time-scales less than an hour; their scintillation patterns are all known to be anisotropic. Here we consider a totally anisotropic model in which the scintillation pattern is effectively one-dimensional. For the persistent rapid scintillators J1819+3845 and PKS1257-326 we show that this model offers a good description of the two-station time-delay measurements and the annual cycle in the scintillation time-scale. Generalising the model to finite anisotropy yields a better match to the data but the improvement is not significant and the two additional parameters which are required to describe this model are not justified by the existing data. The extreme anisotropy we infer for the scintillation patterns must be attributed to the scattering medium rather than a highly elongated source. For J1819+3845 the totally anisotropic model predicts that the particular radio flux variations seen between mid July and late August should repeat between late Au...
Materials Challenges for High Performance Magnetocaloric Refrigeration Devices
DEFF Research Database (Denmark)
Smith, Anders; Bahl, Christian; Bjørk, Rasmus;
2012-01-01
Magnetocaloric materials with a Curie temperature near room temperature have attracted signifi cant interest for some time due to their possible application for high-effi ciency refrigeration devices. This review focuses on a number of key issues of relevance for the characterization, performance...
Anisotropic effective medium properties from interacting Ag nanoparticles in silicon dioxide.
Menegotto, Thiago; Horowitz, Flavio
2014-05-01
Films containing a layer of Ag nanoparticles embedded in silicon dioxide were produced by RF magnetron sputtering. Optical transmittance measurements at several angles of incidence (from normal to 75°) revealed two surface plasmon resonance (SPR) peaks, which depend on electric field direction: one in the ultraviolet and another red-shifted from the dilute Ag/SiO₂ system resonance at 410 nm. In order to investigate the origin of this anisotropic behavior, the structural properties were determined by transmission electron microscopy, revealing the bidimensional plane distribution of Ag nanoparticles with nearly spherical shape as well as the filling factor of metal in the composite. A simple model linked to these experimental parameters allowed description of the most relevant features of the SPR positions, which, depending on the field direction, were distinctly affected by the coupling of oscillations between close nanoparticles, as described by a modified Drude-Lorentz dielectric function introduced into the Maxwell-Garnett relation. This approach allowed prediction of the resonance for light at 75° incidence from the SPR position for light at normal incidence, in good agreement with experimental observation. PMID:24921871
Anisotropic Turbulent Advection of a Passive Vector Field: Effects of the Finite Correlation Time
Antonov, N. V.; Gulitskiy, N. M.
2016-02-01
The turbulent passive advection under the environment (velocity) field with finite correlation time is studied. Inertial-range asymptotic behavior of a vector (e.g., magnetic) field, passively advected by a strongly anisotropic turbulent flow, is investigated by means of the field theoretic renormalization group and the operator product expansion. The advecting velocity field is Gaussian, with finite correlation time and prescribed pair correlation function. The inertial-range behavior of the model is described by two regimes (the limits of vanishing or infinite correlation time) that correspond to nontrivial fixed points of the RG equations and depend on the relation between the exponents in the energy energy spectrum ɛ ∝ k⊥1-ξ and the dispersion law ω ∝ k⊥2-η . The corresponding anomalous exponents are associated with the critical dimensions of tensor composite operators built solely of the passive vector field itself. In contrast to the well-known isotropic Kraichnan model, where various correlation functions exhibit anomalous scaling behavior with infinite sets of anomalous exponents, here the dependence on the integral turbulence scale L has a logarithmic behavior: instead of power-like corrections to ordinary scaling, determined by naive (canonical) dimensions, the anomalies manifest themselves as polynomials of logarithms of L. Due to the presence of the anisotropy in the model, all multiloop diagrams are equal to zero, thus this result is exact.
Epoxy-bonded La–Fe–Co–Si magnetocaloric plates
International Nuclear Information System (INIS)
We report the processing, analysis and testing of magnetocaloric composite materials consisting of La–Fe–Co–Si particles of various size fractions and a polymer matrix. All of the composites have working temperatures close to room temperature. The composites were pressed into thin plates, a geometry favorable for testing the composites in an active magnetic regenerator (AMR). In order to investigate the influence of particle size and binder type (epoxy), eight different epoxy-bonded La–Fe–Co–Si plates were made and analyzed. We found that the higher filling factor that can be achieved by using a mixture of several particle size fractions has beneficial influence on the thermal conductivity. Tests in the AMR revealed that a maximum temperature span of approximately ΔT=10 K under magnetic field change of μ0H=1.15 T can be obtained at no cooling load conditions. The stability of the measured ΔT values and the mechanical integrity of sample after cyclic application of a magnetic field have been monitored for 90,000 cycles and showed no significant changes. We therefore conclude that epoxy-bonded La–Fe–Co–Si magnetocaloric composites have good magnetocaloric properties at low material-processing costs and hence represent a competitive way to produce magnetocaloric materials to be used in AMR. - Highlights: • Thin epoxy-bonded La–Fe–Co–Si plates were processed and tested. • Cycling stability, magnetocaloric and thermal properties were studied. • The impact of the plate composition and of the epoxy was investigated. • AMR from the epoxy-bonded composite plates was built and experimentally tested
Epoxy-bonded La–Fe–Co–Si magnetocaloric plates
Energy Technology Data Exchange (ETDEWEB)
Pulko, Barbara, E-mail: pulko.barbara@gmail.com [University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva cesta 6, 1000 Ljubljana (Slovenia); Tušek, Jaka [University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva cesta 6, 1000 Ljubljana (Slovenia); Moore, James D. [IFW Dresden, Institute for Metallic Materials, Helmholtzstraße 20, D-01069 Dresden (Germany); Weise, Bruno [IFW Dresden, Institute for Complex Materials, Helmholtzstraße 20, D-01069 Dresden (Germany); Skokov, Konstantin [TU Darmstadt, Department of Materials Science, D-64287 Darmstadt (Germany); Mityashkin, Oleg [IFW Dresden, Institute for Metallic Materials, Helmholtzstraße 20, D-01069 Dresden (Germany); Kitanovski, Andrej [University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva cesta 6, 1000 Ljubljana (Slovenia); Favero, Chiara [Parker Hannifin Manufacturing Srl, Hiross Zander Division, Strada Zona Industriale 4, S. Angelo di Piove, 35020 Padova (Italy); Fajfar, Peter [University of Ljubljana, Faculty of Natural Sciences and Engineering, Aškerčeva cesta 12, 1000 Ljubljana (Slovenia); Gutfleisch, Oliver [TU Darmstadt, Department of Materials Science, D-64287 Darmstadt (Germany); Waske, Anja [IFW Dresden, Institute for Complex Materials, Helmholtzstraße 20, D-01069 Dresden (Germany); Poredoš, Alojz [University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva cesta 6, 1000 Ljubljana (Slovenia)
2015-02-01
We report the processing, analysis and testing of magnetocaloric composite materials consisting of La–Fe–Co–Si particles of various size fractions and a polymer matrix. All of the composites have working temperatures close to room temperature. The composites were pressed into thin plates, a geometry favorable for testing the composites in an active magnetic regenerator (AMR). In order to investigate the influence of particle size and binder type (epoxy), eight different epoxy-bonded La–Fe–Co–Si plates were made and analyzed. We found that the higher filling factor that can be achieved by using a mixture of several particle size fractions has beneficial influence on the thermal conductivity. Tests in the AMR revealed that a maximum temperature span of approximately ΔT=10 K under magnetic field change of μ{sub 0}H=1.15 T can be obtained at no cooling load conditions. The stability of the measured ΔT values and the mechanical integrity of sample after cyclic application of a magnetic field have been monitored for 90,000 cycles and showed no significant changes. We therefore conclude that epoxy-bonded La–Fe–Co–Si magnetocaloric composites have good magnetocaloric properties at low material-processing costs and hence represent a competitive way to produce magnetocaloric materials to be used in AMR. - Highlights: • Thin epoxy-bonded La–Fe–Co–Si plates were processed and tested. • Cycling stability, magnetocaloric and thermal properties were studied. • The impact of the plate composition and of the epoxy was investigated. • AMR from the epoxy-bonded composite plates was built and experimentally tested.
Multidisciplinary approach to cylindrical anisotropic metamaterials
Carbonell Olivares, Jorge; Torrent Martí, Daniel; Diaz Rubio, Ana; Sánchez-Dehesa Moreno-Cid, José
2011-01-01
Anisotropic characteristics of cylindrically corrugated microstructures are analyzed in terms of their acoustic and electromagnetic (EM) behavior paying special attention to their differences and similarities. A simple analytical model has been developed using effective medium theory to understand the anisotropic features of both types of waves in terms of radial and angular components of the wave propagation velocity. The anisotropic constituent parameters have been obtained by measuring the...
Anisotropic Stars Exact Solutions
Dev, K; Dev, Krsna; Gleiser, Marcelo
2000-01-01
We study the effects of anisotropic pressure on the properties of spherically symmetric, gravitationally bound objects. We consider the full general relativistic treatment of this problem and obtain exact solutions for various form of equations of state connecting the radial and tangential pressures. It is shown that pressure anisotropy can have significant effects on the structure and properties of stellar objects. In particular, the maximum value of 2M/R can approach unity (2M/R < 8/9 for isotropic objects) and the surface redshift can be arbitrarily large.
International Nuclear Information System (INIS)
Magnetocaloric properties of NdMnO3 were investigated in its bulk polycrystalline and nanocrystalline forms. The nanocrystalline sample (average particle size ∼40 nm) exhibits a maximum in the temperature dependence of magnetic entropy change [−ΔSM(T)] at ∼70 K due to the paramagnetic to ferromagnetic transition, which is absent in case of its bulk counterpart. The absence of peak in −ΔSM(T) in the bulk sample is attributed to the co-existence of antiferromagnetic and ferromagnetic phases. A canted magnetic state (CMS) is stabilized at low temperature for both the samples due to the ordering of Nd3+ giving rise to a peak in −ΔSM(T) at ∼15 K. Interestingly −ΔSM(T) for these two samples show a universal behavior near their transitions at low temperature although their temperature dependence of magnetization is markedly different around those transitions. A detailed analysis of magnetocaloric data conclusively establishes the existence of a canted magnetic state, which is not obvious from magnetometry, demonstrating the usefulness of this method for probing phase coexistence and multiple magnetic states in complex oxide systems. - Highlights: • Effect of reduction of particle size on magnetocaloric properties of NdMnO3 has been investigated. • The roles of Nd3+-ordering and self-doping effect on magnetic and magnetocaloric properties of NdMnO3 have been discussed. • Nanocrystalline NdMnO3 exhibits large magnetocaloric effect (MCE) in two temperature regimes in contrary to bulk sample. • We emphasize how MCE study can be exploited to explore fundamental physics of magnetism
The influence of gadolinium on magnetism and magnetocaloric properties of HoCo2 alloy
International Nuclear Information System (INIS)
A series of Ho1-xGdxCo2 (x = 0, 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1) samples were prepared by arc-melting method. The crystal structure, magnetic and magnetocaloric effect were investigated by X-ray powder diffraction and magnetization measurements. Then the magnetic phase transition was analyzed in term of Landau theory. The experimental results indicate that the ordering temperature TC increases from 81 to 402 K with increasing Gd substitution so that TC of the alloy is near room temperature (300 K) when x = 0.6. This Curie temperature increase is accompanied by a reduction of entropy change -ΔS. For an external magnetic field change from 0 to 5 T, -ΔS at TC is 11, 4.65 and 3 J/(kg K) for x = 0.1, 0.3 and 0.6, respectively. The origin and the evolution of magnetocaloric effect in Ho1-xGdxCo2 compounds are discussed
Enhanced magnetocaloric properties of melt-extracted GdAlCo metallic glass microwires
Energy Technology Data Exchange (ETDEWEB)
Shen, Hongxian; Wang, Huan [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Jingshun, Liu [School of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot 010051 (China); Cao, Fuyang [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Qin, Faxiang [1D Nanomaterials Group, National Institute for Material Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Xing, Dawei; Chen, Dongming; Liu, Yanfen [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Sun, Jianfei, E-mail: jfsun_hit@263.net [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)
2014-12-15
Herein, we report high magnetocaloric performance of melt-extracted metallic glass Gd{sub 60}Al{sub 20}Co{sub 20} microwires, which exhibit a large and reversible magnetocaloric effect (MCE). The isothermal magnetic entropy change (−ΔS{sub m}) reaches as high as 10.1 J kg{sup −1} K{sup −1} and the refrigerant capacity (RC) has a large value of 681 J kg{sup −1} for a field change of 5 T. The as-obtained Gd-based metallic glass microwires hold a great promise for multifunctional applications in MCE-based refrigeration of liquid nitrogen temperature range. - Highlights: • Gd{sub 60}Al{sub 20}Co{sub 20} metallic glass wires were fabricated by melt-extraction method. • The microwires show superior MCE performance versus its counterpart in BMGs. • The excellent result was due to the size effect and amorphous state of wires.
Anisotropic mechanical properties of zircon and the effect of radiation damage
Beirau, Tobias; Nix, William D.; Bismayer, Ulrich; Boatner, Lynn A.; Isaacson, Scott G.; Ewing, Rodney C.
2016-06-01
This study provides new insights into the relationship between radiation-dose-dependent structural damage due to natural U and Th impurities and the anisotropic mechanical properties (Poisson's ratio, elastic modulus and hardness) of zircon. Natural zircon samples from Sri Lanka (see Muarakami et al. in Am Mineral 76:1510-1532, 1991) and synthetic samples, covering a dose range of zero up to 6.8 × 1018 α-decays/g, have been studied by nanoindentation. Measurements along the [100] crystallographic direction and calculations, based on elastic stiffness constants determined by Özkan (J Appl Phys 47:4772-4779, 1976), revealed a general radiation-induced decrease in stiffness (~54 %) and hardness (~48 %) and an increase in the Poisson's ratio (~54 %) with increasing dose. Additional indentations on selected samples along the [001] allowed one to follow the amorphization process to the point that the mechanical properties are isotropic. This work shows that the radiation-dose-dependent changes of the mechanical properties of zircon can be directly correlated with the amorphous fraction as determined by previous investigations with local and global probes (Ríos et al. in J Phys Condens Matter 12:2401-2412, 2000a; Farnan and Salje in J Appl Phys 89:2084-2090, 2001; Zhang and Salje in J Phys Condens Matter 13:3057-3071, 2001). The excellent agreement, revealed by the different methods, indicates a large influence of structural and even local phenomena on the macroscopic mechanical properties. Therefore, this study indicates the importance of acquiring better knowledge about the mechanical long-term stability of radiation-damaged materials.
Energy Technology Data Exchange (ETDEWEB)
Xia, Wei [Inner Mongolia Key Laboratory for Physics and Chemistry of Functional Materials, Inner Mongolia Normal University, Huhhot 010022 (China); Baotou Research Institute of Rare Earth, Baotou 014030 (China); Huang, Jiaohong, E-mail: jiaohongh@163.com [Baotou Research Institute of Rare Earth, Baotou 014030 (China); Sun, Naikun [School of Science, Shenyang Ligong University, Shenyang 110159 (China); Lui, Cuilan [Baotou Research Institute of Rare Earth, Baotou 014030 (China); Ou, Zhiqiang; Song, Lin [Inner Mongolia Key Laboratory for Physics and Chemistry of Functional Materials, Inner Mongolia Normal University, Huhhot 010022 (China)
2015-06-25
Highlights: • Bonded La{sub 0.9}Ce{sub 0.1}(Fe,Mn){sub 11.7}Si{sub 1.3}H{sub 1.8} are prepared by bonding technology. • After bonding the samples have better mechanical properties than bulk alloys. • The T{sub c} of La{sub 0.9}Ce{sub 0.1}Fe{sub 11.7}Si{sub 1.3}H{sub 1.8} is adjusted by adding Mn atoms. • After bonding the good magnetocaloric effects can be remained. - Abstract: Bonded samples of La{sub 0.9}Ce{sub 0.1}Fe{sub 11.7}Si{sub 1.3}H{sub 1.8} and La{sub 0.9}Ce{sub 0.1}Fe{sub 11.41}Mn{sub 0.29}Si{sub 1.3}H{sub 1.8} with NaZn{sub 13}-type cubic structure have been prepared, and their mechanical properties and magnetocaloric effects have been investigated. The bonded samples show a very good compressive strength of 320 and 332 MPa, about 10% and 14% higher than that of bulk LaFe{sub 10.99}Co{sub 0.91}Si{sub 1.1}B{sub 0.2} compound. By partial substitution of Mn for Fe, the Curie temperature (T{sub c}) of bonded La{sub 0.9}Ce{sub 0.1}Fe{sub 11.7}Si{sub 1.3}H{sub 1.8} decreases remarkably from 325 to 279 K. The magnetic entropy change (ΔS{sub m}) for bonded La{sub 0.9}Ce{sub 0.1}Fe{sub 11.7}Si{sub 1.3}H{sub 1.8} and La{sub 0.9}Ce{sub 0.1}Fe{sub 11.41}Mn{sub 0.29}Si{sub 1.3}H{sub 1.8} slightly reduces compared with hydride alloys, but still maintains large values of 8.8 and 7.9 J/kg K. The two bonded samples exhibit the same adiabatic temperature change (ΔT{sub ad}) of about 2.6 K under a field change from 0 to 1.5 T. The bonded La{sub 0.9}Ce{sub 0.1}(Fe,Mn){sub 11.7}Si{sub 1.3} hydrides samples with good magnetocaloric effects and better mechanical properties are promising as high performance magnetic refrigerants materials.
Magnetocaloric response of amorphous and nanocrystalline Cr-containing Vitroperm-type alloys
Moreno-Ramírez, L. M.; Blázquez, J. S.; Franco, V.; Conde, A.; Marsilius, M.; Budinsky, V.; Herzer, G.
2016-07-01
The broad compositional range in which transition metal (TM) based amorphous alloys can be obtained, yields an easily tunable magnetocaloric effect (MCE) in a wide temperature range. In some TM-based alloys, anomalous behaviors are reported, as a non-monotonous trend with magnetic moment (e.g. FeZrB alloys). Moreover, in certain Cr-containing Vitroperm alloys anomalously high values of the magnetic entropy change were published. In this work, a systematic study on MCE response of Cr-containing amorphous alloys of composition Fe74-xCrxCu1Nb3Si15.5B6.5 (with x=2, 8, 10, 12, 13, 14 and 20) has been performed in a broad Curie temperature range from 100 K to 550 K. Curie temperature and magnetic entropy change peak of the amorphous alloys decrease with the increase of Cr content at rates of -25.6 K/at% Cr and -54 mJ kg-1 K-1/at% Cr, respectively, following a linear trend with the magnetic moment in both cases. The presence of nanocrystalline phases has been considered as a possible cause in order to explain the anomalies. The samples were nanocrystallized in different stages, however, the magnetocaloric response decreases as crystallization progresses due to the large separation of the Curie temperatures of the two phases.
Efficient Wavefield Extrapolation In Anisotropic Media
Alkhalifah, Tariq
2014-07-03
Various examples are provided for wavefield extrapolation in anisotropic media. In one example, among others, a method includes determining an effective isotropic velocity model and extrapolating an equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield. The effective isotropic velocity model can be based upon a kinematic geometrical representation of an anisotropic, poroelastic or viscoelastic wavefield. Extrapolating the equivalent propagation can use isotopic, acoustic or elastic operators based upon the determined effective isotropic velocity model. In another example, non-transitory computer readable medium stores an application that, when executed by processing circuitry, causes the processing circuitry to determine the effective isotropic velocity model and extrapolate the equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield. In another example, a system includes processing circuitry and an application configured to cause the system to determine the effective isotropic velocity model and extrapolate the equivalent propagation of an anisotropic, poroelastic or viscoelastic wavefield.
Energy Technology Data Exchange (ETDEWEB)
Yu, H.Y.; Zhu, Z.R.; Lai, J.W. [School of Materials Science & Engineering, South China University of Technology, Guangzhou 510640 (China); Zheng, Z.G., E-mail: mszgzheng@scut.edu.cn [School of Materials Science & Engineering, South China University of Technology, Guangzhou 510640 (China); Zeng, D.C., E-mail: medczeng@scut.edu.cn [School of Materials Science & Engineering, South China University of Technology, Guangzhou 510640 (China); Zhang, J.L. [Department of Physics and Materials Science, City University of Hong Kong, Hong Kong (China)
2015-11-15
The Mn{sub 1.15}Fe{sub 0.85}P{sub 0.52}Si{sub 0.45}B{sub 0.03} rods were prepared by copper mould suction casting. The effects of heat treatments on the structure and magnetocaloric properties have been investigated. The X-ray diffraction patterns indicated that the annealed Mn{sub 1.15}Fe{sub 0.85}P{sub 0.52}Si{sub 0.45}B{sub 0.03} rods present hexagonal Fe{sub 2}P-type structure with a small amount of Mn{sub 3}Fe{sub 2}Si{sub 3} impurity. With elevated annealing temperatures from 1123 K to 1423 K, the Curie temperature increases from 205 K to 251 K, the magnetic entropy change jumps from 0.6 to 19.8 J kg{sup –1}K{sup −1} under a magnetic field change of 0–2 T and the thermal hysteresis is reduced from 17 K to 10.5 K. Thus, the heat treatment is suggested to be an effective way to enhance the magnetocaloric effects of Mn{sub 1.15}Fe{sub 0.85}P{sub 0.52}Si{sub 0.45}B{sub 0.03} alloys. - Highlights: • Mn{sub 1.15}Fe{sub 0.85}P{sub 0.52}Si{sub 0.45}B{sub 0.03} alloy was prepared by copper mould suction casting method. • Curie temperature and magnetic entropy change can be tuned by heat treatment. • The −ΔS{sub M} for annealed alloys reaches 19.8 J kg{sup −1}K{sup −1} under the magnetic field change of 0–2 T. • Magnetic transitions are tuned from second-order to first-order by annealing temperature.
Characterization of anisotropic acoustic metamaterial slabs
Park, Jun Hyeong; Lee, Hyung Jin; Kim, Yoon Young
2016-01-01
In an anisotropic acoustic metamaterial, the off-diagonal components of its effective mass density tensor should be considered in order to describe the anisotropic behavior produced by arbitrarily shaped inclusions. However, few studies have been carried out to characterize anisotropic acoustic metamaterials. In this paper, we propose a method that uses the non-diagonal effective mass density tensor to determine the behavior of anisotropic acoustic metamaterials. Our method accurately evaluates the effective properties of anisotropic acoustic metamaterials by separately dealing with slabs made of single and multiple unit cells along the thickness direction. To determine the effective properties, the reflection and transmission coefficients of an acoustic metamaterial slab are calculated, and then the wave vectors inside of the slab are determined using these coefficients. The effective material properties are finally determined by utilizing the spatial dispersion relation of the anisotropic acoustic metamaterial. Since the dispersion relation of an anisotropic acoustic metamaterial is explicitly used, its effective properties can be easily determined by only using a limited number of normal and oblique plane wave incidences into a metamaterial slab, unlike existing approaches requiring a large number of wave incidences. The validity of the proposed method is verified by conducting wave simulations for anisotropic acoustic metamaterial slabs with Z-shaped elastic inclusions of tilted principal material axes.
Energy Technology Data Exchange (ETDEWEB)
Nisha, P.; Savitha Pillai, S. [Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology NIIST, CSIR, Trivandrum 695 019, Kerala (India); Darbandi, Azad [Gemeinschaftslabor Nanomaterialien, Forschungzentrum Karlsrhue/TU-Darmstadt, Petersenstr. 23 Gebaeude L2/01, 64287 Darmstadt (Germany); Varma, Manoj Raama, E-mail: manoj@niist.res.in [Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology NIIST, CSIR, Trivandrum 695 019, Kerala (India); Suresh, K.G. [Department of Physics, Indian Institute of Technology Bombay, 400076 Mumbai (India); Hahn, Horst [Gemeinschaftslabor Nanomaterialien, Forschungzentrum Karlsrhue/TU-Darmstadt, Petersenstr. 23 Gebaeude L2/01, 64287 Darmstadt (Germany)
2012-09-14
The structure, critical exponents and magnetocaloric effect (MCE) of Nebulized Spray Pyrolysis (NSP) synthesized nano crystalline La{sub 0.67}Ca{sub 0.33}Mn{sub 1-x}Fe{sub x}O{sub 3} (x = 0.05, 0.2) were investigated. The Reitveld refinement of XRD patterns show that the samples adopt an orthorhombic structure with Pnma space group. TEM inspection reveals that the average particle size is about 15 nm and 42 nm for NSP synthesized LCMFe{sub 0.05} and LCMFe{sub 0.2} samples respectively. The temperature and field dependent magnetization studies reveal the superparamagnetic state of La{sub 0.67}Ca{sub 0.33}Mn{sub 0.95}Fe{sub 0.05}O{sub 3} and spin-glass-like state of La{sub 0.67}Ca{sub 0.33}Mn{sub 0.8}Fe{sub 0.2}O{sub 3}. The critical behaviour at the transition region studied using modified Arrott plot provides a second order nature of phase transition for both samples. The magnetocaloric studies show the maximum value of magnetic entropy change ({Delta}S{sub max}) is in the range 2.3 J kg{sup -1} K{sup -1} at 158 K for LCMFe{sub 0.05} and 0.3 J kg{sup -1} K at 92 K for LCMFe{sub 0.2} respectively at 5 T field. The field dependence of the magnetic entropy changes are also analysed, which show a power law dependence ({Delta}S{sub M} {infinity}H{sup n}, n = 0.72 (2)) at transition temperature, T{sub C} = 162 K for LCMFe{sub 0.05} and n = 1.11(3) at 92 K for LCMFe{sub 0.2}. -- Highlights: Black-Right-Pointing-Pointer Nano La{sub 0.67}Ca{sub 0.33}Mn{sub 1-x}Fe{sub x}O{sub 3} (x = 0.05, 0.2) are prepared by NSP method. Black-Right-Pointing-Pointer We examine changes in the structure of the compositions. Black-Right-Pointing-Pointer The temperature and field variations of magnetization were analysed. Black-Right-Pointing-Pointer Super paramagnetic clustered state is observed for La{sub 0.67}Ca{sub 0.33}Mn{sub 0.95}Fe{sub 0.05}O{sub 3}. Black-Right-Pointing-Pointer We report critical behaviour and magnetocaloric effect of LCMOFe{sub 0.05}.
Sakamoto, Kenji; Yasuda, Takeshi; Miki, Kazushi; Chikamatsu, Masayuki; Azumi, Reiko
2011-01-01
We have fabricated organic field-effect transistors (OFETs) with a highly oriented active layer of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2), which was formed with the help of a photoaligned polyimide film. Photoalignment is an attractive technique for integrating OFETs with aligned active layers on the same substrate, because of its potential capability of two-dimensional alignment patterning. The F8T2 layer formed on the photoaligned polyimide film showed an absorption dichroic ratio greater than 15 after annealing at 285 °C. Top-gate/bottom-contact-type OFETs with a parylene gate insulating layer exhibited an enhanced hole mobility (0.016 cm2 V-1 s-1) along the alignment direction of the F8T2 backbone structure and a suppressed one (0.002 cm2 V-1 s-1) along the perpendicular direction. This result shows that the photoaligned polyimide film is an attractive alignment layer for fabricating and integrating OFETs with aligned active layers. Current-direction-dependent bias stress effect was observed for those OFETs; when the current flowed parallel to the alignment direction of the F8T2 backbone structures, a larger negative threshold voltage shift was observed. This anisotropic bias stress effect was discussed on the basis of a microstructure model of aligned F8T2 films.
Influence of Zn on magnetocaloric effect in (0.95)La0.7Sr0.3MnO3/Ni1−xZnxFe2O4 ceramic composites
International Nuclear Information System (INIS)
Highlights: • Synthesis of magnetic ceramic composites. • Magnetization of dual phase ceramics. • Magnetic entropy change in (0.95)La0.7Sr0.3MnO3/(0.05)Ni1−xZnxFe2O4 solid solution. - Abstract: We report the magnetic and magnetocaloric properties of (0.95)La0.7Sr0.3MnO3/(0.05)Ni1−xZnxFe2O4 (x = 0.0, 0.1, 0.3, and 0.5) ceramic composites. The composite samples with nominal compositions were prepared using the conventional solid-state reaction method. The phase purity and structure were confirmed by using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order of magnetic phase transition in the composite samples. A maximum in magnetic entropy change of ∼0.75 J/kg K at 1 T has been observed in (0.95)La0.7Sr0.3MnO3/(0.05)NiFe2O4 sample. The values of magnetic entropy change of these composites make them attractive for potential applications. These composite samples may consider as potential material for magnetic refrigeration near room temperature
Zhang, Hai-Feng; Liu, Shao-Bin; Li, Bing-Xiang
2013-10-01
In this paper, the properties of photonic band gaps (PBGs) for three-dimensional magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with simple-cubic lattices are theoretically investigated by the plane wave expansion (PWE) method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic PBGs in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatband regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency and plasma cyclotron frequency on the characteristics of anisotropic PBGs for the three-dimensional MPPCs are studied in detail and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in simple-cubic lattices and the complete PBGs can be found compared to the conventional three-dimensional MPPCs doped by the isotropic material. The bandwidths of PBGs can be enlarged by introducing the magnetized plasma into three-dimensional PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency and plasma cyclotron frequency. The locations of flatband regions cannot be tuned by any parameters except for the plasma frequency and plasma cyclotron frequency. Introducing the uniaxial material in three-dimensional magnetized plasma-dielectric photonic crystals can enlarge the PBGs and also provide a way to obtain the complete PBGs as the three-dimensional MPPCs with high symmetry.
A novel magnetic valve using room temperature magnetocaloric materials
DEFF Research Database (Denmark)
Eriksen, Dan; Bahl, Christian; Pryds, Nini;
2012-01-01
data a 3D finite element model has been set up to calculate the magnetic force between (graded) blocks of these materials and a permanent magnet assembly. The results have been used to calculate equilibrium points for actuation systems where the magnetic force is balanced by a spring force. On the......Magnetocaloric materials with near-room-temperature tuneable Curie temperatures have been utilized to develop a novel magnetic valve technology. The temperature dependent attractive force between the materials and a permanent magnet assembly is used to actuate valves as a response to temperature...... changes. This is made possible by the strong temperature dependence of the magnetization close to the Curie temperature of the magnetocaloric materials. Different compositions of both La0.67(Ca,Sr)0.33MnO3 and La(Fe,Co,Si)13 have been considered for use in prototype valves. Based on measured magnetization...
Sundqvist, Jon O; Cohen, David H; Leutenegger, Maurice A; Townsend, Richard H D
2011-01-01
We present a generalised formalism for treating the porosity-associated reduction in continuum opacity that occurs when individual clumps in a stochastic medium become optically thick. We consider geometries resulting in either isotropic or anisotropic effective opacity, and, in addition to an idealised model in which all clumps have the same local overdensity and scale, we also treat an ensemble of clumps with optical depths set by Markovian statistics. This formalism is then applied to the specific case of bound-free absorption of X-rays in hot star winds, a process not directly affected by clumping in the optically thin limit. We find that the Markov model gives surprisingly similar results to those found previously for the single clump model, suggesting that porous opacity is not very sensitive to details of the assumed clump distribution function. Further, an anisotropic effective opacity favours escape of X-rays emitted in the tangential direction (the `venetian blind' effect), resulting in a 'bump' of ...
Xu, Wenxiang; Wang, Han; Niu, Yanze; Bai, Jingtao
2016-01-01
With advances in interfacial properties characterization technologies, the interfacial volume fraction is a feasible parameter for evaluating effective physical properties of materials. However, there is a need to determine the interfacial volume fraction around anisotropic fibers and a need to assess the influence of such the interfacial property on effective properties of fibrous materials. Either ways, the accurate prediction of interfacial volume fraction is required. Towards this end, we put forward both theoretical and numerical schemes to determine the interfacial volume fraction in fibrous materials, which are considered as a three-phase composite structure consisting of matrix, anisotropic hard spherocylinder fibers, and soft interfacial layers with a constant dimension coated on the surface of each fiber. The interfacial volume fraction actually represents the fraction of space not occupied by all hard fibers and matrix. The theoretical scheme that adopts statistical geometry and stereological theories is essentially an analytic continuation from spherical inclusions. By simulating such three-phase chopped fibrous materials, we numerically derive the interfacial volume fraction. The theoretical and numerical schemes provide a quantitative insight that the interfacial volume fraction depends strongly on the fiber geometries like fiber shape, geometric size factor, and fiber size distribution. As a critical interfacial property, the present contribution can be further drawn into assessing effective physical properties of fibrous materials, which will be demonstrated in another paper (Part II) of this series.
Properties of magnetocaloric materials with a distribution of Curie temperatures
DEFF Research Database (Denmark)
Bahl, Christian Robert Haffenden; Bjørk, Rasmus; Smith, Anders;
2012-01-01
The magnetocaloric properties of inhomogeneous ferromagnets that contain distributions of Curie temperatures are considered as a function of the width of such a distribution. Assuming a normal distribution of the Curie temperature, the average adiabatic temperature change, ΔTad, the isothermal...... distribution, explaining the observed mismatch of peak temperatures reported in experiments. Also, the field dependence of ΔTad and Δs is found to depend on the width of the distribution....
Thermodynamic properties of the anisotropic frustrated spin-chain compound linarite PbCuSO4(OH)2
Schäpers, M.; Wolter, A. U. B.; Drechsler, S.-L.; Nishimoto, S.; Müller, K.-H.; Abdel-Hafiez, M.; Schottenhamel, W.; Büchner, B.; Richter, J.; Ouladdiaf, B.; Uhlarz, M.; Beyer, R.; Skourski, Y.; Wosnitza, J.; Rule, K. C.; Ryll, H.; Klemke, B.; Kiefer, K.; Reehuis, M.; Willenberg, B.; Süllow, S.
2013-11-01
We present a comprehensive macroscopic thermodynamic study of the quasi-one-dimensional (1D) s=(1)/(2) frustrated spin-chain system linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect, magnetostriction, and thermal-expansion measurements were performed to characterize the magnetic phase diagram. In particular, for magnetic fields along the b axis five different magnetic regions have been detected, some of them exhibiting short-range-order effects. The experimental magnetic entropy and magnetization are compared to a theoretical modeling of these quantities using density matrix renormalization group (DMRG) and transfer matrix renormalization group (TMRG) approaches. Within the framework of a purely 1D isotropic model Hamiltonian, only a qualitative agreement between theory and the experimental data can be achieved. Instead, it is demonstrated that a significant symmetric anisotropic exchange of about 10% is necessary to account for the basic experimental observations, including the three-dimensional (3D) saturation field, and which in turn might stabilize a triatic (three-magnon) multipolar phase.
Innovative ideas for future research on magnetocaloric technologies
Energy Technology Data Exchange (ETDEWEB)
Kitanovski, Andrej; Egolf, Peter W. [University of Applied Sciences of Western Switzerland, Institute for Thermal Sciences and Engineering, Route de Cheseaux 1, CH 1401 Yverdon-les-Bains (Switzerland)
2010-05-15
Magnetic heating, refrigeration and energy conversion have caused awareness of being promising future environmentally benign technologies with much potential to enter some existing markets. An increased research activity is observed, which to the end of the year 2010 lead to approximately forty-two prototypes. As most of these machines contain solid linear moving or rotating beds - consisting of magnetocaloric material - through static magnetic fields or moving magnets, which sweep a magnetic field over a static bed, all researchers face more or less the same problems. These concern materials, fluids, design and the operation characteristics. In this article innovative new system ideas are presented, which may have the potential to overcome existing barriers. The article is a proposal to the research community in the field of magnetocaloric technologies for future R and D activities. Taking into account all the limits and problems that researchers are facing at present, the best chance to bring magnetocaloric technologies to the market is to try some substantially new approaches that go beyond the present state-of-the-art. (author)
The phonon splitting and anisotropic effect of B2H6 molecular in the C2v minima
International Nuclear Information System (INIS)
Based on Jahn-Teller effect theory, quantum theory and group theory, the phonon splitting and anisotropic phenomena of the E ⊗e' system for B2H6 molecules with D3h symmetry are studied in the C2v minima. The vibration frequency of the system after Jahn-Teller distortion is calculated using the unitary shift transformation and modified scale transformation, it is found that the doubly degenerate vibration state e' is split into two states and its degeneration is completely lifted because of Jahn-Teller distortion. No matter which of the four C2v minima the system is in, the phonon splitting of the system is completely same. The Jahn-Teller distortion results in that the ground state of the system has lower energy after the distortion than before the distortion, B2H6 molecules will achieve a more stable state after the distortion just for the energy lessening. The phonon splitting is further discussed using group theory in this paper, the discussed results show that the vibration state e' of the system is split into two states respectively with a1 and b2 symmetries under the group C2v. The phonon splitting signifies that the isotropy of B2H6 molecules is destroyed and its anisotropy should appear. (authors)
Multidisciplinary approach to cylindrical anisotropic metamaterials
International Nuclear Information System (INIS)
Anisotropic characteristics of cylindrically corrugated microstructures are analyzed in terms of their acoustic and electromagnetic (EM) behavior paying special attention to their differences and similarities. A simple analytical model has been developed using effective medium theory to understand the anisotropic features of both types of waves in terms of radial and angular components of the wave propagation velocity. The anisotropic constituent parameters have been obtained by measuring the resonances of cylindrical cavities, as well as from numerical simulations. This permits one to characterize propagation of acoustic and EM waves and to compare the fundamental anisotropic features generated by the corrugated effective medium. Anisotropic coefficients match closely in both physics fields but other relevant parameters show significant differences in the behavior of both types of waves. (paper)
Energy Technology Data Exchange (ETDEWEB)
Khelifi, J. [Universite de Sfax, Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, Sfax (Tunisia); CNRS et Universite Joseph Fourier, Institut Neel, Grenoble (France); Tozri, A.; Dhahri, E. [Universite de Sfax, Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, Sfax (Tunisia)
2014-09-15
Magnetocaloric effect and order of transition in (La{sub 1-x}Nd{sub x}){sub 2/3}(Ca{sub 1-y}Sr{sub y}){sub 1/3}MnO{sub 3}, prepared by conventional solid-state reaction, have been investigated. Using Banerjee criterion, we demonstrate first-order transition for (J1) and (J2) as well as second-order transition for (J3), (J4), and (J5) samples. The ΔS{sub M}{sup max} is ranging between 9.18 Jkg{sup -1} K{sup -1} and 4.87 when Nd and Sr content changes leading to relative cooling power (RCP) varying between 330 and 229.35 J/kg. Both ΔS{sub M}{sup max} and the RCP are found sensitive to the disorder σ{sup 2}. The universal behavior obtained from ΔS variation curves confirmed the first-order transition for (J1) and (J2) samples and second-order transition for (J3), (J4), and (J5) samples obtained by Banerjee criterion. All samples with second-order phase transition exhibit inhomogeneous character estimated from local exponent n. (orig.)
Averaging anisotropic cosmologies
Barrow, J D; Barrow, John D.; Tsagas, Christos G.
2006-01-01
We examine the effects of spatial inhomogeneities on irrotational anisotropic cosmologies by looking at the average properties of pressure-free Bianchi-type models. Adopting the Buchert averaging scheme, we identify the kinematic backreaction effects by focussing on spacetimes with zero or isotropic spatial curvature. This allows us to close the system of the standard scalar formulae with a propagation equation for the shear magnitude. We find no change in the already known conditions for accelerated expansion. The backreaction terms are expressed as algebraic relations between the mean-square fluctuations of the models' irreducible kinematical variables. Based on these we investigate the early evolution of averaged vacuum Bianchi type $I$ universes and those filled with pressureless matter. In the latter case we show that the backreaction effects can modify the familiar Kasner-like singularity and potentially remove Mixmaster-type oscillations. We also discuss the possibility of accelerated expansion due to ...
Magnetocaloric effect in manganite perovskites La 0.77Sr 0.23Mn 1- xCu xO 3(0.1≤ x≤0.3)
El-Hagary, M.; Shoker, Y. A.; Emam-Ismail, M.; Moustafa, A. M.; Abd El-Aal, A.; Ramadan, A. A.
2009-02-01
The magnetocaloric properties of the polycrystalline manganites perovskite La 0.77Sr 0.23Mn 1- xCu xO 3 with 0.1≤x≤0.3 have been investigated. The maximum magnetic entropy change, ΔSMmax, of Cu doped manganites increases gradually with increasing applied magnetic field. The maximum values of magnetic entropy changes of Cu doped manganites samples is found to decrease with the further increasing of Cu concentration in the romboherderal phase ( x≤0.2). However, with increasing Cu contents ( x≥ 0.3) structure transformed into orthorhombic phase and, hence ΔSMmax, start to increase again with increasing Cu doped concentration. It was found that the maximum value of the magnetic entropy change increases near their respective TC from 3.09 J/kg K at 0.1 T and reached highest value of 4.41 J/kg K at 1 T for compound with x=0.1. ΔSMmax in La 0.77Sr 0.23Mn 0.9Cu 0.1O 3 at 1 T is found to be 26% higher than that known for the prototype magnetic refrigerant with pure Gd. The relative cooling power (RCP) of La 0.77Sr 0.23Mn 1- xCu xO 3 is nearly 60% of pure Gd. Thus, due to the high ΔSMmax and RCP values, sample with x=0.1 (at μoΔH=1 T) is the most promising compound to be used as magnetomechnical materials.
International Nuclear Information System (INIS)
Highlights: ► The in-plane electrical conductivity of the GDL must be captured numerically. ► Fuel cell performance is insensitive to the anisotropy in the permeability of GDL. ► The anisotropy in the in-plane electrical conductivity of the GDL can be neglected. ► For the reported conditions, the U-bend has no effect on the fuel cell performance. -- Abstract: A 3-dimensional model for an in-house proton exchange membrane (PEM) fuel cell with serpentine channels has been developed in order to investigate the sensitivity of the fuel cell performance to the anisotropic gas permeability and electrical conductivity of gas diffusion layers (GDLs). For a realistic range of transport properties being investigated, the fuel cell performance was found to be very sensitive to the electrical conductivity but almost insensitive to the gas permeability of the GDL. For the given operating conditions, the current density was found to be a maximum in the vicinity of the edge between the flow channel and the rib of the current collector. Since the most common GDL materials present a rather significant anisotropy in the in-plane directions, the effects of such anisotropy has been evaluated. Given that the through-plane conductivity is maintained constant for all the cases investigated, for a realistic range of the in-plane electrical conductivity, the fuel cell performance was found to be almost insensitive to this parameter. Therefore such anisotropy can be practically ignored. Finally, for single phase operating conditions, the U-bend in the serpentine channel has no effect on the overall performance of the fuel cell. Hence, only a straight channel of the fuel cell may be modelled and used as a quick performance indicator.
A study of phonon anisotropic scattering effect on silicon thermal conductivity at nanoscale
International Nuclear Information System (INIS)
Previous studies have shown that anisotropy in phonon transport exist because of the difference in phonon dispersion relation due to different lattice direction, as observed by a difference in in-plane and cross-plane thermal conductivity. The directional preference (such as forward or backward scattering) in phonon propagation however, remains a relatively unexplored frontier. Our current work adopts a simple scattering probability in radiative transfer, which is called Henyey and Greenstein probability density function, and incorporates it into the phonon Monte Carlo simulation to investigate the effect of directional scattering in phonon transport. In this work, the effect of applying the anisotropy scattering is discussed, as well as its impact on the simulated thermal conductivity of silicon thin films. While the forward and backward scattering will increase and decrease thermal conductivity respectively, the extent of the effect is non-linear such that forward scattering has a more obvious effect than backward scattering
The Effects of Anisotropic Viscosity on Turbulence and Heat Transport in the Intracluster Medium
Parrish, Ian J; Quataert, Eliot; Sharma, Prateek
2012-01-01
In the intracluster medium (ICM) of galaxy clusters, heat and momentum are transported almost entirely along (but not across) magnetic field lines. We perform the first fully self-consistent Braginskii-MHD simulations of galaxy clusters including both of these effects. Specifically, we perform local and global simulations of the magnetothermal instability (MTI) and the heat-flux-driven buoyancy instability (HBI) and assess the effects of viscosity on their saturation and astrophysical implications. We find that viscosity has only a modest effect on the saturation of the MTI. As in previous calculations, we find that the MTI can generate nearly sonic turbulent velocities in the outer parts of galaxy clusters, although viscosity somewhat suppresses the magnetic field amplification. At smaller radii in cool-core clusters, viscosity can decrease the linear growth rates of the HBI. However, it has less of an effect on the HBI's nonlinear saturation, in part because three-dimensional interchange motions (magnetic f...
Effects of anisotropic potentials on the energy gap of Bose gas
Directory of Open Access Journals (Sweden)
F Nabipoor
2010-09-01
Full Text Available We investigate the effect of dipole-dipole and quadrapole- quadrapole interaction of a weakly interacting Bose gas near the transition temperature on the energy spectra of the thermal and condensate parts. We use the two fluid model and mean field approximation. We show that the effects of the condensate part on the shift of energy is greater than the case of contact potential
Wang, Longfei; Liu, Shuhai; Wang, Zheng; Zhou, Yongli; Qin, Yong; Wang, Zhong Lin
2016-02-23
Effective piezoelectric semiconductor based hybrid photocatalysts are successfully developed by assembling TiO2 nanoparticles on ZnO monocrystalline nanoplatelets. The piezopotential can be introduced and tuned by thermal stress on the piezoelectric material of ZnO monocrystalline nanoplatelets through cooling hybrid photocatalysts from high temperature to room temperature with different rates based on the mismatched thermal expansion coefficient of the two materials, which can be used to engineer the heterojunction band structure and significantly enhance the photocatalytic performance in a wide range by improving charge separation. It is proposed that the piezotronic effect enhanced photocatalyst will provide a strategy for high-performance photocatalysis applications. PMID:26745209
Sundqvist, Jon O.; Owocki, Stanley P.; Cohen, David H.; Leutenegger, Maurice A.
2011-01-01
We present a generalised formalism for treating the porosity-associated reduction in continuum opacity that occurs when individual clumps in a stochastic medium become optically thick. As in previous work, we concentrate on developing bridging laws between the limits of optically thin and thick clumps. We consider geometries resulting in either isotropic or anisotropic effective opacity, and, in addition to an idealised model in which all clumps have the same local overdensity and scale, we also treat an ensemble of clumps with optical depths set by Markovian statistics. This formalism is then applied to the specific case of bound-free absorption of X- rays in hot star winds, a process not directly affected by clumping in the optically thin limit. We find that the Markov model gives surprisingly similar results to those found previously for the single clump model, suggesting that porous opacity is not very sensitive to details of the assumed clump distribution function. Further, an anisotropic effective opacity favours escape of X-rays emitted in the tangential direction (the venetian blind effect), resulting in a bump of higher flux close to line centre as compared to profiles computed from isotropic porosity models. We demonstrate how this characteristic line shape may be used to diagnose the clump geometry, and we confirm previous results that for optically thick clumping to significantly influence X-ray line profiles, very large porosity lengths, defined as the mean free path between clumps, are required. Moreover, we present the first X-ray line profiles computed directly from line-driven instability simulations using a 3-D patch method, and find that porosity effects from such models also are very small. This further supports the view that porosity has, at most, a marginal effect on X-ray line diagnostics in O stars, and therefore that these diagnostics do indeed provide a good clumping insensitive method for deriving O star mass-loss rates.
Sundqvist, Jon O.; Owocki, Stanley P.; Cohen, David H.; Leutenegger, Maurice A.; Townsend, Richard H. D.
2012-02-01
We present a generalized formalism for treating the porosity-associated reduction in continuum opacity that occurs when individual clumps in a stochastic medium become optically thick. As in previous work, we concentrate on developing bridging laws between the limits of optically thin and thick clumps. We consider geometries resulting in either isotropic or anisotropic effective opacity, and, in addition to an idealized model in which all clumps have the same local overdensity and scale, we also treat an ensemble of clumps with optical depths set by Markovian statistics. This formalism is then applied to the specific case of bound-free absorption of X-rays in hot star winds, a process not directly affected by clumping in the optically thin limit. We find that the Markov model gives surprisingly similar results to those found previously for the single-clump model, suggesting that porous opacity is not very sensitive to details of the assumed clump distribution function. Further, an anisotropic effective opacity favours escape of X-rays emitted in the tangential direction (the 'venetian blind' effect), resulting in a 'bump' of higher flux close to line centre as compared to profiles computed from isotropic porosity models. We demonstrate how this characteristic line shape may be used to diagnose the clump geometry, and we confirm previous results that for optically thick clumping to significantly influence X-ray line profiles, very large porosity lengths, defined as the mean free path between clumps, are required. Moreover, we present the first X-ray line profiles computed directly from line-driven instability simulations using a 3D patch method, and find that porosity effects from such models also are very small. This further supports the view that porosity has, at most, a marginal effect on X-ray line diagnostics in O stars, and therefore that these diagnostics do indeed provide a good 'clumping insensitive' method for deriving O star mass-loss rates.
Czech Academy of Sciences Publication Activity Database
Kovalev, A.A.; Tserkovnyak, Y.; Výborný, Karel; Sinova, J.
2009-01-01
Roč. 79, č. 19 (2009), 19529/1-19529/19. ISSN 1098-0121 R&D Projects: GA MŠk LC510; GA AV ČR KJB100100802 Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic materials * Hall effect * magnetoresistance * quasiparticles * spin-orbit interactions * two-dimensional electron gas Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.475, year: 2009 http://link.aps.org/doi/10.1103/PhysRevB.79.195129
Kwaadgras, B.W.
2013-01-01
We study the polarizability of colloidal particles, as well as their interparticle interactions in the presence or absence of an external electric field. To this end, we employ the Coupled Dipole Method (CDM), which models the particles as clusters of Lorentz atoms (i.e., inducible dipoles) and uses a Hamiltonian approach and large-matrix manipulation to account for all many-atom effects. In this way, we are able to numerically and, in some cases, analytically calculate London-Van der Waals f...
Interface crack growth for anisotropic plasticity with non-normality effects
DEFF Research Database (Denmark)
Tvergaard, Viggo; Legarth, Brian Nyvang
2007-01-01
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......A plasticity model with a non-normality plastic flow rule is used to analyze crack growth along an interface between a solid with plastic anisotropy and an elastic substrate. The fracture process is represented in terms of a traction-separation law specified on the crack plane. A phenomenological...
DEFF Research Database (Denmark)
Linderoth, T.R.; Mortensen, Jens Jørgen; Jacobsen, Karsten Wedel; Lægsgaard, E.; Stensgaard, I.; Besenbacher, Flemming
1996-01-01
Nucleation and growth of Pt on the reconstructed Pt(100)-hex surface was studied by scanning tunneling microscopy. A detailed autocorrelation analysis of island positions reveals direct evidence for strongly anisotropic diffusion, and from the island size distribution, which obeys a simple scaling...
Energy Technology Data Exchange (ETDEWEB)
Ranke, P. J. von, E-mail: von.ranke@uol.com.br; Nóbrega, E. P.; Ribeiro, P. O.; Alvarenga, T. S. T.; Lopes, P. H. O.; Sousa, V. S. R. de; Oliveira, N. A. de [Instituto de Física, Universidade do Estado do Rio de Janeiro—UERJ, Rua São Francisco Xavier, 524, 20550-013 Rio de Janeiro (Brazil); Caldas, A. [Sociedade Unificada de Ensino Superior e Cultura, SUESC, 20211-351 Rio de Janeiro (Brazil); Alho, B. P. [Instituto de Aplicação Fernando Rodrigues da Silveira, Universidade do Estado do Rio de Janeiro, Rua Santa Alexandrina, 288, 20260-232 Rio de Janeiro (Brazil); Carvalho, G. [Laboratório Nacional de Luz Sincroton—LNLS, 13083-970 Campinas, São Paulo (Brazil); Magnus, A.
2014-10-14
We report theoretical investigations on the magnetocaloric effect, described by the magnetic entropy change in rare earth—transition metal amorphous systems. The model includes the local anisotropy on the rare earth ions in Harris-Plischke-Zuckermann assumptions. The transition metals ions are treated in terms of itinerant electron ferromagnetism and the magnetic moment of rare earth ions is coupled to the polarized d-band by a local exchange interaction. The magnetocaloric effect was calculated in DyCo{sub 3.4} system, which presents amorphous sperimagnetic configuration. The calculations predict higher refrigerant capacity in the amorphous DyCo{sub 3.4} than in DyCo{sub 2} crystal, highlighting the importance of amorphous magnetocaloric materials. Our calculation of the magnetocaloric effect in Dy{sub 70}Zr{sub 30}, which presents amorphous asperomagnetic configuration, is in good agreement with the experimental result. Furthermore, magnetic entropy changes associated with crystal-amorphous configurations change are estimated.
Influence of heat treatment on the magnetic and magnetocaloric properties in Nd0.6Sr0.4MnO3 compound
Ahmed, A. M.; Mohamed, H. F.; Diab, A. K.; Mohamed, Sara A.; García-Granda, S.; Martínez-Blanco, D.
2016-07-01
In the present investigation, the effect of annealing temperature on the structural, electrical transport and the magnetocaloric effect of Nd0.6Sr0.4MnO3 manganites have been studied. Rietveld refinement of XRD data reveals that all samples are single phase with a space group (Pnma). Heat treatment enhances the grain size and decreases the porosity. All samples suffer Curie transition from ferromagnetic to paramagnetic. Magnetocaloric parameters have been determined by the analysis of isothermal M (H) curves around Curie temperature (ΔH = 2 T) for samples. Heat treatment enhances magnetic entropy, which reaches a maximum at Tan = 900 °C. In addition, the rate cooling power records highest value at Tan = 700 °C.
Magnetic and magnetocaloric properties of martensitic Ni{sub 2}Mn{sub 1.4}Sn{sub 0.6} Heusler alloy
Energy Technology Data Exchange (ETDEWEB)
Chernenko, Volodymyr A., E-mail: vladimir_chernenko@ehu.es [Universidad del Pais Vasco, Dept. Electricidad y Electronica, PO Box 644, Bilbao 48080 (Spain); Ikerbasque, Basque Foundation for Science, Bilbao 48011 (Spain); Barandiaran, Jose M. [Universidad del Pais Vasco, Dept. Electricidad y Electronica, PO Box 644, Bilbao 48080 (Spain); Rodriguez Fernandez, Jesus; Rojas, Daniel P. [CITIMAC, Fac. Ciencias, Univ. Cantabria, Santander 39005 (Spain); Gutierrez, Jon; Lazpita, Patricia [Universidad del Pais Vasco, Dept. Electricidad y Electronica, PO Box 644, Bilbao 48080 (Spain); Orue, Inaki [SGiker, Vicerrectorado de Inv. UPV/EHU, Sarriena s/n, Leioa 48940 (Spain)
2012-10-15
The evolutions of magnetic properties at low temperatures and the influence of magnetic field on the temperature dependence of specific heat in martensitic Ni{sub 2}Mn{sub 1.4}Sn{sub 0.6} Heusler alloy are studied. The frequency-dependent blocking temperature and considerable exchange bias below it are measured in the martensitic phase. From the analysis of the specific heat curves under magnetic field, a large inverse magnetocaloric effect manifested as the magnetic field induced rise of isothermal magnetic entropy and/or magnetic field induced adiabatic temperature decrease in the vicinity of the reverse magnetostructural transformation and a significant value of the conventional magnetocaloric effect at the Curie temperature are obtained. The Debye temperature and electronic coefficient equal to {Theta}{sub D}=310{+-}2 K and {gamma}= 16.6{+-}0.3 mJ/K{sup 2}mol, respectively, do not depend on the magnetic field.
Estimation of magnetocaloric properties by using Monte Carlo method for AMRR cycle
Arai, R.; Tamura, R.; Fukuda, H.; Li, J.; Saito, A. T.; Kaji, S.; Nakagome, H.; Numazawa, T.
2015-12-01
In order to achieve a wide refrigerating temperature range in magnetic refrigeration, it is effective to layer multiple materials with different Curie temperatures. It is crucial to have a detailed understanding of physical properties of materials to optimize the material selection and the layered structure. In the present study, we discuss methods for estimating a change in physical properties, particularly the Curie temperature when some of the Gd atoms are substituted for non-magnetic elements for material design, based on Gd as a ferromagnetic material which is a typical magnetocaloric material. For this purpose, whilst making calculations using the S=7/2 Ising model and the Monte Carlo method, we made a specific heat measurement and a magnetization measurement of Gd-R alloy (R = Y, Zr) to compare experimental values and calculated ones. The results showed that the magnetic entropy change, specific heat, and Curie temperature can be estimated with good accuracy using the Monte Carlo method.
Thermodynamics of anisotropic branes
Ávila, Daniel; Patiño, Leonardo; Trancanelli, Diego
2016-01-01
We study the thermodynamics of flavor D7-branes embedded in an anisotropic black brane solution of type IIB supergravity. The flavor branes undergo a phase transition between a `Minkowski embedding', in which they lie outside of the horizon, and a `black hole embedding', in which they fall into the horizon. This transition depends on two independent dimensionless ratios, which are formed out of the black hole temperature, its anisotropy parameter, and the mass of the flavor degrees of freedom. It happens either at a critical temperature or at a critical anisotropy. A general lesson we learn from this analysis is that the anisotropy, in this particular realization, induces similar effects as the temperature. In particular, increasing the anisotropy bends the branes more and more into the horizon. Moreover, we observe that the transition becomes smoother for higher anisotropies.
International Nuclear Information System (INIS)
Although magnetron sputter deposition has been utilized practically for the various kinds of film formation, its detailed process has not yet been fully understood. For example, in spite of the extensive studies on the angular distribution of sputtered particles, a simple question how substrate position affects film properties cannot be precisely answered. Systematic investigation is required to clarify this problem. From this viewpoint, a new type of the deposition system was constructed, in which substrates are arranged in semicircular form in relation to a target. By using this system, the effect that substrate position exerted on the characteristics of films can be studied. Chromium films have been well known as the thin film resistors because of the low temperature coefficient of resistivity. Chromium is also used as the underlaid layer for adhering other films and for longitudinal magnetic recording media. In this study, the chromium films on glass or silicon substrates were prepared with this new system, and their structure and composition were examined. The experimental system, the preparation and evaluation of chromium thin films, and the results of the deposition rate, X-ray diffraction measurement, film composition and surface morphology are reported. (K.I.)
Energy Technology Data Exchange (ETDEWEB)
Berryman, J.G.
2010-06-01
The mechanics of vertically layered porous media has some similarities to and some differences from the more typical layered analysis for purely elastic media. Assuming welded solid contact at the solid-solid interfaces implies the usual continuity conditions, which are continuity of the vertical (layering direction) stress components and the horizontal strain components. These conditions are valid for both elastic and poroelastic media. Differences arise through the conditions for the pore pressure and the increment of fluid content in the context of fluid-saturated porous media. The two distinct conditions most often considered between any pair of contiguous layers are: (1) an undrained fluid condition at the interface, meaning that the increment of fluid content is zero (i.e., {delta}{zeta} = 0), or (2) fluid pressure continuity at the interface, implying that the change in fluid pressure is zero across the interface (i.e., {delta}p{sub f} = 0). Depending on the types of measurements being made on the system and the pertinent boundary conditions for these measurements, either (or neither) of these two conditions might be directly pertinent. But these conditions are sufficient nevertheless to be used as thought experiments to determine the expected values of all the poroelastic coefficients. For quasi-static mechanical changes over long time periods, we expect drained conditions to hold, so the pressure must then be continuous. For high frequency wave propagation, the pore-fluid typically acts as if it were undrained (or very nearly so), with vanishing of the fluid increment at the boundaries being appropriate. Poroelastic analysis of both these end-member cases is discussed, and the general equations for a variety of applications to heterogeneous porous media are developed. In particular, effective stress for the fluid permeability of such poroelastic systems is considered; fluid permeabilities characteristic of granular media or tubular pore shapes are treated
MnxZn1-xFe2-yRyO4 (R = Gd, Eu) Ferrite Nanocrystals for Potential Magnetocaloric Applications
Calderon-Ortiz, Eric; Perales-Perez, Oscar; Voyles, P.; Gutierrez, Gustavo; Tomar, M. S.
2007-01-01
The use of a ferromagnetic fluid for cooling applications represents an encouraging alternative to traditional methods ; the fact that the fluid can be pumped with no moving mechanical parts, using the magnetocaloric effect, can be a great advantage for many applications where high maintenance costs and power consumption are undesirable. The nanocrystalline material suitable for this specific application must exhibit certain specific properties, such as tunable Curie temperature (Tc) and high...
Czech Academy of Sciences Publication Activity Database
Diop, L.V.B.; Kaštil, Jiří; Isnard, O.; Arnold, Zdeněk; Kamarád, Jiří
2015-01-01
Roč. 627, Apr (2015), s. 446-450. ISSN 0925-8388 R&D Projects: GA ČR GAP204/12/0692 Institutional support: RVO:68378271 Keywords : itinerant-electron compounds * magnetic properties * magnetocaloric effect Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.999, year: 2014
Evidence of a canted magnetic state in self-doped LaMnO3+δ (δ = 0.04): a magnetocaloric study
International Nuclear Information System (INIS)
We report a detailed investigation of the magnetocaloric properties of self-doped polycrystalline LaMnO3+δ with δ = 0.04. Due to the self-doping effect, the system exhibits a magnetic transition from a paramagnetic to ferromagnetic-like canted magnetic state (CMS) at ∼120 K, which is associated with an appreciably large magnetocaloric effect (MCE). The CMS is an inhomogeneous magnetic phase developing due to a steady growth of antiferromagnetic correlation in its predominant ferromagnetic state below ∼120 K. The stabilization of CMS in this material is concluded from a comprehensive analysis of magnetocaloric data using Landau theory, which is in excellent agreement with our neutron diffraction study. The magnetic entropy change versus temperature curves for different applied fields collapse into a single curve, revealing a universal behavior of MCE. Our studies suggest that investigation of MCE is an effective technique to acquire fundamental understanding about the basic magnetic structure of a system with complex competing interactions.
Rainbow metric from quantum gravity: anisotropic cosmology
Assanioussi, Mehdi; Dapor, Andrea
2016-01-01
In this paper we present a construction of effective cosmological models which describe the propagation of a massive quantum scalar field on a quantum anisotropic cosmological spacetime. Each obtained effective model is represented by a rainbow metric in which particles of distinct momenta propagate on different classical geometries. Our analysis shows that upon certain assumptions and conditions on the parameters determining such anisotropic models, we surprisingly obtain a unique deformatio...
The new ternary silicide Gd5CoSi2: Structural, magnetic and magnetocaloric properties
International Nuclear Information System (INIS)
Gd5CoSi2 was prepared by annealing at 1003 K. Its investigation by the X-ray powder diffraction shows that the ternary silicide crystallizes in a tetragonal structure deriving from the Cr5B3-type (I4/mcm space group; a=7.5799(4) and c=13.5091(12) A as unit cell parameters). The Rietveld refinement shows a mixed occupancy on the (8h) site between Si and Co atoms. Magnetization and specific heat measurements performed on Gd5CoSi2 reveal a ferromagnetic behaviour below TC=168 K. This magnetic ordering is associated to an interesting magnetocaloric effect; the adiabatic temperature change ΔTad is about 3.1 and 5.9 K, respectively, for a magnetic field change of 2 and 4.6 T. -- Graphical abstract: The adiabatic temperature change ΔTad was determined by combining the heat capacity measurements and the magnetization data. As expected, a peak near the Curie temperature of the Gd5CoSi2 ternary silicide is observed, with a maximum of ΔTad around 3.1 and 5.9 K for ΔH=2 and 4.6 T, respectively. Display Omitted Research Highlights: → We prepare and characterize for the first time the ternary silicide Gd5CoSi2. → Gd5CoSi2 crystallizes in the tetragonal structure deriving from the Cr5B3-type. → Gd5CoSi2 shows a ferromagnetic behaviour below 168 K associated with magnetocaloric properties.
Directory of Open Access Journals (Sweden)
S.N. Gaikwad
2014-01-01
Full Text Available In this paper, we have investigated theoretically the effect of Soret parameter on the onset of double diffusive rotating anisotropic convection in a horizontal sparsely packed porous layer using linear stability theory which is based on the usual normal mode technique. The Brinkman model that includes the Coriolis term is employed for the momentum equation. The effect of anisotropy parameters, Soret parameter, solute Rayleigh number, Taylor number, Lewis number, Darcy and Darcy Prandtl number on stationary and oscillatory convection is shown graphically.
Order-disorder transition of vortex matter in Mg{sub 0.9}B{sub 2}: anisotropic effects
Energy Technology Data Exchange (ETDEWEB)
Oliveira, A A M; Ortiz, W A [Grupo de Supercondutividade e Magnetismo, Departamento de Fisica, Universidade Federal de Sao Carlos, SP (Brazil); Sharma, P A; Hur, N; Cheong, S-W, E-mail: ana@df.ufscar.b, E-mail: ana@df.ufscar.b [Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers, NJ (United States)
2009-03-01
Third-harmonic susceptibility studies have been employed to probe the order-disorder transition of Vortex Matter of a magnesium-deficient sample of MgB{sub 2}. Our results reveal that the measured threshold is anisotropic for different orientations of the applied magnetic field, suggesting that the pinning efficiency of the magnesium-deficient regions depend on the orientation of the penetrated vortices.
Chakraborty, Shuvendu; Debnath, Ujjal
2011-01-01
In this work, we have analyzed two scenarios namely, "intermediate" and "logamadiate" scenarios for closed, open and flat anisotropic universe in presence of phantom field, normal tachyonic field and phantom tachyonic field. We have assumed that there is no interaction between the above mentioned dark energy and dark matter. In these two types of the scenarios of the universe, the nature of the scalar fields and corresponding potentials have been investigated. In intermediate scenario, (i) th...
Directory of Open Access Journals (Sweden)
U. C. Hasar
2015-01-01
Full Text Available We propose a retrieval method for reference-plane-invariant electromagnetic parameter measurements of bi-anisotropic metamaterial slabs without resorting to accurate information of the slab thickness and the branch index. To extract reference-plane distances, the slab thickness, and the branch index, we first approximate wave impedances and refractive index away from the slab resonance frequency and then use scattering parameters to calculate the refractive index and the branch index. Once these quantities are determined, they are used as inputs for the retrieval of electromagnetic properties of slabs over the whole band. Different approximations for refractive index and wave impedances are applied to demonstrate the applicability and accuracy of our proposed method. We tested our method for electromagnetic parameter extraction of bi-anisotropic split-ring-resonator and Omega-shaped MM slabs with different number of unit cells. From our analysis, we note that inaccurate information of reference-plane distances, the slab length, and the branch index not only changes the amplitude but also shifts the response of the electromagnetic properties. We show that the presented method can be applied for accurate electromagnetic parameter extraction of bi-anisotropic MM slabs.
Phase control studies in Gd{sub 5}Si{sub 2}Ge{sub 2} giant magnetocaloric compound
Energy Technology Data Exchange (ETDEWEB)
Belo, J.H. [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Pereira, A.M., E-mail: ampereira@fc.up.pt [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Ventura, J.; Oliveira, G.N.P. [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Araujo, J.P., E-mail: jearaujo@fc.up.pt [IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Tavares, P.B.; Fernandes, L. [Departamento de Quimica and CQ-VR, Universidade de Tras-os-Montes e Alto Douro, 5001-801 Vila Real (Portugal); Algarabel, P.A. [Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza and Consejo Superior de Investigaciones Cientificas, 50009 Zaragoza (Spain); Magen, C. [Instituto de Nanociencia de Aragon-ARAID, Universidad de Zaragoza, 50009 Zaragoza (Spain); Morellon, L. [Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza and Consejo Superior de Investigaciones Cientificas, 50009 Zaragoza (Spain); Instituto de Nanociencia de Aragon, Universidad de Zaragoza, 50009 Zaragoza (Spain); and others
2012-07-15
Highlights: Black-Right-Pointing-Pointer Study of time dependence of O(I) to M phase. Black-Right-Pointing-Pointer Determination of the optimal annealing time. Black-Right-Pointing-Pointer New method for phase amount estimation (O(I) and M). Black-Right-Pointing-Pointer Effect of annealing on the MCE. Black-Right-Pointing-Pointer Analysis of the nature of the magnetic transition through the Arrot plot representation. - Abstract: A systematic set of annealings on arc-melted synthesized Gd{sub 5}Si{sub 2}Ge{sub 2} sample was performed. Through powder X-ray diffraction (XRD) and magnetometry measurements we monitored the effect of varying the annealing time with constant temperature (T = 1473 K) on the formation of the monoclinic (M) crystallographic phase fraction, which is the one responsible for the giant magnetocaloric effect (GMCE) in this compound. The conversion of the orthorhombic O(I) crystallographic phase into M was achieved, resulting in a significant increase of the M mass fraction. Such conversion led to a change in the magnetic transition nature, evolving from a second to a first order transition for the as-cast and annealed samples, respectively. An optimal annealing time range for the M phase conversion was identified to be within 80-120 min at T = 1473 K followed by a rapid quenching to liquid N{sub 2}. Furthermore, an increase up to {approx}50% of the magnetocaloric effect was obtained for the sample annealed during 120 min.
Jeppesen, Claus; Flyvbjerg, Henrik; Mouritsen, Ole G.
1989-11-01
Monte Carlo computer-simulation techniques are used to elucidate the equilibrium phase behavior as well as the late-stage ordering dynamics of some two-dimensional models with ground-state ordering of a high degeneracy Q. The models are Q-state Potts models with anisotropic grain-boundary potential on triangular lattices-essentially clock models, except that the potential is not a cosine, but a sine function of the angle between neighboring grain orientations. For not too small Q, these models display two thermally driven phase transitions, one which takes the system from a low-temperature Potts-ordered phase to an intermediate phase which lacks conventional long-range order, and another transition which takes the system to the high-temperature disordered phase. The linear nature of the sine potential used makes it a marginal case in the sense that it favors neither hard domain boundaries, like the standard Potts models do, nor a wetting of the boundaries, as the standard clock models do. Thermal fluctuations nevertheless cause wetting to occur for not too small temperatures. Specifically, we have studied models with Q=12 and 48. The models are quenched from infinity to zero as well as finite temperatures within the two low-temperature phases. The order parameter is a nonconserved quantity during these quenches. The nonequilibrium ordering process subsequent to the quench is studied as a function of time by calculating the interfacial energy, ΔE, associated with the entire grain-boundary network. The time evolution of this quantity is shown to obey the growth law, ΔE(t)~t-n, over an extended time range at late times. It is found that the zero-temperature dynamics is characterized by a special exponent value which for the Q=48 model is n~=0.25 in accordance with earlier work. However, for quenches to finite temperatures in the Potts-ordered phase there is a distinct crossover to the classical Lifshitz-Allen-Cahn exponent value, n=(1/2, for both values of Q. This
Anisotropic Stars II Stability
Dev, K; Dev, Krsna; Gleiser, Marcelo
2003-01-01
We investigate the stability of self-gravitating spherically symmetric anisotropic spheres under radial perturbations. We consider both the Newtonian and the full general-relativistic perturbation treatment. In the general-relativistic case, we extend the variational formalism for spheres with isotropic pressure developed by Chandrasekhar. We find that, in general, when the tangential pressure is greater than the radial pressure, the stability of the anisotropic sphere is enhanced when compared to isotropic configurations. In particular, anisotropic spheres are found to be stable for smaller values of the adiabatic index $\\gamma$.
Magneto-caloric and magneto-resistive properties of La0.67Ca0.33-xSrxMnO3
International Nuclear Information System (INIS)
This thesis presents results of an experimental investigation of magneto-caloric and magneto-resistive 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 prepared the glycine-nitrate combustion technique. The compounds were ferromagnetic and showed a Curie transition in the temperature range 267370 K (TC increased with increasing x). An analysis of the structural properties was carried out by means of x-ray diffraction and the Rietveld technique. The variation of the Ca/Sr ratio was found to cause a transition from orthorhombic to rhombohedral symmetry in the composition range 0.110 0.67Ca0.33-xSrxMnO3 samples was measured directly and indirectly (by means of magnetization measurements). All the samples showed 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 magneto-caloric 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 magneto-resistive properties of the La0.67Ca0.33-xSrxMnO3 system. It was found that th polycrystalline nature of the compounds played a decisive role for the magnetotransport properties. Characteristic grain boundary effects, such as a low-field magnetoresistance, which is absent in single-crystalline perovskites, were observed. The low-field effect is usually ascribed to spin-dependent scattering in grain boundaries. Qualitatively the results obtained for the La0.67Ca0.33-xSrxMnO3 samples were consistent with this model. The resistivity contribution arising from the presence of grain boundaries increased with
Directory of Open Access Journals (Sweden)
Christianto V.
2007-04-01
Full Text Available In the light of some recent hypotheses suggesting plausible unification of thermostatistics where Fermi-Dirac, Bose-Einstein and Tsallis statistics become its special subsets, we consider further plausible extension to include non-integer Hausdorff dimension, which becomes realization of fractal entropy concept. In the subsequent section, we also discuss plausible extension of this unified statistics to include anisotropic effect by using quaternion oscillator, which may be observed in the context of Cosmic Microwave Background Radiation. Further observation is of course recommended in order to refute or verify this proposition.
International Nuclear Information System (INIS)
We have studied the magnetic, magnetocaloric, and magnetostriction properties of LaFe11.4Si1.6 and La(Fe0.99Z0.01)11.4Si1.6 (Z=Ni, Cu, Cr, V) compounds using magnetization and strain gauge techniques. It was found that substitution of 1% of the Fe by Z-elements results in an increase in the Curie temperature (TC), and affects the magnetostriction and magnetocaloric properties of the parent compound, LaFe11.4Si1.6. A maximum shift in TC of about 11 K, and significantly smaller hysteresis losses in the vicinity of TC compared with those of the base compound, were found for Z=V. The maximum magnetovolume coupling constant was estimated to be ndd∼2.7x10-3 (μB/Fe atom)-2 for the parent compound. The changes in the volume magnetostriction, the magnetovolume coupling constant, and the magnetocaloric properties are strongly correlated with composition. The relative effects of the variation in cell parameters and electron concentration on the magnetostriction, TC, and the magnetocaloric properties are discussed.
Large reversible caloric effect in FeRh thin films via a dual-stimulus multicaloric cycle
Liu, Yang; Phillips, Lee C; Mattana, Richard; Bibes, Manuel; Barthélémy, Agnès; Dkhil, Brahim
2016-01-01
Giant magnetocaloric materials are promising for solid-state refrigeration, as an alternative to hazardous gases used in conventional cooling devices. A giant magnetocaloric effect was discovered near room temperature in near-equiatomic FeRh alloys some years before the benchmark study in Gd5Si2Ge2 that launched the field. However, FeRh has attracted significantly less interest in cooling applications mainly due to irreversibility in magnetocaloric cycles associated with the large hysteresis ...
Anisotropic pressure and hyperons in neutron stars
Sulaksono, A
2014-01-01
We study the effects of anisotropic pressure on properties of the neutron stars with hyperons inside its core within the framework of extended relativistic mean field. It is found that the main effects of anisotropic pressure on neutron star matter is to increase the stiffness of the equation of state, which compensates for the softening of the EOS due to the hyperons. The maximum mass and redshift predictions of anisotropic neutron star with hyperonic core are quite compatible with the result of recent observational constraints if we use the parameter of anisotropic pressure model $h \\le 0.8$[1] and $\\Lambda \\le -1.15$ [2]. The radius of the corresponding neutron star at $M$=1.4 $M_\\odot$ is more than 13 km, while the effect of anisotropic pressure on the minimum mass of neutron star is insignificant. Furthermore, due to the anisotropic pressure in the neutron star, the maximum mass limit of higher than 2.1 $M_\\odot$ cannot rule out the presence of hyperons in the neutron star core.
Searching the conditions for a table-like shape of the magnetic entropy in magneto-caloric materials
Energy Technology Data Exchange (ETDEWEB)
Álvarez, Pablo, E-mail: pablo.alvarez@ehu.es [Departamento de Electricidad y Electrónica, Universidad del País Vasco (UPV/EHU), 48940 Leioa (Spain); Departamento de Física, Universidad de Oviedo, c/ Calvo Sotelo, s/n, 33007 Oviedo (Spain); Gorria, Pedro, E-mail: pgorria@uniovi.es [Departamento de Física, Universidad de Oviedo, c/ Calvo Sotelo, s/n, 33007 Oviedo (Spain); Sánchez Llamazares, José L. [División de Materiales Avanzados, Instituto Potosino de Investigación Científica y Tecnológica, Camino a la presa San José 2055, CP 78216 San Luis Potosí (Mexico); Blanco, Jesús A. [Departamento de Física, Universidad de Oviedo, c/ Calvo Sotelo, s/n, 33007 Oviedo (Spain)
2013-08-15
Highlights: •The magnetic entropy change for two-ribbon (amorphous) composite materials is investigated. •The conditions to obtain a table-like shape of the magnetic entropy change are specified. •We give the essential ingredients to maximize the effective refrigerant capacity and the efficiency. •Our findings could be used in other magneto-caloric materials to tune the temperature range for the table-like behavior. -- Abstract: We show a systematic study of the magneto-caloric response carried out on a series of FeZrB(Cu) amorphous ribbons with different Curie temperature values in the 210–320 K interval. The main aim of the work is to investigate the conditions to obtain, from the isothermal magnetic entropy change vs. temperature curves, ΔS{sub M}(T), a table-like behavior of the entropy using two-ribbon composites. Even though the maximum value of ΔS{sub M} for the composite is lower than those of the single components, the existence of a table-like behavior maximizes the effective refrigerant capacity, reaching values around 80 J/kg for an applied magnetic field change of 2 T. Furthermore, we discuss how the temperature range for such a table-like behavior can be tuned and the refrigerant capacity enhanced in terms of energy efficiency.
Magnetic and Magnetocaloric Exploration of Fe rich (Mn,Fe)2(P,Ge)
Leitao, J. V.; Haar, M. van der; Lefering, A.; Bruck, E.
2013-01-01
We explored the Fe rich side of the (Mn,Fe)2(P,Ge) magnetocaloric system. The transition temperature of this system is extremely easy to tune with careful manipulation of Fe and Ge content as well as stoichiometrical proportions, which gives rise to the real possibility of lowering the price of this compound and thus make it economically viable for practical magnetocaloric applications. Novel and unexpected magnetic properties observed in this system suggest an exciting potential for permanen...
Jeppesen, Claus; Flyvbjerg, Henrik; Ole G. Mouritsen
1989-01-01
Monte Carlo computer-simulation techniques are used to elucidate the equilibrium phase behavior as well as the late-stage ordering dynamics of some two-dimensional models with ground-state ordering of a high degeneracy, Q. The models are Q-state Potts models with anisotropic grain-boundary potential on triangular lattices—essentially clock models, except that the potential is not a cosine, but a sine function of the angle between neighboring grain orientations. For not too small Q, these mode...
The influence of quench atomic disorder on the magnetocaloric properties of Ni–Co–Mn–In alloys
International Nuclear Information System (INIS)
Highlights: • Large magnetic entropy change (ΔSm = 11 J/Kg K) at 1.5 Tesla above 300 K is obtained. • The peak value of ΔSm is higher in disordered system. • Refrigeration capacity (RC) is unaffected by the quenched atomic disorder. - Abstract: The magnetocaloric effect in Ni–Co–Mn–In alloys is studied at low magnetic field, across the first order magnetostructural transition. The Co doping at Ni site induces the large magnetic entropy change (ΔSm) above room temperature. The large ΔSm of 11 J/Kg K has been observed for disordered Ni1.81Co0.22Mn1.46In0.51 alloy at 337 K at an applied field of 1.5 Tesla. The influence of quench atomic disorder on the magnetocaloric properties of Ni–Co–Mn–In alloys has been studied. The atomic disorder significantly increases the peak value of ΔSm and decreases the peak width. The refrigeration capacity (RC) is almost unchanged with atomic disorder
Foronda, F R; Lang, F; Möller, J S; Lancaster, T; Boothroyd, A T; Pratt, F L; Giblin, S R; Prabhakaran, D; Blundell, S J
2015-01-01
Although muon spin relaxation is commonly used to probe local magnetic order, spin freezing, and spin dynamics, we identify an experimental situation in which the measured response is dominated by an effect resulting from the muon-induced local distortion rather than the intrinsic behavior of the host compound. We demonstrate this effect in some quantum spin ice candidate materials Pr(2)B(2)O(7) (B=Sn, Zr, Hf), where we detect a static distribution of magnetic moments that appears to grow on cooling. Using density functional theory we show how this effect can be explained via a hyperfine enhancement arising from a splitting of the non-Kramers doublet ground states on Pr ions close to the muon, which itself causes a highly anisotropic distortion field. We provide a quantitative relationship between this effect and the measured temperature dependence of the muon relaxation and discuss the relevance of these observations to muon experiments in other magnetic materials. PMID:25615502
Magnetocaloric properties of a frustrated Blume-Capel antiferromagnet
Directory of Open Access Journals (Sweden)
Žukovič Milan
2014-07-01
Full Text Available Low-temperature magnetization processes and magnetocaloric properties of a geometrically frustrated spin-1 Blume-Capel model on a triangular lattice are studied by Monte Carlo simulations. The model is found to display qualitatively different behavior depending on the sign of the single-ion anisotropy D. For positive values of D we observe two magnetization plateaus, similar to the spin-1/2 Ising antiferromagnet, and negative isothermal entropy changes for any field intensity. For a range of small negative values of D there are four magnetization plateaus and the entropy changes can be either negative or positive, depending on the field. If D is negative but large in absolute value then the entropy changes are solely positive.
Anisotropic Metamaterial Optical Fibers
Pratap, Dheeraj; Pollock, Justin G; Iyer, Ashwin K
2014-01-01
Internal physical structure can drastically modify the properties of waveguides: photonic crystal fibers are able to confine light inside a hollow air core by Bragg scattering from a periodic array of holes, while metamaterial loaded waveguides for microwaves can support propagation at frequencies well below cutoff. Anisotropic metamaterials assembled into cylindrically symmetric geometries constitute light-guiding structures that support new kinds of exotic modes. A microtube of anodized nanoporous alumina, with nanopores radially emanating from the inner wall to the outer surface, is a manifestation of such an anisotropic metamaterial optical fiber. The nanopores, when filled with a plasmonic metal such as silver or gold, greatly increase the electromagnetic anisotropy. The modal solutions in anisotropic circular waveguides can be uncommon Bessel functions with imaginary orders.
Costa, A. E. B.; Oliveira, L. E.; Cavalcanti, S. B.
2015-11-01
The transmission properties of electromagnetic waves through a one-dimensional layered system containing alternate layers of air and a uniaxial anisotropic left-handed material are investigated. The optical axis of such heterostructure is along the stacking direction and the components of the electric permittivity and magnetic permeability tensors that characterize the metamaterial are modeled by a Drude-type response and a split-ring resonator metamaterial response, respectively. Different plasmon frequencies are considered for directions parallel and perpendicular to the optical axis. For oblique incidence, longitudinal bulk-like plasmon polariton modes are found in the neighborhood of the plasmon frequency along the optical axis and anisotropy leads to the unfolding of nearly dispersionless plasmon-polariton bands either above or below the plasmon frequency. Moreover, it is shown that, even in the presence of loss/absorption, these plasmon polariton modes do survive and, therefore, should be experimentally detected.
Hwu, Chyanbin
2010-01-01
As structural elements, anisotropic elastic plates find wide applications in modern technology. The plates here are considered to be subjected to not only in plane load but also transverse load. In other words, both plane and plate bending problems as well as the stretching-bending coupling problems are all explained in this book. In addition to the introduction of the theory of anisotropic elasticity, several important subjects have are discussed in this book such as interfaces, cracks, holes, inclusions, contact problems, piezoelectric materials, thermoelastic problems and boundary element a
Pérez-Nadal, Guillem
2016-01-01
We consider a non-relativistic free scalar field theory with a type of anisotropic scale invariance in which the number of coordinates "scaling like time" is generically greater than one. We propose the Cartesian product of two curved spaces, with the metric of each space parameterized by the other space, as a notion of curved background to which the theory can be extended. We study this type of geometries, and find a family of extensions of the theory to curved backgrounds in which the anisotropic scale invariance is promoted to a local, Weyl-type symmetry.
Enhancement of non-resonant dielectric cloaks using anisotropic composites
Takezawa, Akihiro
2014-01-01
The effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, they can be efficiently designed by handling the physical properties of anisotropic materials directly. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 10% compared with existing multilayer cloaking by isotropic materials in eight-layer cylindrical cloaking materials. The same performance with eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using anisotropic materials. Cloaking with a about 50% reduct...
Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Liu, Yao; Wu, Rong-Rong; Zhang, Xi-Xiang; Sun, Ji-Rong; Shen, Bao-Gen
2015-04-01
Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.
Zhao, Ying-Ying
2015-04-24
Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.
Indian Academy of Sciences (India)
B B Bhowmik; A Rajput
2004-06-01
Anisotropic Bianchi Type-I cosmological models have been studied on the basis of Lyra's geometry. Two types of models, one with constant deceleration parameter and the other with variable deceleration parameter have been derived by considering a time-dependent displacement field.
Anisotropic Ambient Volume Shading.
Ament, Marco; Dachsbacher, Carsten
2016-01-01
We present a novel method to compute anisotropic shading for direct volume rendering to improve the perception of the orientation and shape of surface-like structures. We determine the scale-aware anisotropy of a shading point by analyzing its ambient region. We sample adjacent points with similar scalar values to perform a principal component analysis by computing the eigenvectors and eigenvalues of the covariance matrix. In particular, we estimate the tangent directions, which serve as the tangent frame for anisotropic bidirectional reflectance distribution functions. Moreover, we exploit the ratio of the eigenvalues to measure the magnitude of the anisotropy at each shading point. Altogether, this allows us to model a data-driven, smooth transition from isotropic to strongly anisotropic volume shading. In this way, the shape of volumetric features can be enhanced significantly by aligning specular highlights along the principal direction of anisotropy. Our algorithm is independent of the transfer function, which allows us to compute all shading parameters once and store them with the data set. We integrated our method in a GPU-based volume renderer, which offers interactive control of the transfer function, light source positions, and viewpoint. Our results demonstrate the benefit of anisotropic shading for visualization to achieve data-driven local illumination for improved perception compared to isotropic shading. PMID:26529745
Dynamics of Anisotropic Universes
Pérez, J
2006-01-01
We present a general study of the dynamical properties of Anisotropic Bianchi Universes in the context of Einstein General Relativity. Integrability results using Kovalevskaya exponents are reported and connected to general knowledge about Bianchi dynamics. Finally, dynamics toward singularity in Bianchi type VIII and IX universes are showed to be equivalent in some precise sence.
International Nuclear Information System (INIS)
We have studied the anisotropic three-dimensional nearest-neighbor Ising model with competitive interactions in an uniform longitudinal magnetic field H. The model consists of ferromagnetic interactions Jz=λ2Jx in the x(z) direction and antiferromagnetic interactions Jy=λ1Jx in the y direction (Ising superantiferromagnet). For the particular case λ1=λ2=1 we obtain the phase diagram in the H−T plane, using the framework of the differential operator technique in the effective-field theory with finite cluster of N=4 spins (EFT-4). It was observed first- and second-order transitions in the low and high temperature limits, respectively, with the presence of a tricritical point and a reentrant behavior is observed at low temperature. The critical curve in the classical approach is also obtained and the results are compared
Bouncing Anisotropic Universes with Varying Constants
Barrow, John D
2013-01-01
We examine the evolution of a closed, homogeneous and anisotropic cosmology subject to a variation of the fine structure 'constant', \\alpha, within the context of the theory introduced by Bekenstein, Sandvik, Barrow and Magueijo, which generalises Maxwell's equations and general relativity. The variation of \\alpha permits an effective ghost scalar field, whose negative energy density becomes dominant at small length scales, leading to a bouncing cosmology. A thermodynamically motivated coupling which describes energy exchange between the effective ghost field and the radiation field leads to an expanding, isotropizing sequence of bounces. In the absence of entropy production we also find solutions with stable anisotropic oscillations around a static universe.
Anisotropic inflation in the Finsler spacetime
International Nuclear Information System (INIS)
We suggest the universe is Finslerian in the stage of inflation. The Finslerian background spacetime breaks rotational symmetry and induces parity violation. The primordial power spectrum is given for the quantum fluctuation of the inflation field. It depends not only on the magnitude of the wavenumber but also on the preferred direction. We derive the gravitational field equations in the perturbed Finslerian background spacetime, and we obtain a conserved quantity outside the Hubble horizon. The angular correlation coefficients are presented in our anisotropic inflation model. The parity violation feature of Finslerian background spacetime requires that the anisotropic effect only appears in the angular correlation coefficients if l' = l + 1. The numerical results of the angular correlation coefficients are given describing the anisotropic effect. (orig.)
Anisotropic inflation in the Finsler spacetime
Energy Technology Data Exchange (ETDEWEB)
Li, Xin [Chongqing University, Department of Physics, Chongqing (China); Institute of Theoretical Physics, Chinese Academy of Sciences, State Key Laboratory of Theoretical Physics, Beijing (China); Wang, Sai [Institute of Theoretical Physics, Chinese Academy of Sciences, State Key Laboratory of Theoretical Physics, Beijing (China); Chang, Zhe [Institute of Theoretical Physics, Chinese Academy of Sciences, State Key Laboratory of Theoretical Physics, Beijing (China); Institute of High Energy Physics, Chinese Academy of Sciences, Beijing (China)
2015-06-15
We suggest the universe is Finslerian in the stage of inflation. The Finslerian background spacetime breaks rotational symmetry and induces parity violation. The primordial power spectrum is given for the quantum fluctuation of the inflation field. It depends not only on the magnitude of the wavenumber but also on the preferred direction. We derive the gravitational field equations in the perturbed Finslerian background spacetime, and we obtain a conserved quantity outside the Hubble horizon. The angular correlation coefficients are presented in our anisotropic inflation model. The parity violation feature of Finslerian background spacetime requires that the anisotropic effect only appears in the angular correlation coefficients if l' = l + 1. The numerical results of the angular correlation coefficients are given describing the anisotropic effect. (orig.)
International Nuclear Information System (INIS)
Dynamic anisotropic elastic constants of CANDU Zr-2.5Nb pressure tube materials were determined by high temperature resonant ultrasound spectroscopy (RUS). The resonance frequencies were measured using a couple of alumina waveguides and wide-band ultrasonic transducers in a small furnace. The rectangular parallelepiped specimens were fabricated along with the longitudinal, radial and transverse direction of the pressure tube. The initial estimates for RUS were obtained from the orientation distribution function by X-ray pole figure and elastic stiffness of single crystal zirconium. A nine elastic stiffness tensor for orthotropic symmetry was determined in the range of room temperature ∼500 deg. C. As the temperature increases, the elastic constant tensor, cij gradually decreases. Higher elastic constants along the transverse direction compared to those along the longitudinal or radial direction are similar to the case of Young's modulus or shear modulus. A crossing of elastic constants along the longitudinal direction and radial direction was observed near 120-150 deg. C. This fact could correlate to the crossing characteristics of c44 and c66 of a zirconium single crystal in the temperature range
Modeling and Measurements of CMUTs with Square Anisotropic Plates
DEFF Research Database (Denmark)
la Cour, Mette Funding; Christiansen, Thomas Lehrmann; Dahl-Petersen, Christian;
2013-01-01
The conventional method of modeling CMUTs use the isotropic plate equation to calculate the deflection, leading to deviations from FEM simulations including anisotropic effects of around 10% in center deflection. In this paper, the deflection is found for square plates using the full anisotropic ...
Magnetic, transport, and magnetocaloric properties of boron doped Ni-Mn-In alloys
Energy Technology Data Exchange (ETDEWEB)
Pandey, S.; Quetz, A.; Aryal, A.; Dubenko, I.; Ali, N. [Department of Physics, Southern Illinois University, Carbondale, Illinois 62902 (United States); Rodionov, I. D.; Blinov, M. I.; Titov, I. S.; Prudnikov, V. N.; Granovsky, A. B. [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Stadler, S. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803 (United States)
2015-05-14
The impact of B substitution in Ni{sub 50}Mn{sub 35}In{sub 15−x}B{sub x} Heusler alloys on the structural, magnetic, transport, and parameters of the magnetocaloric effect (MCE) has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (H) up to 5 T, and in the temperature interval 5–400 K). Direct adiabatic temperature change (ΔT{sub AD}) measurements have been carried out for an applied magnetic field change of 1.8 T. The transition temperatures (T-x) phase diagram has been constructed for H = 0.005 T. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni{sub 50}Mn{sub 34.8}In{sub 14.2}B and Ni{sub 50}Mn{sub 35}In{sub 14}X (X=In, Al, and Ge) Heusler alloys. The maximum absolute value of ΔT{sub AD} = 2.5 K was observed at the magnetostructural transition for Ni{sub 50}Mn{sub 35}In{sub 14.5}B{sub 0.5}.
The influence of gallium on the magnetocaloric properties of Gd5Si2Ge2
International Nuclear Information System (INIS)
Gd5Si2Ge2 was alloyed with varying amounts of Ga to study its influence on the giant magnetocaloric effect. Investigations on Gd5(Si2-xGe2-x)Ga2x with 2x = 0.03, 0.05 and 0.13 were carried out using X-ray powder diffraction, temperature and magnetic field dependent magnetization measurements, and differential scanning calorimetry. We observe that as the Ga content increases, the temperature stability range of the monoclinic phase narrows, and the orthorhombic structure gains stability. This is expected to be related to the decrease in the (Si/Ge)-(Si/Ge) bond distance in the monoclinic phase. The maximum entropy change for the parent compound at 270 K was found to be 9.8 J kg-1 K-1 in an applied field of 5 T. For 2x = 0.03, this value reduces to 8.5 J kg-1 K-1, and the temperature corresponding to the maximum entropy change shifts marginally to 278 K. For other 2x values, the maximum entropy change further decreases
Anisotropic progressive photon mapping
Liu, XiaoDan; Zheng, ChangWen
2014-01-01
Progressive photon mapping solves the memory limitation problem of traditional photon mapping. It gives the correct radiance with a large passes, but it converges slowly. We propose an anisotropic progressive photon mapping method to generate high quality images with a few passes. During the rendering process, different from standard progressive photon mapping, we store the photons on the surfaces. At the end of each pass, an anisotropic method is employed to compute the radiance of each eye ray based on the stored photons. Before move to a new pass, the photons in the scene are cleared. The experiments show that our method generates better results than the standard progressive photon mapping in both numerical and visual qualities.
Quasiparticle anisotropic hydrodynamics for central collisions
Alqahtani, Mubarak; Strickland, Michael
2016-01-01
We use quasiparticle anisotropic hydrodynamics to study an azimuthally-symmetric boost-invariant quark-gluon plasma including the effects of both shear and bulk viscosities. In quasiparticle anisotropic hydrodynamics, a single finite-temperature quasiparticle mass is introduced and fit to the lattice data in order to implement a realistic equation of state. We compare results obtained using the quasiparticle method with the standard method of imposing the equation of state in anisotropic hydrodynamics and viscous hydrodynamics. Using these three methods, we extract the primordial particle spectra, total number of charged particles, and average transverse momentum for various values of the shear viscosity to entropy density ratio eta/s. We find that the three methods agree well for small shear viscosity to entropy density ratio, eta/s, but differ at large eta/s. We find, in particular, that when using standard viscous hydrodynamics, the bulk-viscous correction can drive the primordial particle spectra negative...
CAVITATION BIFURCATION FOR COMPRESSIBLE ANISOTROPIC HYPERELASTIC MATERIALS
Institute of Scientific and Technical Information of China (English)
ChengChangjun; RenJiusheng
2004-01-01
The effect of material anisotropy on the bifurcation for void tormation in anisotropic compressible hyperelastic materials is examined. Numerical solutions are obtained in an anisotropic sphere, whose material is transversely isotropic in the radial direction. It is shown that the bifurcation may occur either to the right or to the left, depending on the degree of material anisotropy. The deformation and stress contribution in the sphere before cavitation are different from those after cavitation. The stability of solutions is discussed through a comparison of energy.
Magnetic and magnetocaloric exploration of Fe rich (Mn,Fe)2(P,Ge)
Leitão, J. V.; van der Haar, M.; Lefering, A.; Brück, E.
2013-10-01
We explored the Fe rich side of the (Mn,Fe)2(P,Ge) magnetocaloric system. The transition temperature of this system is extremely easy to tune with careful manipulation of Fe and Ge content as well as stoichiometrical proportions, which give rise to the real possibility of lowering the price of this compound and thus make it economically viable for practical magnetocaloric applications. Novel and unexpected magnetic properties observed in this system suggest an exciting potential for permanent magnet application in a limited concentration range.
Magnetic and magnetocaloric properties of Cu1−xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites
International Nuclear Information System (INIS)
The effect of Zn substitution on the magnetic and magnetocaloric properties of Cu1−xZnxFe2O4 (x=0.6, 0.7, 0.8) ferrites over a wide temperature range has been investigated. The polycrystalline samples were synthesized using the solid-state reaction at sintering temperature 1050 °C (1323 K) for 2 h and has been characterized by SQUID magnetometry. Magnetization versus temperature showed that all samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature Tc is found to decrease from 373 K for x=0.6 to 140 K for x=0.8 as well as the saturation magnetization Ms which shifts from 100 to 44 emu/gm. The magnetocaloric effect was obtained by measuring a family of M–H curves at set temperature intervals and calculating the entropy change, ΔS for this system using the Maxwell relation. The ΔS of all samples increased with increasing applied field and showed a maximum around their respective Tc. The entropy change (ΔS) decreased with increasing Zn content, whereas the relative cooling power (RCP) slightly increased. The large RCP and ΔS found in Zn substitution Cu–Zn ferrites will be interesting for magnetic refrigeration near room temperature. - Highlights: • Double sintering ceramic technique is used in preparation of samples. • SQUID magnetometry is used to measure magnetic and magnetocaloric properties. • Samples shows a paramagnetic to ferromagnetic transition with decreasing temperature. • The magnetic entropy change (ΔS) shows a maximum around their respective Tc
International Nuclear Information System (INIS)
We report herein on a new route to synthesize La0.7Ca0.11Sr0.19MnO3 perovskite crystalline nanoparticles by using microwave radiation under argon atmosphere in a nonaqueous solvent of benzyl alcohol. It was found that the product shows a large magneto-caloric effect at room temperature. The structure, magnetic properties, and magneto-caloric effect have been investigated. X-ray diffraction and electron diffraction revealed that the products are of a pure single-phase rhombohedral structure. Transmission electron microscopy measurements showed that the particle sizes are in the range of 15–35 nm when the as-prepared material precursor was annealed to 700 °C for 4 h, and 30–40 nm when the calcinated temperature is increased to 900 °C. The Curie temperature of the compound was determined by thermo-magnetic measurements and the magneto-caloric effect was studied in terms of isothermal magnetic entropy change (ΔSm). These results suggest that the material may be a suitable candidate as a working substance in magnetic refrigeration near room temperature. -- Highlights: ► La0.7Ca0.11Sr0.19MnO3 nanocrystals were synthesized by a simple one-step MW radiation process. ► The MW synthesis is completed in 5 min. ► La0.7Ca0.11Sr0.19MnO3 nanoparticles were prepared by using benzyl alcohol as a solvent. ► La0.7Ca0.11Sr0.19MnO3 nanoparticles show a large magneto-caloric effect at room temperature
Directory of Open Access Journals (Sweden)
M. S. Tiwari
2007-03-01
Full Text Available The effect of upgoing ion beam and temperature anisotropy on the dispersion relation, growth rate, parallel and perpendicular resonant energies, and marginal instability of the electromagnetic ion cyclotron (EMIC waves, with general loss-cone distribution function, in a low β homogeneous plasma, is discussed by investigating the trajectories of the charged particles. The whole plasma is considered to consist of resonant and non-resonant particles. The resonant particles participate in an energy exchange with the waves, whereas the non-resonant particles support the oscillatory motion of the waves. The effects of the steepness of the loss-cone distribution, ion beam velocity, with thermal anisotropy on resonant energy transferred, and the growth rate of the EMIC waves are discussed. It is found that the effect of the upgoing ion beam is to reduce the energy of transversely heated ions, whereas the thermal anisotropy acts as a source of free energy for the EMIC waves and enhances the growth rate. It is found that the EMIC wave emissions occur by extracting energy of perpendicularly heated ions in the presence of an upflowing ion beam and a steep loss-cone distribution function in the anisotropic magnetoplasma. The effect of the steepness of the loss-cone is also to enhance the growth rate of the EMIC waves. The results are interpreted for EMIC emissions in the auroral acceleration region.
Electromagnetism on anisotropic fractal media
Ostoja-Starzewski, Martin
2013-04-01
Basic equations of electromagnetic fields in anisotropic fractal media are obtained using a dimensional regularization approach. First, a formulation based on product measures is shown to satisfy the four basic identities of the vector calculus. This allows a generalization of the Green-Gauss and Stokes theorems as well as the charge conservation equation on anisotropic fractals. Then, pursuing the conceptual approach, we derive the Faraday and Ampère laws for such fractal media, which, along with two auxiliary null-divergence conditions, effectively give the modified Maxwell equations. Proceeding on a separate track, we employ a variational principle for electromagnetic fields, appropriately adapted to fractal media, so as to independently derive the same forms of these two laws. It is next found that the parabolic (for a conducting medium) and the hyperbolic (for a dielectric medium) equations involve modified gradient operators, while the Poynting vector has the same form as in the non-fractal case. Finally, Maxwell's electromagnetic stress tensor is reformulated for fractal systems. In all the cases, the derived equations for fractal media depend explicitly on fractal dimensions in three different directions and reduce to conventional forms for continuous media with Euclidean geometries upon setting these each of dimensions equal to unity.
Nucleation in suspensions of anisotropic colloids
Schilling, T.; Frenkel, D.
2005-01-01
We report Monte Carlo studies of liquid crystal nucleation in two types of anisotropic colloidal systems: hard rods and hard ellipsoids. In both cases we find that nucleation pathways differ strongly from the pathways in systems of spherical particles. Short hard rods show an effect of self-poisonin
Spin Wave Theory of Strongly Anisotropic Magnets
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1977-01-01
A strong anisotropy gives rise to a non-spherical precession of the spins with different amplitudes in the x and y directions. The highly anharmonic exchange interaction thereby becomes effectively anisotropic. The possibility of detecting a genuine two-ion anisotropy is discussed, and comments are...
Directory of Open Access Journals (Sweden)
Xi-Nian Zuo
Full Text Available Neuroimaging community usually employs spatial smoothing to denoise magnetic resonance imaging (MRI data, e.g., Gaussian smoothing kernels. Such an isotropic diffusion (ISD based smoothing is widely adopted for denoising purpose due to its easy implementation and efficient computation. Beyond these advantages, Gaussian smoothing kernels tend to blur the edges, curvature and texture of images. Researchers have proposed anisotropic diffusion (ASD and non-local diffusion (NLD kernels. We recently demonstrated the effect of these new filtering paradigms on preprocessing real degraded MRI images from three individual subjects. Here, to further systematically investigate the effects at a group level, we collected both structural and functional MRI data from 23 participants. We first evaluated the three smoothing strategies' impact on brain extraction, segmentation and registration. Finally, we investigated how they affect subsequent mapping of default network based on resting-state functional MRI (R-fMRI data. Our findings suggest that NLD-based spatial smoothing maybe more effective and reliable at improving the quality of both MRI data preprocessing and default network mapping. We thus recommend NLD may become a promising method of smoothing structural MRI images of R-fMRI pipeline.
International Nuclear Information System (INIS)
Ballistic transport characteristics of metal-oxide semiconductor field effect transistors (MOSFETs) based on anisotropic two-dimensional materials monolayer HfS2 and phosphorene are explored through quantum transport simulations. We focus on the effects of the channel crystal orientation and the channel length scaling on device performances. Especially, the role of degenerate conduction band (CB) valleys in monolayer HfS2 is comprehensively analyzed. Benchmarking monolayer HfS2 with phosphorene MOSFETs, we predict that the effect of channel orientation on device performances is much weaker in monolayer HfS2 than in phosphorene due to the degenerate CB valleys of monolayer HfS2. Our simulations also reveal that at 10 nm channel length scale, phosphorene MOSFETs outperform monolayer HfS2 MOSFETs in terms of the on-state current. However, it is observed that monolayer HfS2 MOSFETs may offer comparable, but a little bit degraded, device performances as compared with phosphorene MOSFETs at 5 nm channel length
Zhang, Hai-Feng; Liu, Shao-Bin; Ding, Guo-Wen
2014-10-01
In this paper, the magneto-optical Voigt effects in surface plasmon modes and anisotropic photonic band gaps (PBGs) of the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with face-centered-cubic lattices are theoretically investigated based on the modified plane wave expansion (PWE) method, which are the homogeneous Te (tellurium) spheres immersed in the homogeneous magnetized plasma background, as the mixed polarized modes are considered. The more general condition is considered, and the anisotropic PBGs are not only for the extraordinary and ordinary modes but also for mixed polarized modes. The equations for computing such anisotropic PBGs are theoretically deduced. Theoretical simulations show that the anisotropic PBGs and a flatbands region can be observed in the dispersive curve. Compared to the similar 3D MPPCs containing the isotropic dielectric or uniaxial material spheres, the larger PBGs can be obtained as the extraordinary axis of the inserted uniaxial material is along the Г-H symmetry line although the region of flatbands is also different. However, the relative bandwidths of PBGs for such two cases are almost the same. The interesting properties of surface plasmon modes can also be found, which are that the upper edge of flatbands region cannot be tuned by the filling factor but can almost linearly increase on increasing the plasma frequency and plasma cyclotron frequency (the external magnetic field), respectively. The effects of the filling factor, plasma frequency and plasma cyclotron frequency on the anisotropic PBGs are investigated in detail, respectively. Theoretical calculations also show that such PBGs can be manipulated by the parameters as mentioned above.
Anisotropic Diffusion in Mesh-Free Numerical Magnetohydrodynamics
Hopkins, Philip F
2016-01-01
We extend recently-developed mesh-free Lagrangian methods for numerical magnetohydrodynamics (MHD) to arbitrary anisotropic diffusion equations, including: passive scalar diffusion, Spitzer-Braginskii conduction and viscosity, cosmic ray diffusion/streaming, anisotropic radiation transport, non-ideal MHD (Ohmic resistivity, ambipolar diffusion, the Hall effect), and turbulent 'eddy diffusion.' We study these as implemented in the code GIZMO for both new meshless finite-volume Godunov schemes (MFM/MFV) as well as smoothed-particle hydrodynamics (SPH). We show the MFM/MFV methods are accurate and stable even with noisy fields and irregular particle arrangements, and recover the correct behavior even in arbitrarily anisotropic cases. They are competitive with state-of-the-art AMR/moving-mesh methods, and can correctly treat anisotropic diffusion-driven instabilities (e.g. the MTI and HBI, Hall MRI). We also develop a new scheme for stabilizing anisotropic tensor-valued fluxes with high-order gradient estimators ...
On the Relativistic anisotropic configurations
Shojai, F; Stepanian, A
2016-01-01
In this paper we study anisotropic spherical polytropes within the framework of general relativity. Using the anisotropic Tolman-Oppenheimer-Volkov (TOV) equations, we explore the relativistic anisotropic Lane-Emden equations. We find how the anisotropic pressure affects the boundary conditions of these equations. Also we argue that the behaviour of physical quantities near the center of star changes in the presence of anisotropy. For constant density, a class of exact solution is derived with the aid of a new ansatz and its physical properties are discussed.
Relaxation of Anisotropic Glasses
DEFF Research Database (Denmark)
Deubener, Joachim; Martin, Birgit; Wondraczek, Lothar; Yue, Yuanzheng
2004-01-01
Anisotropic glasses are obtained from uniaxial compressing and pulling of glass forming liquids above the transition temperature range. To freeze-in, at least partly the structural state of the flowing melt, cylindrical samples were subjected to a controlled cooling process under constant load...... differential scanning calorimetry (DSC) and dilatometry. The energy release and expansion-shrinkage behaviour of the glasses are investigated as a function of the applied deformation stress. Structural origins of the frozen-in birefringence induced by viscous flow are discussed and correlation between the...
Anisotropically Inflating Universes
Barrow, J D; Barrow, John D.; Hervik, Sigbjorn
2008-01-01
We show that in theories of gravity that add quadratic curvature invariants to the Einstein-Hilbert action there exist expanding vacuum cosmologies with positive cosmological constant which do not approach the de Sitter universe. Exact solutions are found which inflate anisotropically. This behaviour is driven by the Ricci curvature invariant and has no counterpart in the general relativistic limit. These examples show that the cosmic no-hair theorem does not hold in these higher-order extensions of general relativity and raises new questions about the ubiquity of inflation in the very early universe and the thermodynamics of gravitational fields.
Preparing Magnetocaloric LaFeSi Uniform Microstructures by Spark Plasma Sintering
DEFF Research Database (Denmark)
Vicente, N.; Ocanã, J.; Neves Bez, Henrique;
2014-01-01
Spark Plasma Sintering (SPS) of LaFeSi alloy powders was conducted to prepare magnetocaloric La-Fe-Si-based uniform microstructures. Two electrically insulating discs made of alumina were interposed between the punches and powder sample inhibiting the flow of electric current across the powder...
International Nuclear Information System (INIS)
To investigate systematic changes in dose arising when treatment plans optimised using the Anisotropic Analytical Algorithm (AAA) are recalculated using Acuros XB (AXB) in patients treated with definitive chemoradiotherapy (dCRT) for locally advanced oesophageal cancers. We have compared treatment plans created using AAA with those recalculated using AXB. Although the Anisotropic Analytical Algorithm (AAA) is currently more widely used in clinical routine, Acuros XB (AXB) has been shown to more accurately calculate the dose distribution, particularly in heterogeneous regions. Studies to predict clinical outcome should be based on modelling the dose delivered to the patient as accurately as possible. CT datasets from ten patients were selected for this retrospective study. VMAT (Volumetric modulated arc therapy) plans with 2 arcs, collimator rotation ± 5-10° and dose prescription 50 Gy / 25 fractions were created using Varian Eclipse (v10.0). The initial dose calculation was performed with AAA, and AXB plans were created by re-calculating the dose distribution using the same number of monitor units (MU) and multileaf collimator (MLC) files as the original plan. The difference in calculated dose to organs at risk (OAR) was compared using dose-volume histogram (DVH) statistics and p values were calculated using the Wilcoxon signed rank test. The potential clinical effect of dosimetric differences in the gross tumour volume (GTV) was evaluated using three different TCP models from the literature. PTV Median dose was apparently 0.9 Gy lower (range: 0.5 Gy - 1.3 Gy; p < 0.05) for VMAT AAA plans re-calculated with AXB and GTV mean dose was reduced by on average 1.0 Gy (0.3 Gy −1.5 Gy; p < 0.05). An apparent difference in TCP of between 1.2% and 3.1% was found depending on the choice of TCP model. OAR mean dose was lower in the AXB recalculated plan than the AAA plan (on average, dose reduction: lung 1.7%, heart 2.4%). Similar trends were seen for CRT plans
Optics of anisotropic nanostructures
Rokushima, Katsu; Antoš, Roman; Mistrík, Jan; Višňovský, Štefan; Yamaguchi, Tomuo
2006-07-01
The analytical formalism of Rokushima and Yamakita [J. Opt. Soc. Am. 73, 901-908 (1983)] treating the Fraunhofer diffraction in planar multilayered anisotropic gratings proved to be a useful introduction to new fundamental and practical situations encountered in laterally structured periodic (both isotropic and anisotropic) multilayer media. These are employed in the spectroscopic ellipsometry for modeling surface roughness and in-depth profiles, as well as in the design of various frequency-selective elements including photonic crystals. The subject forms the basis for the solution of inverse problems in scatterometry of periodic nanostructures including magnetic and magneto-optic recording media. It has no principal limitations as for the frequencies and period to radiation wavelength ratios and may include matter wave diffraction. The aim of the paper is to make this formalism easily accessible to a broader community of students and non-specialists. Many aspects of traditional electromagnetic optics are covered as special cases from a modern and more general point of view, e.g., plane wave propagation in isotropic media, reflection and refraction at interfaces, Fabry-Perot resonator, optics of thin films and multilayers, slab dielectric waveguides, crystal optics, acousto-, electro-, and magneto-optics, diffraction gratings, etc. The formalism is illustrated on a model simulating the diffraction on a ferromagnetic wire grating.
Energy Technology Data Exchange (ETDEWEB)
Ricardo de Sousa, J. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000 Manaus, AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Neto, Minos A., E-mail: minos@pq.cnpq.br [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Padilha, Igor T.; Salmon, Octavio D.R.; Viana, J. Roberto [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000 Manaus, AM (Brazil)
2013-12-15
We have studied the anisotropic three-dimensional nearest-neighbor Ising model with competitive interactions in an uniform longitudinal magnetic field H. The model consists of ferromagnetic interactions J{sub z}=λ{sub 2}J{sub x} in the x(z) direction and antiferromagnetic interactions J{sub y}=λ{sub 1}J{sub x} in the y direction (Ising superantiferromagnet). For the particular case λ{sub 1}=λ{sub 2}=1 we obtain the phase diagram in the H−T plane, using the framework of the differential operator technique in the effective-field theory with finite cluster of N=4 spins (EFT-4). It was observed first- and second-order transitions in the low and high temperature limits, respectively, with the presence of a tricritical point and a reentrant behavior is observed at low temperature. The critical curve in the classical approach is also obtained and the results are compared.
Energy Technology Data Exchange (ETDEWEB)
Kim, Sang Joon; Choi, Choong Gon; Kim, Jeong Kon [Dept. of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Yun, Sung Cheol [Dept. of Biostatistics, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Jeong, Ha Kyu [Dept. of Radiology, East-West Neomedical Center, Kyung Hee University College of Medicine, Seoul (Korea, Republic of); Kim, Eun Ju [Clinical Scientist, MR, Philips Healthcare, Seoul (Korea, Republic of)
2015-04-15
To validate the usefulness of a diffusional anisotropic capillary array phantom and to investigate the effects of diffusion tensor imaging (DTI) parameter changes on diffusion fractional anisotropy (FA) and apparent diffusion coefficient (ADC) using the phantom. Diffusion tensor imaging of a capillary array phantom was performed with imaging parameter changes, including voxel size, number of sensitivity encoding (SENSE) factor, echo time (TE), number of signal acquisitions, b-value, and number of diffusion gradient directions (NDGD), one-at-a-time in a stepwise-incremental fashion. We repeated the entire series of DTI scans thrice. The coefficients of variation (CoV) were evaluated for FA and ADC, and the correlation between each MR imaging parameter and the corresponding FA and ADC was evaluated using Spearman's correlation analysis. The capillary array phantom CoVs of FA and ADC were 7.1% and 2.4%, respectively. There were significant correlations between FA and SENSE factor, TE, b-value, and NDGD, as well as significant correlations between ADC and SENSE factor, TE, and b-value. A capillary array phantom enables repeated measurements of FA and ADC. Both FA and ADC can vary when certain parameters are changed during diffusion experiments. We suggest that the capillary array phantom can be used for quality control in longitudinal or multicenter clinical studies.
International Nuclear Information System (INIS)
To validate the usefulness of a diffusional anisotropic capillary array phantom and to investigate the effects of diffusion tensor imaging (DTI) parameter changes on diffusion fractional anisotropy (FA) and apparent diffusion coefficient (ADC) using the phantom. Diffusion tensor imaging of a capillary array phantom was performed with imaging parameter changes, including voxel size, number of sensitivity encoding (SENSE) factor, echo time (TE), number of signal acquisitions, b-value, and number of diffusion gradient directions (NDGD), one-at-a-time in a stepwise-incremental fashion. We repeated the entire series of DTI scans thrice. The coefficients of variation (CoV) were evaluated for FA and ADC, and the correlation between each MR imaging parameter and the corresponding FA and ADC was evaluated using Spearman's correlation analysis. The capillary array phantom CoVs of FA and ADC were 7.1% and 2.4%, respectively. There were significant correlations between FA and SENSE factor, TE, b-value, and NDGD, as well as significant correlations between ADC and SENSE factor, TE, and b-value. A capillary array phantom enables repeated measurements of FA and ADC. Both FA and ADC can vary when certain parameters are changed during diffusion experiments. We suggest that the capillary array phantom can be used for quality control in longitudinal or multicenter clinical studies.
Anisotropic spheres in general relativity
International Nuclear Information System (INIS)
A prescription originally conceived for perfect fluids is extended to the case of anisotropic pressures. The method is used to obtain exact analytical solutions of the Einstein equations for spherically symmetric selfgravitating distribution of anisotropic matter. The solutions are matched to the Schwarzschild exterior metric. (author). 15 refs
A 57Fe Mössbauer study of magnetocaloric Fe doped MnCoGe
International Nuclear Information System (INIS)
MnCoGe-based compounds are of interest with respect to the magnetocaloric effect due to a martensitic phase transition from the low-temperature orthorhombic phase to the high-temperature hexagonal phase. A key feature is that the transition temperature can be readily tuned to obtain a magneto-structural transition. Fe is an effective substitute for Mn or Co to stabilize the hexagonal phase at low temperature. Here we present initial 57Fe Mössbauer spectroscopy measurements on (Mn 0.96Fe 0.04)CoGe and Mn(Co 0.96Fe 0.04)Ge samples doped with 0.5 wt % 57Fe. The martensitic transition temperatures were determined to be 239 K and 304 K with transition full widths at half maximum of 44 K and 39 K respectively as determined from x-ray diffraction experiments over the temperature range 10–310 K. The magnetic properties were studied over the temperature range 5–300 K and a magneto-structural transition found in Mn(Co 0.96Fe 0.04)Ge. Analysis of the 20 K Mössbauer spectra reveals that the Fe atoms are distributed on both the Mn and Co sites and tend to prefer to occupy the Co site in both the (Mn 0.96Fe 0.04)CoGe and Mn(Co 0.96Fe 0.04)Ge samples. The hyperfine fields determined for Fe atoms on the Mn and Co sites at 20 K in the ferromagnetic orthorhombic phases are Bhf−Mn= 16.4(4) T and Bhf−Co= 21.1(4) T
Enhancement of non-resonant dielectric cloaks using anisotropic composites
International Nuclear Information System (INIS)
Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices
Enhancement of non-resonant dielectric cloaks using anisotropic composites
Energy Technology Data Exchange (ETDEWEB)
Takezawa, Akihiro, E-mail: akihiro@hiroshima-u.ac.jp; Kitamura, Mitsuru [Division of Mechanical Systems and Applied Mechanics, Institute of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima (Japan)
2014-01-15
Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices.
Enhancement of non-resonant dielectric cloaks using anisotropic composites
Directory of Open Access Journals (Sweden)
Akihiro Takezawa
2014-01-01
Full Text Available Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices.
Enhancement of non-resonant dielectric cloaks using anisotropic composites
Takezawa, Akihiro; Kitamura, Mitsuru
2014-01-01
Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices.
First-order phase transitions and giant magnetocaloric effect
Nguyen, T.T.
2010-01-01
Modern society relies on cooling technology for food safety, comfort and medical applications. The solid-state cooling technology known as magnetic refrigeration is one of the most promising techniques to replace the current vapor-compression cooling technology. To date, the search for suitable mate
Theoretical approach to the magnetocaloric effect with hysteresis
International Nuclear Information System (INIS)
In this paper a thermodynamic model with internal variables is presented and applied to ferromagnetic hysteresis. The out-of-equilibrium Gibbs free energy of a magnetic system is expressed as a function of the internal state of the Preisach model. Expressions for the system entropy and the entropy production are derived. By this approach it is possible to reproduce the characteristic features of the experimentally observed temperature changes (of the order of 10-4K around room temperature) induced by the magnetic field along the hysteresis loop performed in iron under adiabatic condition
Koshel', K. V.; Shishkarev, A. A.
1993-02-01
A perturbation theory for complex propagation constants is considered, based on the invariant imbedding method. This approach makes it possible to describe the effect of nonstratified fluctuations of the refractive index on transhorizon propagation of ultrashort waves in the framework of the adiabatic approximation in the case when an evaporation duct exists. Examples of calculations are presented, and characteristic stochastic effects are studied.
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Huang, Qingqing
2016-08-01
Rytov theory was employed to establish the transmission model for the optical vortices carried by Bessel-Gaussian (BG) beams in weak anisotropic turbulence based on the generalized anisotropic von Karman spectrum. The influences of asymmetry anisotropic turbulence eddies and source parameters on the signal orbital angular momentum (OAM) mode detection probability of partially coherent BG beams in anisotropic turbulence were discussed. Anisotropic characteristics of the turbulence could enhance the OAM mode transmission performance. The spatial partially coherence of the beam source would increase turbulent aberration's effect on the optical vortices. BG beams could dampen the influences of the turbulence because of their nondiffraction and self-healing characteristics. PMID:27505641
Bond diluted anisotropic quantum Heisenberg model
Akıncı, Ümit
2013-01-01
Effects of the bond dilution on the critical temperatures, phase diagrams and the magnetization behaviors of the isotropic and anisotropic quantum Heisenberg model have been investigated in detail. For the isotropic case, bond percolation threshold values have been determined for several numbers of two (2D) and three (3D) dimensional lattices. In order to investigate the effect of the anisotropy in the exchange interaction on the results obtained for the isotropic model, a detailed investigat...
Modelling anisotropic damage and permeability of mortar under dynamic loads
Chen, W.; MAUREL, O.; REESS, T.; MATALLAH, M.; FERRON, A.; C. La Borderie; G. Pijaudier-Cabot
2011-01-01
This paper deals with the development of a model for concrete subjected to dynamic loads. Shock waves are generated by Pulsed Arc Electro-hydraulic Discharges (PAED) in water and applied to mortar samples. A diphasic model (liquid water and vapour) is implemented in order to describe the electrical discharge and the propagation of shock waves in water. An anisotropic damage model is devised, which takes account of the strain rate effect and the crack closure effect. Coupling between anisotrop...
The Anisotropic Geometrodynamics For Cosmology
Siparov, Sergey V.
2009-05-01
The classical geometrodynamics (GRT) and its modern features based on the use of the Fridman-Robertson-Walker type metrics are still unable to explain several important issues of extragalactic observations like flat rotation curves of the spiral galaxies, Tully-Fisher law, globular clusters behavior in comparisson to that of the stars belonging to the galactic plane etc. The chalenging problem of the Universe expansion acceleration stemming from the supernovae observations demands the existence of the repulsion forces which brings one to the choice between the cosmological constant and some quintessence. The popular objects of discussion are now still dark (matter and energy), nevertheless, they are supposed to correspond to more than 95% of the Universe which seems to be far from satisfactory. According to the equivalence principle we can not experimentally distinguish between the inertial forces and the gravitational ones. Since there exist the inertial forces depending on velocity (Coriolis), it seems plausible to explore the velocity dependent gravitational forces. From the mathematical point of view it means that we should use the anisotropic metric. It immediately turns out that the expression for the Einstein-Hilbert action changes in a natural way - contrary to the cases of f(R)-theories, additional scalar fields, arbitrary MOND functions etc.. We use the linear approximation for the metric and derive the generalized geodesics and the equation for the gravity force that contains not only the Newton-Einstein term. The relation between the obtained results and those of Lense-Thirring approach are discussed. The resulting anisotropic geometrodynamics includes all the results of the GRT and is used to give the explanation to the problems mentioned above. One of the impressive consequences is the possibility to explain the observed Hubble red shift not by the Doppler effect as usually but by the gravitational red shift originating from the metric anisotropy.
Directory of Open Access Journals (Sweden)
R. Sekar
2013-05-01
Full Text Available Instability of themocovection in a multi-component fluid has wide range of applications in ionospheric, geothermal and industries. In this analysis, the effect of rotation and vertical anisotropy on Soret-driven thermoconvective instability in a ferrofluid has been studied. The fluid layer is assumed to be horizontal and is heated from below and salted from above. In momentum equation, the effect of both substantial derivatives and coriolis terms are considered. The resulting eigen value problem is solved using Brinkman model. A linear stability analysis is used for both stationary and oscillatory instabilities for different parameters for which normal mode technique is applied. The effect of rotation tends to stabilize the system and anisotropy and Soret effects tend to destabilize the system.
Anisotropic Cosmological Model with Variable G and Lambda
Tripathy, S K; Routray, T R
2015-01-01
Anisotropic Bianchi-III cosmological model is investigated with variable gravitational and cosmological constants in the framework of Einstein's general relativity. The shear scalar is considered to be proportional to the expansion scalar. The dynamics of the anisotropic universe with variable G and Lambda are discussed. Without assuming any specific forms for Lambda and the metric potentials, we have tried to extract the time variation of G and Lambda from the anisotropic model. The extracted G and Lambda are in conformity with the present day observation. Basing upon the observational limits, the behaviour and range of the effective equation of state parameter are discussed.
Magnetocaloric properties of rapidly solidified Dy{sub 3}Co alloy ribbons
Energy Technology Data Exchange (ETDEWEB)
Sánchez Llamazares, J. L., E-mail: jose.sanchez@ipicyt.edu.mx; Flores-Zúñiga, H.; Sánchez-Valdés, C. F. [Instituto Potosino de Investigación Científica y Tecnológica A.C., Camino a la Presa San José 2055 Col. Lomas 4" a, San Luis Potosí, S.L.P. 78216 (Mexico); Álvarez-Alonso, Pablo [Departamento de Electricidad y Electrónica, UPV/EHU, 48940 Leioa (Spain); Lara Rodríguez, G. A. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, México, D. F. 04510 (Mexico); Fernández-Gubieda, M. L. [Departamento de Electricidad y Electrónica, UPV/EHU, 48940 Leioa (Spain); BC Materials, Camino de Ibaizabal, Edificio 500, Planta 1, Parque Científico y Tecnológico de Zamudio, 48160 Derio (Spain)
2015-05-07
The magnetic and magnetocaloric (MC) properties of melt-spun ribbons of the Dy{sub 3}Co intermetallic compound were investigated. Samples were fabricated in an Ar environment using a homemade melt spinner system at a linear speed of the rotating copper wheel of 40 ms{sup −1}. X-ray diffraction analysis shows that ribbons crystallize into a single-phase with the Fe{sub 3}C-type orthorhombic crystal structure. The M(T) curve measured at 5 mT reveals the occurrence of a transition at 32 K from a first to a second antiferromagnetic (AFM) state and an AFM-to-paramagnetic transition at T{sub N} = 43 K. Furthermore, a metamagnetic transition is observed below T{sub N}, but the magnetization change ΔM is well below the one reported for bulk alloys. Below 12 K, large inverse MC effect and hysteresis losses are observed. This behavior is related to the metamagnetic transition. For a magnetic field change of 5 T (2 T) applied along the ribbon length, the produced ribbons show a peak value of the magnetic entropy change ΔS{sub M}{sup peak} of −6.5 (− 2.1) Jkg{sup −1}K{sup −1} occurring close to T{sub N} with a full-width at half-maximum δT{sub FWHM} of 53 (37) K, and refrigerant capacity RC = 364 (83) Jkg{sup −1} (estimated from the product |ΔS{sub M}{sup peak}| × δT{sub FWHM})
About the mechanical stability of MnFe(P,Si,B) giant-magnetocaloric materials
International Nuclear Information System (INIS)
Highlights: • Electrical resistivity and hardness show an evolution at TC with thermal cycling. • Degradation depends on the (c/a) lattice discontinuity at the transition. • Boron substituted materials present an improved mechanical stability. - Abstract: Due to its ability to control the latent heat and the hysteresis (thermal or magnetic) at the first-order transition (FOT) without deteriorating the saturation magnetisation, boron substitution in MnFe(P,Si) materials has recently been reported to be an ideal parameter to reach promising magnetocaloric performances: ΔS ≈ 10 Jkg−1 K−1 and cyclic ΔT of 2.6 K (and more) at a moderate magnetic field of ΔB = 1 T. Additionally, an interesting aspect for applications is the improvement of the mechanical stability in B doped materials compared to the pristine MnFe(P,Si) compounds. These improved mechanical properties were initially supported by naked-eye inspection and the observation of a constant ΔT during a few thousands of magnetic cycles. (Guillou et al., 2014) Here, the evolution upon cycling of MnFe(P,Si,B) materials is studied in a more quantitative and systematic manner. For that purpose transformation temperatures, electrical resistivity, micro-hardness and the microstructure are tracked as a function of the thermal cycling across the FOT for three prototypical compositions in the MnFe(P,Si,B) system. It turns out this set of data confirms the initial finding that B substitution has a positive effect on the mechanical stability. The origin of this improvement is discussed, in particular in respect to the lattice parameter discontinuities at the phase transition
Directory of Open Access Journals (Sweden)
Kamantsev Alexander
2014-07-01
Full Text Available High cooling power of magnetocaloric refrigeration can be achieved only at large amounts of heat, which can be transferred in one cycle from cold end hot end at quasi-isothermal conditions. The simple and robust experimental method of direct measuring of the transferred heat of materials with magnetocaloric effect (MCE in thermal contact with massive copper block with definite heat capacity in quasi-isothermal regime was proposed. The vacuum calorimeter for the specific transferred heat ΔQ and adiabatic temperature change ΔT measurements of MCE materials in the fields of Bitter coil magnet up to H = 140 kOe was designed and tested on samples of Ni43Mn37.9In12.1Co7 Heusler alloy with inverse MCE in the vicinity of meta-magnetostructural phase transition (PT. It was found, that the magnetic field H = 80 kOe produces complete PT from martensite to austenite with ΔQ = - 1600 J/kg at initial temperature 273 K.
Magnetic and magnetocaloric properties of Gd2In0.8X0.2 compounds (X=Al, Ga, Sn, Pb)
Tencé, Sophie; Chevalier, Bernard
2016-02-01
We show that it is possible to replace in Gd2In some amount of In by X=Al, Ga, Sn and Pb to obtain Gd2In1-xXx samples after melting. The magnetic and magnetocaloric properties of the Gd2In0.8X0.2 intermetallic compounds have been investigated through dc magnetization measurements. We evidence that the substitution of Al and Ga for In barely changes the Curie temperature TC but decreases the second magnetic transition temperature T‧ which corresponds to the transition from a ferromagnetic to an antiferromagnetic state. On the other hand, the substitution of Sn and Pb for In strongly increases TC and changes the nature or even suppresses the transition at lower temperature. This magnetic behavior gives rise to an interesting way to tune the Curie temperature near room temperature without diluting the Gd network and thus to modify the magnetocaloric effect in Gd2In1-xXx compounds.
Shinde, K P; Jang, S H; Kim, J W; Kim, D S; Ranot, M; Chung, K C
2015-12-21
We report for the first time the synthesis of nanopowders of TbN, DyN and HoN crystallized in a cubic structure by the plasma arc discharge (PAD) method and investigate their magnetocaloric properties for magnetic refrigeration applications. The nitridization of terbium, dysprosium and holmium was obtained using a mixture of nitrogen and argon gas inside a discharge chamber with 4 kPa pressure. The structural and microstructural properties of these rare earth nitrides were investigated by using X-ray diffraction and transmission electron microscopy. The studied nitrides undergo a second-order ferromagnetic to paramagnetic phase transition at Curie temperatures of 35.7, 19.9 and 14.2 K for TbN, DyN and HoN, respectively. The magnetocaloric effects were estimated by calculating the magnetic entropy changes from the magnetization data sets measured at the different applied magnetic fields and temperatures. The changes in entropy -ΔSM were found to be 12.0, 13.6 and 24.5 J kg(-1) K(-1) at an applied magnetic field of 5 T. PMID:26492221
DEFF Research Database (Denmark)
Jeppesen, Claus; Flyvbjerg, Henrik; Mouritsen, Ole G.
1989-01-01
universality class, and that all models with nonconserved order parameter, independent of ordering degeneracy and softness and origin of domain boundaries, obey the classical growth law at finite temperatures. In quenches to the Potts-ordered phase vortices and antivortices occur and annihilate mutually...... without pinning the ordering process. The ordering dynamics for quenches into the intermediate phase is also found to be described by an effectively algebraic growth law....