Ferromagnetism and spin glass ordering in transition metal alloys (invited)
Crane, S.; Carnegie, D. W., Jr.; Claus, H.
1982-03-01
Magnetic properties of transition metal alloys near the percolation threshold are often complicated by metallurgical effects. Alloys like AuFe, VFe, CuNi, RhNi, and PdNi are in general not random solid solutions but have various degrees of atomic clustering or short-range order (SRO), depending on the heat treatment. First, it is shown how the magnetic ordering temperature of these alloys varies with the degree of clustering or SRO. Second, by systematically changing this degree of clustering or SRO, important information can be obtained about the magnetic phase diagram. In all these alloys below the percolation limit, the onset of ferromagnetic order is probably preceded by a spin glass-type ordering. However, details of the magnetic phase diagram near the critical point can be quite different alloy systems.
Spin-wave damping in ferromagnets in the ordered regime
International Nuclear Information System (INIS)
Reinecke, T.L.; Stinchcombe, R.B.
1978-01-01
Theoretical results based on a high-density approach are compared with experimental measurements for the damping of long-wavelength spin waves in the nearly isotropic ferromagnet for temperatures up to the critical regime. The theory, which has no adjustable parameters, is shown to account well for the overall magnitude of the spin-wave widths measured in recent neutron scattering experiments on EuO, and it is also in satisfactory agreement with the measured wave vector and temperature dependence of these widths. An estimate is also given for the contribution of dipolar coupling to the spin-wave widths
Spin-lattice dynamics simulation of external field effect on magnetic order of ferromagnetic iron
Directory of Open Access Journals (Sweden)
C. P. Chui
2014-03-01
Full Text Available Modeling of field-induced magnetization in ferromagnetic materials has been an active topic in the last dozen years, yet a dynamic treatment of distance-dependent exchange integral has been lacking. In view of that, we employ spin-lattice dynamics (SLD simulations to study the external field effect on magnetic order of ferromagnetic iron. Our results show that an external field can increase the inflection point of the temperature. Also the model provides a better description of the effect of spin correlation in response to an external field than the mean-field theory. An external field has a more prominent effect on the long range magnetic order than on the short range counterpart. Furthermore, an external field allows the magnon dispersion curves and the uniform precession modes to exhibit magnetic order variation from their temperature dependence.
International Nuclear Information System (INIS)
Kavitha, L.; Mohamadou, A.; Parasuraman, E.; Gopi, D.; Akila, N.; Prabhu, A.
2016-01-01
The nonlinear localization phenomena in ferromagnetic spin lattices have attracted a steadily growing interest and their existence has been predicted in a wide range of physical settings. We investigate the onset of modulational instability of a plane wave in a discrete ferromagnetic spin chain with physically significant higher order dispersive octupole–dipole and dipole–dipole interactions. We derive the discrete nonlinear equation of motion with the aid of Holstein–Primakoff (H–P) transformation combined with Glauber's coherent state representation. We show that the discrete ferromagnetic spin dynamics is governed by an entirely new discrete NLS model with complex coefficients not reported so far. We report the study of modulational instability (MI) of the ferromagnetic chain with long range dispersive interactions both analytically in the frame work of linear stability analysis and numerically by means of molecular dynamics (MD) simulations. Our numerical simulations explore that the analytical predictions correctly describe the onset of instability. It is found that the presence of the various exchange and dispersive higher order interactions systematically favors the local gathering of excitations and thus supports the growth of high amplitude, long-lived discrete breather (DB) excitations. We analytically compute the strongly localized odd and even modes. Further, we employ the Jacobi elliptic function method to solve the nonlinear evolution equation and an exact propagating bubble-soliton solution is explored. - Highlights: • Higher order dispersive interactions plays significant role in ferromagnetic spin chain. • The energy localization is studied both analytically and numerically. • The existence of DBs are studied under the effect of higher order dispersive interaction.
Taskin, A A; Lavrov, A N; Ando, Yoichi
2003-06-06
In RBaCo2O5+x compounds (R is rare earth), a ferromagnetic-antiferromagnetic competition is accompanied by a giant magnetoresistance. We study the magnetization of detwinned GdBaCo2O5.5 single crystals and find a remarkable uniaxial anisotropy of Co3+ spins which is tightly linked with the chain oxygen ordering in GdO0.5 planes. Reflecting the underlying oxygen order, CoO2 planes also develop a spin-state order consisting of Co3+ ions in alternating rows of S=1 and S=0 states. The magnetic structure appears to be composed of weakly coupled ferromagnetic ladders with Ising-like moments, which gives a simple picture for magnetotransport phenomena.
Spin Funneling for Enhanced Spin Injection into Ferromagnets
Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo
2016-07-01
It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory.
Spin Orbit Torque in Ferromagnetic Semiconductors
Li, Hang
2016-06-21
Electrons not only have charges but also have spin. By utilizing the electron spin, the energy consumption of electronic devices can be reduced, their size can be scaled down and the efficiency of `read\\' and `write\\' in memory devices can be significantly improved. Hence, the manipulation of electron spin in electronic devices becomes more and more appealing for the advancement of microelectronics. In spin-based devices, the manipulation of ferromagnetic order parameter using electrical currents is a very useful means for current-driven operation. Nowadays, most of magnetic memory devices are based on the so-called spin transfer torque, which stems from the spin angular momentum transfer between a spin-polarized current and the magnetic order parameter. Recently, a novel spin torque effect, exploiting spin-orbit coupling in non-centrosymmetric magnets, has attracted a massive amount of attention. This thesis addresses the nature of spin-orbit coupled transport and torques in non-centrosymmetric magnetic semiconductors. We start with the theoretical study of spin orbit torque in three dimensional ferromagnetic GaMnAs. Using the Kubo formula, we calculate both the current-driven field-like torque and anti-damping-like torque. We compare the numerical results with the analytical expressions in the model case of a magnetic Rashba two-dimensional electron gas. Parametric dependencies of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described. Subsequently we study spin-orbit torques in two dimensional hexagonal crystals such as graphene, silicene, germanene and stanene. In the presence of staggered potential and exchange field, the valley degeneracy can be lifted and we obtain a valley-dependent Berry curvature, leading to a tunable antidamping torque by controlling the valley degree of freedom. This thesis then addresses the influence of the quantum spin Hall
Muon spin relaxation in ferromagnets. Pt. 1
International Nuclear Information System (INIS)
Lovesey, S.W.; Karlsson, E.B.
1991-04-01
Expressions for the dipolar and hyperfine contributions to the relaxation rate of muons implanted in a ferromagnet are presented and analysed using the Heisenberg model of spin-waves including dipolar and Zeeman energies. Calculations for EuO indicate that relaxation is likely to be dominated by the hyperfine mechanism, even if the ratio of the hyperfine and dipolar coupling constants is small. The hyperfine mechanism is sensitive to the dipolar energy of the atomic spins, whereas the dipolar mechanisms depend essentially on the exchange energy. For both mechanisms there is an almost quadratic dependence on temperature, throughout much of the ordered magnetic phase, which reflects two-spin-wave difference events from the Raman-type relaxation processes. (author)
Spin Currents and Spin Orbit Torques in Ferromagnets and Antiferromagnets
Hung, Yu-Ming
This thesis focuses on the interactions of spin currents and materials with magnetic order, e.g., ferromagnetic and antiferromagnetic thin films. The spin current is generated in two ways. First by spin-polarized conduction-electrons associated with the spin Hall effect in heavy metals (HMs) and, second, by exciting spin-waves in ferrimagnetic insulators using a microwave frequency magnetic field. A conduction-electron spin current can be generated by spin-orbit coupling in a heavy non-magnetic metal and transfer its spin angular momentum to a ferromagnet, providing a means of reversing the magnetization of perpendicularly magnetized ultrathin films with currents that flow in the plane of the layers. The torques on the magnetization are known as spin-orbit torques (SOT). In the first part of my thesis project I investigated and contrasted the quasistatic (slowly swept current) and pulsed current-induced switching characteristics of micrometer scale Hall crosses consisting of very thin (magnetized CoFeB layers on beta-Ta. While complete magnetization reversal occurs at a threshold current density in the quasistatic case, pulses with short duration (≤10 ns) and larger amplitude (≃10 times the quasistatic threshold current) lead to only partial magnetization reversal and domain formation. The partial reversal is associated with the limited time for reversed domain expansion during the pulse. The second part of my thesis project studies and considers applications of SOT-driven domain wall (DW) motion in a perpendicularly magnetized ultrathin ferromagnet sandwiched between a heavy metal and an oxide. My experiment results demonstrate that the DW motion can be explained by a combination of the spin Hall effect, which generates a SOT, and Dzyaloshinskii-Moriya interaction, which stabilizes chiral Neel-type DW. Based on SOT-driven DW motion and magnetic coupling between electrically isolated ferromagnetic elements, I proposed a new type of spin logic devices. I then
Spin waves in two-dimensional ferromagnet with large easy-plane anisotropy
International Nuclear Information System (INIS)
Fridman, Yu.A.; Spirin, D.V.
2002-01-01
Spin waves in easy-plane two-dimensional ferromagnet when anisotropy is much stronger than exchange are investigated. The spectra of magnons, the spin-spin and quadrupolar correlation functions have been derived. It is shown that in such a system there exist spin waves at low temperatures. Some properties of the quadrupolar ordering in ferromagnets are discussed
Spin Hall and spin swapping torques in diffusive ferromagnets
Pauyac, C. O.
2017-12-08
A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precessional effects displays a complex spatial dependence that can be exploited to generate torques and nucleate/propagate domain walls in centrosymmetric geometries without use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.
Spin Hall and spin swapping torques in diffusive ferromagnets
Pauyac, C. O.; Chshiev, M.; Manchon, Aurelien; Nikolaev, S. A.
2017-01-01
A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precessional effects displays a complex spatial dependence that can be exploited to generate torques and nucleate/propagate domain walls in centrosymmetric geometries without use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.
International Nuclear Information System (INIS)
Wang, Pan; Tian, Bo; Jiang, Yan; Wang, Yu-Feng
2013-01-01
For describing the dynamics of alpha helical proteins with internal molecular excitations, nonlinear couplings between lattice vibrations and molecular excitations, and spin excitations in one-dimensional isotropic biquadratic Heisenberg ferromagnetic spin with the octupole–dipole interactions, we consider an inhomogeneous generalized fourth-order nonlinear Schrödinger equation. Based on the Ablowitz–Kaup–Newell–Segur system, infinitely many conservation laws for the equation are derived. Through the auxiliary function, bilinear forms and N-soliton solutions for the equation are obtained. Interactions of solitons are discussed by means of the asymptotic analysis. Effects of linear inhomogeneity on the interactions of solitons are also investigated graphically and analytically. Since the inhomogeneous coefficient of the equation h=α x+β, the soliton takes on the parabolic profile during the evolution. Soliton velocity is related to the parameter α, distance scale coefficient and biquadratic exchange coefficient, but has no relation with the parameter β. Soliton amplitude and width are only related to α. Soliton position is related to β
Spin Transport in Ferromagnetic and Antiferromagnetic Textures
Akosa, Collins A.
2016-12-07
In this dissertation, we provide an accurate description of spin transport in magnetic textures and in particular, we investigate in detail, the nature of spin torque and magnetic damping in such systems. Indeed, as will be further discussed in this thesis, the current-driven velocity of magnetic textures is related to the ratio between the so-called non-adiabatic torque and magnetic damping. Uncovering the physics underlying these phenomena can lead to the optimal design of magnetic systems with improved efficiency. We identified three interesting classes of systems which have attracted enormous research interest (i) Magnetic textures in systems with broken inversion symmetry: We investigate the nature of magnetic damping in non-centrosymmetric ferromagnets. Based on phenomenological and microscopic derivations, we show that the magnetic damping becomes chiral, i.e. depends on the chirality of the magnetic texture. (ii) Ferromagnetic domain walls, skyrmions and vortices: We address the physics of spin transport in sharp disordered magnetic domain walls and vortex cores. We demonstrate that upon spin-independent scattering, the non-adiabatic torque can be significantly enhanced. Such an enhancement is large for vortex cores compared to transverse domain walls. We also show that the topological spin currents owing in these structures dramatically enhances the non-adiabaticity, an effect unique to non-trivial topological textures (iii) Antiferromagnetic skyrmions: We extend this study to antiferromagnetic skyrmions and show that such an enhanced topological torque also exist in these systems. Even more interestingly, while such a non-adiabatic torque inuences the undesirable transverse velocity of ferromagnetic skyrmions, in antiferromagnetic skyrmions, the topological non-adiabatic torque directly determines the longitudinal velocity. As a consequence, scaling down the antiferromagnetic skyrmion results in a much more efficient spin torque.
Kato, Tomohiko; Saita, Takahiro
2011-03-16
The magnetism of Pd(1-x)Mn(x) is investigated theoretically. A localized spin model for Mn spins that interact with short-range antiferromagnetic interactions and long-range ferromagnetic interactions via itinerant d electrons is set up, with no adjustable parameters. A multicanonical Monte Carlo simulation, combined with a procedure of symmetry breaking, is employed to discriminate between the ferromagnetic and spin glass orders. The transition temperature and the low-temperature phase are determined from the temperature variation of the specific heat and the probability distributions of the ferromagnetic order parameter and the spin glass order parameter at different concentrations. The calculation results reveal that only the ferromagnetic phase exists at x glass phase exists at x > 0.04, and that the two phases coexist at intermediate concentrations. This result agrees semi-quantitatively with experimental results.
International Nuclear Information System (INIS)
Zhu Zhengang; Su Gang; Jin Biao; Zheng Qingrong
2003-01-01
We have investigated the current-induced spin transfer torque of a ferromagnet-insulator-ferromagnet tunnel junction by taking the spin-flip scatterings into account. It is found that the spin-flip scattering can induce an additional spin torque, enhancing the maximum of the spin torque and giving rise to an angular shift compared to the case when the spin-flip scatterings are neglected. The effects of the molecular fields of the left and right ferromagnets on the spin torque are also studied. It is found that τ Rx /I e (τ Rx is the spin-transfer torque acting on the right ferromagnet and I e is the tunneling electrical current) does vary with the molecular fields. At two certain angles, τ Rx /I e is independent of the molecular field of the right ferromagnet, resulting in two crossing points in the curve of τ Rx /I e versus the relevant orientation for different molecular fields
Rapid characterizing of ferromagnetic materials using spin rectification
International Nuclear Information System (INIS)
Fan, Xiaolong; Wang, Wei; Wang, Yutian; Zhou, Hengan; Rao, Jinwei; Zhao, Xiaobing; Gao, Cunxu; Xue, Desheng; Gui, Y. S.; Hu, C.-M.
2014-01-01
Spin rectification is a powerful tool for dc electric detections of spin dynamics and electromagnetic waves. Technically, elaborately designed on-chip microwave devices are needed in order to realize that effect. In this letter, we propose a rapid characterizing approach based on spin rectification. By directly sending dynamic current into ferromagnetic films with stripe shape, resonant dc voltages can be detected along the longitudinal or transversal directions. As an example, Fe (010) films with precise crystalline structure and magnetic parameters were used to testify the reliability of such method. We investigated not only the dynamic parameters and the precise anisotropy constants of the Fe crystals but also the principle of spin rectification in this method
Spin Heat Accumulation Induced by Tunneling from a Ferromagnet
Vera-Marun, I.J.; Wees, B.J. van; Jansen, R.
2014-01-01
An electric current from a ferromagnet into a nonmagnetic material can induce a spin-dependent electron temperature. Here, it is shown that this spin heat accumulation, when created by tunneling from a ferromagnet, produces a non-negligible voltage signal that is comparable to that due to the
Spin current and spin transfer torque in ferromagnet/superconductor spin valves
Moen, Evan; Valls, Oriol T.
2018-05-01
Using fully self-consistent methods, we study spin transport in fabricable spin valve systems consisting of two magnetic layers, a superconducting layer, and a spacer normal layer between the ferromagnets. Our methods ensure that the proper relations between spin current gradients and spin transfer torques are satisfied. We present results as a function of geometrical parameters, interfacial barrier values, misalignment angle between the ferromagnets, and bias voltage. Our main results are for the spin current and spin accumulation as functions of position within the spin valve structure. We see precession of the spin current about the exchange fields within the ferromagnets, and penetration of the spin current into the superconductor for biases greater than the critical bias, defined in the text. The spin accumulation exhibits oscillating behavior in the normal metal, with a strong dependence on the physical parameters both as to the structure and formation of the peaks. We also study the bias dependence of the spatially averaged spin transfer torque and spin accumulation. We examine the critical-bias effect of these quantities, and their dependence on the physical parameters. Our results are predictive of the outcome of future experiments, as they take into account imperfect interfaces and a realistic geometry.
Spin-dependent dwell time through ferromagnetic graphene barrier
International Nuclear Information System (INIS)
Sattari, F.
2014-01-01
We investigated the dwell time of electrons tunneling through a ferromagnetic (FM) graphene barrier. The results show that the spin polarization can be efficiently controlled by the barrier width, barrier height, and the incident electron energy. Furthermore, it is found that electrons with different spin orientations will spend different times through the barrier. The difference of the dwell time between spin-up and spin-down electrons arises from the exchange splitting, which is induced by the FM strip. Study results indicate that a ferromagnetic graphene barrier can cause a nature spin filter mechanism in the time domain
Spin heat accumulation induced by tunneling from a ferromagnet.
Vera-Marun, I J; van Wees, B J; Jansen, R
2014-02-07
An electric current from a ferromagnet into a nonmagnetic material can induce a spin-dependent electron temperature. Here, it is shown that this spin heat accumulation, when created by tunneling from a ferromagnet, produces a non-negligible voltage signal that is comparable to that due to the coexisting electrical spin accumulation and can give a different Hanle spin precession signature. The effect is governed by the spin polarization of the Peltier coefficient of the tunnel contact, its Seebeck coefficient, and the spin heat resistance of the nonmagnetic material, which is related to the electrical spin resistance by a spin-Wiedemann-Franz law. Moreover, spin heat injection is subject to a heat conductivity mismatch that is overcome if the tunnel interface has a sufficiently large resistance.
Ballistic spin filtering across the ferromagnetic-semiconductor interface
Directory of Open Access Journals (Sweden)
Y.H. Li
2012-03-01
Full Text Available The ballistic spin-filter effect from a ferromagnetic metal into a semiconductor has theoretically been studied with an intention of detecting the spin polarizability of density of states in FM layer at a higher energy level. The physical model for the ballistic spin filtering across the interface between ferromagnetic metals and semiconductor superlattice is developed by exciting the spin polarized electrons into n-type AlAs/GaAs superlattice layer at a much higher energy level and then ballistically tunneling through the barrier into the ferromagnetic film. Since both the helicity-modulated and static photocurrent responses are experimentally measurable quantities, the physical quantity of interest, the relative asymmetry of spin-polarized tunneling conductance, could be extracted experimentally in a more straightforward way, as compared with previous models. The present physical model serves guidance for studying spin detection with advanced performance in the future.
Spin-current diode with a ferromagnetic semiconductor
International Nuclear Information System (INIS)
Sun, Qing-Feng; Xie, X. C.
2015-01-01
Diode is a key device in electronics: the charge current can flow through the device under a forward bias, while almost no current flows under a reverse bias. Here, we propose a corresponding device in spintronics: the spin-current diode, in which the forward spin current is large but the reversed one is negligible. We show that the lead/ferromagnetic quantum dot/lead system and the lead/ferromagnetic semiconductor/lead junction can work as spin-current diodes. The spin-current diode, a low dissipation device, may have important applications in spintronics, as the conventional charge-current diode does in electronics
Directory of Open Access Journals (Sweden)
A.A. Baker
Full Text Available Topological insulators (TIs have a large potential for spintronic devices owing to their spin-polarized, counter-propagating surface states. Recently, we have investigated spin pumping in a ferromagnet–TI–ferromagnet structure at room temperature. Here, we present the temperature-dependent measurement of spin pumping down to 10 K, which shows no variation with temperature. Keywords: Topological insulator, Spin pumping, Spintronics, Ferromagnetic resonance
Dynamics of magnetization in ferromagnet with spin-transfer torque
Li, Zai-Dong; He, Peng-Bin; Liu, Wu-Ming
2014-11-01
We review our recent works on dynamics of magnetization in ferromagnet with spin-transfer torque. Driven by constant spin-polarized current, the spin-transfer torque counteracts both the precession driven by the effective field and the Gilbert damping term different from the common understanding. When the spin current exceeds the critical value, the conjunctive action of Gilbert damping and spin-transfer torque leads naturally the novel screw-pitch effect characterized by the temporal oscillation of domain wall velocity and width. Driven by space- and time-dependent spin-polarized current and magnetic field, we expatiate the formation of domain wall velocity in ferromagnetic nanowire. We discuss the properties of dynamic magnetic soliton in uniaxial anisotropic ferromagnetic nanowire driven by spin-transfer torque, and analyze the modulation instability and dark soliton on the spin wave background, which shows the characteristic breather behavior of the soliton as it propagates along the ferromagnetic nanowire. With stronger breather character, we get the novel magnetic rogue wave and clarify its formation mechanism. The generation of magnetic rogue wave mainly arises from the accumulation of energy and magnons toward to its central part. We also observe that the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background, and the critical current condition is obtained analytically. At last, we have theoretically investigated the current-excited and frequency-adjusted ferromagnetic resonance in magnetic trilayers. A particular case of the perpendicular analyzer reveals that the ferromagnetic resonance curves, including the resonant location and the resonant linewidth, can be adjusted by changing the pinned magnetization direction and the direct current. Under the control of the current and external magnetic field, several magnetic states, such as quasi-parallel and quasi-antiparallel stable states, out
Spin-polarized tunneling through a ferromagnetic insulator
Kok, M.; Kok, M.; Beukers, J.N.; Brinkman, Alexander
2009-01-01
The polarization of the tunnel conductance of spin-selective ferromagnetic insulators is modeled, providing a generalized concept of polarization including both the effects of electrode and barrier polarization. The polarization model is extended to take additional non-spin-polarizing insulating
Spin-flip inelastic scattering in electron energy loss spectroscopy of a ferromagnetic metal
International Nuclear Information System (INIS)
Yin, S.; Tosatti, E.
1981-08-01
We calculate the spin polarization occuring during electron inelastic scattering from electron-hole pairs in a model ferromagnetic metal. The polarization is found to have contributions from unequal spin flip as well as non-flip energy loss rates. Our results indicate an asymmetry of the order of a few percent with parameters roughly modeling Fsub(e). The possibilities of comparison with experiments in the presence of simultaneous spin-polarizing elastic scattering are discussed. (author)
Diffusive Spin Dynamics in Ferromagnetic Thin Films with a Rashba Interaction
Wang, Xuhui; Manchon, Aurelien
2012-01-01
In a ferromagnetic metal layer, the coupled charge and spin diffusion equations are obtained in the presence of both Rashba spin-orbit interaction and magnetism. The misalignment between the magnetization and the nonequilibrium spin density induced by the Rashba field gives rise to Rashba spin torque acting on the ferromagnetic order parameter. In a general form, we find that the Rashba torque consists of both in-plane and out-of-plane components, i.e., T=T Sy×m+T Sm×(y×m). Numerical simulations on a two-dimensional nanowire consider the impact of diffusion on the Rashba torque and reveal a large enhancement to the ratio T/T S for thin wires. Our theory provides an explanation for the mechanism driving the magnetization switching in a single ferromagnet as observed in the recent experiments. © 2012 American Physical Society.
Diffusive Spin Dynamics in Ferromagnetic Thin Films with a Rashba Interaction
Wang, Xuhui
2012-03-13
In a ferromagnetic metal layer, the coupled charge and spin diffusion equations are obtained in the presence of both Rashba spin-orbit interaction and magnetism. The misalignment between the magnetization and the nonequilibrium spin density induced by the Rashba field gives rise to Rashba spin torque acting on the ferromagnetic order parameter. In a general form, we find that the Rashba torque consists of both in-plane and out-of-plane components, i.e., T=T Sy×m+T Sm×(y×m). Numerical simulations on a two-dimensional nanowire consider the impact of diffusion on the Rashba torque and reveal a large enhancement to the ratio T/T S for thin wires. Our theory provides an explanation for the mechanism driving the magnetization switching in a single ferromagnet as observed in the recent experiments. © 2012 American Physical Society.
Valley and spin thermoelectric transport in ferromagnetic silicene junctions
International Nuclear Information System (INIS)
Ping Niu, Zhi; Dong, Shihao
2014-01-01
We have investigated the valley and spin resolved thermoelectric transport in a normal/ferromagnetic/normal silicene junction. Due to the coupling between the valley and spin degrees of freedom, thermally induced pure valley and spin currents can be demonstrated. The magnitude and sign of these currents can be manipulated by adjusting the ferromagnetic exchange field and local external electric field, thus the currents are controllable. We also find fully valley and/or spin polarized currents. Similar to the currents, owing to the band structure symmetry, tunable pure spin and/or valley thermopowers with zero charge counterpart are generated. The results obtained here suggest a feasible way of generating a pure valley (spin) current and thermopower in silicene
Crowell, Paul A.; Liu, Changjiang; Patel, Sahil; Peterson, Tim; Geppert, Chad C.; Christie, Kevin; Stecklein, Gordon; Palmstrøm, Chris J.
2016-10-01
A distinguishing feature of spin accumulation in ferromagnet-semiconductor devices is its precession in a magnetic field. This is the basis for detection techniques such as the Hanle effect, but these approaches become ineffective as the spin lifetime in the semiconductor decreases. For this reason, no electrical Hanle measurement has been demonstrated in GaAs at room temperature. We show here that by forcing the magnetization in the ferromagnet to precess at resonance instead of relying only on the Larmor precession of the spin accumulation in the semiconductor, an electrically generated spin accumulation can be detected up to 300 K. The injection bias and temperature dependence of the measured spin signal agree with those obtained using traditional methods. We further show that this new approach enables a measurement of short spin lifetimes (C. Liu, S. J. Patel, T. A. Peterson, C. C. Geppert, K. D. Christie, C. J. Palmstrøm, and P. A. Crowell, "Dynamic detection of electron spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance," Nature Communications 7, 10296 (2016). http://dx.doi.org/10.1038/ncomms10296
Spin ordering in three-leg ladders in Ludwigite systems
International Nuclear Information System (INIS)
Vallejo, E.; Avignon, M.
2007-01-01
We study the spin ordering in a three-leg ladder present in Ludwigite systems formed of localized spins interacting with an extra electron per rung. We also consider the competition with super exchange interactions resulting in a very rich phase diagram. Among the phases we find the possibility of ferromagnetic rungs ordered antiferromagnetically and a zigzag spin ordering linked to the formation of a charge ordering as observed
Spin wave scattering and interference in ferromagnetic cross
Energy Technology Data Exchange (ETDEWEB)
Nanayakkara, Kasuni; Kozhanov, Alexander [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States); Center for Nano Optics, Georgia State University, Atlanta, Georgia 30303 (United States); Jacob, Ajey P. [Exploratory Research Device and Integration, GLOBALFOUNDRIES, Albany, New York 12203 (United States)
2015-10-28
Magnetostatic spin wave scattering and interference across a CoTaZr ferromagnetic spin wave waveguide cross junction were investigated experimentally and by micromagnetic simulations. It is observed that the phase of the scattered waves is dependent on the wavelength, geometry of the junction, and scattering direction. It is found that destructive and constructive interference of the spin waves generates switching characteristics modulated by the input phase of the spin waves. Micromagnetic simulations are used to analyze experimental data and simulate the spin wave scattering and interference.
Theory of in-plane current induced spin torque in metal/ferromagnet bilayers
Sakanashi, Kohei; Sigrist, Manfred; Chen, Wei
2018-05-01
Using a semiclassical approach that simultaneously incorporates the spin Hall effect (SHE), spin diffusion, quantum well states, and interface spin–orbit coupling (SOC), we address the interplay of these mechanisms as the origin of the spin–orbit torque (SOT) induced by in-plane currents, as observed in the normal metal/ferromagnetic metal bilayer thin films. Focusing on the bilayers with a ferromagnet much thinner than its spin diffusion length, such as Pt/Co with ∼10 nm thickness, our approach addresses simultaneously the two contributions to the SOT, namely the spin-transfer torque (SHE-STT) due to SHE-induced spin injection, and the inverse spin Galvanic effect spin–orbit torque (ISGE-SOT) due to SOC-induced spin accumulation. The SOC produces an effective magnetic field at the interface, hence it modifies the angular momentum conservation expected for the SHE-STT. The SHE-induced spin voltage and the interface spin current are mutually dependent and, hence, are solved in a self-consistent manner. The result suggests that the SHE-STT and ISGE-SOT are of the same order of magnitude, and the spin transport mediated by the quantum well states may be an important mechanism for the experimentally observed rapid variation of the SOT with respect to the thickness of the ferromagnet.
Spin-orbit-coupled transport and spin torque in a ferromagnetic heterostructure
Wang, Xuhui; Ortiz Pauyac, Christian; Manchon, Aurelien
2014-01-01
Ferromagnetic heterostructures provide an ideal platform to explore the nature of spin-orbit torques arising from the interplay mediated by itinerant electrons between a Rashba-type spin-orbit coupling and a ferromagnetic exchange interaction. For such a prototypic system, we develop a set of coupled diffusion equations to describe the diffusive spin dynamics and spin-orbit torques. We characterize the spin torque and its two prominent—out-of-plane and in-plane—components for a wide range of relative strength between the Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence of the spin torque emerging from our simple Rashba model is in an agreement with experiments. The spin diffusion equation can be generalized to incorporate dynamic effects such as spin pumping and magnetic damping.
Spin-orbit-coupled transport and spin torque in a ferromagnetic heterostructure
Wang, Xuhui
2014-02-07
Ferromagnetic heterostructures provide an ideal platform to explore the nature of spin-orbit torques arising from the interplay mediated by itinerant electrons between a Rashba-type spin-orbit coupling and a ferromagnetic exchange interaction. For such a prototypic system, we develop a set of coupled diffusion equations to describe the diffusive spin dynamics and spin-orbit torques. We characterize the spin torque and its two prominent—out-of-plane and in-plane—components for a wide range of relative strength between the Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence of the spin torque emerging from our simple Rashba model is in an agreement with experiments. The spin diffusion equation can be generalized to incorporate dynamic effects such as spin pumping and magnetic damping.
Spin Orbit Torque in Ferromagnetic Semiconductors
Li, Hang
2016-01-01
Electrons not only have charges but also have spin. By utilizing the electron spin, the energy consumption of electronic devices can be reduced, their size can be scaled down and the efficiency of `read' and `write' in memory devices can
Static properties and spin dynamics of the ferromagnetic spin-1 Bose gas in a magnetic field
International Nuclear Information System (INIS)
Kis-Szabo, Krisztian; Szepfalusy, Peter; Szirmai, Gergely
2005-01-01
The properties of spin-1 Bose gases with ferromagnetic interactions in the presence of a nonzero magnetic field are studied. The equation of state and thermodynamic quantities are worked out with the help of a mean-field approximation. The phase diagram besides Bose-Einstein condensation contains a first-order transition where two values of the magnetization coexist. The dynamics is investigated with the help of the random phase approximation. The soft mode corresponding to the critical point of the magnetic phase transition is found to behave like in conventional theory
Spin Transport in Mesoscopic Superconducting-Ferromagnetic Hybrid Conductor
Directory of Open Access Journals (Sweden)
Zein W. A.
2008-01-01
Full Text Available The spin polarization and the corresponding tunneling magnetoresistance (TMR for a hybrid ferromagnetic / superconductor junction are calculated. The results show that these parameters are strongly depends on the exchange field energy and the bias voltage. The dependence of the polarization on the angle of precession is due to the spin flip through tunneling process. Our results could be interpreted as due to spin imbalance of carriers resulting in suppression of gap energy of the superconductor. The present investigation is valuable for manufacturing magnetic recording devices and nonvolatile memories which imply a very high spin coherent transport for such junction.
Spin Transport in Mesoscopic Superconducting-Ferromagnetic Hybrid Conductor
Directory of Open Access Journals (Sweden)
Zein W. A.
2008-01-01
Full Text Available The spin polarization and the corresponding tunneling magnetoresistance (TMR for a hybrid ferromagnetic/superconductor junction are calculated. The results show that these parameters are strongly depends on the exchange field energy and the bias voltage. The dependence of the polarization on the angle of precession is due to the spin flip through tunneling process. Our results could be interpreted as due to spin imbalance of carriers resulting in suppression of gap energy of the superconductor. The present investigation is valuable for manufacturing magnetic recording devices and nonvolatile memories which imply a very high spin coherent transport for such junction.
Spin transport through electric field modulated graphene periodic ferromagnetic barriers
International Nuclear Information System (INIS)
Sattari, F.; Faizabadi, E.
2014-01-01
Using the transfer matrix method, the spin transmission coefficient and the spin conductivity are studied theoretically through the monolayer and bilayer graphene periodic ferromagnetic barriers modulated by a homogeneous electric field. The spin conductivity of the systems has an oscillatory behavior with respect to the external electric field which depends on the spin state of electron. In addition, the oscillation amplitude of the spin conductivity and spin polarization increase by increasing the number of barriers, but for a monolayer system with number of barriers greater than thirty, also for a bilayer system with the number of barriers greater than four, the oscillation amplitude does not change significantly. Our probes show that for bilayer system unlike monolayer structure the highest value of spin polarization achieved can be 1 or (−1). So, for designing spintronic devices, bilayer graphene is more efficient
Directory of Open Access Journals (Sweden)
Hamidreza Emamipour
2013-01-01
Full Text Available In the framework of scattering theory, we study the tunneling conductance in a system including two junctions, ferromagnetic metal/normal metal/ferromagnetic superconductor, where ferromagnetic superconductor is in spin-singlet -wave pairing state. The non-magnetic normal metal is placed in the intermediate layer with the thickness ( which varies from 1 nm to 10000 nm. The interesting result which we have found is the existence of oscillations in conductance curves. The period of oscillations is independent of FS and FN exchange field while it depends on . The obtained results can serve as a useful tool to determine the kind of pairing symmetry in ferromagnetic superconductors.
Negative tunnel magnetoresistance and spin transport in ferromagnetic graphene junctions
International Nuclear Information System (INIS)
Zou Jianfei; Jin Guojun; Ma Yuqiang
2009-01-01
We study the tunnel magnetoresistance (TMR) and spin transport in ferromagnetic graphene junctions composed of ferromagnetic graphene (FG) and normal graphene (NG) layers. It is found that the TMR in the FG/NG/FG junction oscillates from positive to negative values with respect to the chemical potential adjusted by the gate voltage in the barrier region when the Fermi level is low enough. Particularly, the conventionally defined TMR in the FG/FG/FG junction oscillates periodically from a positive to negative value with increasing the barrier height at any Fermi level. The spin polarization of the current through the FG/FG/FG junction also has an oscillating behavior with increasing barrier height, whose oscillating amplitude can be modulated by the exchange splitting in the ferromagnetic graphene.
Negative tunnel magnetoresistance and spin transport in ferromagnetic graphene junctions.
Zou, Jianfei; Jin, Guojun; Ma, Yu-Qiang
2009-03-25
We study the tunnel magnetoresistance (TMR) and spin transport in ferromagnetic graphene junctions composed of ferromagnetic graphene (FG) and normal graphene (NG) layers. It is found that the TMR in the FG/NG/FG junction oscillates from positive to negative values with respect to the chemical potential adjusted by the gate voltage in the barrier region when the Fermi level is low enough. Particularly, the conventionally defined TMR in the FG/FG/FG junction oscillates periodically from a positive to negative value with increasing the barrier height at any Fermi level. The spin polarization of the current through the FG/FG/FG junction also has an oscillating behavior with increasing barrier height, whose oscillating amplitude can be modulated by the exchange splitting in the ferromagnetic graphene.
Collective spin wave and phonon excitations in ferromagnetic organic polymers
International Nuclear Information System (INIS)
Leong, Jit-Liang; Sun, Shih-Jye
2013-01-01
We proposed a model to investigate the properties of a conductive and ferromagnetic organic-polymer (OCP), which contains two collective excitations—spin wave and phonon—competing with each other; namely, the spin wave excitation accompanies the electron–phonon (e–ph) interactions in the conductive and ferromagnetic OCP. The ferromagnetism of the OCP is induced from the conductive carriers which couple with the phonon to become polarons. Due to the competition between both excitations, the Curie temperature (T C ) is sensitively suppressed by the e–ph interaction. In addition, an optimal T C with a small e–ph interaction exists in a specific density of conduction carrier, yet is contrary to the large e–ph interaction case. Furthermore, the dimerization, i.e. the atomic displacement induced from the e–ph interactions, increases with the strength of the e–ph interaction and decreases upon reaching the maximum dimerization. (paper)
International Nuclear Information System (INIS)
Hagelberg, F.; Das, T.P.; Speidel, K.
1993-01-01
The transient field phenomenon has been ascribed to a polarization transfer between the electrons of the ionic projectiles and the surplus of majority spin electrons of the ferromagnetic host over the minority spin electrons. Earlier attempts to explain this crucial process failed to account for the order of magnitude of the experimentally observed transient field strengths. A recent model which proposes spin exchange scattering between bound projectile electrons and quasifree host electrons as the mechanism of polarization transfer arrives at the correct orders of magnitude but is in conflict with the weak velocity dependence of the experimental polarization, exhibiting a strongly decreasing behavior with increasing velocity. The new model presented here proposes spin exchange between the ionic shell and localized electrons of the ferromagnet as a more adequate approach to the problem. It is shown that calculations involving hydrogenlike ions explain the size of the experimentally observed polarization effects as well as their velocity dependence for various ion probes traversing thin iron foils
Coherence and stiffness of spin waves in diluted ferromagnets
Czech Academy of Sciences Publication Activity Database
Turek, Ilja; Kudrnovský, Josef; Drchal, Václav
2016-01-01
Roč. 94, č. 17 (2016), č. článku 174447. ISSN 2469-9950 R&D Projects: GA ČR GA15-13436S Institutional support: RVO:68081723 ; RVO:68378271 Keywords : spin wave s * diluted ferromagnets * disordered systems Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.836, year: 2016
Spin supercurrent in Josephson contacts with noncollinear ferromagnets
International Nuclear Information System (INIS)
Shomali, Zahra; Zareyan, Malek; Belzig, Wolfgang
2011-01-01
We present a theoretical study of the Josephson coupling of two superconductors that are connected through a diffusive contact consisting of noncollinear ferromagnetic domains. The leads are conventional s-wave superconductors with a phase difference of ψ. Firstly, we consider a contact with two domains with magnetization vectors misoriented by an angle θ. Using the quantum circuit theory, we found that in addition to the charge supercurrent, which shows a 0-π transition relative to the angle θ, a spin supercurrent with a spin polarization normal to the magnetization vectors flows between the domains. While the charge supercurrent is odd in ψ and even in θ, the spin supercurrent is even in ψ and odd in θ. Furthermore, with asymmetric insulating barriers at the interfaces of the junction, the system may experience an antiferromagnetic-ferromagnetic phase transition for ψ=π. Secondly, we discuss the spin supercurrent in an extended magnetic texture with multiple domain walls. We find the position-dependent spin supercurrent. While the direction of the spin supercurrent is always perpendicular to the plane of the magnetization vectors, the magnitude of the spin supercurrent strongly depends on the phase difference between the superconductors and the number of domain walls. In particular, our results reveal the high sensitivity of spin- and charge-transport in the junction to the number of domain walls in the ferromagnet. We show that superconductivity in coexistence with noncollinear magnetism can be used in a Josephson nanodevice to create a controllable spin supercurrent acting as a spin transfer torque on a system. Our results demonstrate the possibility of coupling the superconducting phase to the magnetization dynamics and, hence, constituting a quantum interface, for example between the magnetization and a superconducting qubit.
Spin transfer in an open ferromagnetic layer: from negative damping to effective temperature
Energy Technology Data Exchange (ETDEWEB)
Wegrowe, J-E; Ciornei, M C; Drouhin, H-J [Laboratoire des Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642 and CEA/DSM/DRECAM, 91128 Palaiseau Cedex (France)
2007-04-23
Spin transfer is a typical spintronics effect that allows a ferromagnetic layer to be switched by spin injection. All experimental results concerning spin transfer (quasi-static hysteresis loops or AC resonance measurements) are described on the basis of the Landau-Lifshitz-Gilbert equation of the magnetization, in which additional current dependent terms are added, like current dependent effective fields and current dependent damping factors, that can be positive or negative. The origin of these terms can be investigated further by performing stochastic experiments, like one-shot relaxation experiments under spin injection in the activation regime of the magnetization. In this regime, the Neel-Brown activation law is observed which leads to the introduction of a current dependent effective temperature. In order to define these counterintuitive parameters (effective temperature and negative damping), a detailed thermokinetic analysis of the different sub-systems involved is performed. This report presents a thermokinetic description of the different forms of energy exchanged between the electric and the ferromagnetic sub-systems at a normal/ferromagnetic junction. The derivation of the Fokker-Planck equation in the framework of the thermokinetic theory allows the transport parameters to be defined from the entropy variation and refined with the Onsager reciprocity relations and symmetry properties of the magnetic system. The contribution of the spin polarized current is introduced as an external source term in the conservation laws of the ferromagnetic layer. Due to the relaxation time separation, this contribution can be reduced to an effective damping. The flux of energy transferred between the ferromagnet and the spin polarized current can be positive or negative, depending on the spin accumulation configuration. The effective temperature is deduced in the activation (stationary) regime, provided that the relaxation time that couples the magnetization to the
Spin flip inelastic scattering in electron energy loss spectroscopy of a ferromagnetic metal
International Nuclear Information System (INIS)
Bocchetta, C.J.; Tosatti, E.; Yin, S.
1986-11-01
A model ferromagnetic metal is used to calculate the spin-polarization which occurs during inelastic electron-metal scattering with the production of an electron-hole pair. The polarization is found to have contributions from unequal spin-flip as well as non-flip energy loss rates. Our results indicate an asymmetry of the order of a few percent with parameters roughly modelling iron. (author)
A cluster-bethe-lattice approach to spin-waves in dilute ferromagnets
International Nuclear Information System (INIS)
Salzberg, J.B.; Silva, C.E.T.G. da; Falicov, L.M.
1975-01-01
The spin-wave spectra of a dilute ferromagnet within the cluster-bethe-lattice approximation is studied. Short range order effects for the alloy are included. A study of finite size clusters connected at their edges to Bethe lattices of the same coordination number allows one to determine:(i) the stability condition for the magnetic system; (ii) the continuum spin-wave local density of states and (iii) the existence of localized states below and above the continuum states
Inhomogeneity in the spin channel of ferromagnetic CMR manganites
Energy Technology Data Exchange (ETDEWEB)
Heffner, R.H.; Sonier, J.E.; MacLaughlin, D.E.; Nieuwenhuys, G.J.; Mezei, F.; Ehlers, G.; Mitchell, J.F.; Cheong, S.-W
2003-02-01
Colossal magnetoresistance manganites are archetypes in which to study the strong coupling between spin, charge and lattice degrees of freedom in materials. We present muon spin-lattice relaxation data in ferromagnetic (FM) ground state materials from the manganite series La{sub 1-x}Ca{sub x}MnO{sub 3} and La{sub 1-x-y}Pr{sub y}Ca{sub x}MnO{sub 3}. These measurements reveal several characteristic relaxation modes arising from the strong spin-charge-lattice interactions. We also present results from neutron-spin-echo spectroscopy, which directly measures the spin-spin correlation function in a time domain comparable to {mu}SR. A qualitative model for the FM transition in the manganites involving microscopic phase separation is suggested by these data.
The paramagnetic properties of ferromagnetic mixed-spin chain system
International Nuclear Information System (INIS)
Hu, Ai-Yuan; Wu, Zhi-Min; Cui, Yu-Ting; Qin, Guo-Ping
2015-01-01
The double-time Green's function method is used to investigate the paramagnetic properties of ferromagnetic mixed-spin chain system within the random-phase approximation and Anderson–Callen's decoupling approximation. The analytic expressions of the transverse susceptibility, longitudinal susceptibility and correlation length are obtained under transverse and longitudinal magnetic field. Using the analytic expressions of the transverse and longitudinal susceptibility to fit the experimental results, our results well agree with experimental data and the results from the high temperature series expansion within a simple Padé approximation. - Highlights: • We investigate the magnetic properties of a ferromagnetic mixed-spin chain system. • We use the double-time temperature-dependent Green's function technique. • Different single-ion anisotropy values for different spin values are considered. • Our results agree with experimental data and the results from the other theoretical methods
Long-Distance Entanglement of Spin Qubits via Ferromagnet
Directory of Open Access Journals (Sweden)
Luka Trifunovic
2013-12-01
Full Text Available We propose a mechanism of coherent coupling between distant spin qubits interacting dipolarly with a ferromagnet. We derive an effective two-spin interaction Hamiltonian and find a regime where the dynamics is coherent. Finally, we present a sequence for the implementation of the entangling controlled-not gate and estimate the corresponding operation time to be a few tens of nanoseconds. A particularly promising application of our proposal is to atomistic spin qubits such as silicon-based qubits and nitrogen-vacancy centers in diamond to which existing coupling schemes do not apply.
Energy Technology Data Exchange (ETDEWEB)
Sanchez-Barriga, Jaime; Varykhalov, Andrei; Fink, Joerg; Rader, Oliver; Duerr, Hermann; Eberhardt, Wolfgang [Bessy GmbH, Berlin (Germany)
2008-07-01
Spin dependent low-energy electronic excitations in 3d ferromagnets are of special interest due to the need of a microscopic understanding of the electronic structure of solids. Low-energy electrons (or holes) become dressed by a cloud of excitations resulting in quasiparticles of a finite lifetime and a different effective mass. These type of excitations have been studied by many theoretical methods, and it has been found that because of many body effects no sharp quasiparticle peaks exist for binding energies larger than 2 eV. Interestingly, it has been shown that strong correlation effects could particularly affect majority spin electrons, leading to a pronounced damping of quasiparticles at binding energies around 2 eV and above. In order to give an experimental corroboration to these findings, we have performed a systematic study of the spin-dependent quasiparticle lifetime and band structure of ferromagnetic 3d transition metal surfaces by means of spin and angle-resolved photoemission spectroscopy. On hcp Co(0001), fcc Ni(111) and bcc Fe(110), we have found a more pronounced renormalization of the majority spin quasiparticle spectral weight going from Ni to Co which are both strong ferromagnets. For Fe, a weak ferromagnet, such a process becomes more prominent in the minority channel.
Spin transport in ferromagnetically contacted carbon nanotubes
Energy Technology Data Exchange (ETDEWEB)
Meyer, C.; Morgan, C.; Schneider, C.M. [Peter Gruenberg Institut, PGI-6, Forschungszentrum Juelich and JARA Juelich Aachen Research Alliance, 52425 Juelich (Germany)
2011-11-15
We present magnetoresistance (MR) measurements on carbon nanotubes (CNTs) with different ferromagnetic leads. A sample with permalloy (Ni{sub 80}Fe{sub 20}) contacts shows the expected tunneling-type MR effect. Measurements on devices with CoPd contacts show a larger change of resistance with magnetic field. However, only minor loops are observed, which is explained with domain wall pinning. This is supported by magnetic force microscopy (MFM) measurements, which reveal a complicated bubble and stripe domain pattern. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Proximity effects and Josephson currents in ferromagnet. Spin-triplet superconductors junctions
International Nuclear Information System (INIS)
Terrade, Damien
2015-01-01
Spin-triplet superconductivity, first attached to the description of 3 He, is now generally considered to also occur in heavy-fermions compounds and in perovskite ruthenium oxide Sr 2 RuO 4 . The latter material is especially interesting since many experiments show strong evidences for a unitary chiral spin-triplet state. Moreover, the recent fabrication of thin heterostructures made of ferromagnetic SrRuO 3 on the top of Sr 2 RuO 4 strongly encourages new theoretical studies on the interplay between spin-triplet superconductor and ferromagnet in similar fashion to spin-singlet superconductors. Using an extended tight-binding Hamiltonian to model the superconductor, we discuss in this thesis the specific proximity effects of such interface by solving self-consistently the Bogoliubov-De Gennes equations on two- and three-dimensional lattices in the ballistic limit. We obtain the spatial profile of the superconducting order parameters at the interface as well as the spin-polarisation and the current across the Josephson junctions. In contrast to heterostructures made of spin-singlet superconductor, we show that the physical properties at the interface are not only controlled by the strength of the magnetization inside the ferromagnet but also by its orientation due to the existence of a finite pair spin projection of the spin-triplet Cooper pairs. We analyse in the first part the spin-polarisation and the Gibbs free energy at the three-dimensional ferromagnet-chiral spin-triplet superconductor interface. Then, the second part of the thesis is dedicated to the study of the Josephson junctions made of a chiral spin-triplet superconductor and a ferromagnetic barrier. More precisely, we analyse the existence of 0-π state transitions in two- and three-dimensional junctions with respect to the strength and the orientation of the magnetization. Finally, we study the proximity effects at the interface of helical spin-triplet superconductors. They differ from the chiral
Spin transport in diffusive ferromagnetic Josephson junctions with noncollinear magnetization
Energy Technology Data Exchange (ETDEWEB)
Shomali, Zahra; Zareyan, Malek [Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45195 (Iran, Islamic Republic of); Belzig, Wolfgang [Fachbereich Physik, Universitaet Konstanz, D-78457 Konstanz (Germany)
2011-07-01
We numerically study the Josephson coupling of two s-wave superconductors which are connected through a diffusive contact made of two ferromagnetic domains with the magnetization vectors misoriented by an angle {theta}. The assumed superconducting leads are conventional s-wave type with the phase difference of {phi}. Using the quantum circuit theory, we find that in addition to the charge supercurrent, which shows a 0-{pi} transition relative to the angle {theta}, the spin supercurrent with a spin polarization normal to the magnetization vectors will flow through the contact. Our results present a 0-{pi} quantum phase transition as a function of the wave vector, Q{xi}. Finally, we investigate the spin supercurrent in an extended magnetic texture with multiple domain walls. We find the behavior of spin supercurrent is highly sensitive to the barrier. When asymmetric barriers don't change the value of the spin supercurrent, the symmetric ones decrease the value of it notably. We also investigate some other interesting effects for these systems. In addition, we present when Q{xi} is the even multiple of {pi}, the spin-current which is penetrated into the nonhomogeneous ferromagnets is nearly zero, how ever the odd ones show the large amount of penetrated spin supercurrent.
Energy Technology Data Exchange (ETDEWEB)
Yang, Jin-Wei; Gao, Yi-Tian, E-mail: gaoyt163@163.com; Wang, Qi-Min; Su, Chuan-Qi; Feng, Yu-Jie; Yu, Xin
2016-01-15
In this paper, a fourth-order variable-coefficient nonlinear Schrödinger equation is studied, which might describe a one-dimensional continuum anisotropic Heisenberg ferromagnetic spin chain with the octuple–dipole interaction or an alpha helical protein with higher-order excitations and interactions under continuum approximation. With the aid of auxiliary function, we derive the bilinear forms and corresponding constraints on the variable coefficients. Via the symbolic computation, we obtain the Lax pair, infinitely many conservation laws, one-, two- and three-soliton solutions. We discuss the influence of the variable coefficients on the solitons. With different choices of the variable coefficients, we obtain the parabolic, cubic, and periodic solitons, respectively. We analyse the head-on and overtaking interactions between/among the two and three solitons. Interactions between a bound state and a single soliton are displayed with different choices of variable coefficients. We also derive the quasi-periodic formulae for the three cases of the bound states.
Effects of Rashba and Dresselhaus spin-orbit couplings on itinerant ferromagnetism
Liu, Mengnan; Xu, Liping; Wan, Yong; Yan, Xu
2018-02-01
Based on Stoner model for itinerant ferromagnet, effects of spin-orbit coupling (SOC) on ferromagnetism were investigated at zero temperature. It was found that SOC will enhance the critical ferromagnetic exchange interaction for spontaneous magnetization, and then suppress ferromagnetism. In case of the coexistence of Rashba and Dresselhaus SOCs, the mixture of the two spin-orbit couplings showed stronger suppressed effect on ferromagnetism than only one kind of SOC alone. When the two SOCs mixed with equal magnitude, ferromagnetism in itinerant ferromagnet was suppressed to minimum.
Spin Tunneling in Junctions with Disordered Ferromagnets
Paluskar, P.V.; Attema, J.J.; de Wijs, G.A.; Fiddy, S.; Snoeck, E.; Kohlhepp, J.T.; Swagten, H.J.M.; de Groot, R. A.; Koopmans, H.
2008-01-01
We provide compelling evidence to establish that, contrary to one’s elementary guess, the tunneling spin polarization (TSP) of amorphous CoFeB is larger than that of fcc CoFeB. First-principles atomic and electronic structure calculations reveal striking agreement between the measured TSP and the
Tunable spin-tunnel contacts to silicon using low-work-function ferromagnets
Min, Byoung-Chul; Motohashi, Kazunari; Lodder, Cock; Jansen, Ron
2006-10-01
Magnetic tunnel junctions have become ubiquitous components appearing in magnetic random-access memory, read heads of magnetic disk drives and semiconductor-based spin devices. Inserting a tunnel barrier has been key to achieving spin injection from ferromagnetic (FM) metals into GaAs, but spin injection into Si has remained elusive. We show that Schottky barrier formation leads to a huge conductivity mismatch of the FM tunnel contact and Si, which cannot be solved by the well-known method of adjusting the tunnel barrier thickness. We present a radically different approach for spin-tunnelling resistance control using low-work-function ferromagnets, inserted at the FM/tunnel barrier interface. We demonstrate that in this way the resistance-area (RA) product of FM/Al2O3/Si contacts can be tuned over eight orders of magnitude, while simultaneously maintaining a reasonable tunnel spin polarization. This raises prospects for Si-based spintronics and presents a new category of ferromagnetic materials for spin-tunnel contacts in low-RA-product applications.
The spin-s quantum Heisenberg ferromagnetic models in the physical magnon theory
International Nuclear Information System (INIS)
Liu, B.-G.; Pu, F.-C.
2001-01-01
The spin-s quantum Heisenberg ferromagnetic model is investigated in the physical magnon theory. The effect of the extra unphysical magnon states on every site is completely removed in the magnon Hamiltonian and during approximation procedure so that the condition †n i a n i >=0(n≥2s+1) is rigorously satisfied. The physical multi-magnon occupancy †n i a n i >(1≤n≤2s) is proportional to T 3n/2 at low temperature and is equivalent to 1/(2s+1) at the Curie temperature. The magnetization not only unified but also well-behaved from zero temperature to Curie temperature is obtained in the framework of the magnon theory for the spin-s quantum Heisenberg ferromagnetic model. The ill-behaved magnetizations at high temperature in earlier magnon theories are completely corrected. The relation of magnon (spin wave) theory with spin-operator decoupling theory is clearly understood
The slave-fermion approach of spin fluctuations in ferromagnet metals
Hu, C. D.
2015-11-01
In this work we propose a method to treat the spin fluctuations in itinerant ferromagnets. It is able to do calculation with a convergent series. The slave fermion method is applied to separate the charge (denoted by fermions) and spin (denoted by bosons) degrees of freedom. The spin operators are then replaced by the Schwinger boson fields. This way, the interaction term in the model can be reduced to a very simple form and can be teated without difficulty. Finally the equations of motion are derived in order to obtain the forms of Green's functions of fermions and bosons. The result is applied to the calculation of resistivity as a function temperature.
Spin waves in ferromagnetic Tb/sub 0.76/Y/sub 0.24/
International Nuclear Information System (INIS)
Wakabayashi, N.; Nicklow, R.M.; Child, H.R.
1978-01-01
The conduction electron susceptibility chi (q) is considered to play an important role in the magnetism of rare-earth metals and alloys. In order to obtain information about chi (q), studies of the spin waves in the alloy Tb/sub 0.76/Y/sub 0.24/ have been carried out in a magnetic field. The magnetic structure of this alloy was found to remain spiral down to liquid helium temperature with zero field. The spin-wave dispersion curve in this structure has already been studied along the c*-direction, and the results were analyzed successfully in terms of a susceptibility function corresponding to a one-dimensional system with a slight modification. In order to obtain somewhat independent information about chi (q), the spin-wave dispersion curve for the ferromagnetic phase has been studied. A field of 14 kG was necessary to transform the structure into a ferromagnet at liquid helium temperature. Spin-wave energies which are calculated in terms of the susceptibility function determined from the measurements in the spiral structure agree rather well with the observed energies. A large damping and softening of the spin wave has been observed near the wave vector q=0.16 which characterized the spiral configuration. The origin of the phenomenon may be related to the instability of the ferromagnetic structure
Long range anti-ferromagnetic spin model for prebiotic evolution
International Nuclear Information System (INIS)
Nokura, Kazuo
2003-01-01
I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states
Phase transitions of a spin-one Ising ferromagnetic superlattice
International Nuclear Information System (INIS)
Saber, A.
2001-09-01
Using the effective field theory with a probability distribution technique, the magnetic properties in an infinite superlattice consisting of two different ferromagnets are studied in a spin-one Ising model. The dependence of the Curie temperatures are calculated as a function of two slabs in one period and as a function of the intra- and interlayer exchange interactions. A critical value of the exchange reduced interaction above which the interface magnetism appears is found. (author)
Ferromagnetic domain structures and spin configurations measured in doped manganite
DEFF Research Database (Denmark)
He, J.Q.; Volkov, V.V.; Beleggia, Marco
2010-01-01
We report on measurements of the spin configuration across ferromagnetic domains in La0.325Pr0.3Ca0.375MnO3 films obtained by means of low-temperature Lorentz electron microscopy with in situ magnetizing capabilities. Due to the particular crystal symmetry of the material, we observe two sets of ...... and the crystal symmetry might affect the magnetoresistivity under an applied magnetic field in a strongly correlated electron system....
Muon spin relaxation in ferromagnetic PdMn
International Nuclear Information System (INIS)
Dodds, S.A.; Gist, G.A.; Heffner, R.H.; Leon, M.; MacLaughlin, D.E.; Mydosh, J.A.; Nieuwenhuys, G.J.; Schillaci, M.E.
1983-01-01
Positive-muon (μ + ) spin relaxation experiments have been carried out in the dilute ferromagnetic alloy Pd + 2 at % Mn (T/sub c/ = 5.8 0 K). In the paramagnetic state the inhomogeneous μ + linewidth is proportional to the bulk magnetization. Below T/sub c/ the μ + linewidth and the width of the μ + local field distribution in zero applied field are both in qualitative accord with the Sherrington-Kirkpatrick theory of disordered magnets
Muon spin relaxation in ferromagnetic PdMn
Energy Technology Data Exchange (ETDEWEB)
Dodds, S.A.; Gist, G.A. (Rice Univ., Houston, TX (USA)); Heffner, R.H.; Leon, M.; Schillaci, M.E. (Los Alamos National Lab., NM (USA)); MacLaughlin, D.E. (California Univ., Riverside (USA)); Mydosh, J.A.; Nieuwenhuys, G.J. (Rijksuniversiteit Leiden (Netherlands). Kamerlingh Onnes Lab.)
1984-01-01
Positive-muon (..mu../sup +/) spin relaxation experiments have been carried out in the dilute ferromagnetic alloy Pd + 2 at.% Mn (Tsub(c) = 5.8 K). In the paramagnetic state the inhomogeneous ..mu../sup +/ linewidth is proportional to the bulk magnetization. Below Tsub(c) the ..mu../sup +/ linewidth and the width of the ..mu../sup +/ local field distribution in zero applied field are both in qualitative accord with the Sherrington-Kirkpatrick theory of disordered magnets.
Vortex Flipping in Superconductor-Ferromagnet Spin Valve Structures
Patino, Edgar J.; Aprili, Marco; Blamire, Mark; Maeno, Yoshiteru
2014-03-01
We report in plane magnetization measurements on Ni/Nb/Ni/CoO and Co/Nb/Co/CoO spin valve structures with one of the ferromagnetic layers pinned by an antiferromagnetic layer. In samples with Ni, below the superconducting transition Tc, our results show strong evidence of vortex flipping driven by the ferromagnets magnetization. This is a direct consequence of proximity effect that leads to vortex supercurrents leakage into the ferromagnets. Here the polarized electron spins are subject to vortices magnetic field occasioning vortex flipping. Such novel mechanism has been made possible for the first time by fabrication of the F/S/F/AF multilayered spin valves with a thin-enough S layer to barely confine vortices inside as well as thin-enough F layers to align and control the magnetization within the plane. When Co is used there is no observation of vortex flipping effect. This is attributed to Co shorter coherence length. Interestingly instead a reduction in pinning field of about 400 Oe is observed when the Nb layer is in superconducting state. This effect cannot be explained in terms of vortex fields. In view of these facts any explanation must be directly related to proximity effect and thus a remarkable phenomenon that deserves further investigation. Programa Nacional de Ciencias Basicas COLCIENCIAS (No. 120452128168).
Acharyya, Muktish
2017-07-01
The spin wave interference is studied in two dimensional Ising ferromagnet driven by two coherent spherical magnetic field waves by Monte Carlo simulation. The spin waves are found to propagate and interfere according to the classic rule of interference pattern generated by two point sources. The interference pattern of spin wave is observed in one boundary of the lattice. The interference pattern is detected and studied by spin flip statistics at high and low temperatures. The destructive interference is manifested as the large number of spin flips and vice versa.
Dynamic spin polarization by orientation-dependent separation in a ferromagnet-semiconductor hybrid
Korenev, V. L.; Akimov, I. A.; Zaitsev, S. V.; Sapega, V. F.; Langer, L.; Yakovlev, D. R.; Danilov, Yu. A.; Bayer, M.
2012-07-01
Integration of magnetism into semiconductor electronics would facilitate an all-in-one-chip computer. Ferromagnet/bulk semiconductor hybrids have been, so far, mainly considered as key devices to read out the ferromagnetism by means of spin injection. Here we demonstrate that a Mn-based ferromagnetic layer acts as an orientation-dependent separator for carrier spins confined in a semiconductor quantum well that is set apart from the ferromagnet by a barrier only a few nanometers thick. By this spin-separation effect, a non-equilibrium electron-spin polarization is accumulated in the quantum well due to spin-dependent electron transfer to the ferromagnet. The significant advance of this hybrid design is that the excellent optical properties of the quantum well are maintained. This opens up the possibility of optical readout of the ferromagnet's magnetization and control of the non-equilibrium spin polarization in non-magnetic quantum wells.
Hirayama, Shigeyuki; Mitani, Seiji; Otani, YoshiChika; Kasai, Shinya
2018-06-01
We examined the spin-Hall-induced spin torque ferromagnetic resonance (ST-FMR) in platinum/permalloy bilayer thin films under bias direct current (DC). The bias DC modulated the symmetric components of the ST-FMR spectra, while no dominant modulation was found in the antisymmetric components. A detailed analysis in combination with simple model calculations clarified that the major origin of the modulation can be attributed to the DC resistance change under the precessional motion of magnetization. This effect is the second order contribution for the precession angle, even though the contribution can be comparable to the rectification voltage under some specific conditions.
Železný, J.
2017-01-10
One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný, Phys. Rev. Lett. 113, 157201 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley, Science 351, 587 (2016)]SCIEAS0036-807510.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.
Železný , J.; Gao, H.; Manchon, Aurelien; Freimuth, Frank; Mokrousov, Yuriy; Zemen, J.; Mašek, J.; Sinova, Jairo; Jungwirth, T.
2017-01-01
One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný, Phys. Rev. Lett. 113, 157201 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley, Science 351, 587 (2016)]SCIEAS0036-807510.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.
Spin-dependent transport and functional design in organic ferromagnetic devices
Directory of Open Access Journals (Sweden)
Guichao Hu
2017-09-01
Full Text Available Organic ferromagnets are intriguing materials in that they combine ferromagnetic and organic properties. Although challenges in their synthesis still remain, the development of organic spintronics has triggered strong interest in high-performance organic ferromagnetic devices. This review first introduces our theory for spin-dependent electron transport through organic ferromagnetic devices, which combines an extended Su–Schrieffer–Heeger model with the Green’s function method. The effects of the intrinsic interactions in the organic ferromagnets, including strong electron–lattice interaction and spin–spin correlation between π-electrons and radicals, are highlighted. Several interesting functional designs of organic ferromagnetic devices are discussed, specifically the concepts of a spin filter, multi-state magnetoresistance, and spin-current rectification. The mechanism of each phenomenon is explained by transmission and orbital analysis. These works show that organic ferromagnets are promising components for spintronic devices that deserve to be designed and examined in future experiments.
Spin-dependent Goos–Hänchen shift and spin beam splitter in gate-controllable ferromagnetic graphene
International Nuclear Information System (INIS)
Wang, Y.; Liu, Y.; Wang, B.
2014-01-01
The transmission and Goos–Hänchen (GH) shift for charge carriers in gate-controllable ferromagnetic graphene induced by ferromagnetic insulator are investigated theoretically. Numerical results demonstrate that spin-up and spin-down electrons exhibit remarkably different transmission and GH shifts. The spin-dependent GH shifts directly demonstrate the spin beam splitting effect, which can be controlled by the voltage of gate. We attribute the spin beam splitting effect to the combination of tunneling through potential barrier and Zeeman interaction from the magnetic field and the exchange proximity interaction between the ferromagnetic insulator and graphene. In view of the spin beam splitting effect and the spin-dependent GH shifts, the gate-controllable ferromagnetic graphene might be utilized to design spin beam splitter
Spin-dependent Goos–Hänchen shift and spin beam splitter in gate-controllable ferromagnetic graphene
Energy Technology Data Exchange (ETDEWEB)
Wang, Y. [School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Liu, Y., E-mail: stslyl@mail.sysu.edu.cn [School of Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Wang, B., E-mail: wangbiao@mail.sysu.edu.cn [School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China)
2014-03-15
The transmission and Goos–Hänchen (GH) shift for charge carriers in gate-controllable ferromagnetic graphene induced by ferromagnetic insulator are investigated theoretically. Numerical results demonstrate that spin-up and spin-down electrons exhibit remarkably different transmission and GH shifts. The spin-dependent GH shifts directly demonstrate the spin beam splitting effect, which can be controlled by the voltage of gate. We attribute the spin beam splitting effect to the combination of tunneling through potential barrier and Zeeman interaction from the magnetic field and the exchange proximity interaction between the ferromagnetic insulator and graphene. In view of the spin beam splitting effect and the spin-dependent GH shifts, the gate-controllable ferromagnetic graphene might be utilized to design spin beam splitter.
Spin-independent transparency of pure spin current at normal/ferromagnetic metal interface
Hao, Runrun; Zhong, Hai; Kang, Yun; Tian, Yufei; Yan, Shishen; Liu, Guolei; Han, Guangbing; Yu, Shuyun; Mei, Liangmo; Kang, Shishou
2018-03-01
The spin transparency at the normal/ferromagnetic metal (NM/FM) interface was studied in Pt/YIG/Cu/FM multilayers. The spin current generated by the spin Hall effect (SHE) in Pt flows into Cu/FM due to magnetic insulator YIG blocking charge current and transmitting spin current via the magnon current. Therefore, the nonlocal voltage induced by an inverse spin Hall effect (ISHE) in FM can be detected. With the magnetization of FM parallel or antiparallel to the spin polarization of pure spin currents ({{\\boldsymbol{σ }}}sc}), the spin-independent nonlocal voltage is induced. This indicates that the spin transparency at the Cu/FM interface is spin-independent, which demonstrates that the influence of spin-dependent electrochemical potential due to spin accumulation on the interfacial spin transparency is negligible. Furthermore, a larger spin Hall angle of Fe20Ni80 (Py) than that of Ni is obtained from the nonlocal voltage measurements. Project supported by the National Basic Research Program of China (Grant No. 2015CB921502), the National Natural Science Foundation of China (Grant Nos. 11474184 and 11627805), the 111 Project, China (Grant No. B13029), and the Fundamental Research Funds of Shandong University, China.
Directory of Open Access Journals (Sweden)
Yaser Hajati
2016-02-01
Full Text Available We study the transport properties in a ferromagnetic/nonmagnetic/ferromagnetic (FNF silicene junction in which an electrostatic gate potential, U, is attached to the nonmagnetic region. We show that the electrostatic gate potential U is a useful probe to control the band structure, quasi-bound states in the nonmagnetic barrier as well as the transport properties of the FNF silicene junction. In particular, by introducing the electrostatic gate potential, both the spin and valley conductances of the junction show an oscillatory behavior. The amplitude and frequency of such oscillations can be controlled by U. As an important result, we found that by increasing U, the second characteristic of the Klein tunneling is satisfied as a result of the quasiparticles chirality which can penetrate through a potential barrier. Moreover, it is found that for special values of U, the junction shows a gap in the spin and valley-resolve conductance and the amplitude of this gap is only controlled by the on-site potential difference, Δz. Our findings of high controllability of the spin and valley transport in such a FNF silicene junction may improve the performance of nano-electronics and spintronics devices.
International Nuclear Information System (INIS)
Mi Yilin; Zhang Ming; Yan Hui
2008-01-01
Spin injection across ferromagnet/organic semiconductor system with finite width of the layers was studied theoretically considering spin-dependent conductivity in the organic-semiconductor. It was found that the spin injection efficiency is directly dependent on the difference between the conductivity of the up-spin and down-spin polarons in the spin-injected organic system. Furthermore, the finite width of the structure, interfacial electrochemical-potential and conductivity mismatch have great influence on the spin injection process across ferromagnet/organic semiconductor interface
Switching a Perpendicular Ferromagnetic Layer by Competing Spin Currents
Ma, Qinli; Li, Yufan; Gopman, D. B.; Kabanov, Yu. P.; Shull, R. D.; Chien, C. L.
2018-03-01
An ultimate goal of spintronics is to control magnetism via electrical means. One promising way is to utilize a current-induced spin-orbit torque (SOT) originating from the strong spin-orbit coupling in heavy metals and their interfaces to switch a single perpendicularly magnetized ferromagnetic layer at room temperature. However, experimental realization of SOT switching to date requires an additional in-plane magnetic field, or other more complex measures, thus severely limiting its prospects. Here we present a novel structure consisting of two heavy metals that delivers competing spin currents of opposite spin indices. Instead of just canceling the pure spin current and the associated SOTs as one expects and corroborated by the widely accepted SOTs, such devices manifest the ability to switch the perpendicular CoFeB magnetization solely with an in-plane current without any magnetic field. Magnetic domain imaging reveals selective asymmetrical domain wall motion under a current. Our discovery not only paves the way for the application of SOT in nonvolatile technologies, but also poses questions on the underlying mechanism of the commonly believed SOT-induced switching phenomenon.
Experimental study of mixed ferromagnetic spin glass systems
International Nuclear Information System (INIS)
Mirebeau, I.
1987-01-01
The mixed ferromagnetic spin glass systems are characterized by a distribution of positive and negative exchange interactions whose maximum occurs at a positive value. We have undertaken an experimental study of amorphous (Fe 1-x Mn x ) .75 PBA1, polycrystalline and monocrystalline Ni 1-x Mn x and Au 1-x Fe x alloys. By Moessbauer effect, magnetization and neutron scattering, we show that below a ''canting'' temperature T K , spin components transverse to the mean magnetization become frozen. Small angle neutron scattering studies with an applied field show a magnetic ''structure'' i.e. the intensity exhibits a maximum at a finite q value for temperatures below T K . This structure has been studied as a function of temperature, applied field and concentration using both small angle neutron scattering and 3 axis spectrometry where we separate the elastic from the inelastic components. Possible interpretations of this new structure will be given [fr
High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb
International Nuclear Information System (INIS)
Sirohi, Anshu; Saha, Preetha; Gayen, Sirshendu; Gaurav, Abhishek; Jyotsna, Shubhra; Sheet, Goutam; Singh, Chandan K.; Kabir, Mukul; Thakur, Gohil S.; Haque, Zeba; Gupta, L. C.; Ganguli, Ashok K.
2016-01-01
CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.
High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb
Energy Technology Data Exchange (ETDEWEB)
Sirohi, Anshu; Saha, Preetha; Gayen, Sirshendu; Gaurav, Abhishek; Jyotsna, Shubhra; Sheet, Goutam, E-mail: goutam@iisermohali.ac.in [Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, S. A. S. Nagar, Manauli PO 140306 (India); Singh, Chandan K.; Kabir, Mukul [Department of Physics, Indian Institute of Science Education and Research, Pune 411008 (India); Thakur, Gohil S.; Haque, Zeba; Gupta, L. C. [Department of Chemistry, Indian Institute of Technology, New Delhi 110016 (India); Ganguli, Ashok K. [Department of Chemistry, Indian Institute of Technology, New Delhi 110016 (India); Institute of Nano Science & Technology, Mohali 160064 (India)
2016-06-13
CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.
Energy Technology Data Exchange (ETDEWEB)
Thalmann, Marcel; Rudolf, Marcel; Pietsch, Torsten [Zukunftskolleg and Department of Physics, University of Konstanz, Universitaetsstrasse 10, 78464 Konstanz (Germany)
2016-07-01
Hybrid superconducting nanostructures recently attracted tremendous interest, due to their great potential in dissipation-less spin-electronics with unprecedented switching rates. The practical realisation of such devices, however, requires a complete understanding of the transfer and dynamics of spin- and charge currents between superconducting (S) and ferromagnetic (F) circuit elements, as well as the coupling between spin- and charge degrees of freedom in these systems. We investigate novel transport phenomena in superconductor-ferromagnet hybrid nanostructures under non-equilibrium conditions. Microwave spectroscopy is used to elucidate fundamental questions related to the complex interplay of competing order parameters and the question of relaxation mechanisms of non-equilibrium distributions with respect to spin, charge and energy. Recent experiments on two complimentary device structures are discussed: (I) in diffusive S/F/S Josephson junctions with non-sinusoidal current-phase relationship and (II) local and non-local transport measurements and microwave spectroscopy in F/S/F lateral spin-valves.
Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems
Manchon, Aurelien
2018-01-29
Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures has emerged as a powerful tool to generate complex magnetic textures, interconvert charge and spin under applied current, and control magnetization dynamics. Current-induced spin-orbit torques mediate the transfer of angular momentum from the lattice to the spin system, leading to sustained magnetic oscillations or switching of ferromagnetic as well as antiferromagnetic structures. The manipulation of magnetic order, domain walls and skyrmions by spin-orbit torques provides evidence of the microscopic interactions between charge and spin in a variety of materials and opens novel strategies to design spintronic devices with potentially high impact in data storage, nonvolatile logic, and magnonic applications. This paper reviews recent progress in the field of spin-orbitronics, focusing on theoretical models, material properties, and experimental results obtained on bulk noncentrosymmetric conductors and multilayer heterostructures, including metals, semiconductors, and topological insulator systems. Relevant aspects for improving the understanding and optimizing the efficiency of nonequilibrium spin-orbit phenomena in future nanoscale devices are also discussed.
Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems
Manchon, Aurelien; Miron, I. M.; Jungwirth, T.; Sinova, J.; Zelezný , J.; Thiaville, A.; Garello, K.; Gambardella, P.
2018-01-01
Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures has emerged as a powerful tool to generate complex magnetic textures, interconvert charge and spin under applied current, and control magnetization dynamics. Current-induced spin-orbit torques mediate the transfer of angular momentum from the lattice to the spin system, leading to sustained magnetic oscillations or switching of ferromagnetic as well as antiferromagnetic structures. The manipulation of magnetic order, domain walls and skyrmions by spin-orbit torques provides evidence of the microscopic interactions between charge and spin in a variety of materials and opens novel strategies to design spintronic devices with potentially high impact in data storage, nonvolatile logic, and magnonic applications. This paper reviews recent progress in the field of spin-orbitronics, focusing on theoretical models, material properties, and experimental results obtained on bulk noncentrosymmetric conductors and multilayer heterostructures, including metals, semiconductors, and topological insulator systems. Relevant aspects for improving the understanding and optimizing the efficiency of nonequilibrium spin-orbit phenomena in future nanoscale devices are also discussed.
Suhl instabilities for spin waves in ferromagnetic nanostripes and ultrathin films
Energy Technology Data Exchange (ETDEWEB)
Haghshenasfard, Zahra, E-mail: zhaghshe@uwo.ca; Nguyen, Hoa T.; Cottam, Michael G., E-mail: cottam@uwo.ca
2017-03-15
A microscopic (or Hamiltonian-based) theory is employed for the spin-wave instability thresholds of nonlinear processes in ultrathin ferromagnetic stripes and films under perpendicular pumping with an intense microwave field. The spatially-quantized linear spin waves in these nanostructures may participate in parametric processes through the three-magnon interactions (the first-order Suhl process) and the four-magnon interactions (the second-order Suhl process) when pumped. By contrast with most previous studies of spin-wave instabilities made for larger samples, where macroscopic (or continuum) theories involving Maxwell's equations for magnetic dipolar effects are used, a discrete lattice of effective spins is employed. Then a dipole-exchange spin Hamiltonian is employed to investigate the behavior of the quantized spin waves under perpendicular pumping, when modifications due to the more extensive spatial confinement and edges effects in these nanostructures become pronounced. The instability thresholds versus applied magnetic field are calculated, with emphasis on the size effects and geometries of the nanostructures and on the different relative strengths of the magnetic dipole-dipole and exchange interactions in materials. Numerical results are presented using parameters for Permalloy, YIG, and EuS. - Highlights: • Suhl instabilities for spin waves in magnetic stripes and films are investigated. • Three- and four-magnon processes in perpendicular pumping are taken into account. • Numerical applications are made to Permalloy, YIG, and EuS.
The semi-infinite anisotropic spin-1/2 Heisenberg ferromagnet
International Nuclear Information System (INIS)
Benyoussef, A.; Boubekri, A.; Ez-Zahraouy, H.; Saber, M.
1998-08-01
Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions, the phase transitions in the semi-infinite anisotropic spin-1/2 Heisenberg ferromagnet on a simple cubic lattice are examined. For fixed values of the reduced exchange anisotropic parameter, the critical temperature of the system is studied as a function of the ratio R of the surface exchange couplings to the bulk ones. It was found that if R ≤ R c , the system orders at the bulk critical temperature T B c /J and if R ≥ R c , the system exhibits two successive transitions. The surface orders at the surface critical temperature T S c /J which is higher than T B c /J and as the temperature is lowered, in the presence of ordered surface, the bulk orders at T B c /J. (author)
100% spin accumulation in non-half-metallic ferromagnet-semiconductor junctions
International Nuclear Information System (INIS)
Petukhov, A G; Niggemann, J; Smelyanskiy, V N; Osipov, V V
2007-01-01
We show that the spin polarization of electron density in non-magnetic degenerate semiconductors can achieve 100%. The effect of 100% spin accumulation does not require a half-metallic ferromagnetic contact and can be realized in ferromagnet-semiconductor FM-n + -n junctions even at moderate spin selectivity of the FM-n + contact when the electrons with spin 'up' are extracted from n semiconductor through the heavily doped n + layer into the ferromagnet and the electrons with spin 'down' are accumulated near the n + -n interface. We derived a general equation relating spin polarization of the current to that of the electron density in non-magnetic semiconductors. We found that the effect of complete spin polarization is achieved near the n + -n interface when the concentration of the spin 'up' electrons tends to zero in this region while the diffusion current of these electrons remains finite
Wang, Haiou; Li, Jinwei; Su, Kunpeng; Huo, Dexuan; Tan, Weishi
2015-10-01
Microstructure, magnetoresistance (MR) and magnetic properties of Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3/Pr0.7Sr0.3MnO3 trilayers, which are shown to be tunable with different La0.5Ca0.5MnO3 spacer thickness, are investigated. The trilayer with 6 nm thick La0.5Ca0.5MnO3 spacer show \\text{MR}∼37{%} at 195 K in 1 T and \\text{MR}∼80{%} at 220 K in 9 T, which is realized through the double-exchange mechanism. In contrast, trilayers with the thicker La0.5Ca0.5MnO3 spacer show enhanced MR at a wide low-temperature range. The obtained \\text{MR}∼52{%} at 50 K in 1 T in the trilayer with 18 nm thick La0.5Ca0.5MnO3 spacer is superior to that of other magnetic nanoscales. We surmise that this MR originates in the ferromagnetic/antiferromagnetic competition accompanied with the formation of a charge-ordered antiferromagnetic state and the collapse of the charge-ordered state at the applied magnetic field, rather than in the double-exchange mechanism. Large and tunable MR can be realized by controlling the strain state (the thickness of the La0.5Ca0.5MnO3 spacer), which can be applied in the used devices.
Magnon–magnon interactions in O(3) ferromagnets and equations of motion for spin operators
International Nuclear Information System (INIS)
Radošević, Slobodan M.
2015-01-01
The method of equations of motion for spin operators in the case of O(3) Heisenberg ferromagnet is systematically analyzed starting from the effective Lagrangian. It is shown that the random phase approximation and the Callen approximation can be understood in terms of perturbation theory for type B magnons. Also, the second order approximation of Kondo and Yamaji for one dimensional ferromagnet is reduced to the perturbation theory for type A magnons. An emphasis is put on the physical picture, i.e. on magnon–magnon interactions and symmetries of the Heisenberg model. Calculations demonstrate that all three approximations differ in manner in which the magnon–magnon interactions arising from the Wess–Zumino term are treated, from where specific features and limitations of each of them can be deduced.
Magnon–magnon interactions in O(3) ferromagnets and equations of motion for spin operators
Energy Technology Data Exchange (ETDEWEB)
Radošević, Slobodan M., E-mail: slobodan@df.uns.ac.rs
2015-11-15
The method of equations of motion for spin operators in the case of O(3) Heisenberg ferromagnet is systematically analyzed starting from the effective Lagrangian. It is shown that the random phase approximation and the Callen approximation can be understood in terms of perturbation theory for type B magnons. Also, the second order approximation of Kondo and Yamaji for one dimensional ferromagnet is reduced to the perturbation theory for type A magnons. An emphasis is put on the physical picture, i.e. on magnon–magnon interactions and symmetries of the Heisenberg model. Calculations demonstrate that all three approximations differ in manner in which the magnon–magnon interactions arising from the Wess–Zumino term are treated, from where specific features and limitations of each of them can be deduced.
International Nuclear Information System (INIS)
Lipperheide, R.; Wille, U.
2006-01-01
A theory of spin-polarized electron transport in ferromagnet-semiconductor heterostructures, based on a unified semiclassical description of ballistic and diffusive transport in semiconductors, is outlined. The aim is to provide a framework for studying the interplay of spin relaxation and transport mechanism in spintronic devices. Transport inside the (nondegenerate) semiconductor is described in terms of a thermoballistic current, in which electrons move ballistically in the electric field arising from internal and external electrostatic potentials, and are thermalized at randomly distributed equilibration points. Spin relaxation is allowed to take place during the ballistic motion. For arbitrary potential profile and arbitrary values of the momentum and spin relaxation lengths, an integral equation for a spin transport function determining the spin polarization in the semiconductor is derived. For field-driven transport in a homogeneous semiconductor, the integral equation can be converted into a second-order differential equation that generalizes the spin drift-diffusion equation. The spin polarization in ferromagnet-semiconductor structures is obtained by matching the spin-resolved chemical potentials at the interfaces, with allowance for spin-selective interface resistances. Illustrative examples are considered
Scaling behavior of the spin pumping effect in conductive ferromagnet/platinum bilayers
Energy Technology Data Exchange (ETDEWEB)
Czeschka, Franz D.; Althammer, Matthias; Huebl, Hans; Gross, Rudolf; Goennenwein, Sebastian T.B. [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Dreher, Lukas; Brandt, Martin S. [Walter Schottky Institut, Technische Universitaet Muenchen, Garching (Germany); Imort, Inga-Mareen; Reiss, Guenter; Thomas, Andy [Fakultaet fuer Physik, Universitaet Bielefeld (Germany); Schoch, Wladimir; Limmer, Wolfgang [Abteilung Halbleiterphysik, Universitaet Ulm (Germany)
2011-07-01
Spin pumping experiments allow to measure spin currents or the spin Hall angle. We have systematically studied the spin pumping DC voltage occurring in conjunction with ferromagnetic resonance in a series of conductive ferromagnet/platinum bilayers, made from elemental 3d transition metals, Heusler compounds, ferrite spinel oxides, and magnetic semiconductors. In all bilayers, we invariably observe the same DC voltage polarity. Moreover, we find that the voltage magnitude scales with the magnetization precession cone angle with a universal prefactor, irrespective of the magnetic properties, the charge carrier transport mechanism, and the charge carrier type in a given ferromagnet. These findings quantitatively corroborate the present theoretical understanding of spin pumping in combination with the inverse spin Hall effect, and establish spin pumping as a generic phenomenon.
Scaling Behavior of the Spin Pumping Effect in Ferromagnet-Platinum Bilayers
Czeschka, F. D.; Dreher, L.; Brandt, M. S.; Weiler, M.; Althammer, M.; Imort, I.-M.; Reiss, G.; Thomas, A.; Schoch, W.; Limmer, W.; Huebl, H.; Gross, R.; Goennenwein, S. T. B.
2011-07-01
We systematically measured the dc voltage VISH induced by spin pumping together with the inverse spin Hall effect in ferromagnet-platinum bilayer films. In all our samples, comprising ferromagnetic 3d transition metals, Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, VISH invariably has the same polarity, and scales with the magnetization precession cone angle. These findings, together with the spin mixing conductance derived from the experimental data, quantitatively corroborate the present theoretical understanding of spin pumping in combination with the inverse spin Hall effect.
Multiterminal semiconductor/ferromagnet probes for spin-filter scanning tunneling microscopy
Vera Marun, I.J.; Jansen, R.
2009-01-01
We describe the fabrication of multiterminal semiconductor/ferromagnet probes for a new technique to study magnetic nanostructures: spin-filter scanning tunneling microscopy. We describe the principle of the technique, which is based on spin-polarized tunneling and subsequent analysis of the spin
Spin thermopower and thermoconductance in a ferromagnetic graphene nanoribbon
International Nuclear Information System (INIS)
Cheng Shuguang
2012-01-01
The spin thermoelectric properties of a zigzag edged ferromagnetic (FM) graphene nanoribbon are studied theoretically by using the non-equilibrium Green’s function method combined with the Landauer-Büttiker formula. By applying a temperature gradient along the ribbon, under closed boundary conditions, there is a spin voltage ΔV s inside the terminal as the response to the temperature difference ΔT between two terminals. Meanwhile, the heat current ΔQ is accompanied from the ‘hot’ terminal to the ‘cold’ terminal. The spin thermopower S = ΔV s /ΔT and thermoconductance κ = ΔQ/ΔT are obtained. When there is no magnetic field, S versus E R curves show peaks and valleys as a result of band selective transmission and Klein tunneling with E R being the on-site energy of the right terminal. The results are in agreement with the semi-classical Mott relation. When |E R | R | > M, the quantized value of κ=π 2 k B 2 T/3 h appears. In the quantum Hall regime, because Klein tunneling is suppressed, S peaks are eliminated and the quantized value of κ is much clearer. We also investigate how the thermoelectric properties are affected by temperature, FM exchange split energy and Anderson disorder. The results indicate that S and κ are sensitive to disorder. S is suppressed for even small disorder strengths. For small disorder strengths, κ is enhanced and for moderate disorder strengths, κ shows quantized values.
Kim, Dong-Jun; Jeon, Chul-Yeon; Choi, Jong-Guk; Lee, Jae Wook; Surabhi, Srivathsava; Jeong, Jong-Ryul; Lee, Kyung-Jin; Park, Byong-Guk
2017-11-09
Electric generation of spin current via spin Hall effect is of great interest as it allows an efficient manipulation of magnetization in spintronic devices. Theoretically, pure spin current can be also created by a temperature gradient, which is known as spin Nernst effect. Here, we report spin Nernst effect-induced transverse magnetoresistance in ferromagnet/non-magnetic heavy metal bilayers. We observe that the magnitude of transverse magnetoresistance in the bilayers is significantly modified by heavy metal and its thickness. This strong dependence of transverse magnetoresistance on heavy metal evidences the generation of thermally induced pure spin current in heavy metal. Our analysis shows that spin Nernst angles of W and Pt have the opposite sign to their spin Hall angles. Moreover, our estimate implies that the magnitude of spin Nernst angle would be comparable to that of spin Hall angle, suggesting an efficient generation of spin current by the spin Nernst effect.
Formation of quadrupolar phase in non-Heisenberg ferromagnets with half-integer spin
International Nuclear Information System (INIS)
Fridman, Yu.A.; Kosmachev, O.A.; Spirin, D.V.
2005-01-01
Possibility of realization of quadrupolar phase in non-Heisenberg ferromagnet with magnetic ion spin 32 is studied. It is shown that such phase state exists only in ferromagnets with high value of biquadratic exchange when external magnetic field is not applied. Phase diagram of the system is built
Ferromagnets as pure spin current generators and detectors
Qu, Danru; Miao, Bingfeng; Chien, Chia -Ling; Huang, Ssu -Yen
2015-09-08
Provided is a spintronics device. The spintronics can include a ferromagnetic metal layer, a positive electrode disposed on a first surface portion of the ferromagnetic metal layer, and a negative electrode disposed on a second surface portion of the ferromagnetic metal.
Search for Spin Filtering By Electron Tunneling Through Ferromagnetic EuS Barriers in Pbs
Figielski, T.; Morawski, A.; Wosinski, T.; Wrotek, S.; Makosa, A.; Lusakowska, E.; Story, T.; Sipatov, A. Yu.; Szczerbakow, A.; Grasza, K.;
2002-01-01
Perpendicular transport through single- and double-barrier heterostructures consisting of ferromagnetic EuS layers embedded into PbS matrix was investigated. Manifestations of both resonant tunneling and spin filtering through EuS barrier have been observed.
Modelization of nanospace interaction involving a ferromagnetic atom: a spin polarization effect study by thermogravimetric analysis.
Santhanam, K S V; Chen, Xu; Gupta, S
2014-04-01
Ab initio studies of ferromagnetic atom interacting with carbon nanotubes have been reported in the literature that predict when the interaction is strong, a higher hybridization with confinement effect will result in spin polarization in the ferromagnetic atom. The spin polarization effect on the thermal oxidation to form its oxide is modeled here for the ferromagnetic atom and its alloy, as the above studies predict the 4s electrons are polarized in the atom. The four models developed here provide a pathway for distinguishing the type of interaction that exists in the real system. The extent of spin polarization in the ferromagnetic atom has been examined by varying the amount of carbon nanotubes in the composites in the thermogravimetric experiments. In this study we report the experimental results on the CoNi alloy which appears to show selective spin polarization. The products of the thermal oxidation has been analyzed by Fourier Transform Infrared Spectroscopy.
Superconducting spin switch based on superconductor-ferromagnet nanostructures for spintronics
International Nuclear Information System (INIS)
Kehrle, Jan; Mueller, Claus; Obermeier, Guenter; Schreck, Matthias; Gsell, Stefan; Horn, Siegfried; Tidecks, Reinhard; Zdravkov, Vladimir; Morari, Roman; Sidorencko, Anatoli; Prepelitsa, Andrei; Antropov, Evgenii; Socrovisciiuc, Alexei; Nold, Eberhard; Tagirov, Lenar
2011-01-01
Very rapid developing area, spintronics, needs new devices, based on new physical principles. One of such devices - a superconducting spin-switch, consists of ferromagnetic and superconducting layers, and is based on a new phenomenon - reentrant superconductivity. The tuning of the superconducting and ferromagnetic layers thickness is investigated to optimize superconducting spin-switch effect for Nb/Cu 41 Ni 59 based nanoscale layered systems.
Spin injection into a two-dimensional electron gas using inter-digital-ferromagnetic contacts
DEFF Research Database (Denmark)
Hu, C.M.; Nitta, J.; Jensen, Ane
2002-01-01
We present a model that describes the spin injection across a single interface with two electrodes. The spin-injection rate across a typical hybrid junction made of ferromagnet (FM) and a two-dimensional electron gas (2DEG) is found at the percentage level. We perforin spin-injection-detection ex......-injection-detection experiment on devices with two ferromagnetic contacts on a 2DEG confined in an InAs quantum well. A spin-injection rate of 4.5% is estimated from the measured magnetoresistance....
Influence of external magnetic field on parameters of surface two-focus spin-wave ferromagnetic lens
International Nuclear Information System (INIS)
Reshetnyak, S.A.; Berezhinskij, A.S.
2012-01-01
The influence of external magnetic field on refraction of surface spin wave propagating through inhomogeneity created in the form of a lens, that is a biaxial ferromagnet placed into uniaxial ferromagnetic medium, is studied.
International Nuclear Information System (INIS)
Mills, D.M.
1988-12-01
The dominant term in the x-ray Compton cross-section of an electron is the interaction of the photon and the electron's charge. Platzman and Tsoar many years ago pointed out that there is also an interaction between an x-ray and the electron's spin and in principle this interaction can give information on the momentum distribution of the unpaired spin electrons in the solid. Unfortunately, the spin sensitive term is not only small compared to the charge term, but in addition couples to the photons in first order only with that components of the x-ray beam that is circularly polarized. A lack of intense sources of circularly polarized x-rays combined with the relative small size of the spin sensitive term makes measurements of the momentum distributions of unpaired spin electrons difficult, resulting in little experiment progress initially made in spin or magnetic Compton scattering. In the past several years, interest in spin sensitive Compton scattering has been revived due in large part to the availability of intense beams of high energy photons from synchrotron radiation sources. The radiation from storage ring sources has well defined polarization states; highly linearly polarized in the orbital plane and elliptically polarized above and below the plane of the orbit of the circulating particles. The high flux and unique polarization properties of synchrotron radiation sources have greatly facilitated measurements of the momentum distributions of the unpaired spin electrons in ferromagnetic solids. Recent results of the work of several groups will be presented, along with some thoughts on the impact that the next generation of storage rings, such as the Advanced Photon Source, and insertion devices specifically designed to produce circularly polarized x-ray beams will have on the field of magnetic Compton scattering. 21 refs., 6 figs
Quantum spin and charge pumping through double quantum dots with ferromagnetic leads
Energy Technology Data Exchange (ETDEWEB)
Pan, Hui, E-mail: hpan@buaa.edu.cn [Department of Physics, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Key Laboratory of Micro-Nano Measurement-Manipulation and Physics (Ministry of Education), Beihang University, Beijing 100191 (China); Chen, Ziyu; Zhao, Sufen [Department of Physics, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Lue, Rong [Department of Physics, Tsinghua University, Beijing 100084 (China)
2011-06-06
The pumping of electrons through double quantum dots (DQDs) attached to ferromagnetic leads have been theoretically investigated by using the nonequilibrium Green's function method. It is found that an oscillating electric field applied to the quantum dot may give rise to the pumped charge and spin currents. In the case that both leads are ferromagnet, a pure spin current can be generated in the antiparallel magnetization configuration, where no net charge current exists. The possibility of manipulating the pumped spin current is explored by tuning the dot level and the ac field. By making use of various tunings, the magnitude and direction of the pumped spin current can be well controlled. For the case that only one lead is ferromagnetic, both of the charge and spin currents can be pumped and flow in opposite directions on the average. The control of the magnitude and direction of the pumped charge and spin currents is also discussed by means of the magnetic flux threading through the DQD ring. -- Highlights: → We theoretically investigate the pumping of electrons through double quantum dots attached to ferromagnetic leads. → An oscillating electric field applied to the quantum dot may give rise to the pumped charge and spin currents. → When both leads are ferromagnet, a pure spin current can be generated in the antiparallel magnetization configuration. → By making use of various tunings, the magnitude and direction of the pumped spin current can be well controlled. → When only one lead is ferromagnetic, both of the charge and spin currents can be pumped and flow in opposite directions.
Spin pumping through a topological insulator probed by x-ray detected ferromagnetic resonance
Energy Technology Data Exchange (ETDEWEB)
Figueroa, A.I., E-mail: aifigueg@gmail.com [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom); Baker, A.A. [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom); Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Collins-McIntyre, L.J.; Hesjedal, T. [Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Laan, G. van der [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom)
2016-02-15
In the field of spintronics, the generation of a pure spin current (without macroscopic charge flow) through spin pumping of a ferromagnetic (FM) layer opens up the perspective of a new generation of dissipation-less devices. Microwave driven ferromagnetic resonance (FMR) can generate a pure spin current that enters adjacent layers, allowing for both magnetization reversal (through spin-transfer torque) and to probe spin coherence in non-magnetic materials. However, standard FMR is unable to probe multilayer dynamics directly, since the measurement averages over the contributions from the whole system. The synchrotron radiation-based technique of x-ray detected FMR (XFMR) offers an elegant solution to this drawback, giving access to element-, site-, and layer-specific dynamical measurements in heterostructures. In this work, we show how XFMR has provided unique information to understand spin pumping and spin transfer torque effects through a topological insulator (TI) layer in a pseudo-spin valve heterostructure. We demonstrate that TIs function as efficient spin sinks, while also allowing a limited dynamic coupling between ferromagnetic layers. These results shed new light on the spin dynamics of this novel class of materials, and suggest future directions for the development of room temperature TI-based spintronics. - Highlights: • X-ray detected ferromagnetic resonance is used to study the spin pumping phenomenon. • We show a powerful way to get information of spin transfer between magnetic layers. • We observe spin pumping through a topological insulators at room temperature. • Topological insulators function as efficient spin sinks.
Spin pumping through a topological insulator probed by x-ray detected ferromagnetic resonance
International Nuclear Information System (INIS)
Figueroa, A.I.; Baker, A.A.; Collins-McIntyre, L.J.; Hesjedal, T.; Laan, G. van der
2016-01-01
In the field of spintronics, the generation of a pure spin current (without macroscopic charge flow) through spin pumping of a ferromagnetic (FM) layer opens up the perspective of a new generation of dissipation-less devices. Microwave driven ferromagnetic resonance (FMR) can generate a pure spin current that enters adjacent layers, allowing for both magnetization reversal (through spin-transfer torque) and to probe spin coherence in non-magnetic materials. However, standard FMR is unable to probe multilayer dynamics directly, since the measurement averages over the contributions from the whole system. The synchrotron radiation-based technique of x-ray detected FMR (XFMR) offers an elegant solution to this drawback, giving access to element-, site-, and layer-specific dynamical measurements in heterostructures. In this work, we show how XFMR has provided unique information to understand spin pumping and spin transfer torque effects through a topological insulator (TI) layer in a pseudo-spin valve heterostructure. We demonstrate that TIs function as efficient spin sinks, while also allowing a limited dynamic coupling between ferromagnetic layers. These results shed new light on the spin dynamics of this novel class of materials, and suggest future directions for the development of room temperature TI-based spintronics. - Highlights: • X-ray detected ferromagnetic resonance is used to study the spin pumping phenomenon. • We show a powerful way to get information of spin transfer between magnetic layers. • We observe spin pumping through a topological insulators at room temperature. • Topological insulators function as efficient spin sinks.
On the theory of elastic scattering of spin polarized electrons from ferromagnets
International Nuclear Information System (INIS)
Helman, J.S.
1984-01-01
The first Born approximation supposedly inadequate for dealing with elastic scattering of spin polarized electrons on ferromagnets is reconsidered. It is found that when used in conjunction with a spin dependent pseudopotential, it can describe the gross features of the ansisotropy. (Author) [pt
On the theory of elastic scattering of spin polarized electrons from ferromagnets
International Nuclear Information System (INIS)
Helman, J.S.; Baltenspenger, W.
1984-01-01
The first Born approximation supposedly inadequate for dealing with the elastic scattering of spin polarized electrons on ferromagnets is reconsidered. It is found that when used in conjunction with a spin dependent pseudo-potential, it can describe the gross features of the anisotropy. (author) [pt
Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts
DEFF Research Database (Denmark)
Hu, C.-M.; Nitta, Junsaku; Jensen, Ane
2001-01-01
Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spi...
International Nuclear Information System (INIS)
Li Hong; Yang Wei; Yang Xinjian; Qin Minghui; Xu Yihong
2007-01-01
Taking into account the thickness of the ferromagnetic insulator (FI), the spin-filtering effect and proximity effect in normal metal/ferromagnetic insulator/normal metal/superconductor (NM/FI/NM/SC) junctions are studied based on an extended Blonder-Tinkham-Klapwijk (BTK) theory. It is shown that a spin-dependent energy shift during the tunneling process induces splitting of the sub-energy gap conductance peaks and the spin polarization in the ferromagnetic insulator causes an imbalance of the peak heights. Different from the ferromagnet the spin-filtering effect of the FI cannot cause the reversion of the normalized conductance in NM/FI/NM/SC junctions
Spin pumping through a topological insulator probed by x-ray detected ferromagnetic resonance
Figueroa, A. I.; Baker, A. A.; Collins-McIntyre, L. J.; Hesjedal, T.; van der Laan, G.
2016-02-01
In the field of spintronics, the generation of a pure spin current (without macroscopic charge flow) through spin pumping of a ferromagnetic (FM) layer opens up the perspective of a new generation of dissipation-less devices. Microwave driven ferromagnetic resonance (FMR) can generate a pure spin current that enters adjacent layers, allowing for both magnetization reversal (through spin-transfer torque) and to probe spin coherence in non-magnetic materials. However, standard FMR is unable to probe multilayer dynamics directly, since the measurement averages over the contributions from the whole system. The synchrotron radiation-based technique of x-ray detected FMR (XFMR) offers an elegant solution to this drawback, giving access to element-, site-, and layer-specific dynamical measurements in heterostructures. In this work, we show how XFMR has provided unique information to understand spin pumping and spin transfer torque effects through a topological insulator (TI) layer in a pseudo-spin valve heterostructure. We demonstrate that TIs function as efficient spin sinks, while also allowing a limited dynamic coupling between ferromagnetic layers. These results shed new light on the spin dynamics of this novel class of materials, and suggest future directions for the development of room temperature TI-based spintronics.
Wolf, M. S.; Badea, R.; Berezovsky, J.
2016-01-01
The core of a ferromagnetic vortex domain creates a strong, localized magnetic field, which can be manipulated on nanosecond timescales, providing a platform for addressing and controlling individual nitrogen-vacancy centre spins in diamond at room temperature, with nanometre-scale resolution. Here, we show that the ferromagnetic vortex can be driven into proximity with a nitrogen-vacancy defect using small applied magnetic fields, inducing significant nitrogen-vacancy spin splitting. We also find that the magnetic field gradient produced by the vortex is sufficient to address spins separated by nanometre-length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the nitrogen-vacancy spins, resulting in enhanced coherent rotation of the spin state. Finally, we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on ∼100 ns timescales. PMID:27296550
Spin-dependent current in resonant tunneling diode with ferromagnetic GaMnN layers
International Nuclear Information System (INIS)
Tang, N.Y.
2009-01-01
The spin-polarized tunneling current through a double barrier resonant tunneling diode (RTD) with ferromagnetic GaMnN emitter/collector is investigated theoretically. Two distinct spin splitting peaks can be observed at current-voltage (I-V) characteristics at low temperature. The spin polarization decreases with the temperature due to the thermal effect of electron density of states. When charge polarization effect is considered at the heterostructure, the spin polarization is enhanced significantly. A highly spin-polarized current can be obtained depending on the polarization charge density.
Ferromagnetic Spin Coupling as the Origin of 0.7 Anomaly in Quantum Point Contacts
Aryanpour, K.; Han, J. E.
2008-01-01
We study one-dimensional itinerant electron models with ferromagnetic coupling to investigate the origin of 0.7 anomaly in quantum point contacts. Linear conductance calculations from the quantum Monte Carlo technique for spin interactions of different spatial range suggest that $0.7(2e^{2}/h)$ anomaly results from a strong interaction of low-density conduction electrons to ferromagnetic fluctuations formed across the potential barrier. The conductance plateau appears due to the strong incohe...
International Nuclear Information System (INIS)
Wu, Stephen M.; Hoffman, Jason; Pearson, John E.; Bhattacharya, Anand
2014-01-01
The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe 3 O 4 with the ferromagnetic metal Co 0.2 Fe 0.6 B 0.2 (CoFeB) as the spin detector. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe 3 O 4 into CoFeB. It is shown that in a single ferromagnetic metal, the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between the two magnets, it is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response. These experiments show conclusively that the ISHE and ANE in CoFeB are separate phenomena with different origins and can coexist in the same material with opposite response to a thermal gradient.
Oxide Ferromagnetic Semiconductors for Spin-Electronic Transprt
International Nuclear Information System (INIS)
Pandey, R.K.
2008-01-01
The objective of this research was to investigate the viability of oxide magnetic semiconductors as potential materials for spintronics. We identified some members of the solid solution series of ilmenite (FeTiO3) and hematite (Fe2O3), abbreviated as (IH) for simplicity, for our investigations based on their ferromagnetic and semiconducting properties. With this objective in focus we limited our investigations to the following members of the modified Fe-titanates: IH33 (ilmenitehematite with 33 atomic percent hematite), IH45 (ilmenite-hematite with 45 atomic percent hematite), Mn-substituted ilmenite (Mn-FeTiO3), and Mn-substituted pseudobrookite (Mn- Fe2TiO5). All of them are: (1) wide bandgap semiconductors with band gaps ranging in values between 2.5 to 3.5 eV; (2) n-type semiconductors; (3) they exhibit well defined magnetic hysteresis loops and (4) their magnetic Curie points are greater than 400K. Ceramic, film and single crystal samples were studied and based on their properties we produced varistors (also known as voltage dependent resistors) for microelectronic circuit protection from power surges, three-terminal microelectronic devices capable of generating bipolar currents, and an integrated structured device with controlled magnetic switching of spins. Eleven refereed journal papers, three refereed conference papers and three invention disclosures resulted from our investigations. We also presented invited papers in three international conferences and one national conference. Furthermore two students graduated with Ph.D. degrees, three with M.S. degrees and one with B.S. degree. Also two post-doctoral fellows were actively involved in this research. We established the radiation hardness of our devices in collaboration with a colleague in an HBCU institution, at the Cyclotron Center at Texas A and M University, and at DOE National Labs (Los Alamos and Brookhaven). It is to be appreciated that we met most of our goals and expanded vastly the scope of
Ferromagnetic spin coupling as the origin of 0.7 anomaly in quantum point contacts.
Aryanpour, K; Han, J E
2009-02-06
We study one-dimensional itinerant electron models with ferromagnetic coupling to investigate the origin of the 0.7 anomaly in quantum point contacts. Linear conductance calculations from the quantum Monte Carlo technique for spin interactions of different spatial range suggest that 0.7(2e;{2}/h) anomaly results from a strong interaction of low-density conduction electrons to ferromagnetic fluctuations formed across the potential barrier. The conductance plateau appears due to the strong incoherent scattering at high temperature when the electron traversal time matches the time scale of dynamic ferromagnetic excitations.
Spin-transfer torque in tunnel junctions with ferromagnetic layer of finite thickness
International Nuclear Information System (INIS)
Wilczynski, M.
2011-01-01
Two components of the spin torque exerted on a free ferromagnetic layer of finite thickness and a half-infinite ferromagnetic electrode in single tunnel junctions have been calculated in the spin-polarized free-electron-like one-band model. It has been found that the torque oscillates with the thickness of ferromagnetic layer and can be enhanced in the junction with the special layer thickness. The bias dependence of torque components also significantly changes with layer thickness. It is non-symmetric for the normal torque, in contrast to the symmetric junctions with two identical half-infinite ferromagnetic electrodes. The asymmetry of the bias dependence of the normal component of the torque can be also observed in the junctions with different spin splitting of the electron bands in the ferromagnetic electrodes. - Research highlights: → The torque oscillates with the thickness of ferromagnetic layer. → Bias dependence of the torque changes with the layer thickness. → Bias dependence of the normal torque can be asymmetric.
Room-temperature spin-polarized organic light-emitting diodes with a single ferromagnetic electrode
Energy Technology Data Exchange (ETDEWEB)
Ding, Baofu, E-mail: b.ding@ecu.edu.au; Alameh, Kamal, E-mail: k.alameh@ecu.edu.au [Electron Science Research Institute, Edith Cowan University, 270 Joondalup Drive, Joondalup WA 6027 Australia (Australia); Song, Qunliang [Institute for Clean Energy and Advanced Materials, Southwest University, Chongqing 400715 (China)
2014-05-19
In this paper, we demonstrate the concept of a room-temperature spin-polarized organic light-emitting diode (Spin-OLED) structure based on (i) the deposition of an ultra-thin p-type organic buffer layer on the surface of the ferromagnetic electrode of the Spin-OLED and (ii) the use of oxygen plasma treatment to modify the surface of that electrode. Experimental results demonstrate that the brightness of the developed Spin-OLED can be increased by 110% and that a magneto-electroluminescence of 12% can be attained for a 150 mT in-plane magnetic field, at room temperature. This is attributed to enhanced hole and room-temperature spin-polarized injection from the ferromagnetic electrode, respectively.
Spin-filter effect in normal metal/ferromagnetic insulator/normal metal/superconductor structures
International Nuclear Information System (INIS)
Li, Hong; Yang, Wei; Yang, Xinjian; Qin, Minghui; Guo, Jianqin
2007-01-01
Taking into account the thickness of the ferromagnetic insulator, the spin-filter effect in normal metal/ferromagnetic insulator/normal metal/superconductor (NM/FI/NM/SC) junctions is studied based on the Blonder-Tinkham-Klapwijk (BTK) theory. It is shown that a spin-dependent energy shift during the tunneling process induces splitting of the subgap resonance peaks. The spin polarization due to the spin-filter effect of the FI causes an imbalance of the peaks heights and can enhance the Zeeman splitting of the gap peaks caused by an applied magnetic field. The spin-filter effect has no contribution to the proximity-effect-induced superconductivity in NM interlayer
International Nuclear Information System (INIS)
Popescu, Voicu; Ebert, Hubert; Papanikolaou, Nikolaos; Zeller, Rudolf; Dederichs, Peter H
2004-01-01
We present a fully relativistic generalization of the Landauer-Buettiker formalism that has been implemented within the framework of the spin-polarized relativistic screened Korringa-Kohn-Rostoker Green function method. This approach, going beyond the two-current model, supplies a more general description of the electronic transport. It is shown that the relativistic conductance can be split in terms of individual spin-diagonal and spin-off-diagonal (spin-flip) components, which allows a detailed analysis of the influence of spin-orbit-coupling-induced spin-flip processes on the spin-dependent transport. We apply our method to calculate the ballistic conductance in Fe/GaAs/Fe magnetic tunnel junctions. We find that, by removing the spin selection rules, the spin-orbit coupling strongly influences the conductance, not only qualitatively but also quantitatively, especially in the anti-parallel alignment of the magnetization in the two Fe leads
Energy Technology Data Exchange (ETDEWEB)
Zhang, G. P., E-mail: gpzhang@indstate.edu [Department of Physics, Indiana State University, Terre Haute, Indiana 47809 (United States); Si, M. S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); George, Thomas F. [Office of the Chancellor and Center for Nanoscience, Departments of Chemistry and Biochemistry and Physics and Astronomy, University of Missouri-St. Louis, St. Louis, Missouri 63121 (United States)
2015-05-07
When a laser pulse excites a ferromagnet, its spin undergoes a dramatic change. The initial demagnetization process is very fast. Experimentally, it is found that the demagnetization time is related to the spin moment in the sample. In this study, we employ the first-principles method to directly simulate such a process. We use the fixed spin moment method to change the spin moment in ferromagnetic nickel, and then we employ the Liouville equation to couple the laser pulse to the system. We find that in general the dependence of demagnetization time on the spin moment is nonlinear: It decreases with the spin moment up to a point, after which an increase with the spin moment is observed, followed by a second decrease. To understand this, we employ an extended Heisenberg model, which includes both the exchange interaction and spin-orbit coupling. The model directly links the demagnetization rate to the spin moment itself and demonstrates analytically that the spin relaxes more slowly with a small spin moment. A future experimental test of our predictions is needed.
Energy Technology Data Exchange (ETDEWEB)
Blundell, S.J.; Pratt, F.L.; Lancaster, T.; Marshall, I.M.; Steer, C.A.; Hayes, W.; Sugano, T.; Letard, J.-F.; Caneschi, A.; Gatteschi, D.; Heath, S.L
2003-02-01
We present the results of recent {mu}SR experiments on a variety of novel organic and molecular magnetic systems. Muons are sensitive to local static fields and magnetic fluctuations, but can probe much more than just the onset of long-range magnetic order. We review our work on nitronyl nitroxide organic ferromagnets and antiferromagnets. We describe a muon study of the spin-crossover phenomenon which has been studied in Fe(PM-PEA){sub 2}(NCS){sub 2}, and which shows Gaussian and root-exponential muon relaxation in the high-spin and low-spin phases, respectively. Experiments on a disc-shaped molecular complex containing Fe{sub 19} (with spin ((31)/(2))) reveal the effects of quantum tunneling of magnetization and allow an estimate of the quantum tunneling rate.
International Nuclear Information System (INIS)
Blundell, S.J.; Pratt, F.L.; Lancaster, T.; Marshall, I.M.; Steer, C.A.; Hayes, W.; Sugano, T.; Letard, J.-F.; Caneschi, A.; Gatteschi, D.; Heath, S.L.
2003-01-01
We present the results of recent μSR experiments on a variety of novel organic and molecular magnetic systems. Muons are sensitive to local static fields and magnetic fluctuations, but can probe much more than just the onset of long-range magnetic order. We review our work on nitronyl nitroxide organic ferromagnets and antiferromagnets. We describe a muon study of the spin-crossover phenomenon which has been studied in Fe(PM-PEA) 2 (NCS) 2 , and which shows Gaussian and root-exponential muon relaxation in the high-spin and low-spin phases, respectively. Experiments on a disc-shaped molecular complex containing Fe 19 (with spin ((31)/(2))) reveal the effects of quantum tunneling of magnetization and allow an estimate of the quantum tunneling rate
Thermodynamics of the frustrated ferromagnetic spin-1/2 Heisenberg chain
International Nuclear Information System (INIS)
Richter, J; Haertel, M; Ihle, D; Drechsler, S-L
2009-01-01
We studied the thermodynamics of the one-dimensional J 1 -J 2 spin-1/2 Heisenberg chain for ferromagnetic nearest-neighbor bonds J 1 2 > 0 using full diagonalization of finite rings and a second-order Green-function formalism. Thereby we focus on J 2 1 |/4 where the ground state is still ferromagnetic, but the frustration influences the thermodynamic properties. We found that their critical indices are not changed by J 2 . The analysis of the low-temperature behavior of the susceptibility χ leads to the conclusion that this behavior changes from χ ∝ T -2 at J 2 1 |/4 to χ ∝ T -3/2 at the quantum-critical point J 2 = |J 1 |/4. Another effect of the frustration is the appearance of an extra low-T maximum in the specific heat C v (T) for J 2 and |J 1 |/8, indicating its strong influence on the low-energy spectrum.
Control of spin-orbit torques through crystal symmetry in WTe2/ferromagnet bilayers
MacNeill, D.; Stiehl, G. M.; Guimaraes, M. H. D.; Buhrman, R. A.; Park, J.; Ralph, D. C.
2017-03-01
Recent discoveries regarding current-induced spin-orbit torques produced by heavy-metal/ferromagnet and topological-insulator/ferromagnet bilayers provide the potential for dramatically improved efficiency in the manipulation of magnetic devices. However, in experiments performed to date, spin-orbit torques have an important limitation--the component of torque that can compensate magnetic damping is required by symmetry to lie within the device plane. This means that spin-orbit torques can drive the most current-efficient type of magnetic reversal (antidamping switching) only for magnetic devices with in-plane anisotropy, not the devices with perpendicular magnetic anisotropy that are needed for high-density applications. Here we show experimentally that this state of affairs is not fundamental, but rather one can change the allowed symmetries of spin-orbit torques in spin-source/ferromagnet bilayer devices by using a spin-source material with low crystalline symmetry. We use WTe2, a transition-metal dichalcogenide whose surface crystal structure has only one mirror plane and no two-fold rotational invariance. Consistent with these symmetries, we generate an out-of-plane antidamping torque when current is applied along a low-symmetry axis of WTe2/Permalloy bilayers, but not when current is applied along a high-symmetry axis. Controlling spin-orbit torques by crystal symmetries in multilayer samples provides a new strategy for optimizing future magnetic technologies.
Electric-field-controlled spin reversal in a quantum dot with ferromagnetic contacts
Hauptmann, J. R.; Paaske, J.; Lindelof, P. E.
2008-05-01
Manipulation of the spin states of a quantum dot by purely electrical means is a highly desirable property of fundamental importance for the development of spintronic devices such as spin filters, spin transistors and single spin memories as well as for solid-state qubits. An electrically gated quantum dot in the Coulomb blockade regime can be tuned to hold a single unpaired spin-1/2, which is routinely spin polarized by an applied magnetic field. Using ferromagnetic electrodes, however, the quantum dot becomes spin polarized by the local exchange field. Here, we report on the experimental realization of this tunnelling-induced spin splitting in a carbon-nanotube quantum dot coupled to ferromagnetic nickel electrodes with a strong tunnel coupling ensuring a sizeable exchange field. As charge transport in this regime is dominated by the Kondo effect, we can use this sharp many-body resonance to read off the local spin polarization from the measured bias spectroscopy. We demonstrate that the exchange field can be compensated by an external magnetic field, thus restoring a zero-bias Kondo resonance, and we demonstrate that the exchange field itself, and hence the local spin polarization, can be tuned and reversed merely by tuning the gate voltage.
On the mechanism of spin-dependent (e,2e) scattering from a ferromagnetic surface
International Nuclear Information System (INIS)
Samarin, S N; Sergeant, A D; Pravica, L; Cvejanovic, D; Wilkie, P; Guagliardo, P; Williams, J F; Artamonov, O M; Suvorova, A A
2009-01-01
A simple model is suggested for a qualitative analysis of spin-dependent (e,2e) reaction on a ferromagnetic surface. The model is based on the scattering of the primary electron with the average spin projection 1 > by the valence electron with the average spin projection 2 >. To test the model the energy distributions of correlated electron pairs are measured for parallel and anti-parallel orientations of the magnetic moment of the cobalt film and polarization vector of the incident beam. The proposed model explains qualitatively the spin-asymmetry of the measured binding energy spectrum.
Modulation of pure spin currents with a ferromagnetic insulator
Villamor, Estitxu; Isasa, Miren; Vélez, Saül; Bedoya-Pinto, Amilcar; Vavassori, Paolo; Hueso, Luis E.; Bergeret, F. Sebastián; Casanova, Fèlix
2015-01-01
We propose and demonstrate spin manipulation by magnetically controlled modulation of pure spin currents in cobalt/copper lateral spin valves, fabricated on top of the magnetic insulator Y3F e5O12 (YIG). The direction of the YIG magnetization can be controlled by a small magnetic field. We observe a clear modulation of the nonlocal resistance as a function of the orientation of the YIG magnetization with respect to the polarization of the spin current. Such a modulation can only be explained by assuming a finite spin-mixing conductance at the Cu/YIG interface, as it follows from the solution of the spin-diffusion equation. These results open a path towards the development of spin logics.
Spin-polarized transport in a normal/ferromagnetic/normal zigzag graphene nanoribbon junction
International Nuclear Information System (INIS)
Tian Hong-Yu; Wang Jun
2012-01-01
We investigate the spin-dependent electron transport in single and double normal/ferromagnetic/normal zigzag graphene nanoribbon (NG/FG/NG) junctions. The ferromagnetism in the FG region originates from the spontaneous magnetization of the zigzag graphene nanoribbon. It is shown that when the zigzag-chain number of the ribbon is even and only a single transverse mode is actived, the single NG/FG/NG junction can act as a spin polarizer and/or a spin analyzer because of the valley selection rule and the spin-exchange field in the FG, while the double NG/FG/NG/FG/NG junction exhibits a quantum switching effect, in which the on and the off states switch rapidly by varying the cross angle between two FG magnetizations. Our findings may shed light on the application of magnetized graphene nanoribbons to spintronics devices. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Spin filtering through ferromagnetic BiMn O3 tunnel barriers
Gajek, M.; Bibes, M.; Barthélémy, A.; Bouzehouane, K.; Fusil, S.; Varela, M.; Fontcuberta, J.; Fert, A.
2005-07-01
We report on experiments of spin filtering through ultrathin single-crystal layers of the insulating and ferromagnetic oxide BiMnO3 (BMO). The spin polarization of the electrons tunneling from a gold electrode through BMO is analyzed with a counterelectrode of the half-metallic oxide La2/3Sr1/3MnO3 (LSMO). At 3K we find a 50% change of the tunnel resistances according to whether the magnetizations of BMO and LSMO are parallel or opposite. This effect corresponds to a spin-filtering efficiency of up to 22%. Our results thus show the potential of complex ferromagnetic insulating oxides for spin filtering and injection.
Current-induced spin transfer torque in ferromagnet-marginal Fermi liquid double tunnel junctions
International Nuclear Information System (INIS)
Mu Haifeng; Zheng Qingrong; Jin Biao; Su Gang
2005-01-01
Current-induced spin transfer torque through a marginal Fermi liquid (MFL) which is connected to two noncollinearly aligned ferromagnets via tunnel junctions is discussed in terms of the nonequilibrium Green function method. It is found that in the absence of the spin-flip scattering, the magnitude of the torque increases with the polarization and the coupling constant λ of the MFL, whose maximum increases with λ linearly, showing that the interactions between electrons tend to enhance the spin torque. When the spin-flip scattering is included, an additional spin torque is induced. It is found that the spin-flip scattering enhances the spin torque and gives rise to a nonlinear angular shift
Prokeš, K.; de Visser, A.; Huang, Y.K.; Fåk, B.; Ressouche, E.
2010-01-01
We report a polarized neutron-diffraction study conducted to reveal the nature of the weak ferromagnetic moment in the superconducting ferromagnet UCoGe. We find that the ordered moment in the normal phase in low magnetic fields (B∥c) is predominantly located at the U atom and has a magnitude of
Vacancy-induced ferromagnetism in ZnO probed by spin-polarized positron annihilation spectroscopy
Maekawa, Masaki; Abe, Hiroshi; Miyashita, Atsumi; Sakai, Seiji; Yamamoto, Shunya; Kawasuso, Atsuo
2017-04-01
We investigated the ferromagnetism of ZnO induced by oxygen implantation by using spin-polarized positron annihilation spectroscopy together with magnetization measurements. The magnetization measurements showed the appearance of ferromagnetism after oxygen implantation and its disappearance during post-implantation annealing at temperatures above 573 K. The Doppler broadening of annihilation radiation (DBAR) spectrum showed asymmetry upon field reversal after oxygen implantation. The obtained differential DBAR spectrum between positive and negative magnetic fields was well-explained with a theoretical calculation considering zinc vacancies. The disappearance of the field-reversal asymmetry of the DBAR spectrum as a result of annealing agreed with the observations of ferromagnetism by magnetization measurements. These results suggest the radiation-induced zinc vacancies to be the source of the observed ferromagnetism of ZnO.
Energy Technology Data Exchange (ETDEWEB)
Riegler, Andreas
2011-11-25
-beam lithography and measured by ferromagnetic resonance. The damping remains in the low 10{sup -3} range as determined directly by extracting the Gilbert damping from the line width. Additionally magnetostatic modes are observed in arrays of elements, which is further evidence of high material quality of the samples. By sputtering various metals on top of the NiMnSb, spin pumping from the ferromagnet into the non-magnetic layer is investigated. After these material investigations, pseudo-spin-valves using NiMnSb as one of the ferromagnet, in combination with Permalloy were fabricating using a self-aligned lithography process. These samples show a GMR ratio of 3.4% at room temperature and almost double at low temperature, comparing favourably to the best single stack GMR structures reported to date. Moreover, current induced switching measurements show promisingly low current densities are necessary to change the magnetic orientation of the free layer. These current densities compete with state-of-the-art GMR devices for metal based structures and almost with tunnel junction devices. The true potential of these devices however comes to light when they are operated as spin torque oscillators to emit high frequency, tunable, narrow spectrum electromagnetic waves. These Heusler based STOs show an outstanding q-factor of 4180, even when operating in the absence of an external field, a value which bests the highest value in the literature by more than an order of magnitude. While these devices currently still suffer from the same limited output power as all STO reported to date, their sub-micron lateral dimensions make the fabrication of an on-chip array of coupled oscillators, which is a promising path forward towards industrially relevant output power.
The Landau-Lifshitz equation of the ferromagnetic spin chain and harmonic maps
International Nuclear Information System (INIS)
Guo Boling; Hong Minchun.
1992-05-01
We prove a global existence of solutions for the Landau-Lifshitz equation of the ferromagnetic spin chain from an m-dimensional manifold M into the unit sphere S 2 of R 3 and establish some new links between harmonic maps and the solutions of the Landau-Lifshitz equation. (author). 25 refs
Chaotic dynamics of Heisenberg ferromagnetic spin chain with bilinear and biquadratic interactions
Blessy, B. S. Gnana; Latha, M. M.
2017-10-01
We investigate the chaotic dynamics of one dimensional Heisenberg ferromagnetic spin chain by constructing the Hamiltonian equations of motion. We present the trajectory and phase plots of the system with bilinear and also biquadratic interactions. The stability of the system is analysed in both cases by constructing the Jacobian matrix and by measuring the Lyapunov exponents. The results are illustrated graphically.
Tateiwa, Naoyuki; Pospíšil, Jiří; Haga, Yoshinori; Sakai, Hironori; Matsuda, Tatsuma D.; Yamamoto, Etsuji
2017-07-01
We have carried out an analysis of magnetic data in 69 uranium, 7 neptunium, and 4 plutonium ferromagnets with the spin fluctuation theory developed by Takahashi [Y. Takahashi, J. Phys. Soc. Jpn. 55, 3553 (1986), 10.1143/JPSJ.55.3553]. The basic and spin fluctuation parameters of the actinide ferromagnets are determined and the applicability of the spin fluctuation theory to actinide 5 f system has been discussed. Itinerant ferromagnets of the 3 d transition metals and their intermetallics follow a generalized Rhodes-Wohlfarth relation between peff/ps and TC/T0 , viz., peff/ps∝(TC/T0) -3 /2 . Here, ps, peff, TC, and T0 are the spontaneous and effective magnetic moments, the Curie temperature, and the width of spin fluctuation spectrum in energy space, respectively. The same relation is satisfied for TC/T0uranium and neptunium ferromagnets below (TC/T0)kink=0.32 ±0.02 , where a kink structure appears in relation between the two quantities. ps increases more weakly above (TC/T0)kink. A possible interpretation with the TC/T0 dependence of ps is given.
Energy Technology Data Exchange (ETDEWEB)
Wang, Tianhan; Zhu, Diling; Benny Wu,; Graves, Catherine; Schaffert, Stefan; Rander, Torbjorn; Muller, leonard; Vodungbo, Boris; Baumier, Cedric; Bernstein, David P.; Brauer, Bjorn; Cros, Vincent; Jong, Sanne de; Delaunay, Renaud; Fognini, Andreas; Kukreja, Roopali; Lee, Sooheyong; Lopez-Flores, Victor; Mohanty, Jyoti; Pfau, Bastian; Popescu, 5 Horia
2012-05-15
We present the first single-shot images of ferromagnetic, nanoscale spin order taken with femtosecond x-ray pulses. X-ray-induced electron and spin dynamics can be outrun with pulses shorter than 80 fs in the investigated fluence regime, and no permanent aftereffects in the samples are observed below a fluence of 25 mJ/cm{sup 2}. Employing resonant spatially-muliplexed x-ray holography results in a low imaging threshold of 5 mJ/cm{sup 2}. Our results open new ways to combine ultrafast laser spectroscopy with sequential snapshot imaging on a single sample, generating a movie of excited state dynamics.
Angular dependence and symmetry of Rashba spin torque in ferromagnetic heterostructures
Ortiz Pauyac, Christian; Wang, Xuhui; Chshiev, Mairbek; Manchon, Aurelien
2013-01-01
In a ferromagnetic heterostructure, the interplay between Rashba spin-orbit coupling and exchange splitting gives rise to a current-driven spin torque. In a realistic device setup, we investigate the Rashba spin torque in the diffusive regime and report two major findings: (i) a nonvanishing torque exists at the edges of the device even when the magnetization and effective Rashba field are aligned; (ii) anisotropic spin relaxation rates driven by the Rashba spin-orbit coupling assign the spin torque a general expression T = T y (θ) m × (y × m) + T y (θ) y × m + T z (θ) m × (z × m) + T z (θ) z × m, where the coefficients T, y, z depend on the magnetization direction. Our results agree with recent experiments. © 2013 AIP Publishing LLC.
Angular dependence and symmetry of Rashba spin torque in ferromagnetic heterostructures
Ortiz Pauyac, Christian
2013-06-26
In a ferromagnetic heterostructure, the interplay between Rashba spin-orbit coupling and exchange splitting gives rise to a current-driven spin torque. In a realistic device setup, we investigate the Rashba spin torque in the diffusive regime and report two major findings: (i) a nonvanishing torque exists at the edges of the device even when the magnetization and effective Rashba field are aligned; (ii) anisotropic spin relaxation rates driven by the Rashba spin-orbit coupling assign the spin torque a general expression T = T y (θ) m × (y × m) + T y (θ) y × m + T z (θ) m × (z × m) + T z (θ) z × m, where the coefficients T, y, z depend on the magnetization direction. Our results agree with recent experiments. © 2013 AIP Publishing LLC.
International Nuclear Information System (INIS)
Chen Yuan; Song Chuangchuang; Xiang Ying
2010-01-01
In this paper, we apply the two-time Green's function method, and provide a simple way to study the magnetic properties of one-dimensional spin-(S,s) Heisenberg ferromagnets. The magnetic susceptibility and correlation functions are obtained by using the Tyablikov decoupling approximation. Our results show that the magnetic susceptibility and correlation length are a monotonically decreasing function of temperature regardless of the mixed spins. It is found that in the case of S=s, our results of one-dimensional mixed-spin model is reduced to be those of the isotropic ferromagnetic Heisenberg chain in the whole temperature region. Our results for the susceptibility are in agreement with those obtained by other theoretical approaches. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Direct observation of spin-resolved full and empty electron states in ferromagnetic surfaces
Energy Technology Data Exchange (ETDEWEB)
Berti, G., E-mail: giulia.berti@polimi.it; Calloni, A.; Brambilla, A.; Bussetti, G.; Duò, L.; Ciccacci, F. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133, Milano (Italy)
2014-07-15
We present a versatile apparatus for the study of ferromagnetic surfaces, which combines spin-polarized photoemission and inverse photoemission spectroscopies. Samples can be grown by molecular beam epitaxy and analyzed in situ. Spin-resolved photoemission spectroscopy analysis is done with a hemispherical electron analyzer coupled to a 25 kV-Mott detector. Inverse photoemission spectroscopy experiments are performed with GaAs crystals as spin-polarized electron sources and a UV bandpass photon detector. As an example, measurements on the oxygen passivated Fe(100)-p(1×1)O surface are presented.
Magnetoanisotropic spin-triplet Andreev reflection in ferromagnet-Ising superconductor junctions
Lv, Peng; Zhou, Yan-Feng; Yang, Ning-Xuan; Sun, Qing-Feng
2018-04-01
We theoretically study the electronic transport through a ferromagnet-Ising superconductor junction. A tight-binding Hamiltonian describing the Ising superconductor is presented. Then by combining the nonequilibrium Green's function method, the expressions of Andreev reflection coefficient and conductance are obtained. A strong magnetoanisotropic spin-triplet Andreev reflection is shown, and the magnetoanisotropic period is π instead of 2 π as in the conventional magnetoanisotropic system. We demonstrate a significant increase of the spin-triplet Andreev reflection for the single-band Ising superconductor. Furthermore, the dependence of the Andreev reflection on the incident energy and incident angle are also investigated. A complete Andreev reflection can occur when the incident energy is equal to the superconducting gap, regardless of the Fermi energy (spin polarization) of the ferromagnet. For the suitable oblique incidence, the spin-triplet Andreev reflection can be strongly enhanced. In addition, the conductance spectroscopies of both zero bias and finite bias are studied, and the influence of gate voltage, exchange energy, and spin-orbit coupling on the conductance spectroscopy are discussed in detail. The conductance exhibits a strong magnetoanisotropy with period π as the Andreev reflection coefficient. When the magnetization direction is parallel to the junction plane, a large conductance peak always emerges at the superconducting gap. This work offers a comprehensive and systematic study of the spin-triplet Andreev reflection and has an underlying application of π -periodic spin valve in spintronics.
Controllable spin filter composed of ferromagnetic AB-stacking bilayer graphenes
International Nuclear Information System (INIS)
Yu, Yong; Liang, Qifeng; Dong, Jinming
2011-01-01
The electron's tunneling and spin transport in the normal/ferromagnetic/normal (N/FM/N) AB-stacking bilayer graphene (BLG) junction have been studied using Landauer-Buettiker formula. It is found that the resonant conductance peaks could be split well into spin-up and down ones by the exchange field in its FM barrier, leading to a very large spin polarization. More importantly, if a perpendicular electric field is also applied on the FM barrier, a completely spin-polarized flow can be realized by changing its barrier height, making the N/FM/N AB-stacking BLG junction act as a controllable spin filter. -- Highlights: → A study of spin transport in the ferromagnetic bilayer graphene junctions. → A serious of resonant conductance peaks could appear by tuning the barrier height. → The exchange splitting in FM barrier leads to a large spin polarization P. → P=±1 can be realized if a perpendicular electric field is applied to the FM barrier.
Electron-spin polarization in tunnel junctions with ferromagnetic EuS barriers
International Nuclear Information System (INIS)
Hao, X.; Moodera, J.S.; Meservey, R.
1989-01-01
The authors report here spin-polarized tunneling experiments using non-ferromagnetic electrodes and ferromagnetic EuS barriers. Because of the conduction band in EuS splits into spin-up and spin-down subbands when the temperature is below 16.7 K, the Curie temperature of EuS, the tunnel barrier for electrons with different spin directions is different, therefore giving rise to tunnel current polarization. The spin-filter effect, as it may be called, was observed earlier, directly or indirectly, by several groups: Esaki et al. made a tunneling study on junctions having EuS and EuSe barriers; Thompson et al. studied Schottky barrier tunneling between In and doped EuS; Muller et al. and Kisker et al. performed electron field emission experiments on EuS-coated tungsten tips. The field emission experiments gave a maximum polarization of (89 + 7)% for the emitted electrons. Although the previous tunneling studies did not directly show electron polarization, their results were explained by the same spin- filter effect. This work uses the spin-polarized tunneling technique to show directly that tunnel current is indeed polarized and polarization can be as high as 85%
Spin-resolved x-ray photoemission studies of ferromagnetic metals
International Nuclear Information System (INIS)
Klebanoff, L.E.
1996-01-01
Recent spin-resolved x-ray photoelectron spectroscopy (SRXPS) studies of ferromagnetic metals are reviewed. SRXPS studies of metallic Fe, Co, Co 66 Fe 4 Ni 1 B 14 Si 15 , and Ni demonstrate that core-level photoemission, and the itinerant electron response to core-hole creation, are highly spin-dependent. The exchange splitting of the Fe 2p 3/2 level is found to be 0.48±0.05 eV. Lifetime broadening results for the Fe 2p 3/2 N↑ (majority spin) and N↓ (minority spin) components indicate conservation of spin in core-hole filling processes involving the valence band. SRXPS study of the Fe 2p 3/2 peak asymmetry α reveals a dependence of electron endash hole excitation on the spin of the core hole. Spin analysis of the Fe 3s XPS line shape shows it to be a three-component spectrum, rather than the two-component line shape assumed previously. A photon energy dependence of one of the Fe 3s components explains disagreement among previous Fe 3s XPS results. Comparisons of SRXPS from Co metal and Co 66 Fe 4 Ni 1 B 14 Si 15 directly demonstrate the effect of a reduced atomic magnetic moment on the spin dependence of core-level XPS. The behavior of lifetime broadenings for the N↑ and N↓ Co 2p 3/2 components show that the reduced Co magnetic moment found in the Co 66 Fe 4 Ni 1 B 14 Si 15 amorphous glass is due to the transfer of ↑-spin valence electron density to the ↓-spin valence band upon glass formation. SRXPS also allows investigation of spin-dependent core-hole screening processes and satellite production, as demonstrated in SRXPS studies of ferromagnetic Ni. Future directions of SRXPS are also explored. copyright 1996 American Vacuum Society
Global mean-field phase diagram of the spin-1 Ising ferromagnet in a random crystal field
Borelli, M. E. S.; Carneiro, C. E. I.
1996-02-01
We study the phase diagram of the mean-field spin-1 Ising ferromagnet in a uniform magnetic field H and a random crystal field Δi, with probability distribution P( Δi) = pδ( Δi - Δ) + (1 - p) δ( Δi). We analyse the effects of randomness on the first-order surfaces of the Δ- T- H phase diagram for different values of the concentration p and show how these surfaces are affected by the dilution of the crystal field.
Large spin-valve effect in a lateral spin-valve device based on ferromagnetic semiconductor GaMnAs
Asahara, Hirokatsu; Kanaki, Toshiki; Ohya, Shinobu; Tanaka, Masaaki
2018-03-01
We investigate the spin-dependent transport properties of a lateral spin-valve device based on the ferromagnetic semiconductor GaMnAs. This device is composed of a GaMnAs channel layer grown on GaAs with a narrow trench across the channel. Its current-voltage characteristics show tunneling behavior. Large magnetoresistance (MR) ratios of more than ˜10% are obtained. These values are much larger than those (˜0.1%) reported for lateral-type spin metal-oxide-semiconductor field-effect transistors. The magnetic field direction dependence of the MR curve differs from that of the anisotropic magnetoresistance of GaMnAs, which confirms that the MR signal originates from the spin-valve effect between the GaMnAs electrodes.
Energy Technology Data Exchange (ETDEWEB)
Iniama, G.; Ita, B. I. [Department of Pure and Applied Chemistry, University of Calabar, Calabar (Nigeria); Presa, P. de la, E-mail: pmpresa@ucm.es; Hernando, A. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Fac. CC Físicas, Dpto. Física de Materiales, Univ. Complutense de Madrid, 28040 Madrid (Spain); Alonso, J. M. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Instituto de Ciencia de Materiales, CSIC, 28049-Madrid (Spain); Multigner, M. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Cortés-Gil, R.; Ruiz-González, M. L. [Fac. CC Químicas, Dpto. Química Inorgánica, Univ. Complutense de Madrid, 28040 Madrid (Spain); Gonzalez-Calbet, J. M. [Instituto de Magnetismo Aplicado, UCM-ADIF-CSIC, 28230 Las Rozas (Spain); Fac. CC Químicas, Dpto. Química Inorgánica, Univ. Complutense de Madrid, 28040 Madrid (Spain)
2014-09-21
In this paper, the physical properties of half-doped manganite La{sub 0.5}Ca{sub 0.5}MnO₃ with crystallite sizes ranging from 15 to 40 nm are investigated. As expected, ferromagnetic order strengthens at expense of antiferromagnetic one as crystallite size is reduced to 15 nm. However, contrary to previously reported works, an enhancement of saturation magnetization is observed as crystallite size increases from 15 to 22 nm. This unexpected behavior is accompanied by an unusual cell volume variation that seems to induce ferromagnetic-like behavior at expense of antiferromagnetic one. Besides, field cooled hysteresis loops show exchange bias field and coercivity enhancement for increasing cooling fields, which suggest a kind of core-shell structure with AFM-FM coupling for crystallite sizes as small as 15 nm. It is expected that inner core orders antiferromagnetically, whereas uncompensated surface spins behave as spin glass with ferromagnetic-like ordering.
Effect of ferromagnetic exchange field on band gap and spin ...
Indian Academy of Sciences (India)
Partha Goswami
2018-02-19
Feb 19, 2018 ... of an electric-field tunable band gap, but like graphene it is a better .... ate energy dispersion of the pristine, pure graphene. ...... The rotation is known as the Faraday .... pave the way to the efficient control of spin generation.
The design and investigation of hybrid ferromagnetic/silicon spin electronic devices
International Nuclear Information System (INIS)
Pugh, D.I.
2001-01-01
The focus of this study concerns the design and investigation of ferromagnetic/silicon hybrid spin electronic devices as part of a wider project to design a novel spin valve transistor. The key issue to obtain a room temperature spin electronic device is the electrical injection of a spin polarised current from a ferromagnetic contact into a semiconductor. Despite many attempts concentrating on GaAs and InAs only small (< 1%) effects have been observed, making it difficult to confirm spin injection. Lateral devices were designed and fabricated using standard device fabrication procedures to produce arrays of Co/Si/So junctions. Subsequent designs aimed to reduce the number of junctions and improve device isolation. Evidence for spin dependent MR of up to 0.56% was observed in Co/p-Si/Co junctions with silicon gaps up to 16 μm in length. The maximum MR was observed when the first Co/Si Schottky barrier was reverse biased forming a high resistance interface. Vertical devices were designed in an attempt to eliminate any alternative current paths by using a well defined, 1 μm thick silicon membrane. Despite attempts to include oxide barriers, no spin dependent MR was observed in these devices. However, a novel vertical silicon based design has been made which should facilitate further advanced studies of spin injection and transport. The spin diffusion length in n-type silicon has been calculated as a function of doping concentration and temperature by considering the spin relaxation mechanisms in the semiconductor. Discussion has been made concerning p-type silicon and comparisons made with GaAs, indicating that n-Si should show longer spin diffusion lengths. The key design criteria for designing room temperature spin electronic devices have been highlighted. These include the use of a high leakage Schottky barrier or tunnel barrier between the ferromagnet and p-Si and a contact to the silicon to enable appropriate biasing to each FM/Si interface. (author)
Coexistence of ferromagnetism and spin glass behavior in antiferromagnetic Y2BaCuO5
International Nuclear Information System (INIS)
Zhu, Zhonghua; Gao, Daqiang; Zhang, Jing; Shi, Zhenhua; Gao, Hua; Yang, Zhaolong; Zhang, Zhipeng; Xue, Desheng
2013-01-01
Highlights: • Room temperature ferromagnetism is observed in ultrafine Y 2 BaCuO 5 particles. • The observed ferromagnetism originates from the oxygen defects. • A very interesting spin glass transition located at about 110 K is found. -- Abstract: We report the synthesis of a series of Y 2 BaCuO 5 samples by varying the annealing temperature with a citrate pyrolysis technique. X-ray diffraction patterns, scanning electron microscopy and transmission electron microscopy observation show the formation of a columnar Y 2 BaCuO 5 phase and these samples are composed of many irregular particles with different particle size. Magnetic measurements show that these samples exhibit room temperature ferromagnetism and the saturation magnetization decreases with increasing sintering temperature. Post-heating treatment under argon atmosphere can enhance the ferromagnetism greatly, suggesting that the magnetism is attributed to the surface oxygen defects. By measuring magnetization versus temperature curves after zero field cooling with various applied magnetic fields, two magnetic phase transitions located at about 11 and 110 K are revealed. The position of the peak at about 11 K is independent of the magnetic field; the other peak, however, becomes rounder and shifts to lower temperatures with increasing the magnetic field, showing a strong field dependence. In addition, the virgin magnetization curves with the measured temperature below 110 K display an S-type. These features are suggestive of an antiferromagnetic phase transition at about 11 K and a spin glass transition at about 110 K
Pseudo spin-valve behavior in oxide ferromagnet/superconductor/ferromagnet trilayers
International Nuclear Information System (INIS)
Pang, B.S.H.; Bell, C.; Tomov, R.I.; Durrell, J.H.; Blamire, M.G.
2005-01-01
La 0.7 Ca 0.3 MnO 3 /YBa 2 Cu 3 O 7-δ /La 0.67 Sr 0.33 MnO 3 heterostructural devices with double coercivity have been fabricated. The superconducting critical current (I c ) and critical temperature in both parallel (P) and antiparallel (AP) magnetic configurations remained unchanged within our measurement limits. This observation is contrary to results obtained elsewhere using similar metallic systems. A pseudo spin-valve magnetoresistive (MR) characteristic was observed at bias current (I bias )∼I c at temperatures below the onset of superconductivity. The effect increased with decreasing temperature and I bias and can be explained using the assumption of the electron spin-charge separation
Formation of spin-polarons in the ferromagnetic Kondo lattice model away from half-filling
International Nuclear Information System (INIS)
Arredondo, Y; Navarro, O; Vallejo, E; Avignon, M
2012-01-01
Even though realistic one-dimensional experiments in the field of half-metallic semiconductors are not at hand yet, we are interested in the underlying fundamental physics. In this regard we study a one-dimensional ferromagnetic Kondo lattice model, a model in which a conduction band is coupled ferromagnetically to a background of localized d moments with coupling constant J H , and investigate the T = 0 phase diagram as a function of the antiferromagnetic interaction J between the localized moments and the band-filling n, since it has been observed that doping of the compounds has led to formation of magnetic domains. We explore the spin-polaron formation by looking at the nearest-neighbour correlation functions in the spin and charge regimes for which we use the density matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems. (paper)
Intraband and interband spin-orbit torques in noncentrosymmetric ferromagnets
Li, Hang; Gao, H.; Zâ rbo, Liviu P.; Vý borný , K.; Wang, Xuhui; Garate, Ion; Dogan, Fatih; Čejchan, A.; Sinova, Jairo; Jungwirth, T.; Manchon, Aurelien
2015-01-01
Intraband and interband contributions to the current-driven spin-orbit torque in magnetic materials lacking inversion symmetry are theoretically studied using the Kubo formula. In addition to the current-driven fieldlike torque TFL=τFLm×uso (uso being a unit vector determined by the symmetry of the spin-orbit coupling), we explore the intrinsic contribution arising from impurity-independent interband transitions and producing an anti-damping-like torque of the form TDL=τDLm×(uso×m). Analytical expressions are obtained in the model case of a magnetic Rashba two-dimensional electron gas, while numerical calculations have been performed on a dilute magnetic semiconductor (Ga,Mn)As modeled by the Kohn-Luttinger Hamiltonian exchange coupled to the Mn moments. Parametric dependencies of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described.
Intraband and interband spin-orbit torques in noncentrosymmetric ferromagnets
Li, Hang
2015-04-01
Intraband and interband contributions to the current-driven spin-orbit torque in magnetic materials lacking inversion symmetry are theoretically studied using the Kubo formula. In addition to the current-driven fieldlike torque TFL=τFLm×uso (uso being a unit vector determined by the symmetry of the spin-orbit coupling), we explore the intrinsic contribution arising from impurity-independent interband transitions and producing an anti-damping-like torque of the form TDL=τDLm×(uso×m). Analytical expressions are obtained in the model case of a magnetic Rashba two-dimensional electron gas, while numerical calculations have been performed on a dilute magnetic semiconductor (Ga,Mn)As modeled by the Kohn-Luttinger Hamiltonian exchange coupled to the Mn moments. Parametric dependencies of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described.
Li, Peng; Xia, Chuan; Zhu, Zhiyong; Wen, Yan; Zhang, Qiang; Alshareef, Husam N.; Zhang, Xixiang
2016-01-01
In spintronics, identifying an effective technique for generating spin-polarized current has fundamental importance. The spin-filtering effect across a ferromagnetic insulating layer originates from unequal tunneling barrier heights for spin
Energy Technology Data Exchange (ETDEWEB)
Verma, Kuldeep Chand, E-mail: dkuldeep.physics@gmail.com [Department of Physics, Panjab University, Chandigarh 160014 (India); Kotnala, R.K., E-mail: rkkotnala@gmail.com [CSIR-National Physical Laboratory, New Delhi 110012 (India)
2017-02-15
Future spintronics technologies based on diluted magnetic semiconductors (DMS) will rely heavily on a sound understanding of the microscopic origins of ferromagnetism in such materials. It remains unclear, however, whether the ferromagnetism in DMS is intrinsic - a precondition for spintronics - or due to dopant clustering. For this, we include a simultaneous doping from transition metal (Ni, Cu) and rare earth (Ce) ions in ZnO nanoparticles that increase the antiferromagnetic ordering to achieve high-T{sub c} ferromagnetism. Rietveld refinement of XRD patterns indicate that the dopant ions in ZnO had a wurtzite structure and the dopants, Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions, are highly influenced the lattice constants to induce lattice defects. The Ni, Cu, Ce ions in ZnO have nanoparticles formation than nanorods was observed in pure sample. FTIR involve some organic groups to induce lattice defects and the metal-oxygen bonding of Zn, Ni, Cu, Ce and O atoms to confirm wurtzite structure. Raman analysis evaluates the crystalline quality, structural disorder and defects in ZnO lattice with doping. Photoluminescence spectra have strong near-band-edge emission and visible emission bands responsible for defects due to oxygen vacancies. The energy band gap is calculated using Tauc relation. Room temperature ferromagnetism has been described due to bound magnetic polarons formation with Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions in ZnO via oxygen vacancies. The zero field and field cooling SQUID measurement confirm the strength of antiferromagnetism in ZnO. The field cooling magnetization is studied by Curie-Weiss law that include antiferromagnetic interactions up to low temperature. The XPS spectra have involve +3/+4 oxidation states of Ce ions to influence the observed ferromagnetism. - Graphical abstract: The lattice defects/vacancies attributed by Ni and Ce ions in the wurtzite ZnO structure are responsible in high T{sub c} -ferromagnetism due to long-range magnetic
Origin of spin-dependent asymmetries in electron transmission through ultrathin ferromagnetic films
International Nuclear Information System (INIS)
Gokhale, M.P.; Mills, D.L.
1991-01-01
We present theoretical calculations of exchange asymmetries in the transmission of electrons through ultrathin films of ferromagnetic Fe. The results account nicely for the magnitude of the asymmetries observed by Pappas et al. in photoemission studies of Cu covered by an ultrathin film of Fe. We argue that exchange asymmetry in the transmissivity of the Fe film, rather than the spin dependence of the electron mean free path, is responsible for the effects reported by these authors
Spin wave isolator based on frequency displacement nonreciprocity in ferromagnetic bilayer
Energy Technology Data Exchange (ETDEWEB)
Shichi, Shinsuke, E-mail: shinsuke-shichi@murata.com; Matsuda, Kenji; Okajima, Shingo; Hasegawa, Takashi; Okada, Takekazu [Murata Manufacturing Co., Ltd., Kyoto 617-8555 (Japan); Kanazawa, Naoki; Goto, Taichi, E-mail: goto@ee.tut.ac.jp; Takagi, Hiroyuki; Inoue, Mitsuteru [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibari-Ga-Oka, Tempaku, Toyohashi, Aichi 441-8580 (Japan)
2015-05-07
We demonstrated the spin wave isolator using bilayer ferromagnetic media comprising single crystalline and poly-crystalline yttrium iron garnet films, which can control the propagation frequency of magnetostatic waves by the direction of applied magnetic field. This isolator's property does not depend on their thickness then this can be downsized and integrated for nano-scale magnonic circuits. Calculated dispersion relationship shows good agreement with measured one.
Ferromagnetic transitions of a spin-one Ising film in a surface and bulk transverse fields
International Nuclear Information System (INIS)
Saber, A.; Lo Russo, S.; Mattei, G.; Mattoni, A.
2002-01-01
Using the effective field theory method, we have calculated the Curie temperature of a spin-one Ising ferromagnetic film in a surface and bulk transverse fields. Numerical calculations give phase diagrams under various parameters. Surface exchange enhancement is considered. The dependence of the critical transverse field on film thickness, and phase diagrams in the fields, critical surface transverse field versus the bulk one are presented
Lazic, Predrag; Sipahi, Guilherme; Kawakami, Roland; Zutic, Igor
2013-03-01
Recent experimental advances in graphene suggest intriguing opportunities for novel spintronic applications which could significantly exceed the state-of-the art performance of their conventional charge-based counterparts. However, for reliable operation of such spintronic devices it is important to achieve an efficient spin injection and large magnetoresistive effects. We use the first principles calculations to guide the choice of a ferromagnetic region and its relative orientation to optimize the desired effects. We propose structures which could enable uniform spin injection, one of the key factors in implementing scalable spintronic circuits. Supported by NSF-NRI, SRC, ONR, Croatian Ministry of Science, Education, and Sports, and CCR at SUNY UB.
Spin spring behavior in exchange coupled soft and high-coercivity hard ferromagnets.
Energy Technology Data Exchange (ETDEWEB)
Shull, R. D.; Shapiro, A. J.; Gornakov, V. S.; Nikitenko, V. I.; Jiang, J. S.; Kaper, H.; Leaf, G.; Bader, S. D.
2000-11-01
The magnetization reversal processes in an epitaxial Fe/Sm{sub 2}Co{sub 7} structure were investigated using the magneto-optical indicator film technique. The dependence of the magnitude and the orientation of the structure average magnetization have been studied on both cycling and rotating the external magnetic field. It was discovered that the magnetization reversal of the soft ferromagnet can proceed by formation of not only one-dimensional, but also two-dimensional, exchange spin springs. Experimental data is compared with a theoretical estimation of the rotational hysteresis loop for a spin system containing a one-dimensional exchange spring.
The ferromagnet spin-1/2 Ising superlattice in a transverse field
International Nuclear Information System (INIS)
Bouziane, T.; Saber, M.; Belaaraj, A.; Ainane, A.
1998-09-01
The phase transitions of a ferromagnet spin-1/2 Ising superlattice consisting of two different materials in a transverse field is examined with the use of effective field theory that accounts for the self-spin function correlation. The critical temperature of the system is studied as a function of the thickness of the constituents in a unit cell and of exchange interactions in each material. A critical interface exchange interaction above which the interface magnetism appears is found. The effects of a uniform transverse field and the interface exchange interaction on the parameters of the system are also investigated. (author)
Electronic heat, charge and spin transport in superconductor-ferromagnetic insulator structures
Energy Technology Data Exchange (ETDEWEB)
Bergeret, Sebastian [Materials Physics Center (CFM-CSIC), San Sebastian (Spain); Donostia International Physics Center (DIPC), San Sebastian (Spain)
2015-07-01
It is known for some time that a superconducting (S) film in contact with a ferromagnetic insulator (FI) exhibits a spin-splitting in the density of states (DoS). Recently we have explored different S-FI hybrid structures and predicted novel effects exploiting such spin-splitting of the DoS. In this talk I will briefly discuss (i) a heat valve based on a FI-S-I-S-FI Josephson junction; (ii) a thermoelectric transistor and (iii) the occurrence of a giant thermophase in a thermally-biased Josephson junction.
Kally, James; Lv, Yang; Zhang, Delin; Lee, Joon Sue; Samarth, Nitin; Wang, Jian-Ping; Department of Electrical; Computer Engineering, University of Minnesota, Minneapolis Collaboration; Department of Physics, Pennsylvania State University Collaboration
The surface states of topological insulators offer a potentially very efficient way to generate spins and spin-orbit torques to magnetic moments in proximity. The switching by spin-orbit torque itself only requires two terminals so that a charge current can be applied. However, a third terminal with additional magnetic tunneling junction structure is needed to sense the magnetization state if such devices are used for memory and logic applications. The recent discovery of unidirectional spin Hall magnetoresistance in heavy metal/ferromagnetic and topological insulator/magnetically doped topological insulator systems offers an alternative way to sense magnetization while still keeping the number of terminals to minimal two. The unidirectional spin Hall magnetoresistance in topological insulator/strong ferromagnetic layer heterostructure system has yet not been reported. In this work, we report our experimental observations of such magnetoresistance. It is found to be present and comparable to the best result of the previous reported Ta/Co systems in terms of magnetoresistance per current density per total resistance.
Lv, Yang; Kally, James; Zhang, Delin; Lee, Joon Sue; Jamali, Mahdi; Samarth, Nitin; Wang, Jian-Ping
2018-01-09
The large spin-orbit coupling in topological insulators results in helical spin-textured Dirac surface states that are attractive for topological spintronics. These states generate an efficient spin-orbit torque on proximal magnetic moments. However, memory or logic spin devices based upon such switching require a non-optimal three-terminal geometry, with two terminals for the writing current and one for reading the state of the device. An alternative two-terminal device geometry is now possible by exploiting the recent discovery of the unidirectional spin Hall magnetoresistance in heavy metal/ferromagnet bilayers and unidirectional magnetoresistance in magnetic topological insulators. Here, we report the observation of such unidirectional magnetoresistance in a technologically relevant device geometry that combines a topological insulator with a conventional ferromagnetic metal. Our devices show a figure of merit (magnetoresistance per current density per total resistance) that is more than twice as large as the highest reported values in all-metal Ta/Co bilayers.
Electron spin resonance for the detection of long-range spin nematic order
Furuya, Shunsuke C.; Momoi, Tsutomu
2018-03-01
Spin nematic phase is a quantum magnetic phase characterized by a quadrupolar order parameter. Since the quadrupole operators are directly coupled to neither the magnetic field nor the neutron, currently, it is an important issue to develop a method for detecting the long-range spin nematic order. In this paper, we propose that electron spin resonance (ESR) measurements enable us to detect the long-range spin nematic order. We show that the frequency of the paramagnetic resonance peak in the ESR spectrum is shifted by the ferroquadrupolar order parameter together with other quantities. The ferroquadrupolar order parameter is extractable from the angular dependence of the frequency shift. In contrast, the antiferroquadrupolar order parameter is usually invisible in the frequency shift. Instead, the long-range antiferroquadrupolar order yields a characteristic resonance peak in the ESR spectrum, which we call a magnon-pair resonance peak. This resonance corresponds to the excitation of the bound magnon pair at the wave vector k =0 . Reflecting the condensation of bound magnon pairs, the field dependence of the magnon-pair resonance frequency shows a singular upturn at the saturation field. Moreover, the intensity of the magnon-pair resonance peak shows a characteristic angular dependence and it vanishes when the magnetic field is parallel to one of the axes that diagonalize the weak anisotropic interactions. We confirm these general properties of the magnon-pair resonance peak in the spin nematic phase by studying an S =1 bilinear-biquadratic model on the square lattice in the linear flavor-wave approximation. In addition, we argue applications to the S =1/2 frustrated ferromagnets and also the S =1/2 orthogonal dimer spin system SrCu2(BO3)2, both of which are candidate materials of spin nematics. Our theory for the antiferroquadrupolar ordered phase is consistent with many features of the magnon-pair resonance peak experimentally observed in the low
Ferromagnetic ordering and halfmetallic state in a shandite: Co3Sn2S2
Schnelle, Walter; Leithe-Jasper, Andreas; Rosner, Helge; Weihrich, Richard
2013-03-01
The rapid advance in spintronics challenges an improved understanding of the underlying microscopic properties. Here, we present a joint experimental and theoretical study of Co3Sn2S2 (shandite) and related compounds. From magnetic susceptibility, specific heat and magneto-transport measurements on a shandite single crystal sample we find a phase transition to a ferromagnetic metallic state at 177 K with a saturation moment of 0.92 μB/f.u. Full potential electronic structure calculations within the local spin density approximation result in a halfmetallic ferromagnetic groundstate with a moment of 1 μB/f.u. and a tiny gap in the minority spin channel. The calculated structure optimization and structure variations show that the size of the gap is rather sensitive to the lattice geometry. Possiblities to stabilize the halfmetallic ferromagnetic behavior by various substitutions have been studied theoretically and will be discussed.
International Nuclear Information System (INIS)
Crisanti, Andrea; Leuzzi, Luca
2013-01-01
We report some results on the quenched disordered Spherical multi-p-Spin Model in presence of ferromagnetic couplings. In particular, we present the phase diagrams of some representative cases that schematically describe, in the mean-field approximation, the behavior of most known transitions in glassy materials, including dynamic arrest in super-cooled liquids, amorphous–amorphous transitions and spin–glass transitions. A simplified notation is introduced in order to compute systems properties in terms of an effective, self-induced, field encoding the whole ferromagnetic information
The Order Parameter in a Spin Glass
Enter, A.C.D. van; Griffiths, Robert B.
1983-01-01
Various possible precise definitions of an Edwards-Anderson type of order parameter for an Ising model spin glass are considered, using boundary conditions for a finite system, states of an infinite system, and a duplicate-system approach. Several of these definitions are shown to yield identical
Evolution of ferromagnetic interactions from cluster spin glass state in Co–Ga alloy
Energy Technology Data Exchange (ETDEWEB)
Mohammad Yasin, Sk. [Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India); Saha, Ritwik [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005 (India); Srinivas, V., E-mail: veeturi@iitm.ac.in [Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India); Kasiviswanathan, S. [Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India); Nigam, A.K. [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005 (India)
2016-11-15
Low temperature magnetic properties of binary Co{sub x}Ga{sub 100−x} (x=54–57) alloy have been investigated. Analysis of frequency dependence of ac susceptibility provided a conclusive evidence for the existence of cluster spin glass like behavior with the freezing temperature ~8, 14 K for x=54, 55.5 respectively. The parameters for conventional ‘slowing down’ of the spin dynamics have been extracted from the acs data, which confirm the presence of glassy phase. The magnitude of Mydosh parameter obtained from the fits is larger than that reported for typical canonical spin glasses and smaller than those for non-interacting ideal superparamagnetic systems but comparable to those of known cluster-glass systems. Memory phenomena using specific cooling protocols also support the spin-glass features in Co{sub 55.5}Ga{sub 44.5} composition. Further the development of ferromagnetic clusters from the cluster spin glass state has been observed in x=57 composition. - Highlights: • Temperature dependence of DC and AC susceptibility (acs) analysis has been carried out on Co{sub x}Ga{sub 1−x,} (x=54–57). • M–H data above transition suggests presence of spin clusters. • A detailed analysis of acs data suggests a cluster glass behavior as oppose to SPM state for x=54 and 55.5. • Memory phenomena using specific cooling protocols also support the spin-glass features in Co{sub 55.5}Ga{sub 44.5} composition. • Development of ferromagnetic like behavior for x≥57 has been suggested from DC and AC magnetization data.
Spin wave dynamics in Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes
Energy Technology Data Exchange (ETDEWEB)
Mi, Bin-Zhou, E-mail: mbzfjerry2008@126.com [Department of Basic Curriculum, North China Institute of Science and Technology, Beijing 101601 (China); Department of Physics, School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083 (China)
2016-09-15
The spin wave dynamics, including the magnetization, spin wave dispersion relation, and energy level splitting, of Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes are systematically calculated by use of the double-time Green’s function method within the random phase approximation. The role of temperature, diameter of the tube, and wave vector on spin wave energy spectrum and energy level splitting are carefully analyzed. There are two categories of spin wave modes, which are quantized and degenerate, and the total number of independent magnon branches is dependent on diameter of the tube, caused by the physical symmetry of nanotubes. Moreover, the number of flat spin wave modes increases with diameter of the tube rising. The spin wave energy and the energy level splitting decrease with temperature rising, and become zero as temperature reaches the critical point. At any temperature, the energy level splitting varies with wave vector, and for a larger wave vector it is smaller. When pb=π, the boundary of first Brillouin zone, spin wave energies are degenerate, and the energy level splittings are zero.
Nonlinear nano-scale localized breather modes in a discrete weak ferromagnetic spin lattice
International Nuclear Information System (INIS)
Kavitha, L.; Parasuraman, E.; Gopi, D.; Prabhu, A.; Vicencio, Rodrigo A.
2016-01-01
We investigate the propagation dynamics of highly localized discrete breather modes in a weak ferromagnetic spin lattice with on-site easy axis anisotropy due to crystal field effect. We derive the discrete nonlinear equation of motion by employing boson mappings and p-representation. We explore the onset of modulational instability both analytically in the framework of linear stability analysis and numerically by means of molecular dynamics (MD) simulations, and a perfect agreement was demonstrated. It is also explored that how the antisymmetric nature of the canted ferromagnetic lattice supports highly localized discrete breather (DBs) modes as shown in the stability/instability windows. The energy exchange between low amplitude discrete breathers favours the growth of higher amplitude DBs, resulting eventually in the formation of few long-lived high amplitude DBs. - Highlights: • The effects of DM and anisotropy interaction on the DB modes are studied. • The antisymmetric nature of the canted ferromagnetic medium supports the DB modes. • Dynamics of ferromagnetic chain is governed by boson mappings and p-representation.
Pressure-induced spin reorientation transition in layered ferromagnetic insulator Cr2Ge2Te6
Lin, Zhisheng; Lohmann, Mark; Ali, Zulfikhar A.; Tang, Chi; Li, Junxue; Xing, Wenyu; Zhong, Jiangnan; Jia, Shuang; Han, Wei; Coh, Sinisa; Beyermann, Ward; Shi, Jing
2018-05-01
The anisotropic magnetoresistance (AMR) of Cr2Ge2Te6 (CGT), a layered ferromagnetic insulator, is investigated under an applied hydrostatic pressure up to 2 GPa. The easy-axis direction of the magnetization is inferred from the AMR saturation feature in the presence and absence of an applied pressure. At zero applied pressure, the easy axis is along the c direction or perpendicular to the layer. Upon application of a hydrostatic pressure > 1 GPa, the uniaxial anisotropy switches to easy-plane anisotropy which drives the equilibrium magnetization from the c axis to the a b plane at zero magnetic field, which amounts to a giant magnetic anisotropy energy change (> 100%). As the temperature is increased across the Curie temperature, the characteristic AMR effect gradually decreases and disappears. Our first-principles calculations confirm the giant magnetic anisotropy energy change with moderate pressure and assign its origin to the increased off-site spin-orbit interaction of Te atoms due to a shorter Cr-Te distance. Such a pressure-induced spin reorientation transition is very rare in three-dimensional ferromagnets, but it may be common to other layered ferromagnets with similar crystal structures to CGT, and therefore offers a unique way to control magnetic anisotropy.
Zhang, Shuhui; Rong, Jianhong; Wang, Huan; Wang, Dong; Zhang, Lei
2018-01-01
We have investigated the dependence of spin-wave resonance(SWR) frequency on the surface anisotropy, the interlayer exchange coupling, the ferromagnetic layer thickness, the mode number and the external magnetic field in a ferromagnetic superlattice film by means of the linear spin-wave approximation and Green's function technique. The SWR frequency of the ferromagnetic thin film is shifted to higher values corresponding to those of above factors, respectively. It is found that the linear behavior of SWR frequency curves of all modes in the system is observed as the external magnetic field is increasing, however, SWR frequency curves are nonlinear with the lower and the higher modes for different surface anisotropy and interlayer exchange coupling in the system. In addition, the SWR frequency of the lowest (highest) mode is shifted to higher (lower) values when the film thickness is thinner. The interlayer exchange coupling is more important for the energetically higher modes than for the energetically lower modes. The surface anisotropy has a little effect on the SWR frequency of the highest mode, when the surface anisotropy field is further increased.
International Nuclear Information System (INIS)
Ning, Deng; Lei, Zhang; Shu-Chao, Zhang; Pei-Yi, Chen; Jian-Shi, Tang
2010-01-01
For ferromagnetic metal (FM)/semiconductor (SC) structure with ohmic contact, the effect of carrier polarization in the semiconductor combined with drift part of injection current on current polarization is investigated. Based on the general model we established here, spin injection efficiency under different injection current levels is calculated. Under a reasonable high injection current, current polarization in the semiconductor is actually much larger than that predicted by the conductivity mismatch model because the effect of carrier polarization is enhanced by the increasing drift current. An appreciable current polarization of 1% could be achieved for the FM/SC structure via ohmic contact, which means that efficient spin injection from FM into SC via ohmic contact is possible. The reported dependence of current polarization on temperature is verified quantitatively. To achieve even larger spin injection efficiency, a gradient doping semiconductor is suggested to enhance the drift current effect
Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer
Gross, I.; Akhtar, W.; Garcia, V.; Martínez, L. J.; Chouaieb, S.; Garcia, K.; Carrétéro, C.; Barthélémy, A.; Appel, P.; Maletinsky, P.; Kim, J.-V.; Chauleau, J. Y.; Jaouen, N.; Viret, M.; Bibes, M.; Fusil, S.; Jacques, V.
2017-09-01
Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin-orbit effects that enable efficient spin-charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen-vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.
An effective correlated mean-field theory applied in the spin-1/2 Ising ferromagnetic model
Energy Technology Data Exchange (ETDEWEB)
Roberto Viana, J.; Salmon, Octávio R. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil); National Institute of Science and Technology for Complex Systems, Universidade Federal do Amazonas, 3000, Japiim, 69077-000 Manaus, AM (Brazil); Neto, Minos A.; Padilha, Igor T. [Universidade Federal do Amazonas – UFAM, Manaus 69077-000, AM (Brazil)
2014-11-15
We developed a new treatment for mean-field theory applied in spins systems, denominated effective correlated mean-field (ECMF). We apply this theory to study the spin-1/2 Ising ferromagnetic model with nearest-neighbor interactions on a square lattice. We use clusters of finite sizes and study the criticality of the ferromagnetic system, where we obtain a convergence of critical temperature for the value k{sub B}T{sub c}/J≃2.27905±0.00141. Also the behavior of magnetic and thermodynamic properties, using the condition of minimum energy of the physical system is obtained. - Highlights: • We developed spin models to study real magnetic systems. • We study the thermodynamic and magnetic properties of the ferromagnetism. • We enhanced a mean-field theory applied in spins models.
Magnetic properties of a ferromagnet spin-S, Ising, XY and Heisenberg models semi-infinites systems
International Nuclear Information System (INIS)
Masrour, R.; Hamedoun, M.; Hourmatallah, A.; Bouslykhane, K.; Benzakour, N.
2008-01-01
The magnetic properties of a ferromagnet spin-S a disordered semi-infinite system with a face-centered cubic lattice are investigated using the high-temperature series expansions technique extrapolated with Pade approximants method for Heisenberg, XY and Ising models. The reduced critical temperature of the system τ c =(k B T c )/(2S(S+1)J b ) is studied as function of the thickness of the film and the exchange interactions in the bulk, and within the surfaces J b ,J s and J perpendicular , respectively. It is found that τ c increases with the exchange interactions of surface. The magnetic phase diagrams (τ c versus the dilution x) and the percolation threshold are obtained
Rezende, Sergio M.; Azevedo, Antonio; Rodríguez-Suárez, Roberto L.
2018-05-01
In magnetic insulators, spin currents are carried by the elementary excitations of the magnetization: spin waves or magnons. In simple ferromagnetic insulators there is only one magnon mode, while in two-sublattice antiferromagnetic insulators (AFIs) there are two modes, which carry spin currents in opposite directions. Here we present a theory for the diffusive magnonic spin current generated in a magnetic insulator layer by a thermal gradient in the spin Seebeck effect. We show that the formulations describing magnonic perturbation using a position-dependent chemical potential and those using a magnon accumulation are completely equivalent. Then we develop a drift–diffusion formulation for magnonic spin transport treating the magnon accumulation governed by the Boltzmann transport and diffusion equations and considering the full boundary conditions at the surfaces and interfaces of an AFI/normal metal bilayer. The theory is applied to the ferrimagnetic yttrium iron garnet and to the AFIs MnF2 and NiO, providing good quantitative agreement with experimental data.
Topological Hall effect in diffusive ferromagnetic thin films with spin-flip scattering
Zhang, Steven S.-L.; Heinonen, Olle
2018-04-01
We study the topological Hall (TH) effect in a diffusive ferromagnetic metal thin film by solving a Boltzmann transport equation in the presence of spin-flip scattering. A generalized spin-diffusion equation is derived which contains an additional source term associated with the gradient of the emergent magnetic field that arises from skyrmions. Because of the source term, spin accumulation may build up in the vicinity of the skyrmions. This gives rise to a spin-polarized diffusion current that in general suppresses the bulk TH current. Only when the spin-diffusion length is much smaller than the skyrmion size does the TH resistivity approach the value derived by Bruno et al. [Phys. Rev. Lett. 93, 096806 (2004), 10.1103/PhysRevLett.93.096806]. We derive a general expression of the TH resistivity that applies to thin-film geometries with spin-flip scattering, and show that the corrections to the TH resistivity become large when the size of room temperature skyrmions is further reduced to tens of nanometers.
Energy Technology Data Exchange (ETDEWEB)
Rashidian, Zeinab; Rezaeipour, Saeid [Department of Physics, Faculty of Science, Lorestan University, Lorestan (Iran, Islamic Republic of); Hajati, Yaser [Department of Physics, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of); Lorestaniweiss, Zeinab, E-mail: rashidian1983z@gmail.com [Department of Physics, Faculty of Science, Lorestan University, Lorestan (Iran, Islamic Republic of); Ueda, Akiko [Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba (Japan)
2017-02-15
In this work, we study the transport properties of Dirac fermions through the ferromagnetic silicene which is sandwiched between the Graphene leads (G/FS/G). Spin/valley conductance, spin/valley polarization, and also Fano factor are theoretically calculated using the Landauer-Buttiker formula. We find that the fully valley and spin polarized currents through the G/FS/G junction can be obtained by increasing the electric field strength and the length of ferromagnetic silicene region. Moreover, the valley polarization can be tuned from negative to positive values by changing the electric field. We find that the Fano factor also changes with the spin and valley polarization. Our findings of high controllability of the spin and valley transport in such a G/FS/G junction the potential of this junction for spin-valleytronics applications.
Da Pieve, F.
2016-01-01
A method for mapping the local spin and orbital nature of the ground state of a system via corresponding flip excitations is proposed based on angle-resolved resonant photoemission and related diffraction patterns, obtained here via an ab initio modified one-step theory of photoemission. The analysis is done on the paradigmatic weak itinerant ferromagnet bcc Fe, whose magnetism, a correlation phenomenon given by the coexistence of localized moments and itinerant electrons, and the observed non-Fermi-Liquid behavior at extreme conditions both remain unclear. The combined analysis of energy spectra and diffraction patterns offers a mapping of local pure spin-flip, entangled spin-flip-orbital-flip excitations and chiral transitions with vortexlike wave fronts of photoelectrons, depending on the valence orbital symmetry and the direction of the local magnetic moment. Such effects, mediated by the hole polarization, make resonant photoemission a promising tool to perform a full tomography of the local magnetic properties even in itinerant ferromagnets or macroscopically nonmagnetic systems.
Electrical detection of spin transport in lateral ferromagnet-semiconductor devices
Lou, Xiaohua
2007-03-01
A fully electrical scheme of spin injection, transport, and detection in a single ferromagnet-semiconductor structure has been a long-standing goal in the field of spintronics. In this talk, we report on an experimental demonstration of such a scheme. The devices are fabricated from epitaxial Fe/GaAs (100) heterostructures with highly doped GaAs as a Schottky tunnel barrier. A set of closely spaced Fe contacts on the top of an n-GaAs channel are used as spin injectors and detectors. Reference electrodes are placed at the far ends of the channel, allowing for non-local spin detection [1]. The electro-chemical potential of the detector is sensitive to the relative magnetizations of the injector and detector. In spin-valve measurements, a magnetic field is applied along the Fe easy axis to switch the relative magnetizations of injector and detector from parallel to antiparallel, resulting in a voltage jump that is proportional to the non-equilibrium spin polarization in the channel. A more rigorous test of electrical spin detection is the observation of the Hanle effect, in which an out-of-plane magnetic field is used to modulate and dephase the spin polarization in the channel. The magnitudes of the observed Hanle curves agree with the results of the spin-valve measurements. The dependence of the Hanle curves on temperature and contact separation is studied in detail and is consistent with a drift-diffusion model incorporating spin precession and relaxation. The spin polarization generated by spin injection (reverse bias at the injector) or spin accumulation (forward bias at the injector) is measured using the magneto-optical Kerr effect and is found to be in good agreement with the spin-dependent non-local voltage. Both the transport and optical measurements show a non-linear relationship between the bias voltage at the injector and the spin polarization in the channel. [1] M. Johnson and R. H. Silsbee, Phys. Rev. Lett. 55, 1790 (1985).
Spin-polarized neutron matter at different orders of chiral effective field theory
Sammarruca, F.; Machleidt, R.; Kaiser, N.
2015-01-01
Spin-polarized neutron matter is studied using chiral two- and three-body forces. We focus, in particular, on predictions of the energy per particle in ferromagnetic neutron matter at different orders of chiral effective field theory and for different choices of the resolution scale. We discuss the convergence pattern of the predictions and their cutoff dependence. We explore to which extent fully polarized neutron matter behaves (nearly) like a free Fermi gas. We also consider the more gener...
Tilted spin torque-driven ferromagnetic resonance in a perpendicular-analyzer magnetic trilayer
International Nuclear Information System (INIS)
Wang Rixing; He Pengbin; Liu Quanhui; Li Zaidong; Pan Anlian; Zou Bingsuo; Wang Yanguo
2010-01-01
A theoretical study is presented on the current-driven ferromagnetic resonance in the magnetic trilayers. On the basis of the Landau-Lifshitz-Gilbert-Slonczewski equation, we derive the output dc voltage for arbitrary anisotropy in the free and pinned layers by the linearization method. As an example, the resonance spectra of the tilted-polarizer and perpendicular-analyzer trilayer show that the equilibrium position, the resonant linewidth and the resonant location can be tuned by changing the magnitude and the direction of spin torque. The effective damping can be minimized through adjusting the current and the pinned-layer magnetization direction.
Directory of Open Access Journals (Sweden)
A. F. Kravets
2017-05-01
Full Text Available In this work we focus on magnetic relaxation in Mn80Ir20(12 nm/Cu(6 nm/Py(dF antiferromagnet/Cu/ferromagnet (AFM/Cu/FM multilayers with different thickness of the ferromagnetic permalloy layer. An effective FM-AFM interaction mediated via the conduction electrons in the nonmagnetic Cu spacer – the spin-pumping effect – is detected as an increase in the linewidth of the ferromagnetic resonance (FMR spectra and a shift of the resonant magnetic field. We further find experimentally that the spin-pumping-induced contribution to the linewidth is inversely proportional to the thickness of the Py layer. We show that this thickness dependence likely originates from the dissipative dynamics of the free and localized spins in the AFM layer. The results obtained could be used for tailoring the dissipative properties of spintronic devices incorporating antiferromagnetic layers.
Field-induced quantum criticality of a spin-1/2 planar ferromagnet
International Nuclear Information System (INIS)
Mercaldo, M T; Rabuffo, I; Cesare, L De; D'Auria, A Caramico
2009-01-01
The low-temperature critical properties and crossovers of a spin- 1/2 planar ferromagnet in a longitudinal magnetic field are explored in terms of an anisotropic bosonic action, suitable to describe the spin model in the low-temperature regime. This is performed adopting a procedure which combines an averaging over dynamic degrees of freedom and the classical Wilson renormalization group transformation. Within this framework we get the phase boundary, ending in a quantum critical point, and general expressions for the correlation length and susceptibility as functions of the temperature and the applied magnetic field within the disordered phase. In particular, two crossovers occur decreasing the temperature with the magnetic field fixed at its quantum critical point value, which might be actually observable in complex magnetic compounds, as suggested by recent experiments.
Spin-orbit driven ferromagnetic resonance: a nanoscale magnetic characterisation technique
Czech Academy of Sciences Publication Activity Database
Fang, D.; Kurebayashi, H.; Wunderlich, Joerg; Výborný, Karel; Zarbo, Liviu; Campion, R. P.; Casiraghi, A.; Gallagher, B. L.; Jungwirth, Tomáš; Ferguson, A.J.
2011-01-01
Roč. 6, č. 7 (2011), s. 413-417 ISSN 1748-3387 R&D Projects: GA AV ČR KAN400100652; GA MŠk LC510; GA AV ČR KJB100100802; GA MŠk(CZ) 7E08087 EU Projects: European Commission(XE) 214499 - NAMASTE; European Commission(XE) 215368 - SemiSpinNet Grant - others:AV ČR(CZ) AP0801 Program:Akademická prémie - Praemium Academiae Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic resonance * spin-orbit coupling * nanomagnets Subject RIV: BM - Solid Matter Physics ; Magnet ism Impact factor: 27.270, year: 2011
Investigation of ferromagnetic resonance and magnetoresistance in anti-spin ice structures
Ribeiro, I. R. B.; Felix, J. F.; Figueiredo, L. C.; Morais, P. C.; Ferreira, S. O.; Moura-Melo, W. A.; Pereira, A. R.; Quindeau, A.; de Araujo, C. I. L.
2016-11-01
In this work, we report experimental and theoretical investigations performed in anti-spin ice structures, composed by square lattice of elongated antidots, patterned in nickel thin film. The magnetic vortex crystal state was obtained by micromagnetic simulation as the ground state magnetization, which arises due to the magnetic stray field at the antidot edges inducing chirality in the magnetization of platters among antidots. Ferromagnetic resonance (FMR) and magnetoresistance (MR) measurements were utilized to investigate the vortex crystal magnetization dynamics and magnetoelectric response. By using FMR, it was possible to detect the spin wave modes and vortex crystal resonance, in good agreement with dynamic micromagnetic simulation results. The vortex crystal magnetization configuration and its response to the external magnetic field, were used to explain the isotropic MR behaviour observed.
Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep
2016-06-01
High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.
Gan, Liyong; Cheng, Yingchun; Schwingenschlö gl, Udo; Zhang, Qingyun
2013-01-01
We study the ferromagnet/semiconductor contacts formed by transition metal dichalcogenide monolayers, focusing on semiconducting MoS2 and WS2 and ferromagnetic VS2. We investigate the degree of p-type doping and demonstrate tuning of the Schottky barrier height by vertical compressive pressure. An analytical model is presented for the barrier heights that accurately describes the numerical findings and is expected to be of general validity for all transition metal dichalcogenide metal/semiconductor contacts. Furthermore, magnetic proximity effects induce a 100% spin polarization at the Fermi level in the semiconductor where the spin splitting increases up to 0.70 eV for increasing pressure.
Gan, Liyong
2013-09-26
We study the ferromagnet/semiconductor contacts formed by transition metal dichalcogenide monolayers, focusing on semiconducting MoS2 and WS2 and ferromagnetic VS2. We investigate the degree of p-type doping and demonstrate tuning of the Schottky barrier height by vertical compressive pressure. An analytical model is presented for the barrier heights that accurately describes the numerical findings and is expected to be of general validity for all transition metal dichalcogenide metal/semiconductor contacts. Furthermore, magnetic proximity effects induce a 100% spin polarization at the Fermi level in the semiconductor where the spin splitting increases up to 0.70 eV for increasing pressure.
Jurčišinová, E.; Jurčišin, M.
2017-11-01
We investigate the influence of the multisite interaction among sites within elementary triangles of the kagome-like recursive lattice on the properties of the classical spin- 1 / 2 ferromagnetic Ising model in the external magnetic field. The exact solution of the model is found and it is shown that the model exhibits a nontrivial structure of the first order as well as second order phase transitions in nonzero external magnetic fields related to the multisite interaction. The equation for the exact determination of the positions of the critical points of the second order phase transitions is derived. The thermodynamic properties of the model are investigated in detail and it is shown that the competition between the ferromagnetic interaction and the multisite interaction leads to the appearance of strong ferromagnetic frustration effects represented by the formation of a nontrivial system of macroscopically degenerated plateau-like and single-point-like ground states. The residual entropies of all ground states are found and the kagome spin-ice-like highly macroscopically degenerated plateau state with nonzero magnetization is identified with the exact residual entropy per site s /kB = ln(4 / 3) / 3 ≈ 0 . 095894. The properties of the specific heat are investigated, its Schottky-type behavior near the single-point ground state values of the magnetic field is identified, the existence of large magnetocaloric effect is discussed, and the existence of the first order phase transitions without the specific heat capacity change is demonstrated.
Goswami, Partha
2018-03-01
We calculate the electronic band dispersion of graphene monolayer on a two-dimensional transition metal dichalcogenide substrate (GrTMD) around K and K^' } points by taking into account the interplay of the ferromagnetic impurities and the substrate-induced interactions. The latter are (strongly enhanced) intrinsic spin-orbit interaction (SOI), the extrinsic Rashba spin-orbit interaction (RSOI) and the one related to the transfer of the electronic charge from graphene to substrate. We introduce exchange field ( M) in the Hamiltonian to take into account the deposition of magnetic impurities on the graphene surface. The cavalcade of the perturbations yield particle-hole symmetric band dispersion with an effective Zeeman field due to the interplay of the substrate-induced interactions with RSOI as the prime player. Our graphical analysis with extremely low-lying states strongly suggests the following: The GrTMDs, such as graphene on WY2, exhibit (direct) band-gap narrowing / widening (Moss-Burstein (MB) gap shift) including the increase in spin polarisation ( P) at low temperature due to the increase in the exchange field ( M) at the Dirac points. The polarisation is found to be electric field tunable as well. Finally, there is anticrossing of non-parabolic bands with opposite spins, the gap closing with same spins, etc. around the Dirac points. A direct electric field control of magnetism at the nanoscale is needed here. The magnetic multiferroics, like BiFeO3 (BFO), are useful for this purpose due to the coupling between the magnetic and electric order parameters.
Competing Spin Liquids and Hidden Spin-Nematic Order in Spin Ice with Frustrated Transverse Exchange
Directory of Open Access Journals (Sweden)
Mathieu Taillefumier
2017-12-01
Full Text Available Frustration in magnetic interactions can give rise to disordered ground states with subtle and beautiful properties. The spin ices Ho_{2}Ti_{2}O_{7} and Dy_{2}Ti_{2}O_{7} exemplify this phenomenon, displaying a classical spin-liquid state, with fractionalized magnetic-monopole excitations. Recently, there has been great interest in closely related “quantum spin-ice” materials, following the realization that anisotropic exchange interactions could convert spin ice into a massively entangled, quantum spin liquid, where magnetic monopoles become the charges of an emergent quantum electrodynamics. Here we show that even the simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice, can realize a still-richer scenario. Using a combination of classical Monte Carlo simulation, semiclassical molecular-dynamics simulation, and analytic field theory, we explore the properties of this model for frustrated transverse exchange. We find not one, but three competing forms of spin liquid, as well as a phase with hidden, spin-nematic order. We explore the experimental signatures of each of these different states, making explicit predictions for inelastic neutron scattering. These results show an intriguing similarity to experiments on a range of pyrochlore oxides.
Passarelli, G.; De Filippis, G.; Cataudella, V.; Lucignano, P.
2018-02-01
We investigate the quantum annealing of the ferromagnetic p -spin model in a dissipative environment (p =5 and p =7 ). This model, in the large-p limit, codifies Grover's algorithm for searching in an unsorted database [L. K. Grover, Proceedings of the 28th Annual ACM Symposium on Theory of Computing (ACM, New York, 1996), pp. 212-219]. The dissipative environment is described by a phonon bath in thermal equilibrium at finite temperature. The dynamics is studied in the framework of a Lindblad master equation for the reduced density matrix describing only the spins. Exploiting the symmetries of our model Hamiltonian, we can describe many spins and extrapolate expected trends for large N and p . While at weak system-bath coupling the dissipative environment has detrimental effects on the annealing results, we show that in the intermediate-coupling regime, the phonon bath seems to speed up the annealing at low temperatures. This improvement in the performance is likely not due to thermal fluctuation but rather arises from a correlated spin-bath state and persists even at zero temperature. This result may pave the way to a new scenario in which, by appropriately engineering the system-bath coupling, one may optimize quantum annealing performances below either the purely quantum or the classical limit.
Graziosi, Patrizio; Neophytou, Neophytos
2018-02-01
Newly emerged materials from the family of Heuslers and complex oxides exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much higher than even room temperature. In this work, using the semiclassical top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that utilizes such ferromagnetic semiconductors as channel materials, in addition to ferromagnetic source/drain contacts. Such a device could retain the spin polarization of injected electrons in the channel, the loss of which limits the operation of traditional spin transistors with non-ferromagnetic channels. We examine the operation of four material systems that are currently considered some of the most prominent known ferromagnetic semiconductors: three Heusler-type alloys (Mn2CoAl, CrVZrAl, and CoVZrAl) and one from the oxide family (NiFe2O4). We describe their band structures by using data from DFT (Density Functional Theory) calculations. We investigate under which conditions high spin polarization and significant ION/IOFF ratio, two essential requirements for the spin-MOSFET operation, are both achieved. We show that these particular Heusler channels, in their bulk form, do not have adequate bandgap to provide high ION/IOFF ratios and have small magnetoconductance compared to state-of-the-art devices. However, with confinement into ultra-narrow sizes down to a few nanometers, and by engineering their spin dependent contact resistances, they could prove promising channel materials for the realization of spin-MOSFET transistor devices that offer combined logic and memory functionalities. Although the main compounds of interest in this paper are Mn2CoAl, CrVZrAl, CoVZrAl, and NiFe2O4 alone, we expect that the insight we provide is relevant to other classes of such materials as well.
Coexisting Ferromagnetic and Ferroelectric Order in a CuCl4-based Organic-Inorganic Hybrid
Polyakov, Alexey O.; Arkenbout, Anne H.; Baas, Jacob; Blake, Graeme R.; Meetsma, Auke; Caretta, Antonio; van Loosdrecht, Paul H. M.; Palstra, Thomas T. M.
2012-01-01
We investigate the structural, magnetic, and dielectric properties of the organic-inorganic hybrid material CuCl4(C6H5CH2CH2NH3)(2) and demonstrate that spontaneous ferroelectric order sets in below 340 K, which coexists with ferromagnetic ordering below 13 K. We use X-ray diffraction to show that
Energy Technology Data Exchange (ETDEWEB)
Halterman, Klaus [Physics and Computational Sciences, Research and Engineering Sciences Department, Naval Air Warfare Center, China Lake, CA 93555 (United States)]. E-mail: klaus.halterman@navy.mil; Valls, Oriol T. [School of Physics and Astronomy and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455 (United States)]. E-mail: otvalls@umn.edu
2005-04-01
We analyze the local density of states (LDOS) of heterostructures consisting of alternating ferromagnet, F, and superconductor, S, layers. We consider structures of the SFS and SFSFSFS type, with thin nanometer scale F and S layers, within the ballistic regime. The spin-splitting effects of the ferromagnet and the mutual coupling between the S regions, yield several nontrivial stable and metastable pair amplitude configurations, and we find that the details of the spatial behavior of the pair amplitude govern the calculated electronic spectra. These are reflected in discernible signatures of the LDOS. The roles that the magnetic exchange energy, interface scattering strength, and the Fermi wavevector mismatch each have on the LDOS for the different allowed junction configurations, are systematically investigated.
International Nuclear Information System (INIS)
Halterman, Klaus; Valls, Oriol T.
2005-01-01
We analyze the local density of states (LDOS) of heterostructures consisting of alternating ferromagnet, F, and superconductor, S, layers. We consider structures of the SFS and SFSFSFS type, with thin nanometer scale F and S layers, within the ballistic regime. The spin-splitting effects of the ferromagnet and the mutual coupling between the S regions, yield several nontrivial stable and metastable pair amplitude configurations, and we find that the details of the spatial behavior of the pair amplitude govern the calculated electronic spectra. These are reflected in discernible signatures of the LDOS. The roles that the magnetic exchange energy, interface scattering strength, and the Fermi wavevector mismatch each have on the LDOS for the different allowed junction configurations, are systematically investigated
Ferromagnetic resonance and spin-wave resonances in GaMnAsP films
Liu, Xinyu; Li, Xiang; Bac, Seul-Ki; Zhang, Xucheng; Dong, Sining; Lee, Sanghoon; Dobrowolska, Margaret; Furdyna, Jacek K.
2018-05-01
A series of Ga1-xMnxAs1-yPy films grown by MBE on GaAs (100) substrates was systematically studied by ferromagnetic resonance (FMR). Magnetic anisotropy parameters were obtained by analyzing the angular dependence of the FMR data. The results clearly show that the easy axis of the films shifts from the in-plane [100] direction to the out-of-plane [001], indicating the emergence of a strong tensile-strain-induced perpendicular anisotropy when the P content exceeds y ≈ 0.07. Multiple resonances were observed in Ga1-xMnxAs1-yPy films with thicknesses over 48 nm, demonstrating the existence of exchange-dominated non-propagating spin-wave modes governed by surface anisotropy.
Transport Through a Precessing Spin Coupled to Noncollinearly Polarized Ferromagnetic Leads
International Nuclear Information System (INIS)
Wang Xianchao; Xin Zihua; Feng Liya
2010-01-01
The quantum electronic transport through a precessing magnetic spin coupled to noncollinearly polarized ferromagnetic leads (F-MS-F) has been studied in this paper. The nonequilibrium Green function approach is used to calculate local density of states (LDOS) and current in the presence of external bias. The characters of LDOS and the electronic current are obtained. The tunneling current is investigated for different precessing angle and different configurations of the magnetization of the leads. The investigation reveals that when the precessing angle takes θ < π/2 and negative bias is applied, the resonant tunneling current appears, otherwise, it appears when positive bias is applied. When the leads are totally polarized and the precessing angel takes 0, the tunneling current changes with the configuration of two leads; and it becomes zero when the two leads are antiparallel. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Nonlinear spin fluctuations in the Fermi liquid of itinerant electron ferromagnets
International Nuclear Information System (INIS)
Solontsov, A.; Lacroix, C.
2003-01-01
A microscopic derivation of nonlinear equations of magnetic dynamics for itinerant ferromagnets is presented within the electron Fermi liquid model accounting for both long-range Coulomb and short-range interactions of quasiparticles, which founds the basis for the phenomenological description of nonlinear spin fluctuations (SF) using the Ginsburg-Landau formalism. Crystal lattice is shown to play a significant role screening the long-range Coulomb interaction and affecting magnetic dynamics. The spectrum of longitudinal SF with account of nonlinear mode-mode coupling is shown to result from an interplay of quasielastic SF and inelastic excitations near the magnon frequencies, both having mainly the nonlinear nature and arising due to their emission (absorption) by magnons
International Nuclear Information System (INIS)
Ho, Le Bin; Lan, Tran Nguyen; Hai, Tran Hoang
2013-01-01
In this work, we have used the Monte Carlo simulation to investigate the magnetic properties of an isolated composite magnetic nanoparticle with ferromagnetic (FM) core and antiferromagnetic (AFM) shell morphology. The defects were assumed to be randomly located at the AFM interface. The Néel anisotropy was used for the FM interface spins at where there are the lacks of crystal symmetry due to the vacancies at AFM interface. With a moderate defect concentration, the coercive field non-monotonously depends on the Néel anisotropy. We have examined the dependence of coercivity, exchange bias field, and vertical shift on defect concentration. We found that in addition to AFM shell, the disordered FM interface is another pining-source for exchange bias phenomenon. We discuss our simulated results in the relation to recent experimental findings
Spin-glass-like dynamics of ferromagnetic clusters in La0.75Ba0.25CoO3
International Nuclear Information System (INIS)
Kumar, Devendra
2014-01-01
We report a magnetization study of the compound La 0.75 Ba 0.25 CoO 3 where the Ba 2+ doping is just above the critical limit for percolation of ferromagnetic clusters. The field cooled and zero-field cooled (ZFC) magnetization exhibit thermomagnetic irreversibility and the ac susceptibility shows a frequency dependent peak at the ferromagnetic ordering temperature (T C ≈ 203 K) of the clusters. These features indicate the presence of a non-equilibrium state below T C . For the non-equilibrium state, the dynamic scaling of the imaginary part of the ac susceptibility and the static scaling of the nonlinear susceptibility clearly establish a spin-glass-like cooperative freezing of ferromagnetic clusters at 200.9(2) K. The assertion of the occurrence of spin-glass-like freezing of ferromagnetic clusters is further substantiated by ZFC ageing and memory experiments. We also observe certain dynamical features which are not present in a typical spin glass, such as: the initial magnetization after ZFC ageing first increases and then decreases with the waiting time; and there is an imperfect recovery of relaxation in negative temperature cycling experiments. This imperfect recovery transforms to perfect recovery for concurrent field cycling. Our analysis suggests that these additional dynamical features have their origin in the inter-cluster exchange interaction and cluster size distribution. The inter-cluster exchange interaction above the magnetic percolation level gives a superferromagnetic state in some granular thin films, but our results show the absence of a typical superferromagnetic-like state in La 0.75 Ba 0.25 CoO 3 . (paper)
Roberto Viana, J.; Rodriguez Salmon, Octavio D.; Neto, Minos A.; Carvalho, Diego C.
2018-02-01
A new approximation technique is developed so as to study the quantum ferromagnetic spin-1 Blume-Capel model in the presence of a transverse crystal field in the square lattice. Our proposal consists of approaching the spin system by considering islands of finite clusters whose frontiers are surrounded by noninteracting spins that are treated by the effective-field theory. The resulting phase diagram is qualitatively correct, in contrast to most effective-field treatments, in which the first-order line exhibits spurious behavior by not being perpendicular to the anisotropy axis at low-temperatures. The effect of the transverse anisotropy is also verified by the presence of quantum phase transitions. The possibility of using larger sizes constitutes an advantage to other approaches where the implementation of larger sizes is computationally costly.
International Nuclear Information System (INIS)
Shihab, S.; Thevenard, L.; Bardeleben, H. J. von; Gourdon, C.; Riahi, H.; Lemaître, A.
2015-01-01
We study the dependence of the spin stiffness constant on the phosphorus concentration in the ferromagnetic semiconductor (Ga,Mn)(As,P) with the aim of determining whether alloying with phosphorus is detrimental, neutral, or advantageous to the spin stiffness. Time-resolved magneto-optical experiments are carried out in thin epilayers. Laser pulses excite two perpendicular standing spin wave modes, which are exchange related. We show that the first mode is spatially uniform across the layer corresponding to a k≈0 wavevector. From the two frequencies and k-vector spacings we obtain the spin stiffness constant for different phosphorus concentrations using weak surface pinning conditions. The mode assessment is checked by comparison to the spin stiffness obtained from domain pattern analysis for samples with out-of-plane magnetization. The spin stiffness is found to exhibit little variation with phosphorus concentration in contradiction with ab-initio predictions
Heisenberg spin glass experiments and the chiral ordering scenario
International Nuclear Information System (INIS)
Campbell, Ian A.; Petit, Dorothee C.M.C.
2010-01-01
An overview is given of experimental data on Heisenberg spin glass materials so as to make detailed comparisons with numerical results on model Heisenberg spin glasses, with particular reference to the chiral driven ordering transition scenario due to Kawamura and collaborators. On weak anisotropy systems, experiments show critical exponents which are very similar to those estimated numerically for the model Heisenberg chiral ordering transition but which are quite different from those at Ising spin glass transitions. Again on weak anisotropy Heisenberg spin glasses, experimental torque data show well defined in-field transverse ordering transitions up to strong applied fields, in contrast to Ising spin glasses where fields destroy ordering. When samples with stronger anisotropies are studied, critical and in-field behavior tend progressively towards the Ising limit. It can be concluded that the essential physics of laboratory Heisenberg spin glasses mirrors that of model Heisenberg spin glasses, where chiral ordering has been demonstrated numerically. (author)
Percolative transport in the vicinity of charge-order ferromagnetic ...
Indian Academy of Sciences (India)
field driven charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ... The charge-ordered phase for incommensurate distribution of man- ganese ions (i.e. ... position x = 0.35 measured in a constant voltage mode. The electric ... a drop in resistance on decreasing the temperature.
Symmetry-selected spin-split hybrid states in C-_{60}/ferromagnetic interfaces
DEFF Research Database (Denmark)
Li, Dongzhe; Barreteau, Cyrille; Kawahara, Seiji Leo
2016-01-01
ferromagnetic surfaces: bcc-Cr(001), bcc-Fe(001), bcc-Co(001), fcc-Co(001), and hcp-Co(0001). We show that the adsorption geometry of the molecule with respect to the surface crystallographic orientation of the magnetic substrate as well as the strength of the interaction play a crucial role in the spin...... tunneling spectroscopy measurements on single C60 adsorbed on Cr(001) and Co/Pt(111) also confirm that the symmetry both of the substrate and of the molecular conformation has a strong influence on the induced spin polarization. Our finding may give valuable insights for further engineering of spin...
Modepalli, Vijayakumar; Jin, Mi-Jin; Park, Jungmin; Jo, Junhyeon; Kim, Ji-Hyun; Baik, Jeong Min; Seo, Changwon; Kim, Jeongyong; Yoo, Jung-Woo
2016-04-26
Electrical control of ferromagnetism in semiconductor nanostructures offers the promise of nonvolatile functionality in future semiconductor spintronics. Here, we demonstrate a dramatic gate-induced change of ferromagnetism in ZnO nanowire (NW) field-effect transistors (FETs). Ferromagnetism in our ZnO NWs arose from oxygen vacancies, which constitute deep levels hosting unpaired electron spins. The magnetic transition temperature of the studied ZnO NWs was estimated to be well above room temperature. The in situ UV confocal photoluminescence (PL) study confirmed oxygen vacancy mediated ferromagnetism in the studied ZnO NW FET devices. Both the estimated carrier concentration and temperature-dependent conductivity reveal the studied ZnO NWs are at the crossover of the metal-insulator transition. In particular, gate-induced modulation of the carrier concentration in the ZnO NW FET significantly alters carrier-mediated exchange interactions, which causes even inversion of magnetoresistance (MR) from negative to positive values. Upon sweeping the gate bias from -40 to +50 V, the MRs estimated at 2 K and 2 T were changed from -11.3% to +4.1%. Detailed analysis on the gate-dependent MR behavior clearly showed enhanced spin splitting energy with increasing carrier concentration. Gate-voltage-dependent PL spectra of an individual NW device confirmed the localization of oxygen vacancy-induced spins, indicating that gate-tunable indirect exchange coupling between localized magnetic moments played an important role in the remarkable change of the MR.
Ghosh, Sumit; Manchon, Aurelien
2017-01-01
Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore, our model accounts for spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large damping torque reported recently is more likely attributed to interfacial magnetoelectric effect, while spin Hall torque remains small even in the bulk-dominated regime.
Ghosh, Sumit; Manchon, Aurelien
2018-01-01
Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three-dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore our model accounts for the spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large dampinglike torque reported recently is more likely attributed to the Berry curvature of interfacial states, while spin Hall torque remains small even in the bulk-dominated regime.
Ghosh, Sumit
2017-11-29
Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore, our model accounts for spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large damping torque reported recently is more likely attributed to interfacial magnetoelectric effect, while spin Hall torque remains small even in the bulk-dominated regime.
Ghosh, Sumit
2018-04-02
Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three-dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore our model accounts for the spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large dampinglike torque reported recently is more likely attributed to the Berry curvature of interfacial states, while spin Hall torque remains small even in the bulk-dominated regime.
Sant, T; Ksenzov, D; Capotondi, F; Pedersoli, E; Manfredda, M; Kiskinova, M; Zabel, H; Kläui, M; Lüning, J; Pietsch, U; Gutt, C
2017-11-08
Exciting a ferromagnetic material with an ultrashort IR laser pulse is known to induce spin dynamics by heating the spin system and by ultrafast spin diffusion processes. Here, we report on measurements of spin-profiles and spin diffusion properties in the vicinity of domain walls in the interface region between a metallic Al layer and a ferromagnetic Co/Pd thin film upon IR excitation. We followed the ultrafast temporal evolution by means of an ultrafast resonant magnetic scattering experiment in surface scattering geometry, which enables us to exploit the evolution of the domain network within a 1/e distance of 3 nm to 5 nm from the Al/FM film interface. We observe a magnetization-reversal close to the domain wall boundaries that becomes more pronounced closer to the Al/FM film interface. This magnetization-reversal is driven by the different transport properties of majority and minority carriers through a magnetically disordered domain network. Its finite lateral extension has allowed us to measure the ultrafast spin-diffusion coefficients and ultrafast spin velocities for majority and minority carriers upon IR excitation.
International Nuclear Information System (INIS)
Iniama, G.; Ita, B. I.; Presa, P. de la; Hernando, A.; Alonso, J. M.; Multigner, M.; Cortés-Gil, R.; Ruiz-González, M. L.; Gonzalez-Calbet, J. M.
2014-01-01
In this paper, the physical properties of half-doped manganite La 0.5 Ca 0.5 MnO 3 with crystallite sizes ranging from 15 to 40 nm are investigated. As expected, ferromagnetic order strengthens at expense of antiferromagnetic one as crystallite size is reduced to 15 nm. However, contrary to previously reported works, an enhancement of saturation magnetization is observed as crystallite size increases from 15 to 22 nm. This unexpected behavior is accompanied by an unusual cell volume variation that seems to induce ferromagnetic-like behavior at expense of antiferromagnetic one. Besides, field cooled hysteresis loops show exchange bias field and coercivity enhancement for increasing cooling fields, which suggest a kind of core-shell structure with AFM-FM coupling for crystallite sizes as small as 15 nm. It is expected that inner core orders antiferromagnetically, whereas uncompensated surface spins behave as spin glass with ferromagnetic-like ordering.
Energy Technology Data Exchange (ETDEWEB)
Friedlaender, Stefan; Poeppl, Andreas [Abteilung Magnetische Resonanz komplexer Quantenfestkoerper, Fakultaet fuer Physik und Geowissenschaften, Universitaet Leipzig (Germany); Liu, Jinxuan [Institute of Artificial Photosynthesis, State Key Laboratory of Fine Chemicals, Dalian University of Technology (China); Addicoat, Matt; Petkov, Petko; Vankova, Nina; Rueger, Robert; Kuc, Agnieszka [Wilhelm-Ostwald-Institut fuer Physikalische und Theoretische Chemie, Leipzig (Germany); Guo, Wei; Zhou, Wencai; Wang, Zhengbang; Weidler, Peter G.; Woell, Christof [Institut fuer Funktionelle Grenzflaechen, Karlsruher Institut fuer Technologie, Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen (Germany); Lukose, Binit [Engineering and Science, Department of Physics and Earth Science, Jacobs University Bremen (Germany); Ziese, Michael [Abteilung Supraleitung und Magnetismus, Fakultaet fuer Physik und Geowissenschaften, Universitaet Leipzig (Germany); Heine, Thomas [Engineering and Science, Department of Physics and Earth Science, Jacobs University Bremen (Germany); Wilhelm-Ostwald-Institut fuer Physikalische und Theoretische Chemie, Leipzig (Germany)
2016-10-04
We have studied the magnetic properties of the SURMOF-2 series of metal-organic frameworks (MOFs). Contrary to bulk MOF-2 crystals, where Cu{sup 2+} ions form paddlewheels and are antiferromagnetically coupled, in this case the Cu{sup 2+} ions are connected via carboxylate groups in a zipper-like fashion. This unusual coupling of the spin {sup 1}/{sub 2} ions within the resulting one-dimensional chains is found to stabilize a low-temperature, ferromagnetic (FM) phase. In contrast to other ordered 1D systems, no strong magnetic fields are needed to induce the ferromagnetism. The magnetic coupling constants describing the interaction between the individual metal ions have been determined in SQUID experiments. They are fully consistent with the results of ab initio DFT electronic structure calculations. The theoretical results allow the unusual magnetic behavior of this exotic, yet easy-to-fabricate, material to be described in a detailed fashion. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Spin-dependent quasiparticle tunneling in junction superconductor-isolator-ferromagnetic
International Nuclear Information System (INIS)
Shlapak, Yu.V.; Shaternik, V.E.; Rudenko, E.M.
2001-01-01
The influence of Andreev reflection of quasiparticles in transparent tunnel junctions of superconductor-isolator-ferromagnetic on electric-current transport is studied within the framework of the Blonder-Tinkham-Klapwijk (BTK) model. It's obtained that current and signal-to-noise ratio can be increased for the memory cell by using in it the double-barrier tunnel junction ferromagnetic-isolator-superconductor-isolator-ferromagnetic instead off the usual tunnel junction ferromagnetic-isolator-ferromagnetic. The evolution of non-linear (tunnel-type) current-voltage characteristics with increasing of the junction transparency is described. (orig.)
International Nuclear Information System (INIS)
Morari, Roman
2013-01-01
The main goal of our research group is the elaboration of superconducting spin-switch (valve) based on Ferromagnetic/Superconductor/Ferromagnetic core. We could realize all building blocks necessary for the fabrication of the core structure of the superconducting spin valve, consisting of two mirror symmetric bilayers. In other words, the spin valve consists of a F/S * /F trilayer, which can be regarded as a package of a F/S and S/F bilayer so that S * =2S in the trilayer. For such a trilayer, the theory predicts that the critical temperature depends on the relative orientation of the magnetization of the ferromagnetic layers. To enable a reversal of one of the magnetizations of the layers with respect to the other by an external magnetic field, the coercive forces of the F layers have to be different due to either intrinsic properties or to an antiferromagnetic pinning layer delivering an exchange bias. The main points of our study are presented here. (author)
Cansever, H.; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.
2018-06-01
Similar to electrical currents flowing through magnetic multilayers, thermal gradients applied across the barrier of a magnetic tunnel junction may induce pure spin-currents and generate ‘thermal’ spin-transfer torques large enough to induce magnetization dynamics in the free layer. In this study, we describe a novel experimental approach to observe spin-transfer torques induced by thermal gradients in magnetic multilayers by studying their ferromagnetic resonance response in microwave cavities. Utilizing this approach allows for measuring the magnetization dynamics on micron/nano-sized samples in open-circuit conditions, i.e. without the need of electrical contacts. We performed first experiments on magnetic tunnel junctions patterned into 6 × 9 µm2 ellipses from Co2FeAl/MgO/CoFeB stacks. We conducted microresonator ferromagnetic resonance (FMR) under focused laser illumination to induce thermal gradients in the layer stack and compared them to measurements in which the sample was globally heated from the backside of the substrate. Moreover, we carried out broadband FMR measurements under global heating conditions on the same extended films the microstructures were later on prepared from. The results clearly demonstrate the effect of thermal spin-torque on the FMR response and thus show that the microresonator approach is well suited to investigate thermal spin-transfer-driven processes for small temperatures gradients, far below the gradients required for magnetic switching.
Parallel ferromagnetic resonance and spin-wave excitation in exchange-biased NiFe/IrMn bilayers
Energy Technology Data Exchange (ETDEWEB)
Sousa, Marcos Antonio de, E-mail: marcossharp@gmail.com [Instituto de Física, Universidade Federal de Goiás, Goiânia, 74001-970 (Brazil); Pelegrini, Fernando [Instituto de Física, Universidade Federal de Goiás, Goiânia, 74001-970 (Brazil); Alayo, Willian [Departamento de Física, Universidade Federal de Pelotas, Pelotas, 96010-900 (Brazil); Quispe-Marcatoma, Justiniano; Baggio-Saitovitch, Elisa [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, 22290-180 (Brazil)
2014-10-01
Ferromagnetic Resonance study of sputtered Ru(7 nm)/NiFe(t{sub FM})/IrMn(6 nm)/Ru(5 nm) exchange-biased bilayers at X and Q-band microwave frequencies reveals the excitation of spin-wave and NiFe resonance modes. Angular variations of the in-plane resonance fields of spin-wave and NiFe resonance modes show the effect of the unidirectional anisotropy, which is about twice larger for the spin-wave mode due to spin pinning at the NiFe/IrMn interface. At Q-band frequency the angular variations of in-plane resonance fields also reveal the symmetry of a uniaxial anisotropy. A modified theoretical model which also includes the contribution of a rotatable anisotropy provides a good description of the experimental results.
Thickness dependence of the triplet spin-valve effect in superconductor-ferromagnet heterostructures
Energy Technology Data Exchange (ETDEWEB)
Lenk, Daniel; Zdravkov, Vladimir I.; Kehrle, Jan; Obermeier, Guenther; Krug von Nidda, Hans-Albrecht; Mueller, Claus; Horn, Siegfried; Tidecks, Reinhard [Institut fuer Physik, Universitaet Augsburg (Germany); Morari, Roman [Institut fuer Physik, Universitaet Augsburg (Germany); D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Kishinev (Moldova, Republic of); Sidorenko, Anatolie S. [D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Kishinev (Moldova, Republic of); Tagirov, Lenar [Solid State Physics Department, Kazan Federal University (Russian Federation)
2015-07-01
We investigated the triplet spin-valve effect in nanoscale layered S/F{sub 1}/N/F{sub 2}/AF heterostructures with varying F{sub 1}-layer thickness (where S=Nb is a singlet superconducting, F{sub 1}=Cu{sub 41}Ni{sub 59} and F{sub 2}=Co a ferromagnetic, and N a normal-conducting, non-magnetic layer). The theory predicts a long-range, odd-in-frequency triplet component of superconductivity at non-collinear alignment of the magnetizations of F{sub 1} and F{sub 2}. This triplet component exhausts the singlet state and, thus, lowers the superconducting transition temperature, T{sub c}, yielding a global minimum of T{sub c} close to the perpendicular mutual orientations of the magnetizations. We found an oscillating decay of T{sub c} suppression, due to the generation of the triplet component, with increasing F{sub 1} layer thickness, which we discuss in the framework of recent theories.
Element-specific ferromagnetic resonance in epitaxial Heusler spin valve systems
Energy Technology Data Exchange (ETDEWEB)
Klaer, P; Jorge, E Arbelo; Jourdan, M; Elmers, H J [Institut fuer Physik, Johannes Gutenberg-Universitaet Mainz, D-55128 Mainz (Germany); Hoffmann, F; Woltersdorf, G; Back, C H, E-mail: elmers@uni-mainz.de [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, D-93040 Regensburg (Germany)
2011-10-26
Time-resolved x-ray magnetic circular dichroism was used to investigate epitaxial MgO(100)/Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al and MgO(100)/Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al/Cr/CoFe films. The precessional motion of the individual sublattice magnetization, excited by continuous microwave excitation in the range 2-10 GHz, was detected by tuning the x-ray photon energy to the L{sub 3} absorption edges of Cr, Fe and Co. The relative phase angle of the sublattice magnetization's response is smaller than the detection limit of 2{sup 0}. A weakly antiferromagnetically coupled CoFe layer causes an increase in the ferromagnetic resonance linewidth consisting of a constant offset and a component linearly increasing with frequency that we partly attribute to non-local damping due to spin pumping.
Energy Technology Data Exchange (ETDEWEB)
Akazaki, T [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198 Japan (Japan); Sawa, Y; Yokoyama, T; Tanaka, Y [Department of Applied Physics, Nagoya University, Nagoya, 464-8603 Japan (Japan); Golubov, A A [Faculty of Science and Technology, University of Twente, Enschede (Netherlands); Munekata, H [Image Science and Engineering Lab., Tokyo Institute of Technology, Yokohama, Kanagawa, 226-8503 Japan (Japan); Nishizawa, N; Takayanagi, H [International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 3-13 Sakura, Tsukuba, 305-0003 Japan (Japan)], E-mail: h-taka@rs.kagu.tus.ac.jp
2009-02-01
We study the transport properties of a p-InMnAs/n-InAs/Nb junction where a p-InMnAs can be regarded as a spin injector. Differential conductance of the n-InAs channel is measured as a function of injection current from p-InMnAs or from Nb at 20 mK. A conductance minimum appears at zero-bias voltage with no current injection. As the injection current from p-InMnAs increases, the minimum gradually disappears. This conductance behaviour is very different from that of the injection case from Nb. We also calculate the conductance in the n-InAs channel by taking account of the exchange field in the InAs channel that is induced by InMnAs ferromagnet. The difference between the conductance behaviours on injection current direction can be explained by the inverse proximity effect that the exchange field is also induced in the superconducting electrode.
A model study of tunneling conductance spectra of ferromagnetically ordered manganites
Panda, Saswati; Kar, J. K.; Rout, G. C.
2018-02-01
We report here the interplay of ferromagnetism (FM) and charge density wave (CDW) in manganese oxide systems through the study of tunneling conductance spectra. The model Hamiltonian consists of strong Heisenberg coupling in core t2g band electrons within mean-field approximation giving rise to ferromagnetism. Ferromagnetism is induced in the itinerant eg electrons due to Kubo-Ohata type double exchange (DE) interaction among the t2g and eg electrons. The charge ordering (CO) present in the eg band giving rise to CDW interaction is considered as the extra-mechanism to explain the colossal magnetoresistance (CMR) property of manganites. The magnetic and CDW order parameters are calculated using Zubarev's Green's function technique and solved self-consistently and numerically. The eg electron density of states (DOS) calculated from the imaginary part of the Green's function explains the experimentally observed tunneling conductance spectra. The DOS graph exhibits a parabolic gap near the Fermi energy as observed in tunneling conductance spectra experiments.
Oxygen vacancy induced by La and Fe into ZnO nanoparticles to modify ferromagnetic ordering
International Nuclear Information System (INIS)
Verma, Kuldeep Chand; Kotnala, R.K.
2016-01-01
We reported long-range ferromagnetic interactions in La doped Zn 0.95 Fe 0.05 O nanoparticles that mediated through lattice defects or vacancies. Zn 0.92 Fe 0.05 La 0.03 O (ZFLaO53) nanoparticles were synthesized by a sol–gel process. X-ray fluorescence spectrum of ZFLaO53 detects the weight percentage of Zn, Fe, La and O. X-ray diffraction shows the hexagonal Wurtzite ZnO phase. The Rietveld refinement has been used to calculate the lattice parameters and the position of Zn, Fe, La and O atoms in the Wurtzite unit cell. The average size of ZFLaO53 nanoparticles is 99 nm. The agglomeration type product due to OH ions with La results into ZnO nanoparticles than nanorods that found in pure ZnO and Zn 0.95 Fe 0.05 O sample. The effect of doping concentration to induce Wurtzite ZnO structure and lattice defects has been analyzed by Raman active vibrational modes. Photoluminescence spectra show an abnormal emission in both UV and visible region, and a blue shift at near band edge is formed with doping. The room temperature magnetic measurement result into weak ferromagnetism but pure ZnO is diamagnetic. However, the temperature dependent magnetic measurement using zero-field and field cooling at dc magnetizing field 500 Oe induces long-range ferromagnetic ordering. It results into antiferromagnetic Neel temperature of ZFLaO53 at around 42 K. The magnetic hysteresis is also measured at 200, 100, 50 and 10 K measurement that indicate enhancement in ferromagnetism at low temperature. Overall, the La doping into Zn 0.95 Fe 0.05 O results into enhanced antiferromagnetic interaction as well as lattice defects/vacancies. The role of the oxygen vacancy as the dominant defects in doped ZnO must form Bound magnetic polarons has been described. - Graphical abstract: The long-range ferromagnetic order in Zn 0.92 Fe 0.05 La 0.03 O nanoparticles at low temperature measurements involves oxygen vacancy as the medium of magnetic interactions. - Highlights: • The La and Fe doping
Gurram, Mallikarjuna; Omar, Siddharta; van Wees, Bart
2017-01-01
We study spin transport in a fully hBN encapsulated monolayer-graphene van der Waals heterostructure at room temperature. A top-layer of bilayer-hBN is used as a tunnel barrier for spin-injection and detection in graphene with ferromagnetic cobalt electrodes. We report surprisingly large and
Shen, L.; Greaves, C.; Riyat, R.; Hansen, T. C.; Blackburn, E.
2017-09-01
The consequences of random nonmagnetic-ion dilution for the pyrochlore family Y2(M 1 -xN x)2O7 (M = magnetic ion, N = nonmagnetic ion) have been investigated. As a first step, we experimentally examine the magnetic properties of Y2CrSbO7 (x =0.5 ), in which the magnetic sites (Cr3 +) are percolative. Although the effective Cr-Cr spin exchange is ferromagnetic, as evidenced by a positive Curie-Weiss temperature, ΘCW ≃19.5 K , our high-resolution neutron powder diffraction measurements detect no sign of magnetic long-range order down to 2 K. In order to understand our observations, we construct a lattice model to numerically study the bond disorder introduced by the ionic size mismatch between M and N , which reveals that the bond disorder percolates at xb ≃0.23 , explaining the absence of magnetic long-range order. This model could be applied to a series of frustrated magnets with a pyrochlore sublattice, for example, the spinel compound Zn (Cr1 -xGax )2O4 , wherein a Néel to spin glass phase transition occurs between x =0.2 and 0.25 [Lee et al., Phys. Rev. B 77, 014405 (2008), 10.1103/PhysRevB.77.014405]. Our study stresses the non-negligible role of bond disorder on magnetic frustration, even in ferromagnets.
Srisongmuang, B.; Pasanai, K.
2018-04-01
We theoretically studied the effect of interfacial scattering on the transport of charge and spin across the junction of a two-dimensional electron gas with Dresselhaus spin-orbit coupling and ferromagnetic material junction, via the conductance (G) and the spin-polarization of the conductance spectra (P) using the scattering method. At the interface, not only were the effects of spin-conserving (Z0) and spin-flip scattering (Zf) considered, but also the interfacial Rashba spin-orbit coupling scattering (ZRSOC) , which was caused by the asymmetry of the interface, was taken into account, and all of them were modeled by the delta potential. It was found that G was suppressed with increasing Z0 , as expected. Interestingly, a particular value of Zf can cause G and P to reach a maximum value. In particular, ZRSOC plays a crucial role to reduce G and P in the metallic limit, but its influence on the tunneling limit was quite weak. On the other hand, the effect of ZRSOC was diminished in the tunneling limit of the magnetic junction.
Li, Peng
2016-06-01
In spintronics, identifying an effective technique for generating spin-polarized current has fundamental importance. The spin-filtering effect across a ferromagnetic insulating layer originates from unequal tunneling barrier heights for spin-up and spin-down electrons, which has shown great promise for use in different ferromagnetic materials. However, the low spin-filtering efficiency in some materials can be ascribed partially to the difficulty in fabricating high-quality thin film with high Curie temperature and/or partially to the improper model used to extract the spin-filtering efficiency. In this work, a new technique is successfully developed to fabricate high quality, ferrimagnetic insulating γ-Fe2O3 films as spin filter. To extract the spin-filtering effect of γ-Fe2O3 films more accurately, a new model is proposed based on Fowler–Nordheim tunneling and Zeeman effect to obtain the spin polarization of the tunneling currents. Spin polarization of the tunneled current can be as high as −94.3% at 2 K in γ-Fe2O3 layer with 6.5 nm thick, and the spin polarization decays monotonically with temperature. Although the spin-filter effect is not very high at room temperature, this work demonstrates that spinel ferrites are very promising materials for spin injection into semiconductors at low temperature, which is important for development of novel spintronics devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Half metallic ferromagnet Pr_0_._9_5Mn_0_._9_3_9O_3 for spin based devices
International Nuclear Information System (INIS)
Santhosh Kumar, B.; Praveen Shankar, N.; Venkateswaran, C.; Manimuthu, P.
2016-01-01
Half Metallic Ferromagnets (HMF) are excellent candidates for spintronics devices due to their unusual 3d and 4s bands. Band theory and first principles calculations strongly predict that Pr based compounds are promising HMF candidates due to their spin hybridisation. Among all Pr based HMF, Pr_0_._9_5Mn_0_._9_3_9O_3 is special because of its pervoskite structure. The different oxidation states of Mn and Pr will enhance the hybridisation of 3d and 4f bands. The present study is experimental effort on the preparation of Pr based compounds
Energy Technology Data Exchange (ETDEWEB)
Lu Jianduo, E-mail: l_j316@163.co [Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Wuhan University of Science and Technology, Wuhan 430081 (China); Li Yunbao; Yun Meijuan [Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Wuhan University of Science and Technology, Wuhan 430081 (China); Zheng Wei [Key Laboratory of Dynamic Geodesy, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077 (China)
2011-03-28
We investigate the effect of the bias in an electron-spin filter based on a two-dimensional electron gas modulated by ferromagnetic-Schottky metal stripes. The numerical results show that the electron transmission and the conductance as well as the spin polarization are strongly dependent on the bias applied to the device. - Research highlights: We propose a bias-tunable electron-spin filter. The transmission and the conductance depend on the bias and the electron energy. The spin polarization depends on the bias and the electron energy. The results are helpful for making new types of bias-tunable spin filters.
Hoi, Bui Dinh; Yarmohammadi, Mohsen; Kazzaz, Houshang Araghi
2017-10-01
We studied how the strain, induced exchange field and extrinsic Rashba spin-orbit coupling (RSOC) enhance the electronic band structure (EBS) and electronic heat capacity (EHC) of ferromagnetic silicene in presence of external electric field (EF) by using the Kane-Mele Hamiltonian, Dirac cone approximation and the Green's function approach. Particular attention is paid to investigate the EHC of spin-up and spin-down bands at Dirac K and K‧ points. We have varied the EF, strain, exchange field and RSOC to tune the energy of inter-band transitions and consequently EHC, leading to very promising features for future applications. Evaluation of EF exhibits three phases: Topological insulator (TI), valley-spin polarized metal (VSPM) and band insulator (BI) at given aforementioned parameters. As a new finding, we have found a quantum anomalous Hall phase in BI regime at strong RSOCs. Interestingly, the effective mass of carriers changes with strain, resulting in EHC behaviors. Here, exchange field has the same behavior with EF. Finally, we have confirmed the reported and expected symmetry results for both Dirac points and spins with the study of valley-dependent EHC.
Spiral correlations in frustrated one-dimensional spin-1/2 Heisenberg J1-J2-J3 ferromagnets
International Nuclear Information System (INIS)
Zinke, R; Richter, J; Drechsler, S-L
2010-01-01
We use the coupled cluster method for infinite chains complemented by exact diagonalization of finite periodic chains to discuss the influence of a third-neighbor exchange J 3 on the ground state of the spin- 1/2 Heisenberg chain with ferromagnetic nearest-neighbor interaction J 1 and frustrating antiferromagnetic next-nearest-neighbor interaction J 2 . A third-neighbor exchange J 3 might be relevant to describe the magnetic properties of the quasi-one-dimensional edge-shared cuprates, such as LiVCuO 4 or LiCu 2 O 2 . In particular, we calculate the critical point J 2 c as a function of J 3 , where the ferromagnetic ground state gives way for a ground state with incommensurate spiral correlations. For antiferromagnetic J 3 the ferro-spiral transition is always continuous and the critical values J 2 c of the classical and the quantum model coincide. On the other hand, for ferromagnetic J 3 ∼ 1 | the critical value J 2 c of the quantum model is smaller than that of the classical model. Moreover, the transition becomes discontinuous, i.e. the model exhibits a quantum tricritical point. We also calculate the height of the jump of the spiral pitch angle at the discontinuous ferro-spiral transition.
Energy Technology Data Exchange (ETDEWEB)
Halm, Simon
2009-05-19
In this thesis it is demonstrated that fringe fields of nanostructured ferromagnets provide the opportunity to manipulate both incoherent and coherent spin ensembles in a dilute magnetic semiconductor (DMS). Fringe fields of Fe/Tb ferromagnets with a remanent out-of-plane magnetization induce a local magnetization in a (Zn,Cd,Mn)Se DMS. Due to the sp-d exchange interaction, optically generated electron-hole pairs align their spin along the DMS magnetization. One obtains a local, remanent spin polarization which was probed by spatially resolved, polarization sensitive photoluminescence spectroscopy. Fringe fields from in-plane magnetized Co ferromagnets allow to locally modify the precession frequency of the Manganese magnetic moments of the DMS in an external magnetic field. This was probed by time-resolved Kerr rotation technique. The inhomogeneity of the fringe field leads to a shortening of the ensemble decoherence time and to the effect of a time-dependent ensemble precession frequency. (orig.)
Bekele, Zelalem Abebe; Meng, Kangkang; Zhao, Bing; Wu, Yong; Miao, Jun; Xu, Xiaoguang; Jiang, Yong
2017-08-01
Symmetry breaking provides new insight into the physics of spin-orbit torque (SOT) and the switching without a magnetic field could lead to significant impact. In this work, we demonstrate the robust zero-field SOT switching of a perpendicular ferromagnet (FM) layer where the symmetry is broken by a bilayer of heavy metals (HMs) with the strong spin-orbit coupling (SOC). We observed the change of coercivity value by 31% after inserting Co2FeAl in the multilayer structure. These two HM layers (Ta and Pt) are used to strengthen the SOC by linear combination. With different angles between the magnetization and the current (i.e. parallel and anti-parallel), the structures show different switching behaviors such as clockwise or counterclockwise.
Spin-isotropic continuum of spin excitations in antiferromagnetically ordered Fe1.07Te
Song, Yu; Lu, Xingye; Regnault, L.-P.; Su, Yixi; Lai, Hsin-Hua; Hu, Wen-Jun; Si, Qimiao; Dai, Pengcheng
2018-02-01
Unconventional superconductivity typically emerges in the presence of quasidegenerate ground states, and the associated intense fluctuations are likely responsible for generating the superconducting state. Here we use polarized neutron scattering to study the spin space anisotropy of spin excitations in Fe1.07Te exhibiting bicollinear antiferromagnetic (AF) order, the parent compound of FeTe1 -xSex superconductors. We confirm that the low-energy spin excitations are transverse spin waves, consistent with a local-moment origin of the bicollinear AF order. While the ordered moments lie in the a b plane in Fe1.07Te , it takes less energy for them to fluctuate out of plane, similar to BaFe2As2 and NaFeAs. At energies above E ≳20 meV, we find magnetic scattering to be dominated by an isotropic continuum that persists up to at least 50 meV. Although the isotropic spin excitations cannot be ascribed to spin waves from a long-range-ordered local-moment antiferromagnet, the continuum can result from the bicollinear magnetic order ground state of Fe1.07Te being quasidegenerate with plaquette magnetic order.
Spin Current Noise of the Spin Seebeck Effect and Spin Pumping
Matsuo, M.; Ohnuma, Y.; Kato, T.; Maekawa, S.
2018-01-01
We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal-metal-(NM-)ferromagnet(FM) bilayer system. Starting with a simple ferromagnet-insulator-(FI-)NM interface model with both spin-conserving and non-spin-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for a yttrium-iron-garnet-platinum interface. We show that the spin-current noise can be used to determine the effective spin carried by a magnon modified by the non-spin-conserving process at the interface. In addition, we show that it provides information on the effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.
Ordered alternating binary polymer nanodroplet array by sequential spin dewetting.
Bhandaru, Nandini; Das, Anuja; Salunke, Namrata; Mukherjee, Rabibrata
2014-12-10
We report a facile technique for fabricating an ordered array of nearly equal-sized mesoscale polymer droplets of two constituent polymers (polystyrene, PS and poly(methyl methacrylate), PMMA) arranged in an alternating manner on a topographically patterned substrate. The self-organized array of binary polymers is realized by sequential spin dewetting. First, a dilute solution of PMMA is spin-dewetted on a patterned substrate, resulting in an array of isolated PMMA droplets arranged along the substrate grooves due to self-organization during spin coating itself. The sample is then silanized with octadecyltrichlorosilane (OTS), and subsequently, a dilute solution of PS is spin-coated on to it, which also undergoes spin dewetting. The spin-dewetted PS drops having a size nearly equal to the pre-existing PMMA droplets position themselves between two adjacent PMMA drops under appropriate conditions, forming an alternating binary polymer droplet array. The alternating array formation takes place for a narrow range of solution concentration for both the polymers and depends on the geometry of the substrate. The size of the droplets depends on the extent of confinement, and droplets as small as 100 nm can be obtained by this method, on a suitable template. The findings open up the possibility of creating novel surfaces having ordered multimaterial domains with a potential multifunctional capability.
Garcia-Adeva, Angel J.; Huber, David L.
2001-07-01
In this work we generalize and subsequently apply the effective-field renormalization-group (EFRG) technique to the problem of ferro- and antiferromagnetically coupled Ising spins with local anisotropy axes in geometrically frustrated geometries (kagomé and pyrochlore lattices). In this framework, we calculate the various ground states of these systems and the corresponding critical points. Excellent agreement is found with exact and Monte Carlo results. The effects of frustration are discussed. As pointed out by other authors, it turns out that the spin-ice model can be exactly mapped to the standard Ising model, but with effective interactions of the opposite sign to those in the original Hamiltonian. Therefore, the ferromagnetic spin ice is frustrated and does not order. Antiferromagnetic spin ice (in both two and three dimensions) is found to undergo a transition to a long-range-ordered state. The thermal and magnetic critical exponents for this transition are calculated. It is found that the thermal exponent is that of the Ising universality class, whereas the magnetic critical exponent is different, as expected from the fact that the Zeeman term has a different symmetry in these systems. In addition, the recently introduced generalized constant coupling method is also applied to the calculation of the critical points and ground-state configurations. Again, a very good agreement is found with exact, Monte Carlo, and renormalization-group calculations for the critical points. Incidentally, we show that the generalized constant coupling approach can be regarded as the lowest-order limit of the EFRG technique, in which correlations outside a frustrated unit are neglected, and scaling is substituted by strict equality of the thermodynamic quantities.
Resurvey of order and chaos in spinning compact binaries
International Nuclear Information System (INIS)
Wu Xin; Xie Yi
2008-01-01
This paper is mainly devoted to applying the invariant, fast, Lyapunov indicator to clarify some doubt regarding the apparently conflicting results of chaos in spinning compact binaries at the second-order post-Newtonian approximation of general relativity from previous literatures. It is shown with a number of examples that no single physical parameter or initial condition can be described as responsible for causing chaos, but a complicated combination of all parameters and initial conditions is responsible. In other words, a universal rule for the dependence of chaos on each parameter or initial condition cannot be found in general. Chaos does not depend only on the mass ratio, and the maximal spins do not necessarily bring the strongest effect of chaos. Additionally, chaos does not always become drastic when the initial spin vectors are nearly perpendicular to the orbital plane, and the alignment of spins cannot trigger chaos by itself
International Nuclear Information System (INIS)
Song Hongyan; Zhou Shiping
2008-01-01
We investigate Andreev reflection (AR) tunneling through a ferromagnet-quantum dot-superconductor (F-QD-S) system in the presence of an external ac field. The intradot spin-flip scattering in the QD is involved. Using the nonequilibrium Green function and BCS quasiparticle spectrum for superconductor, time-averaged AR conductance is formulated. The competition between the intradot spin-flip scattering and photon-assisted tunneling dominates the resonant behaviors of the time-averaged AR conductance. For weak intradot spin-flip scattering strengths, the AR conductance shows a series of equal interval resonant levels. However, the single-peak at main resonant level develops into a well-resolved double-peak resonance at a strong intradot spin-flip scattering strength. Remarkable, multiple-photon-assisted tunneling that generates photonic sideband peaks with a variable interval has been found. In addition, the AR conductance-bias voltage characteristic shows a transition between the single-peak to double-peak resonance as the ratio of the two tunneling strengths varies
Nanoscale spin-dependent transport of electrons and holes in Si-ferromagnet structures
Ul Haq, E.
Given the rapid development of magnetic data storage and spin-electronics into the realm of nanotechnology, the understanding of the spin-dependent electronic transport and switching behavior of magnetic structures at the nanoscale is an important issue. We have developed spin-sensitive techniques
Lu, Hongcheng; Hayashi, Naoaki; Matsumoto, Yuki; Takatsu, Hiroshi; Kageyama, Hiroshi
2017-08-07
A diamond spin chain system, one of the one-dimensional frustrated lattices, is known to exhibit novel properties, but experimental studies have been exclusively confined to materials with a single spin component. Here, we report on the synthesis, structure, and magnetic properties of a new diamond chain compound Cu 2 FePO 4 F 4 (H 2 O) 4 1 composed of mixed-spins of Cu 2+ (S = 1/2 × 2) and Fe 3+ (S = 5/2). Compound 1 crystallizes in the space group C2/c of the monoclinic crystal system with a = 7.7546(4) Å, b = 12.1290(6) Å, c = 9.9209(6) Å, β = 105.29(1)°, and Z = 4. DC magnetization, Mössbauer spectroscopy, and heat capacity measurements revealed an antiferromagnetic order at 11.3 K with a small ferromagnetic component. It is suggested that ferrimagnetic diamond chains are arranged in an antiferromagnetic fashion (i.e., [...Fe(↑)-2Cu(↓↓)-Fe(↑)...] and [...Fe(↓)-2Cu(↑↑)-Fe(↓)...]) within the ab plane to cancel net magnetization, and the spin orientation of the diamond chains changes alternately along the c axis due to the magnetic anisotropy, leading to a noncollinear spin order. Furthermore, another anomaly is observed in the heat capacity at around 3 K, suggesting a successive magnetic transition or crossover due to competing magnetic interactions.
Spectral properties of an extended Hubbard ladder with long range anti-ferromagnetic order
Yang, Chun; Feiguin, Adrian
We study the spectral properties of a Hubbard ladder with anti-ferromagnetic long range order by introducing a staggered Heisenberg interaction that decays algebraically. Unlike an alternating field or the t -Jz model, our problem preserves both SU (2) and translational invariance. We solve the problem with the time-dependent density matrix renormalization group and analyze the binding between holons and spinons and the structure of the elementary excitations. We discuss the implications in the context of the 2D Hubbard model at, and away from half-filling by using cluster perturbation theory (CPT). AF acknowledges the U.S. Department of Energy, Office of Basic Energy Sciences, for support under Grant DE-SC0014407.
Large-scale calculation of ferromagnetic spin systems on the pyrochlore lattice
Energy Technology Data Exchange (ETDEWEB)
Soldatov, Konstantin, E-mail: soldatov_ks@students.dvfu.ru [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Nefedev, Konstantin, E-mail: nefedev.kv@dvfu.ru [School of Natural Sciences, Far Eastern Federal University, Vladivostok (Russian Federation); Institute of Applied Mathematics, Far Eastern Branch, Russian Academy of Science, Vladivostok (Russian Federation); Komura, Yukihiro [CIJ-solutions, Chuo-ku, Tokyo 103-0023 (Japan); Okabe, Yutaka, E-mail: okabe@phys.se.tmu.ac.jp [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 (Japan)
2017-02-19
We perform the high-performance computation of the ferromagnetic Ising model on the pyrochlore lattice. We determine the critical temperature accurately based on the finite-size scaling of the Binder ratio. Comparing with the data on the simple cubic lattice, we argue the universal finite-size scaling. We also calculate the classical XY model and the classical Heisenberg model on the pyrochlore lattice. - Highlights: • Calculations of the ferromagnetic models on the pyrochlore lattice were performed. • Precise critical temperatures were determined using Binder ratio finite-size scaling. • The universal finite-size scaling was argued.
Reentrant spin glass ordering in an Fe-based bulk metallic glass
Energy Technology Data Exchange (ETDEWEB)
Luo, Qiang; Shen, Jun, E-mail: junshen@tongji.edu.cn [School of Materials Science and Engineering, Tongji University, Shanghai 201804 (China)
2015-02-07
We report the results of the complex susceptibility, temperature, and field dependence of DC magnetization and the nonequilibrium dynamics of a bulk metallic glass Fe{sub 40}Co{sub 8}Cr{sub 15}Mo{sub 14}C{sub 15}B{sub 6}Er{sub 2}. Solid indication of the coexistence of reentrant spin glass (SG) and ferromagnetic orderings is determined from both DC magnetization and AC susceptibility under different DC fields. Dynamics scaling of AC susceptibility indicates critical slowing down to a reentrant SG state with a static transition temperature T{sub s} = ∼17.8 K and a dynamic exponent zv = ∼7.3. The SG nature is further corroborated from chaos and memory effects, magnetic hysteresis, and aging behavior. We discuss the results in terms of the competition among random magnetic anisotropy and exchange interactions and compare them with simulation predictions.
Ferromagnetic clustering and ordering in manganese deficient LaMnO3: An EMR probe
International Nuclear Information System (INIS)
Auslender, M.; Shames, A.I.; Rozenberg, E.; Gorodetsky, G.; Hebert, S.; Martin, C.
2007-01-01
Electron magnetic resonance (EMR) properties of LaMn 1-x O 3 (x=0, 0.02 and 0.06) are studied in the range 115-600K. It is shown that above 200K either ferromagnetic clusters or long-range ferromagnetic correlation present in all samples, and that LaMn 0.94 O 3 is ferromagnetic below 113.4+/-1.5K
Erratum: Spin dynamics in ferromagnets: Gilbert damping and two-magnon scattering
Czech Academy of Sciences Publication Activity Database
Zakeri, Kh.; Lindner, J.; Barsukov, I.; Meckenstock, R.; Farle, M.; von Horsten, U.; Wende, H.; Keune, W.; Rocker, J.; Kalarickal, S.S.; Lenz, K.; Kuch, W.; Baberschke, K.; Frait, Zdeněk
2009-01-01
Roč. 80, č. 5 (2009), 059901/1-059901/3 ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100520 Keywords : ferromagnetic resonance * Heusler alloys Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.475, year: 2009
Next to leading order semi-inclusive spin asymmetries
International Nuclear Information System (INIS)
Florian, D. de; Epele, L.N.; Fanchiotti, H.; Garcia C, C.A.; Sassot, R.
1996-04-01
We have computed semi-inclusive spin asymmetries for proton and deuteron targets including next to leading order (NLO) QCD corrections and contributions coming from the target fragmentation region. These corrections have been estimated using NLO fragmentation functions, parton distributions and also a model for spin dependent fracture functions which is proposed here. We have found that NLO corrections are small but non-negligible in a scheme where gluons are polarised and that our estimate for target fragmentation effects, which is in agreement with the available semi-inclusive data, does not modify significantly charged asymmetries but is non-negligible for the so called difference asymmetries. (author). 18 refs., 7 figs
k-asymmetric spin splitting at the interface between transition metal ferromagnets and heavy metals
Grytsiuk, Sergii
2016-05-23
We systematically investigate the spin-orbit coupling-induced band splitting originating from inversion symmetry breaking at the interface between a Co monolayer and 4d (Tc, Ru, Rh, Pd, and Ag) or 5d (Re, Os, Ir, Pt, and Au) transition metals. In spite of the complex band structure of these systems, the odd-in-k spin splitting of the bands displays striking similarities with the much simpler Rashba spin-orbit coupling picture. We establish a clear connection between the overall strength of the odd-in-k spin splitting of the bands and the charge transfer between the d orbitals at the interface. Furthermore, we show that the spin splitting of the Fermi surface scales with the induced orbital moment, weighted by the spin-orbit coupling.
k-asymmetric spin splitting at the interface between transition metal ferromagnets and heavy metals
Grytsyuk, Sergiy; Belabbes, Abderrezak; Haney, Paul M.; Lee, Hyun-Woo; Lee, Kyung-Jin; Stiles, M. D.; Schwingenschlö gl, Udo; Manchon, Aurelien
2016-01-01
We systematically investigate the spin-orbit coupling-induced band splitting originating from inversion symmetry breaking at the interface between a Co monolayer and 4d (Tc, Ru, Rh, Pd, and Ag) or 5d (Re, Os, Ir, Pt, and Au) transition metals. In spite of the complex band structure of these systems, the odd-in-k spin splitting of the bands displays striking similarities with the much simpler Rashba spin-orbit coupling picture. We establish a clear connection between the overall strength of the odd-in-k spin splitting of the bands and the charge transfer between the d orbitals at the interface. Furthermore, we show that the spin splitting of the Fermi surface scales with the induced orbital moment, weighted by the spin-orbit coupling.
Magnetic order and spin dynamics in the heavy Fermion system YbNi{sub 4}P{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Spehling, Johannes; Guenther, Marco; Yeche, Nicholas; Klauss, Hans-Henning [Institut fuer Festkoerperphysik, TU Dresden (Germany); Luetkens, Hubertus; Baines, Chris [Laboratory for Muonm Spin Spectroscopy, Paul Scherrer Institut, Villigen (Switzerland); Krellner, Cornelius; Geibel, Christoph; Steglich, Frank [Max-Planck-Institut fuer Chemische Physik Fester Stoffe, Dresden (Germany)
2012-07-01
A longstanding question in the field of quantum criticality relates to the possible existence of a ferromagnetic (FM) quantum critical point (QCP). At a QCP, collective quantum fluctuations tune the system continuously from a magnetically ordered to a non-magnetic ground state. However, so far no 4f-material with a FM QCP is found. Recently, in the HF metal YbNi{sub 4}P{sub 2} with a quasi 1D-electronic structure, FM quantum criticality above a low FM transition temperature of T{sub C}=170 mK was suggested. Our zero field muon spin relaxation on YbNi{sub 4}P{sub 2} proves static magnetic order with a strongly reduced ordered Yb{sup 3+} moment below T{sub C}. Above T{sub C}, the muon asymmetry function P(t,B) is dominated by quasi homogeneous spin fluctuations and exhibits a time-field scaling relation P(t,B)=P(t/B{sup {gamma}}) indicating cooperative critical spin dynamics. At T=190 mK, slightly above T{sub C}, {gamma}=0.81(5) K suggesting time-scale invariant power-law behavior for the dynamic electronic spin-spin autocorrelation function. The results are discussed in comparison with the AFM compound YbRh{sub 2}Si{sub 2}.
Awan, Saif Ullah; Hasanain, S. K.; Anjum, Dalaver H.; Awan, M. S.; Shah, Saqlain A.
2014-01-01
for long range order ferromagnetic coupling in Li doped samples. Room temperature ferroelectric hysteresis loops were observed in 8% and 10% Li doped samples. We demonstrated ferroelectric coercivity (remnant polarization) 2.5kV/cm (0.11 μC/cm2) and 2.8k
Spin dynamics in ferromagnets: Gilbert dymping and two-magnon scattering
Czech Academy of Sciences Publication Activity Database
Zakeri, Kh.; Lindner, J.; Barsukov, I.; Meckenstock, R.; Farle, M.; von Horsten, U.; Wende, H.; Keune, W.; Rocker, J.; Kalarickal, S.S.; Lenz, K.; Kuch, W.; Baberschke, K.; Frait, Zdeněk
2007-01-01
Roč. 76, č. 10 (2007), 104416/1-104416/8 ISSN 1098-0121 Grant - others:Deutsche Forschunggemeinschaft(DE) Sfb 491; EC Marie Curie Research Training Network(XE) MRTN-CT-2004-005567, 2004-2008 Institutional research plan: CEZ:AV0Z10100520 Keywords : ferromagnetic resonance * Gilbert damping * two-magnon scattering * Fe 3 Si films Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.172, year: 2007
Role of spin diffusion in current-induced domain wall motion for disordered ferromagnets
Akosa, Collins Ashu; Kim, Won-Seok; Bisig, André
2015-01-01
Current-induced spin transfer torque and magnetization dynamics in the presence of spin diffusion in disordered magnetic textures is studied theoretically. We demonstrate using tight-binding calculations that weak, spin-conserving impurity scattering dramatically enhances the nonadiabaticity. To further explore this mechanism, a phenomenological drift-diffusion model for incoherent spin transport is investigated. We show that incoherent spin diffusion indeed produces an additional spatially dependent torque of the form ∼∇2[m×(u⋅∇)m]+ξ∇2[(u⋅∇)m], where m is the local magnetization direction, u is the direction of injected current, and ξ is a parameter characterizing the spin dynamics (precession, dephasing, and spin-flip). This torque, which scales as the inverse square of the domain wall width, only weakly enhances the longitudinal velocity of a transverse domain wall but significantly enhances the transverse velocity of vortex walls. The spatial-dependent spin transfer torque uncovered in this study is expected to have significant impact on the current-driven motion of abrupt two-dimensional textures such as vortices, skyrmions, and merons.
Role of spin diffusion in current-induced domain wall motion for disordered ferromagnets
Akosa, Collins Ashu
2015-03-12
Current-induced spin transfer torque and magnetization dynamics in the presence of spin diffusion in disordered magnetic textures is studied theoretically. We demonstrate using tight-binding calculations that weak, spin-conserving impurity scattering dramatically enhances the nonadiabaticity. To further explore this mechanism, a phenomenological drift-diffusion model for incoherent spin transport is investigated. We show that incoherent spin diffusion indeed produces an additional spatially dependent torque of the form ∼∇2[m×(u⋅∇)m]+ξ∇2[(u⋅∇)m], where m is the local magnetization direction, u is the direction of injected current, and ξ is a parameter characterizing the spin dynamics (precession, dephasing, and spin-flip). This torque, which scales as the inverse square of the domain wall width, only weakly enhances the longitudinal velocity of a transverse domain wall but significantly enhances the transverse velocity of vortex walls. The spatial-dependent spin transfer torque uncovered in this study is expected to have significant impact on the current-driven motion of abrupt two-dimensional textures such as vortices, skyrmions, and merons.
Seki, T.; Iguchi, R.; Takanashi, K.; Uchida, K.
2018-04-01
Spatial distribution of temperature modulation due to the anomalous Ettingshausen effect (AEE) is visualized in a ferromagnetic FePt thin film with in-plane and out-of-plane magnetizations using the lock-in thermography technique. Comparing the AEE of FePt with the spin Peltier effect (SPE) of a Pt/yttrium iron garnet junction provides direct evidence of different symmetries of AEE and SPE. Our experiments and numerical calculations reveal that the distribution of heat sources induced by AEE strongly depends on the direction of magnetization, leading to the remarkable different temperature profiles in the FePt thin film between the in-plane and perpendicularly magnetized configurations.
Superconductivity and spin excitations in orbitally ordered FeSe
Energy Technology Data Exchange (ETDEWEB)
Kreisel, Andreas; Andersen, Brian M. [Niels Bohr Institute, University of Copenhagen (Denmark); Mukherjee, Shantanu [Niels Bohr Institute, University of Copenhagen (Denmark); Dept. of Physics, State University of New York at Binghamton, Binghamton, NY (United States); Hirschfeld, Peter J. [University of Florida, Gainesville, FL (United States)
2016-07-01
We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the d{sub xz}/d{sub yz} channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π,0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π,0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies.
Superconductivity and spin excitations in orbitally ordered FeSe
Kreisel, Andreas; Mukherjee, Shantanu; Hirschfeld, P. J.; Andersen, B. M.
We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the dxz /dyz channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π , 0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π , 0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies A.K. and B.M.A. acknowledge financial support from a Lundbeckfond fellowship (Grant No. A9318). P.J.H. was partially supported by the Department of Energy under Grant No. DE-FG02-05ER46236.
Majd, Nayereh; Ghasemi, Zahra
2016-10-01
We have investigated a TPTQ state as an input state of a non-ideal ferromagnetic detectors. Minimal spin polarization required to demonstrate spin entanglement according to entanglement witness and CHSH inequality with respect to (w.r.t.) their two free parameters have been found, and we have numerically shown that the entanglement witness is less stringent than the direct tests of Bell's inequality in the form of CHSH in the entangled limits of its free parameters. In addition, the lower limits of spin detection efficiency fulfilling secure cryptographic key against eavesdropping have been derived. Finally, we have considered TPTQ state as an output of spin decoherence channel and the region of ballistic transmission time w.r.t. spin relaxation time and spin dephasing time has been found.
Sarwar, T.; Qamar, A.; Nadeem, M.
2017-07-01
Dynamics of spin ordering in the manganite Nd0.5Ca0.5MnO3 have been investigated in this paper. It was observed that the complex mixed magnetic ordering in pellets is comprised of antiferromagnetic ordering at 160 K (TN) and complete charge ordering at 250 K (TCO). Under ac field, appearance of unstable ferromagnetic correlations is observed above TCO, which is badly frustrated due to strong spin disorder induced by Jahn Teller distortions. Impedance measurements reveal the spin glass like scenario, suppressing the strong antiferromagnetic and charge ordering states below TN.
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.
International Nuclear Information System (INIS)
Huang, Chonghui; Wang, Yu; Tang, Zhao; Liao, Xiaoqi; Yang, Sen; Song, Xiaoping
2015-01-01
Highlights: • Ni 51 Cu 4 Mn 20 Ga 25 alloy exhibits normal elastocaloric and magnetocaloric effects. • L2 1 atomic order of the alloy is increased after annealing at 773 K for 10 h. • Increasing L2 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 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 51 Cu 4 Mn 20 Ga 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
Mn induced ferromagnetism spin fluctuation enhancement in Sr{sub 2}Ru{sub 1−x}Mn{sub x}O{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Zheng, Long; Cai, Jinzhu; Xie, Qiyun; Lv, Bin [Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Mao, Z.Q. [Department of Physics and Engineering Physics, Tulane University, New Orleans, LA 70118 (United States); Wu, X.S., E-mail: xswu@nju.edu.cn [Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China)
2013-09-15
We establish that Sr{sub 2}RuO{sub 4} is extremely close to incommensurate spin density wave instability. With increasing Mn content, the RuO{sub 6} octahedron in the unit cell varies. The octahedron of RuO{sub 6} contracts along c-axis for x<0.20, Mn element mainly showing the +3 chemical valence (Mn{sup 3+}), and it expands along c-axis with further increasing Mn content (x>0.20), and Mn element shows the +4 chemical valence (Mn{sup 4+}). Spin-glass-related ferromagnetism enhancement is observed for x>0.20, which indicates the critical ferromagnetic spin fluctuation due to Mn doping in Sr{sub 2}Ru{sub 1−x}Mn{sub x}O{sub 4}. - Highlights: • The chemical valence of Mn ions changed from Mn{sup 3+} to Mn{sup 4+} with the increase of Mn content. • Spin-glass-related ferromagnetism enhancement behavior is observed. • The electrical resistivity can be fitted using Mott's variable-range hopping model. • The evolution of octahedron with increase of Mn content is given. • The spin fluctuation effect plays an important role in the magnetic property.
Bunyaev, S. A.; Golub, V. O.; Salyuk, O. Yu.; Tartakovskaya, E. V.; Santos, N. M.; Timopheev, A. A.; Sobolev, N. A.; Serga, A. A.; Chumak, A. V.; Hillebrands, B.; Kakazei, G. N.
2015-01-01
The spin wave dynamics in patterned magnetic nanostructures is under intensive study during the last two decades. On the one hand, this interest is generated by new physics that can be explored in such structures. On the other hand, with the development of nanolithography, patterned nanoelements and their arrays can be used in many practical applications (magnetic recording systems both as media and read-write heads, magnetic random access memory, and spin-torque oscillators just to name a fe...
Awan, Saif Ullah
2014-10-28
Memory and switching devices acquired new materials which exhibit ferroelectric and ferromagnetic order simultaneously. We reported multiferroic behavior in Zn1-yLiyO(0.00≤y≤0.10) nanoparticles. The analysis of transmission electron micrographs confirmed the hexagonal morphology and wurtzite crystalline structure. We investigated p-type conductivity in doped samples and measured hole carriers in range 2.4×1017/cc to 7.3×1017/cc for different Li contents. We found that hole carriers are responsible for long range order ferromagnetic coupling in Li doped samples. Room temperature ferroelectric hysteresis loops were observed in 8% and 10% Li doped samples. We demonstrated ferroelectric coercivity (remnant polarization) 2.5kV/cm (0.11 μC/cm2) and 2.8kV/cm (0.15 μC/cm2) for y=0.08 and y=0.10 samples. We propose that the mechanism of Li induced ferroelectricity in ZnO is due to indirect dipole interaction via hole carriers. We investigated that if the sample has hole carriers ≥5.3×1017/cc, they can mediate the ferroelectricity. Ferroelectric and ferromagnetic measurements showed that higher electric polarization and larger magnetic moment is attained when the hole concentration is larger and vice versa. Our results confirmed the hole dependent coexistence of ferromagnetic and ferroelectric behavior at room temperature, which provide potential applications for switchable and memory devices.
STM observations of ferromagnetic clusters
International Nuclear Information System (INIS)
Wawro, A.; Kasuya, A.
1998-01-01
Co, Fe and Ni clusters of nanometer size, deposited on silicon and graphite (highly oriented pyrolytic graphite), were observed by a scanning tunneling microscope. Deposition as well as the scanning tunneling microscope measurements were carried out in an ultrahigh vacuum system at room temperature. Detailed analysis of Co cluster height was done with the scanning tunneling microscope equipped with a ferromagnetic tip in a magnetic field up to 70 Oe. It is found that bigger clusters (few nanometers in height) exhibit a dependence of their apparent height on applied magnetic field. We propose that such behaviour originates from the ferromagnetic ordering of cluster and associate this effect to spin polarized tunneling. (author)
Energy Technology Data Exchange (ETDEWEB)
Aragón, F. H.; Coaquira, J. A. H. [Núcleo de Física Aplicada, Institute of Physics, University of Brasília, Brasília DF 70910-900 (Brazil); Chitta, V. A. [Instituto de Física, Universidade de São Paulo, São Paulo, SP 05508-000 (Brazil); Hidalgo, P. [Faculdade Gama-FGA, Sector Central Gama, Universidade de Brasília, Brasília, DF72405-610 (Brazil); Brito, H. F. [Instituto de Química, Universidade de São Paulo, São Paulo, SP 05508-000 (Brazil)
2013-11-28
In this work, the structural and magnetic properties of Er-doped SnO{sub 2} (SnO{sub 2}:Er) nanoparticles are reported. The SnO{sub 2}:Er nanoparticles have been synthesized by a polymer precursor method with Er content from 1.0% to 10.0%. X-ray diffraction results indicate the formation of only the rutile-type structure in all samples. The estimated mean crystallite size shows a decrease from ∼10 to ∼4 nm when the Er content is increased from 1.0% to 10.0%. The particle size values have been corroborated by transmission electron microscopy technique. The thermal dependence of the magnetization is consistent with the 3+ oxidation state of erbium ions for all samples. A strong paramagnetic-like behavior coexisting with a ferromagnetic phase has been determined for samples with Er content below 5.0%. Above this concentration, only a paramagnetic behavior has been determined. Isothermal magnetization curves are consistent with the occurrence of long-range ferromagnetic order mediated by donor electrons forming bound magnetic polarons which overlap to produce a spin-split impurity band.
International Nuclear Information System (INIS)
Snowman, Daniel P.
2009-01-01
Phase diagrams have been produced and critical exponents calculated for a Blume-Emery-Griffiths system with competing biquadratic and crystal-field interactions with uniform ferromagnetic bilinear interactions. This competition directly effects the clustering and density of nonmagnetic impurities. These results have been produced using renormalization-group methods with a hierarchical lattice. A series of planes of constant, repulsive biquadratic coupling have been probed while varying the temperature and concentration of annealed vacancies in the system. The sinks have been analyzed and interpreted, and critical exponents calculated for the higher order transitions.
Energy Technology Data Exchange (ETDEWEB)
Plötzing, M.; Adam, R., E-mail: r.adam@fz-juelich.de; Weier, C.; Plucinski, L.; Schneider, C. M. [Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI-6), 52425 Jülich (Germany); Eich, S.; Emmerich, S.; Rollinger, M.; Aeschlimann, M. [University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern (Germany); Mathias, S. [Georg-August-Universität Göttingen, I. Physikalisches Institut, 37077 Göttingen (Germany)
2016-04-15
The fundamental mechanism responsible for optically induced magnetization dynamics in ferromagnetic thin films has been under intense debate since almost two decades. Currently, numerous competing theoretical models are in strong need for a decisive experimental confirmation such as monitoring the triggered changes in the spin-dependent band structure on ultrashort time scales. Our approach explores the possibility of observing femtosecond band structure dynamics by giving access to extended parts of the Brillouin zone in a simultaneously time-, energy- and spin-resolved photoemission experiment. For this purpose, our setup uses a state-of-the-art, highly efficient spin detector and ultrashort, extreme ultraviolet light pulses created by laser-based high-order harmonic generation. In this paper, we present the setup and first spin-resolved spectra obtained with our experiment within an acquisition time short enough to allow pump-probe studies. Further, we characterize the influence of the excitation with femtosecond extreme ultraviolet pulses by comparing the results with data acquired using a continuous wave light source with similar photon energy. In addition, changes in the spectra induced by vacuum space-charge effects due to both the extreme ultraviolet probe- and near-infrared pump-pulses are studied by analyzing the resulting spectral distortions. The combination of energy resolution and electron count rate achieved in our setup confirms its suitability for spin-resolved studies of the band structure on ultrashort time scales.
Experimental study of the spin density of metastable fcc ferromagnetic Fe-Cu alloys
International Nuclear Information System (INIS)
Bove, L. E.; Petrillo, C.; Sacchetti, F.; Mazzone, G.
2000-01-01
Magnetization density measurements on metastable Fe x Cu 1-x alloys at four compositions (x=20, 40, 50, and 60 at. %) and at 5 K temperature were carried out by means of polarized neutron diffraction. The samples were produced by high-energy ball milling and characterized by x-ray diffraction and fluorescence measurements. Additional bulk magnetization measurements were carried out on the two samples at high Fe concentration. Over the present concentration region, the Fe-Cu system is ferromagnetic and the four samples were found to be in the fcc phase. Fe-Cu is therefore a very suitable system to investigate the magnetic state of Fe in an fcc environment. Other than confirming that the Fe-Cu system is not a simple dilution alloy, the present results were compatible with a two-state model for fcc Fe--that is, two different coexisting electronic states associated with different magnetic moments and form factors
Ferromagnetic resonance characterization of nano-FePt by electron spin resonance
CSIR Research Space (South Africa)
Nkosi, SS
2013-01-01
Full Text Available Electron spin resonance (ESR) measurements at room temperature and X-band microwave frequency were performed on highly crystalline FePt system thin films. Fairly high DC static magnetic field absorption of about 300 mT was observed in these films...
Energy Technology Data Exchange (ETDEWEB)
Kim, Sang-Il [Department of Materials Science and Engineering, Korea University, Seoul, 136-713 (Korea, Republic of); Spin Engineering Physics Team, Division of Scientific Instrumentation, Korea Basic Science Institute, Daejeon, 305-806 (Korea, Republic of); Seo, Min-Su [Spin Engineering Physics Team, Division of Scientific Instrumentation, Korea Basic Science Institute, Daejeon, 305-806 (Korea, Republic of); Choi, Yeon Suk, E-mail: ychoi@kbsi.re.kr [Spin Engineering Physics Team, Division of Scientific Instrumentation, Korea Basic Science Institute, Daejeon, 305-806 (Korea, Republic of); Park, Seung-Young, E-mail: parksy@kbsi.re.kr [Spin Engineering Physics Team, Division of Scientific Instrumentation, Korea Basic Science Institute, Daejeon, 305-806 (Korea, Republic of)
2017-01-01
Magnetic field (H) sweeping direction dependences of the mixed voltage V{sub mix} induced by the inverse-spin Hall effect(ISHE) and spin-rectified effect (SRE) in a CoFeB (5 nm)/Pt (10 nm) bilayer structure are investigated using the ferromagnetic resonance in the TE mode cavities and coplanar waveguide methods. Conventionally, the magnitude of ISHE voltage V{sub ISH} (symmetric) excluding the SRE (antisymmetric component) was unavoidably separated from the fitting curve of V{sub mix} (a sum of a symmetric and an antisymmetric part) for one direction of H-source. By studying the ratio of the two voltage parts with the bi-directional H sweeping, the optimized V{sub ISH} (no SRE condition) value which also include a well-defined spin Hall angle can be obtained via the linear response relation of ISHE and SRE components. - Highlights: • Hysteretic behavior of ferromagnetic resonance spectra in the CoFeB/Pt sample. • Hysteretic behavior of inverse-spin Hall effect voltage in the CoFeB/Pt sample. • Proportion of inverse spin-Hall effect voltage can be determined by the cavity mode. • The hysteretic behavior arise from the unsaturated magnetization limit. • The well-defined spin Hall angle which consider a hysteresis can be obtained.
Superconducting Ferromagnetic Nanodiamond.
Zhang, Gufei; Samuely, Tomas; Xu, Zheng; Jochum, Johanna K; Volodin, Alexander; Zhou, Shengqiang; May, Paul W; Onufriienko, Oleksandr; Kačmarčík, Jozef; Steele, Julian A; Li, Jun; Vanacken, Johan; Vacík, Jiri; Szabó, Pavol; Yuan, Haifeng; Roeffaers, Maarten B J; Cerbu, Dorin; Samuely, Peter; Hofkens, Johan; Moshchalkov, Victor V
2017-06-27
Superconductivity and ferromagnetism are two mutually antagonistic states in condensed matter. Research on the interplay between these two competing orderings sheds light not only on the cause of various quantum phenomena in strongly correlated systems but also on the general mechanism of superconductivity. Here we report on the observation of the electronic entanglement between superconducting and ferromagnetic states in hydrogenated boron-doped nanodiamond films, which have a superconducting transition temperature T c ∼ 3 K and a Curie temperature T Curie > 400 K. In spite of the high T Curie , our nanodiamond films demonstrate a decrease in the temperature dependence of magnetization below 100 K, in correspondence to an increase in the temperature dependence of resistivity. These anomalous magnetic and electrical transport properties reveal the presence of an intriguing precursor phase, in which spin fluctuations intervene as a result of the interplay between the two antagonistic states. Furthermore, the observations of high-temperature ferromagnetism, giant positive magnetoresistance, and anomalous Hall effect bring attention to the potential applications of our superconducting ferromagnetic nanodiamond films in magnetoelectronics, spintronics, and magnetic field sensing.
International Nuclear Information System (INIS)
Gulpinar, Gul; Vatansever, Erol
2012-01-01
In this study, the temperature variations of the equilibrium and the non-equilibrium antiferromagnetic and ferromagnetic susceptibilities of a metamagnetic system are examined near the critical point. The kinetic equations describing the time dependencies of the total and staggered magnetizations are derived by utilizing linear response theory. In order to obtain dynamic magnetic relaxation behavior of the system, the stationary solutions of the kinetic equations in existence of sinusoidal staggered and physical external magnetic fields are performed. In addition, the static and dynamical mean field critical exponents are calculated in order to formulate the critical behavior of antiferromagnetic and ferromagnetic magnetic response of a metamagnetic system. Finally, a comparison of the findings of this study with previous theoretical and experimental studies is represented and it is shown that a good agreement is found with our results. - Highlights: ► Staggered dynamic susceptibility diverges as T→T N in the low frequency region. ► Dynamic total susceptibility exhibits a finite jump discontinuity as T→T N while wτ 2 ⪡1. ► The slope of the staggered magnetic dispersion curve chances in sign as T→T N .
Theory of Collective Spin-Wave Modes of Interacting Ferromagnetic Spheres
2004-09-29
Office (Durham) through Contract No. CS0001028. R. A. thanks also Proyecto Fondecyt Grant No. 7030063. *Present address: Universidad de Chile...Departamento de Fisica FCFM, Santiago, Chile. 1 For examples of experimental studies of the collective spin wave modes of superlattices and multilayers, see M...character to those shown above. In this case, there is no simple symmetry de - composition one canmake for the collective modes, so all branches appear
Directory of Open Access Journals (Sweden)
I.I. Gimazov, Yu.I. Talanov
2015-12-01
Full Text Available The results of the electron spin resonance study of the La1-xCaxMnO3 manganite and the diphenyl-picrylhydrazyl thin films for the magnetic field parallel and perpendicular to plane of the films are presented. The temperature dependence of the demagnetizing field is obtained. The parameters of the Curie-Weiss law are estimated for the paramagnetic thin film.
Energy Technology Data Exchange (ETDEWEB)
Hong, Jhen-Yong; Ou Yang, Kui-Hon; Li, Kai-Shin [Department of Physics, National Taiwan University, 10617 Taipei, Taiwan (China); Wang, Bo-Yao [Department of Physics, National Taiwan University, 10617 Taipei, Taiwan (China); Department of Physics, National Changhua University of Education, Changhua 500, Taiwan (China); Shiu, Hung-Wei; Chen, Chia-Hao; Chan, Yuet-Loy; Wei, Der-Hsin; Chang, Fan-Hsiu; Lin, Hong-Ji [National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan (China); Chiang, Wen-Chung, E-mail: wchiang@faculty.pccu.edu.tw [Department of Physics, Chinese Culture University, 11114 Taipei, Taiwan (China); Lin, Minn-Tsong, E-mail: mtlin@phys.ntu.edu.tw [Department of Physics, National Taiwan University, 10617 Taipei, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, 10617 Taipei, Taiwan (China)
2014-02-24
We report interfacial characterization of 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA)-based organic spin valves (OSV) dusted with a thin layer of partially oxidized alumina at the organic semiconductor (OSC)/ferromagnet (FM) interfaces. Up to 13.5% magnetoresistance is achieved at room temperature. X-ray photoelectron spectroscopy measurements reveal interfacial electronic interaction between PTCDA and FM while the application of a thin alumina layer at the PTCDA/FM interfaces prevents the electronic hybridization and effectively preserves the spin injection into the OSC spacer. This finding demonstrates the critical effect of interfacial structure on magnetotransport behavior in OSV.
International Nuclear Information System (INIS)
Jezewski, W.
1979-01-01
Properties of the Bloch self-consistently renormalized spin wave approximation are analyzed near the zero-field transition temperature Tsub(m). The analysis is carried out on the basis of the application of this approximation to the Heisenberg ferromagnet involving nearest neighbour interaction. Series expansions for the resulting Helmholtz free energy, magnetization, and specific heat in the reduced temperature t=(Tsub(m)-T)/Tsub(m) are derived and the critical exponents β and α' are obtained. The limiting case of infinite spin (the classical limit) is also investigated. (author)
Ti{sub 3}CrCu{sub 4}: A possible 2-D ferromagnetic spin fluctuating system
Energy Technology Data Exchange (ETDEWEB)
Dhar, S. K.; Kulkarni, R.; Goyal, Neeraj [Department of Condensed Matter Physics & Materials Science, T.I.F.R., Homi Bhabha Road, Colaba, Mumbai, 400005 (India); Provino, A.; Manfrinetti, P. [Department of Chemistry, University of Genova, Via Dodecaneso 31, 16146 Genova (Italy); Paudyal, D. [The Ames Laboratory, US Department of Energy, Iowa State University, Ames, IA 50011-3020 (United States)
2016-05-15
Ti{sub 3}CrCu{sub 4} is a new ternary compound which crystallizes in the tetragonal Ti{sub 3}Pd{sub 5} structure type. The Cr atoms form square nets in the a-b plane (a = 3.124 Å) which are separated by an unusually large distance c = 11.228 Å along the tetragonal axis, thus forming a -2-D Cr-sublattice. The paramagnetic susceptibility is characterized by a low effective moment, μ{sub eff} = 1.1 μ{sub B}, a low paramagnetic Curie temperature θ{sub P} (below 7 K) and a temperature independent χ{sub 0} = 6.7 x 10{sup −4} emu/mol. The magnetization at 1.8 K increases rapidly with field nearly saturating to 0.2 μ{sub B}/f.u. The zero field heat capacity C/T shows an upturn below 7 K (∼190 mJ/mol K{sup 2} at ∼0.1K) which is suppressed in applied magnetic fields and interpreted as suggesting the presence of spin fluctuations. The resistivity at low temperatures shows non-Fermi liquid behavior. Overall, the experimental data thus reveal an unusual magnetic state in Ti{sub 3}CrCu{sub 4}, which likely has its origin in the layered nature of the Cr sub-lattice and ferromagnetic spin fluctuations. Density functional theoretical calculations reveal a sharp Cr density of states peak just above the Fermi level, indicating the propensity of Ti{sub 3}CrCu{sub 4} to become magnetic.
Energy Technology Data Exchange (ETDEWEB)
Kostylev, M. [School of Physics, M013, University of Western Australia, Crawley, Perth 6009, Western Australia (Australia)
2014-06-21
In this work, we derive the interface exchange boundary conditions for the classical linear dynamics of magnetization in ferromagnetic layers with the interface Dzyaloshinskii-Moriya interaction (IDMI). We show that IDMI leads to pinning of dynamic magnetization at the interface. An unusual peculiarity of the IDMI-based pinning is that its scales as the spin-wave wave number. We incorporate these boundary conditions into an existing numerical model for the dynamics of the Damon-Eshbach spin wave in ferromagnetic films. IDMI affects the dispersion and the frequency non-reciprocity of the travelling Damon-Eshbach spin wave. For a broad range of film thicknesses L and wave numbers, the results of the numerical simulations of the spin wave dispersion are in a good agreement with a simple analytical expression, which shows that the contribution of IDMI to the dispersion scales as 1/L, similarly to the effect of other types of interfacial anisotropy. Suggestions to experimentalists how to detect the presence of IDMI in a spin wave experiment are given.
International Nuclear Information System (INIS)
Uhrmann, T; Dimopoulos, T; Brueckl, H; Kovacs, A; Kohn, A; Weyers, S; Paschen, U; Smoliner, J
2009-01-01
In this work we present the electrical properties of sputter-deposited ferromagnetic (FM) Schottky diodes and MgO-based tunnelling diodes to n-doped (0 0 1) silicon. The effective Schottky barrier height (SBH) has been evaluated as a function of the FM electrode (Co 70 Fe 30 , Co 40 Fe 40 B 20 and Ni 80 Fe 20 ), the silicon doping density (10 15 to 10 18 cm -3 ), the MgO tunnelling barrier thickness (0, 1.5 and 2.5 nm) and post-deposition annealing up to 400 0 C. The ideality factors of the Schottky diodes are close to unity, indicating transport by thermionic emission and the absence of an interfacial oxide layer, which is confirmed by transmission electron microscopy. The effective SBH is found to be approximately 0.65 eV, independent of the FM material and decreasing with increasing doping density. The changes induced by high temperature annealing at the current-voltage characteristic of the Schottky diodes depend strongly on the FM electrode. The effective SBH for the tunnelling diodes is as low as 0.3 eV, which suggests a high density of oxide and interface traps. It is again independent of the FM electrode, decreasing with increasing doping density and annealing temperature. The inclusion of MgO leads to higher thermal stability of the tunnelling diodes. The measured contact resistance values are discussed with respect to the conductivity mismatch for spin injection and detection.
Marmolejo-Tejada, Juan Manuel; Dolui, Kapildeb; Lazić, Predrag; Chang, Po-Hao; Smidstrup, Søren; Stradi, Daniele; Stokbro, Kurt; Nikolić, Branislav K
2017-09-13
The control of recently observed spintronic effects in topological-insulator/ferromagnetic-metal (TI/FM) heterostructures is thwarted by the lack of understanding of band structure and spin textures around their interfaces. Here we combine density functional theory with Green's function techniques to obtain the spectral function at any plane passing through atoms of Bi 2 Se 3 and Co or Cu layers comprising the interface. Instead of naively assumed Dirac cone gapped by the proximity exchange field spectral function, we find that the Rashba ferromagnetic model describes the spectral function on the surface of Bi 2 Se 3 in contact with Co near the Fermi level E F 0 , where circular and snowflake-like constant energy contours coexist around which spin locks to momentum. The remnant of the Dirac cone is hybridized with evanescent wave functions from metallic layers and pushed, due to charge transfer from Co or Cu layers, a few tenths of an electron-volt below E F 0 for both Bi 2 Se 3 /Co and Bi 2 Se 3 /Cu interfaces while hosting distorted helical spin texture wounding around a single circle. These features explain recent observation of sensitivity of spin-to-charge conversion signal at TI/Cu interface to tuning of E F 0 . Crucially for spin-orbit torque in TI/FM heterostructures, few monolayers of Co adjacent to Bi 2 Se 3 host spectral functions very different from the bulk metal, as well as in-plane spin textures (despite Co magnetization being out-of-plane) due to proximity spin-orbit coupling in Co induced by Bi 2 Se 3 . We predict that out-of-plane tunneling anisotropic magnetoresistance in Cu/Bi 2 Se 3 /Co vertical heterostructure can serve as a sensitive probe of the type of spin texture residing at E F 0 .
Dey, Rik; Register, Leonard F.; Banerjee, Sanjay K.
2018-04-01
The spin-momentum locking of the surface states in a three-dimensional topological insulator (TI) allows a charge current on the surface of the TI induced by an applied spin current onto the surface, which is known as the inverse Edelstein effect (IEE), that could be achieved either by injecting pure spin current by spin-pumping from a ferromagnetic metal (FM) layer or by injecting spin-polarized charge current by direct tunneling of electrons from the FM to the TI. Here, we present a theory of the observed IEE effect in a TI-FM heterostructure for the spin-polarized tunneling experiments. If an electrical current is passed from the FM to the surface of the TI, because of density-of-states polarization of the FM, an effective imbalance of spin-polarized electrons occurs on the surface of the TI. Due to the spin-momentum helical locking of the surface states in the TI, a difference of transverse charge accumulation appears on the TI surface in a direction orthogonal to the direction of the magnetization of the FM, which is measured as a voltage difference. Here, we derive the two-dimensional transport equations of electrons on the surface of a diffusive TI, coupled to a FM, starting from the quantum kinetic equation, and analytically solve the equations for a rectangular geometry to calculate the voltage difference.
International Nuclear Information System (INIS)
Suzuki, Masatsugu; Suzuki, Itsuko S; Matsuura, Motohiro
2007-01-01
Stage-2 CoCl 2 -graphite intercalation compound (GIC) is a spin ceramic which shows hierarchical successive transitions at T cu (= 8.9 K) and T cl (= 7.0 K) from the paramagnetic phase into an intra-cluster (two-dimensional ferromagnetic) order with inter-cluster disorder and then to an inter-cluster (three-dimensional antiferromagnetic like) order over the whole system. The nature of the inter-cluster disorder was suggested to be of spin glass by nonlinear magnetic response analyses around T cu and by studies on dynamical aspects of ordering between T cu and T cl . Here, we present a further extensive examination of a series of time dependence of zero-field cooled magnetization M ZFC after the ageing protocol below T cu . The time dependence of the relaxation rates S ZFC (t) = (1/H) dM ZFC (t)/dlnt dramatically changes from the curves of simple spin glass ageing effect below T cl to those of two peaks above T cl . The characteristic relaxation behaviour apparently indicates that there coexist two different kinds of glassy correlated region below T cu
Local Weak Ferromagnetism in Single-Crystalline Ferroelectric BiFeO3
DEFF Research Database (Denmark)
Ramazanoglu, M.; Laver, Mark; Ratcliff, W.
2011-01-01
Polarized small-angle neutron scattering studies of single-crystalline multiferroic BiFeO3 reveal a long-wavelength spin density wave generated by ∼1° spin canting of the spins out of the rotation plane of the antiferromagnetic cycloidal order. This signifies weak ferromagnetism within mesoscopic...
Optical orientation in ferromagnet/semiconductor hybrids
Korenev, V. L.
2008-11-01
The physics of optical pumping of semiconductor electrons in ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of a ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of a semiconductor. Spin-spin interactions near the ferromagnet/semiconductor interface play a crucial role in the optical readout and the manipulation of ferromagnetism.
Optical Orientation in Ferromagnet/Semiconductor Hybrids
Korenev, V. L.
2008-01-01
The physics of optical pumping of semiconductor electrons in the ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of the ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of the semiconductor. Spin-spin interactions near the interface ferromagnet/semiconductor play crucial role in the optical readout and the manipulation of ferromagnetism.
International Nuclear Information System (INIS)
Furman, G.B.; Panich, A.M.; Goren, S.D.
1998-01-01
The phenomena of spin diffusion and spin lattice relaxation of nuclear dipolar order in solids containing paramagnetic impurities (PI) is considered. We show that at the beginning of the relaxation process the diffusion vanishing regime realizes with non-exponential time dependence, R(t) ∼ exp [- (t/T 1d ) α ], where T 1d ∼ C p -1/α , C p is PI's concentration. For a homogeneous distribution of Pis and nuclear spins, α=Q/6, where Q is the sample dimensionality; for an inhomogeneous distribution, the sample is divided into q-dimensional subsystems, each containing one PI, yield- ing α= (Q + q) /6. This result coincides with experimental data for CaF 2 doped with 0.8 - 10 -3 ωt % of Mn 2+ , where the non-exponential decay of the dipolar signal with α= 0.83 has been observed [3]. Fitting the experimental data yields a good agreement with T 1d = 66 ms . For another independent check of the obtained results we use dependence of the relaxation time on impurities concentration. In accordance that 1/α=1.2 , we have T 1d ∼ C p -1 '. 2 . Exactly this dependence on impurity concentration of the relaxation time has been found in the experiment. Then the relaxation regime starts as a non-exponential time dependent, proceed asymptotically to an to an exponential function of time, to so called diffusion limited relaxation regime with relaxation time T 1d D is inversely depends on impurities concentration. This kind of relaxation behavior of the dipolar order takes place in the experiment [2]. Using experimental results [2] from this two regime we can estimate the diffusion coefficient of the nuclear dipolar order in CaF 2 , which gives for typical values of impurity concentration C p ∼ 10 18 cm 3 the diffusion coefficient of dipolar order in the interval D ∼ 10 -11 -i- 10 -12 cm 2 /sec which is coincide to the case of Zeeman energy spin diffusion
Topological order in an exactly solvable 3D spin model
International Nuclear Information System (INIS)
Bravyi, Sergey; Leemhuis, Bernhard; Terhal, Barbara M.
2011-01-01
Research highlights: RHtriangle We study exactly solvable spin model with six-qubit nearest neighbor interactions on a 3D face centered cubic lattice. RHtriangle The ground space of the model exhibits topological quantum order. RHtriangle Elementary excitations can be geometrically described as the corners of rectangular-shaped membranes. RHtriangle The ground space can encode 4g qubits where g is the greatest common divisor of the lattice dimensions. RHtriangle Logical operators acting on the encoded qubits are described in terms of closed strings and closed membranes. - Abstract: We study a 3D generalization of the toric code model introduced recently by Chamon. This is an exactly solvable spin model with six-qubit nearest-neighbor interactions on an FCC lattice whose ground space exhibits topological quantum order. The elementary excitations of this model which we call monopoles can be geometrically described as the corners of rectangular-shaped membranes. We prove that the creation of an isolated monopole separated from other monopoles by a distance R requires an operator acting on Ω(R 2 ) qubits. Composite particles that consist of two monopoles (dipoles) and four monopoles (quadrupoles) can be described as end-points of strings. The peculiar feature of the model is that dipole-type strings are rigid, that is, such strings must be aligned with face-diagonals of the lattice. For periodic boundary conditions the ground space can encode 4g qubits where g is the greatest common divisor of the lattice dimensions. We describe a complete set of logical operators acting on the encoded qubits in terms of closed strings and closed membranes.
Next-order spin-orbit contributions to chaos in compact binaries
International Nuclear Information System (INIS)
Wang Yuzhao; Wu Xin
2011-01-01
This paper is mainly devoted to numerically investigating the effects of the next-order spin-orbit interactions including the 2.5 post-Newtonian order term of the equations of motion and the second post-Newtonian order terms of the spin precession equations on chaos in the conservative Lagrangian dynamics of a spinning compact binary system. It is shown sufficiently through individual orbit simulations, the dependence of the invariant fast Lyapunov indicators on the variations of initial spin angles and the phase space scans for chaos, that the next-order spin-orbit contributions do play an important role in the amplification of chaos.
Dynamics of massless higher spins in the second order in curvatures
International Nuclear Information System (INIS)
Vasiliev, M.A.
1989-08-01
The consistent equations of motion of interacting fields of all spins s=0,1/2,1...∞ are constructed explicitly to the second order of the expansion in powers of the higher spin strengths. (author). 14 refs
Dynamics of massless higher spins in the second order in curvatures
Energy Technology Data Exchange (ETDEWEB)
Vasiliev, M A [International Centre for Theoretical Physics, Trieste (Italy)
1990-04-05
The consistent equations of motion of interacting massless fields of all spins s=0, 1/2, 1, ..., {infinity} are constructed explicitly to the second order of the expansion in powers of the higher spin strengths. (orig.).
Observation of ferromagnetic ordering in a stable α -Co (OH) 2 phase grown on a Mo S2 surface
Debnath, Anup; Bhattacharya, Shatabda; Saha, Shyamal K.
2017-12-01
Because of the potential application of Co (OH) 2 in a magnetic cooling system as a result of its superior magnetocaloric effect many people have investigated magnetic properties of Co (OH) 2 . Unfortunately, most of the works have been carried out on the β -Co (OH) 2 phase due to the fact that the α -Co (OH) 2 phase is very unstable and continuously transformed into the stable β -Co (OH) 2 phase. However, in the present work, using a Mo S2 sheet as a two-dimensional template, we have been able to synthesize a stable α -Co (OH) 2 phase in addition to a β -Co (OH) 2 phase by varying the layer thickness. It is seen that for thinner samples the β phase, while for thicker samples α phase, is grown on the Mo S2 surface. Magnetic measurements are carried out for the samples over the temperature range from 2 to 300 K and it is seen that for the β phase, ferromagnetic ordering with fairly large coercivity (1271 Oe) at 2 K is obtained instead of the usual antiferromagnetism. The most interesting result is the observation of ferromagnetic ordering with a transition temperature (Curie temperature) more than 100 K in the α -Co (OH) 2 phase. Complete saturation in the hysteresis curve under application of very low field having coercivity of ˜162 Oe at 2 K and 60 Oe at 50 K is obtained. A thin stable α -Co (OH) 2 phase grown on Mo S2 surface with very soft ferromagnetic ordering will be very useful as the core material in electromagnets.
Resonant-spin-ordering of vortex cores in interacting mesomagnets
Jain, Shikha
2013-03-01
The magnetic system of interacting vortex-state elements have a dynamically reconfigurable ground state characterized by different relative polarities and chiralities of the individual disks; and have a corresponding dynamically controlled spectrum of collective excitation modes that determine the microwave absorption of the crystal. The development of effective methods for dynamic control of the ground state in this vortex-type magnonic crystal is of interest both from fundamental and technological viewpoints. Control of vortex chirality has been demonstrated previously using various techniques; however, control and manipulation of vortex polarities remain challenging. In this work, we present a robust and efficient way of selecting the ground state configuration of interacting magnetic elements using resonant-spin-ordering approach. This is achieved by driving the system from the linear regime of constant vortex gyrations to the non-linear regime of vortex-core reversals at a fixed excitation frequency of one of the coupled modes. Subsequently reducing the excitation field to the linear regime stabilizes the system to a polarity combination whose resonant frequency is decoupled from the initialization frequency. We have utilized the resonant approach to transition between the two polarity combinations (parallel or antiparallel) in a model system of connected dot-pairs which may form the building blocks of vortex-based magnonic crystals. Taking a step further, we have extended the technique by studying many-particle system for its potential as spin-torque oscillators or logic devices. Work at Argonne was supported by the U. S. DOE, Office of BES, under Contract No. DE-AC02-06CH11357. This work was in part supported by grant DMR-1015175 from the U. S. National Science Foundation, by a Contract from the U.S. Army TARDEC and RDECOM.
International Nuclear Information System (INIS)
Venkatesh, S; Vaidya, Ulhas; Rakhecha, Veer Chand; Ramakrishnan, S; Grover, A K
2010-01-01
A compensated magnetic state in an ideally homogeneous system with long range magnetic order is characterized by a net zero magnetization (M) throughout the sample (macroscopic). In the pristine state of the sample (i.e. with no external field, H = 0), this implies that at the magnetic compensation temperature (T comp ) we must have M = 0 at H = 0 irrespective of any thermal and magnetic history of the sample and any underlying physics. This simple fact voids the usual identification (and interpretation) of M-H loop parameters at and in the vicinity of magnetic compensation temperature, specifically the coercivity, the remanence, and the exchange bias characteristics. The physics of coercivity and exchange bias continues to be fully relevant, but its manifestation in an M-H loop would get camouflaged at (and near) a magnetic compensation because M→0 at H = 0. We present an experimental elucidation of the above premise through a case study in the spin ferromagnetic Sm 1-x Gd x Al 2 alloys [x = 0.01-0.06], where the specimens with x ≤ 0.03 show compensation below the Curie temperature T c , while those with x ≥ 0.03 have rather small magnetization due to near cancellation of opposing contributions, but are otherwise devoid of compensation. The experiments comprised low field (near zero) as well as high field (70 kOe) magnetization measurements from the paramagnetic state down to 5 K in the ordered regime (T c ∼ 125 K) and isothermal M-H loop studies on the remnant magnetic state of polycrystalline samples.
Kanagawa, Kazunari; Teki, Yoshio; Shikoh, Eiji
2018-05-01
The inverse spin-Hall effect (ISHE) is produced even in a "single-layer" ferromagnetic material film. Previously, the self-induced ISHE in a Ni80Fe20 film under the ferromagnetic resonance (FMR) was discovered. In this study, we observed an electromotive force (EMF) in an iron (Fe) and a cobalt (Co) single-layer films themselves under the FMR. As origins of the EMFs in the films themselves, the ISHE was main for Fe and dominant for Co, respectively 2 and 18 times larger than the anomalous Hall effect. Thus, we demonstrated the self-induced ISHE in an Fe and a Co single-layer films themselves under the FMR.
Large spin limit of AdS5xS5 string theory and low energy expansion of ferromagnetic spin chains
International Nuclear Information System (INIS)
Kruczenski, M.; Ryzhov, A.V.; Tseytlin, A.A.
2004-01-01
By considering AdS 5 xS 5 string states with large S 5 angular momenta one can provide non-trivial quantitative checks of the AdS/CFT duality. A string rotating in S 5 with two angular momenta J 1 , J 2 is dual to an operator in N=4 SYM theory whose conformal dimension can be computed by diagonalizing a (generalization of) spin 1/2 Heisenberg chain Hamiltonian. It was recently argued and verified to lowest order in a large J=J 1 +J 2 expansion, that the Heisenberg chain can be described using a non-relativistic low energy effective 2d action for a unit vector field n i which exactly matches the corresponding large J limit of the classical AdS 5 xS 5 string action. In this paper we show that this agreement extends to the next order and develop a systematic procedure for computing higher orders in such large angular momentum expansion. This involves several non-trivial steps. On the string side, we need to choose a special gauge with a non-diagonal world-sheet metric which insures that the angular momentum is uniformly distributed along the string, as indeed is the case on the spin chain side. We need also to implement an order by order redefinition of the field n i to get an action linear in the time derivative. On the spin chain side, it turns out to be crucial to include the effects of integrating out short wave-length modes. In this way we gain a better understanding of how (a subsector of) the string sigma model emerges from the dual gauge theory, allowing us to demonstrate the duality beyond comparing particular examples of states with large J
Zhou, Jian; Sun, Qiang; Wang, Qian; Kawazoe, Yoshiyuki; Jena, Puru
2016-06-07
Exploring a two-dimensional intrinsic quantum spin Hall state with a large band gap as well as an anomalous Hall state in realizable materials is one of the most fundamental and important goals for future applications in spintronics, valleytronics, and quantum computing. Here, by combining first-principles calculations with a tight-binding model, we predict that Sb or Bi can epitaxially grow on a stable and ferromagnetic MnO2 thin film substrate, forming a flat honeycomb sheet. The flatness of Sb or Bi provides an opportunity for the existence of Dirac points in the Brillouin zone, with its position effectively tuned by surface hydrogenation. The Dirac points in spin up and spin down channels split due to the proximity effects induced by MnO2. In the presence of both intrinsic and Rashba spin-orbit coupling, we find two band gaps exhibiting a large band gap quantum spin Hall state and a nearly quantized anomalous Hall state which can be tuned by adjusting the Fermi level. Our findings provide an efficient way to realize both quantized intrinsic spin Hall conductivity and anomalous Hall conductivity in a single material.
International Nuclear Information System (INIS)
Balbashov, A.M.; Berezin, A.G.; Gufan, Yu.M.; Kolyadko, G.S.; Marchukov, P.Yu.; Rudashevskij, E.G.
1987-01-01
A pronounced energy gap of a nonmagnetoelastic origin is observed experimentally in the spectrum of the low-frequency (quasiferromagnetic) antiferromagnetic resonance branch during a second order spin-flip phase transition in an external magnetic field directed along the a axis of the rhombic weak ferromagnetic YFeO 3 . From the theory developed which takes into account the susceptibility along the antiferromagnetism axis and dissipation processes, it follows that beside the usual AFMR oscillatory branches there should also be a relaxation mode which is ''soft'' fo the given transition. The magnitude of the energy gaps, the values of the kinetic coefficients, Dzyaloshinsky field strengths and ratio of the longitudinal susceptibility to the transverse susceptibility are determined by analyzing the experimental data obtained in fields up to 130 kOe in the frequency range from 60 to 400 GHz at room temperature
Spin nematics next to spin singlets
Yokoyama, Yuto; Hotta, Chisa
2018-05-01
We provide a route to generate nematic order in a spin-1/2 system. Unlike the well-known magnon-binding mechanism, our spin nematics requires neither the frustration effect nor spin polarization in a high field or in the vicinity of a ferromagnet, but instead appears next to the spin singlet phase. We start from a state consisting of a quantum spin-1/2 singlet dimer placed on each site of a triangular lattice, and show that interdimer ring exchange interactions efficiently dope the SU(2) triplets that itinerate and interact, easily driving a stable singlet state to either Bose-Einstein condensates or a triplet crystal, some hosting a spin nematic order. A variety of roles the ring exchange serves includes the generation of a bilinear-biquadratic interaction between nearby triplets, which is responsible for the emergent nematic order separated from the singlet phase by a first-order transition.
Charge ordering and opening of spin gap in NaV2O5
Mostovoy, M.V.; Khomskii, D.I.
1999-01-01
We argue that the origin of the phase transition in quasi-one-dimensional antiferromagnet NaV2O5 is not the spin-Peierls (SP) instability, but a charge ordering. The opening of the spin gap and the lattice dimerization, characteristic for the spin-Peierls systems, in NaV2O5 result from the interplay
Spin waves and the order-disorder transition in chromium
DEFF Research Database (Denmark)
Als-Nielsen, Jens Aage; Dietrich, O.W.
1969-01-01
The inelastic magnetic scattering of neutrons has been studied in Cr and Cr0.95-Mn0.05 both below and above the Neel temperature. The temperature dependence of the spin-wave velocity in the alloy has been measured below TN. The scattering above TN may also be interpreted in terms of spin-wavelike...
Vodopyanov, B P
2010-05-12
The influence of the spin-dependent phase shifts (SDPSs) associated with the electronic reflection and transmission amplitudes acquired by electrons upon scattering at the potential barrier on the Andreev reflection probability of electron and hole excitations for a ferromagnet/isolator/d-wave superconductor (FIS) contact and on the charge conductance of the FIS contact is studied. Various superconductor orientations are considered. It has been found that for strong ferromagnets and ultrathin interface potential for the {110} oriented d-wave superconductor the presence of the SDPS can lead to the appearance of finite-voltage peaks in the charge conductance of the F/I/d-wave superconductor contact. On the contrary, for the {100} orientation of the d-wave superconductor the presence of the SDPS can lead to restoration of the zero-voltage peak and suppression of finite-voltage peaks. The spin-dependent amplitudes of the Andreev reflection probability and energy levels of the spin-dependent Andreev bound states are found.
Novel room temperature ferromagnetic semiconductors
Energy Technology Data Exchange (ETDEWEB)
Gupta, Amita [KTH Royal Inst. of Technology, Stockholm (Sweden)
2004-06-01
Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous
Avdeev, M. V.; Proshin, Yu. N.
2018-03-01
A possible explanation for the long-range proximity effect observed in single-crystalline cobalt nanowires sandwiched between two tungsten superconducting electrodes [Nat. Phys. 6, 389 (2010), 10.1038/nphys1621] is proposed. The theoretical model uses properties of a ferromagnet band structure. Specifically, to connect the exchange field with the momentum of quasiparticles the distinction between the effective masses in majority and minority spin subbands and the Fermi-surface anisotropy are considered. The derived Eilenberger-like equations allowed us to obtain a renormalized exchange interaction that is completely compensated for some crystallographic directions under certain conditions. The proposed theoretical model is compared with previous approaches.
Leading order finite size effects with spins for inspiralling compact binaries
Energy Technology Data Exchange (ETDEWEB)
Levi, Michele [Université Pierre et Marie Curie-Paris VI, CNRS-UMR 7095, Institut d’Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris (France); Sorbonne Universités, Institut Lagrange de Paris, 98 bis Boulevard Arago, 75014 Paris (France); Steinhoff, Jan [Max-Planck-Institute for Gravitational Physics - Albert-Einstein-Institute,Am Mühlenberg 1, 14476 Potsdam-Golm (Germany); Centro Multidisciplinar de Astrofisica, Instituto Superior Tecnico, Universidade de Lisboa,Avenida Rovisco Pais 1, 1049-001 Lisboa (Portugal)
2015-06-10
The leading order finite size effects due to spin, namely that of the cubic and quartic in spin interactions, are derived for the first time for generic compact binaries via the effective field theory for gravitating spinning objects. These corrections enter at the third and a half and fourth post-Newtonian orders, respectively, for rapidly rotating compact objects. Hence, we complete the leading order finite size effects with spin up to the fourth post-Newtonian accuracy. We arrive at this by augmenting the point particle effective action with new higher dimensional nonminimal coupling worldline operators, involving higher-order derivatives of the gravitational field, and introducing new Wilson coefficients, corresponding to constants, which describe the octupole and hexadecapole deformations of the object due to spin. These Wilson coefficients are fixed to unity in the black hole case. The nonminimal coupling worldline operators enter the action with the electric and magnetic components of the Weyl tensor of even and odd parity, coupled to even and odd worldline spin tensors, respectively. Moreover, the non relativistic gravitational field decomposition, which we employ, demonstrates a coupling hierarchy of the gravito-magnetic vector and the Newtonian scalar, to the odd and even in spin operators, respectively, which extends that of minimal coupling. This observation is useful for the construction of the Feynman diagrams, and provides an instructive analogy between the leading order spin-orbit and cubic in spin interactions, and between the leading order quadratic and quartic in spin interactions.
Romano, S.
1992-01-01
The present paper considers a classical system, consisting of n-component unit vectors (n=2 or 3), associated with a one-dimensional lattice \\{uk||k∈openZ\\}, and interacting via a translationally invariant pair potential of the long-range, ferromagnetic and anisotropic form W=Wjk=-ɛ||j-k||-2(auj,nuk,n +b tsumλuk,λ denotes the Cartesian components of the unit vectors. According to the available rigorous results, the system disorders at all finite temperatures when a=b, or n=3, a=0, and possesses an ordering transition at finite temperature when b=0. Approximate arguments and simulation results suggest that the isotropic models (a=b) produce a transition to a low-temperature phase with infinite susceptibility and power-law decay of the correlation function. If this is true, the available correlation inequalities entail that it also happens in the anisotropic but O(2)-invariant case n=3, b=0. We report here Monte Carlo calculations for this latter potential model; simulation results were found to be consistent with this conjecture, and to suggest that T*c=0.65+/-0.01.
Proximity effects in ferromagnet/superconductor structures
International Nuclear Information System (INIS)
Yu, H.L.; Sun, G.Y.; Yang, L.Y.; Xing, D.Y.
2004-01-01
The Nambu spinor Green's function approach is applied to study proximity effects in ferromagnet/superconductor (FM/SC) structures. They include the induced superconducting order parameter and density of states (DOS) with superconducting feature on the FM side, and spin-dependent DOS within the energy gap on the SC side. The latter indicates an appearance of gapless superconductivity and a coexistence of ferromagnetism and superconductivity in a small regime near the interface. The influence of exchange energy in FM and barrier strength at interface on the proximity effects is discussed
Boekema, C.; Brabers, V.A.M.; Lichti, R.L.; Denison, A.B.; Cooke, D.W.; Heffner, R.H.; Hutson, R.L.; Schillaci, M.E.; MacLaughlin, D.E.; Dodds, S.A.
1986-01-01
Zero-field longitudinal muon-spin-relaxation (µSR) experiments have been performed on single crystals of pseudo-brookite (Fe2-xTil+x O 5; x=0.25), an anisotropic spin-glass system. The spinglass temperature (Tg) is determined to be 44.0±0.5K. Above Tg, a distinct exponential muon-spin-relaxation
Energy Technology Data Exchange (ETDEWEB)
Feng, Cong; Lin, Xuejun; Wang, Xinqiang, E-mail: xqwang@sdu.edu.cn; Liu, Hongjing; Liu, Benxue; Zhu, Luyi; Zhang, Guanghui; Xu, Dong
2016-02-15
Highlights: • NiO and hollow Co{sub 3}O{sub 4} fibers with the diameter of about 10 μm were prepared through centrifugal-spinning technique. • The evolution mechanism from precursor to crystalline fibers was explored. • Both NiO and hollow Co{sub 3}O{sub 4} fibers show ferromagnetism. • The NiO fibers exhibit good photocatalytic performance. - Abstract: Both NiO and hollow Co{sub 3}O{sub 4} fibers with the diameter of about 10 μm have been successfully prepared through spinning high viscous sols into precursor fibers and followed calcination process. The evolution process from precursor to crystalline fibers and the microstructures of the obtained fibers were characterized by TG-DSC, FT-IR, XRD, HRTEM, SEM and the like. The method is facile and cost-effective for mass production of fibers and the obtained fibers are pure phase with high crystallinity. Their magnetic properties were investigated, showing that both the fibers are ferromagnetic. Meanwhile, the NiO fibers exhibit good photocatalytic performance for the removal of Congo red from water under UV light irradiation.
Energy Technology Data Exchange (ETDEWEB)
Yarmohammadi, Mohsen, E-mail: m.yarmohammadi69@gmail.com
2017-03-15
In this paper, we have investigated the effects of strain on DC transverse and spin-valley Hall conductivity (SHC-VHC) of two-dimensional buckled materials ferromagnetic graphene's analog, MoS{sub 2} and silicene due to their spin–orbit coupling. The Kubo formalism has been used to investigate the dynamics of carriers under strain along the armchair (AC) direction of systems in the context of the Kane–Mele Hamiltonian and the Dirac cone approximation. The effective mass of carriers increases with strain and this leads to the reduction of their transport. We have found that SHC-VHC changes symmetrically with respect to a critical strain around 13% and 45% for MoS{sub 2} and silicene, respectively. Furthermore, the reflection symmetry of silicene has been broken with electric field and a phase transition to topological insulator for strained ferromagnetic silicene has been seen. - Highlights: • Theoretical calculation of strain effects on band structure of MoS{sub 2} and silicene in the presence of electric field. • Investigation of DC transverse and spin-valley Hall conductivity of strained-MoS{sub 2} and silicene in the presence of electric field. • Theoretical calculation of external electric field effects on topological phase transition of silicene in the presence of strain.
Optical orientation in ferromagnet/semiconductor hybrids
International Nuclear Information System (INIS)
Korenev, V L
2008-01-01
The physics of optical pumping of semiconductor electrons in ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of a ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of a semiconductor. Spin–spin interactions near the ferromagnet/semiconductor interface play a crucial role in the optical readout and the manipulation of ferromagnetism
Spin ordered phase transitions in neutron matter under the presence of a strong magnetic field
International Nuclear Information System (INIS)
Isayev, A.A.; Yang, J.
2011-01-01
In dense neutron matter under the presence of a strong magnetic field, considered in the model with the Skyrme effective interaction, there are possible two types of spin ordered states. In one of them the majority of neutron spins are aligned opposite to magnetic field (thermodynamically preferable state), and in other one the majority of spins are aligned along the field (metastable state). The equation of state, incompressibility modulus and velocity of sound are determined in each case with the aim to find the peculiarities allowing to distinguish between two spin ordered phases.
Order and chaos in the nonlinear response of driven nuclear spin systems
Energy Technology Data Exchange (ETDEWEB)
Brun, E; Derighetti, B; Holzner, R; Ravani, M [Zurich Univ. (Switzerland). Inst. fuer Physik
1984-01-01
The authors report on observations of ordered and chaotic behavior of a nonlinear system of strongly polarized nuclear spins inside the tuning coil of an NMR detector. The combined system: spins plus LC-circuit, may act as a nonlinear bistable absorber or a spin-flip laser, depending on the sign of the nuclear spin polarization. For the NMR laser experimental evidence is presented for limit-cycle behavior, sequences of bifurcations which lead to chaos, intermittency, multistability, and pronounced hysteresis effects. The experimental facts are compared with computer solutions of appropriate Bloch equations for the macroscopic order parameters.
Dynamics of High-Order Spin-Orbit Couplings about Linear Momenta in Compact Binary Systems*
International Nuclear Information System (INIS)
Huang Li; Wu Xin; Huang Guo-Qing; Mei Li-Jie
2017-01-01
This paper relates to the post-Newtonian Hamiltonian dynamics of spinning compact binaries, consisting of the Newtonian Kepler problem and the leading, next-to-leading and next-to-next-to-leading order spin-orbit couplings as linear functions of spins and momenta. When this Hamiltonian form is transformed to a Lagrangian form, besides the terms corresponding to the same order terms in the Hamiltonian, several additional terms, third post-Newtonian (3PN), 4PN, 5PN, 6PN and 7PN order spin-spin coupling terms, yield in the Lagrangian. That means that the Hamiltonian is nonequivalent to the Lagrangian at the same PN order but is exactly equivalent to the full Lagrangian without any truncations. The full Lagrangian without the spin-spin couplings truncated is integrable and regular. Whereas it is non-integrable and becomes possibly chaotic when any one of the spin-spin terms is dropped. These results are also supported numerically. (paper)
Josephson tunnel junctions with ferromagnetic interlayer
International Nuclear Information System (INIS)
Weides, M.P.
2006-01-01
Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al 2 O 3 tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or π coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, π) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-π Josephson junction. At a certain temperature this 0-π junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum Φ 0 . Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T → 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)
Josephson tunnel junctions with ferromagnetic interlayer
Energy Technology Data Exchange (ETDEWEB)
Weides, M.P.
2006-07-01
Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al{sub 2}O{sub 3} tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or {pi} coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, {pi}) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-{pi} Josephson junction. At a certain temperature this 0-{pi} junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum {phi}{sub 0}. Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T {yields} 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)
Das, Kalipada
2017-10-01
In our present study, we address in detail the magnetic and magneto-transport properties of ferromagnetic-charge ordered core-shell nanostructures. In these core-shell nanostructures, well-known half metallic La0.67Sr0.33MnO3 nanoparticles (average particle size, ˜20 nm) are wrapped by the charge ordered antiferromagnetic Pr0.67Ca0.33MnO3 (PCMO) matrix. The intrinsic properties of PCMO markedly modify it into such a core-shell form. The robustness of the PCMO matrix becomes fragile and melts at an external magnetic field (H) of ˜20 kOe. The analysis of magneto-transport data indicates the systematic reduction of the electron-electron and electron-magnon interactions in the presence of an external magnetic field in these nanostructures. The pronounced training effect appears in this phase separated compound, which was analyzed by considering the second order tunneling through the grain boundaries of the nanostructures. Additionally, the analysis of low field magnetoconductance data supports the second order tunneling and shows the close value of the universal limit (˜1.33).
Recoil velocity at second post-Newtonian order for spinning black hole binaries
International Nuclear Information System (INIS)
Racine, Etienne; Buonanno, Alessandra; Kidder, Larry
2009-01-01
We compute the flux of linear momentum carried by gravitational waves emitted from spinning binary black holes at second post-Newtonian (2PN) order for generic orbits. In particular we provide explicit expressions of three new types of terms, namely, next-to-leading order spin-orbit terms at 1.5 post-Newtonian (1.5PN) order, spin-orbit tail terms at 2PN order, and spin-spin terms at 2PN order. Restricting ourselves to quasicircular orbits, we integrate the linear-momentum flux over time to obtain the recoil velocity as function of orbital frequency. We find that in the so-called superkick configuration the higher-order spin corrections can increase the recoil velocity up to a factor ∼3 with respect to the leading-order PN prediction. Whereas the recoil velocity computed in PN theory within the adiabatic approximation can accurately describe the early inspiral phase, we find that its fast increase during the late inspiral and plunge, and the arbitrariness in determining until when it should be trusted, makes the PN predictions for the total recoil not very accurate and robust. Nevertheless, the linear-momentum flux at higher PN orders can be employed to build more reliable resummed expressions aimed at capturing the nonperturbative effects until merger. Furthermore, we provide expressions valid for generic orbits, and accurate at 2PN order, for the energy and angular momentum carried by gravitational waves emitted from spinning binary black holes. Specializing to quasicircular orbits we compute the spin-spin terms at 2PN order in the expression for the evolution of the orbital frequency and found agreement with Mikoczi, Vasuth, and Gergely. We also verified that in the limit of extreme mass ratio our expressions for the energy and angular momentum fluxes match the ones of Tagoshi, Shibata, Tanaka, and Sasaki obtained in the context of black hole perturbation theory.
Kar, J. K.; Panda, Saswati; Rout, G. C.
2017-05-01
We propose here a tight binding model study of the interplay between charge and spin orderings in the CMR manganites taking anisotropic effect due to electron hoppings and spin exchanges. The Hamiltonian consists of the kinetic energies of eg and t2g electrons of manganese ion. It further includes double exchange and Heisenberg interactions. The charge density wave interaction (CDW) describes an extra mechanism for the insulating character of the system. The CDW gap and spin parameters are calculated using Zubarev's Green's function technique and computed self-consistently. The results are reported in this communication.
International Nuclear Information System (INIS)
Vaz, C A F; Hayward, T J; Llandro, J; Schackert, F; Morecroft, D; Bland, J A C; Klaeui, M; Laufenberg, M; Backes, D; Ruediger, U; Castano, F J; Ross, C A; Heyderman, L J; Nolting, F; Locatelli, A; Faini, G; Cherifi, S; Wernsdorfer, W
2007-01-01
Ferromagnetic metal rings of nanometre range widths and thicknesses exhibit fundamentally new spin states, switching behaviour and spin dynamics, which can be precisely controlled via geometry, material composition and applied field. Following the discovery of the 'onion state', which mediates the switching to and between vortex states, a range of fascinating phenomena has been found in these structures. In this overview of our work on ring elements, we first show how the geometric parameters of ring elements determine the exact equilibrium spin configuration of the domain walls of rings in the onion state, and we show how such behaviour can be understood as the result of the competition between the exchange and magnetostatic energy terms. Electron transport provides an extremely sensitive probe of the presence, spatial location and motion of domain walls, which determine the magnetic state in individual rings, while magneto-optical measurements with high spatial resolution can be used to probe the switching behaviour of ring structures with very high sensitivity. We illustrate how the ring geometry has been used for the study of a wide variety of magnetic phenomena, including the displacement of domain walls by electric currents, magnetoresistance, the strength of the pinning potential introduced by nanometre size constrictions, the effect of thermal excitations on the equilibrium state and the stochastic nature of switching events
International Nuclear Information System (INIS)
Zheng, X.G.; Hagihala, Masato; Toriyi, Takato
2007-01-01
Recently, we observed the co-existence of a long-range magnetic order and spin fluctuation in a clean compound of clinoatacamite, Cu 2 (OH) 3 Cl (PRL95 (2005) 057201). The present work reports magnetic studies on other compounds of this transition metal series M 2 (OH) 3 Cl, where M represents three-dimensional (3D)-electron magnetic ions of Co 2+ , Fe 2+ , etc., respectively. The present study shows that this co-existence is a common feature of the M 2 Cl(OH) 3 series, no matter whether it is anti-ferromagnetic, as in the case of Fe 2 (OH) 3 Cl (T N =15 K), or ferromagnetic, as in the case of Co 2 (OH) 3 Cl (T C =10.5 K). These compounds show a 3D network of corner-sharing tetrahedrons for the magnetic ions. The tetrahedron is slightly tilted with roughly 10% longer distance between the M-M bonded by Cl than those bonded by O and this distortion is suspected to be responsible for the partial order. This research suggests that the transition metal hydroxyhalide M 2 Cl(OH) 3 series are new geometric frustration system on tetrahedral lattice for d-electron spins
Spin-phonon induced magnetic order in magnetized Spin Ice systems
International Nuclear Information System (INIS)
Albarracín, F A Gómez; Cabra, D C; Rosales, H D; Rossini, G L
2014-01-01
We study the behavior of spin ice pyrochlore systems above the well known [111] 1/3 plateau, under slight deviations of the direction of the external field. We model the relevant degrees of freedom by Ising spins on the kagome lattice. We propose the inclusion of lattice deformations, which imply phononic degrees of freedom in the adiabatic limit. We use analytical calculations to estimate how these new degrees of freedom affect the short and long range spin interactions in the presence of an external magnetic field. We then obtain the magnetization curves, explore the phases and the ground states of this system in the presence of magnetic field by Monte Carlo simulations. We discuss comparisons with experimental results
International Nuclear Information System (INIS)
Schreier, Michael; Lotze, Johannes; Gross, Rudolf; Goennenwein, Sebastian T B; Bauer, Gerrit E W; Uchida, Ken-ichi; Daimon, Shunsuke; Kikkawa, Takashi; Saitoh, Eiji; Vasyuchka, Vitaliy I; Lauer, Viktor; Chumak, Andrii V; Serga, Alexander A; Hillebrands, Burkard; Flipse, Joost; Van Wees, Bart J
2015-01-01
We carried out a concerted effort to determine the absolute sign of the inverse spin Hall effect voltage generated by spin currents injected into a normal metal. We focus on yttrium iron garnet (YIG)∣platinum bilayers at room temperature, generating spin currents by microwaves and temperature gradients. We find consistent results for different samples and measurement setups that agree with theory. We suggest a right-hand-rule to define a positive spin Hall angle corresponding to the voltage expected for the simple case of scattering of free electrons from repulsive Coulomb charges. (paper)
Jiang, Yuan; Qin, Lei; Li, Guanghua; Abbas, Ghulam; Cao, Yaqun; Wu, Gang; Han, Tian; Zheng, Yan-Zhen; Qiu, Shilun
2015-01-01
© The Royal Society of Chemistry 2015. The controlled organization of high-spin complexes into 1D coordination polymers is a challenge in molecular magnetism. In this work, we report a ferromagnetic Mn trimer Mn3(HL)2(CH3OH)6(Br)4·Br·(CH3OH)21 (H2L
Higher-order spin and charge dynamics in a quantum dot-lead hybrid system.
Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Stano, Peter; Noiri, Akito; Ito, Takumi; Loss, Daniel; Ludwig, Arne; Wieck, Andreas D; Tarucha, Seigo
2017-09-22
Understanding the dynamics of open quantum systems is important and challenging in basic physics and applications for quantum devices and quantum computing. Semiconductor quantum dots offer a good platform to explore the physics of open quantum systems because we can tune parameters including the coupling to the environment or leads. Here, we apply the fast single-shot measurement techniques from spin qubit experiments to explore the spin and charge dynamics due to tunnel coupling to a lead in a quantum dot-lead hybrid system. We experimentally observe both spin and charge time evolution via first- and second-order tunneling processes, and reveal the dynamics of the spin-flip through the intermediate state. These results enable and stimulate the exploration of spin dynamics in dot-lead hybrid systems, and may offer useful resources for spin manipulation and simulation of open quantum systems.
Energy Technology Data Exchange (ETDEWEB)
Sarwar, T., E-mail: sarwartuba@gmail.com [EMMG, Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); Qamar, A., E-mail: afzaal.qamar@griffithuni.edu.au [Queensland Micro-Nanotechnology Centre, Griffith University, Nathan, QLD 4111 (Australia); Nadeem, M. [EMMG, Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan)
2017-07-15
Highlights: • Electronic & magnetic behavior of Nd{sub 0.5}Ca{sub 0.5}MnO{sub 3} is explored using impedance spectroscopy. • Under ac field, possible signature of suppression of robust CO/OO antiferromagnetism is studied. • We propose the existence of spin glass state at low temperature. • A novel tactic is used to estimate the existence of weak ferromagnetism at high temperature. - Abstract: Dynamics of spin ordering in the manganite Nd{sub 0.5}Ca{sub 0.5}MnO{sub 3} have been investigated in this paper. It was observed that the complex mixed magnetic ordering in pellets is comprised of antiferromagnetic ordering at 160 K (T{sub N}) and complete charge ordering at 250 K (T{sub CO}). Under ac field, appearance of unstable ferromagnetic correlations is observed above T{sub CO}, which is badly frustrated due to strong spin disorder induced by Jahn Teller distortions. Impedance measurements reveal the spin glass like scenario, suppressing the strong antiferromagnetic and charge ordering states below T{sub N}.
Anh, Le Duc; Hai, Pham Nam; Tanaka, Masaaki
2018-03-01
We report a strong bias dependence of the magnetoconductance (MC) of a spin-Esaki diode composed of n+-type ferromagnetic semiconductor (FMS) (In,Fe)As and p+-type Be doped InAs grown on a p+-InAs (001) substrate by molecular beam epitaxy. When the bias voltage V is increased above 450 mV in the forward bias, we found that the MC, measured at 3.5 K under a magnetic field H of 1 T in the in-plane [110] direction, changes its sign from positive to negative and its magnitude rises rapidly from 0.5% at V fluid model, we explain both the magnitude and the anisotropy of the MC based on the evolution of the spin-Esaki diode's band profile with V. This analysis provides insights into the density of states and spin-polarization of the conduction band and the Fe-related impurity band in n-type FMS (In,Fe)As.
Murtaza, Adil; Yang, Sen; Chang, Tieyan; Ghani, Awais; Khan, Muhammad Tahir; Zhang, Rui; Zhou, Chao; Song, Xiaoping; Suchomel, Matthew; Ren, Yang
2018-03-01
The spin reorientation (SR) and magnetoelastic properties of pseudobinary ferromagnetic T b1 -xN dxC o2 (0 ≤x ≤1.0 ) systems involving a morphotropic phase boundary (MPB) were studied by high-resolution synchrotron x-ray diffraction (XRD), magnetization, and magnetostriction measurements. The easy magnetization direction of the Laves phase lies along the 〈111 〉 axis with x 0.65 below Curie temperature (TC). The temperature-dependent magnetization curves showed SR; this can be explained by a two-sublattice model. Based on the synchrotron (XRD) and magnetization measurements, the SR phase diagram for a MPB composition of T b0.35N d0.65C o2 was obtained. Contrary to previously reported ferromagnetic systems involving MPB, the MPB composition of T b0.35N d0.65C o2 exhibits a low saturation magnetization (MS), indicating a compensation of the Tb and Nd magnetic moments at MPB. The anisotropic magnetostriction (λS) first decreased until x =0.8 and then continuously increased in the negative direction with further increase of Nd concentration. The decrease in magnetostriction can be attributed to the decrease of spontaneous magnetostriction λ111 and increase of λ100 with opposite sign to λ111. This paper indicates an anomalous type of MPB in the ferromagnetic T b1 -xN dxC o2 system and provides an active way to design novel functional materials with exotic properties.
Phase transitions in spin systems with modulated order
International Nuclear Information System (INIS)
Coutinho Filho, M.D.
1984-01-01
Spin systems which may display modulated structures are treated. A layered Ising model with competing interactions between nearest and next-nearest layers in the presence of a magnetic field is studied. In the context of a mean-field approximation, the high-temperature region of the phase diagram is studied analytically. The Λ surface, separating the paramagnetic and the modulated phases, is bounded by two lines of tricritical points which join smoothly at the Lifshitz point and terminate at multicritical points, beyond which lines of critical and double critical end points are expected to appear. The low-temperature region is studied numerically. T-H phase diagrams, which exhibit a variety of modulated phases, for various values of the ratio of the strength of the competing interactions are constructed. A theoretical interpretation for the occurrence of a Lifshitz point in the field-temperature phase diagram of MnP is presented. These results, which are based on a X-Y localized spin Hamiltonian, are in qualitative agreement with recently reported experiments. In particular, asymptotic expressions are obtained for the phase boundaries, which meet tangentially at the Lifshitz point, and for some other thermodynamic quantities of interest, such as the longitudinal and transverse susceptibilities. (Author) [pt
Ferromagnetic ordering in ThSi{sub 2} type CeAu{sub 0.28}Ge{sub 1.72}
Energy Technology Data Exchange (ETDEWEB)
Sebastian, C. Peter, E-mail: s-peter@northwestern.ed [Department of Chemistry, Northwestern University, 2145 N. Sheridan Road, Evanston, IL 60208-3113 (United States); Kanatzidis, Mercouri G., E-mail: m-kanatzidis@northwestern.ed [Department of Chemistry, Northwestern University, 2145 N. Sheridan Road, Evanston, IL 60208-3113 (United States)
2010-04-15
The compound CeAu{sub 0.28}Ge{sub 1.72} crystallizes in the ThSi{sub 2} structure type in the tetragonal space group I4{sub 1}/amd with lattice parameters a=b=4.2415(6) A c=14.640(3) A. CeAu{sub 0.28}Ge{sub 1.72} is a polar intermetallic compound having a three-dimensional Ge/Au polyanion sub-network filled with Ce atoms. The magnetic susceptibility data show Curie-Weiss law behavior above 50 K. The compound orders ferromagnetically at {approx}8 K with estimated magnetic moment of 2.48 mu{sub B}/Ce. The ferromagnetic ordering is confirmed by the heat capacity data which show a rise at {approx}8 K. The electronic specific heat coefficient (gamma) value obtained from the paramagnetic temperature range 15-25 K is {approx}124(5) mJ/ mol K{sup 2}. The entropy change due to the ferromagnetic transition is {approx}4.2 J/mol K which is appreciably reduced compared to the value of R ln(2) expected for a crystal-field-split doublet ground state and/or Kondo exchange interactions. - Graphical abstract: CeAu{sub 0.28}Ge{sub 1.72} crystallizes in the ThSi{sub 2} structure type in the tetragonal space group I4{sub 1}/amd and orders ferromagnetically at {approx}8 K.
Energy Technology Data Exchange (ETDEWEB)
Samantaray, B., E-mail: iitg.biswanath@gmail.com; Ranganathan, R.; Mandal, P. [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700 064 (India); Singh, Akhilesh K.; Perumal, A. [Department of Physics, Indian Institute of Technology Guwahati, Guwahati - 781039 (India)
2015-06-15
Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key factors for the free layer magnetization switching by spin transfer torque technique in magnetic tunnel junction devices. The magnetization precessional dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure was explored in broad band frequency range by employing micro-strip ferromagnetic resonance technique. The polar angle variation of resonance field and linewidth at different frequencies have been analyzed numerically using Landau-Lifshitz-Gilbert equation by taking into account the total free energy density of the film. The numerically estimated parameters Landé g-factor, PMA constant, and effective magnetization are found to be 2.1, 2 × 10{sup 5} erg/cm{sup 3} and 7145 Oe, respectively. The frequency dependence of Gilbert damping parameter (α) is evaluated by considering both intrinsic and extrinsic effects into the total linewidth analysis. The value of α is found to be 0.006 at 10 GHz and it increases monotonically with decreasing precessional frequency.
Creation of Spin-Triplet Cooper Pairs in the Absence of Magnetic Ordering
Breunig, Daniel; Burset, Pablo; Trauzettel, Björn
2018-01-01
In superconducting spintronics, it is essential to generate spin-triplet Cooper pairs on demand. Up to now, proposals to do so concentrate on hybrid structures in which a superconductor (SC) is combined with a magnetically ordered material (or an external magnetic field). We, instead, identify a novel way to create and isolate spin-triplet Cooper pairs in the absence of any magnetic ordering. This achievement is only possible because we drive a system with strong spin-orbit interaction—the Dirac surface states of a strong topological insulator (TI)-out of equilibrium. In particular, we consider a bipolar TI-SC-TI junction, where the electrochemical potentials in the outer leads differ in their overall sign. As a result, we find that nonlocal singlet pairing across the junction is completely suppressed for any excitation energy. Hence, this junction acts as a perfect spin-triplet filter across the SC, generating equal-spin Cooper pairs via crossed Andreev reflection.
Spin-Resolved Photoemission on Anti-Ferromagnets: Direct Observation of Zhang-Rice Singlets in CuO
Tjeng, L.H.; Sinkovic, B.; Brookes, N.B.; Goedkoop, J.B.; Hesper, R.; Pellegrin, E.; Groot, F.M.F. de; Altieri, S.; Hulbert, S.L.; Shekel, E.; Sawatzky, G.A.
1997-01-01
We demonstrate that it is possible to obtain spin-resolved valence band spectra with a very high degree of spin polarization from antiferromagnetic transition metal materials if the excitation light is circularly polarized and has an energy close to the cation 2p3/2 (L3) white line. We are able to
Jabar, A.; Tahiri, N.; Bahmad, L.; Benyoussef, A.
2016-11-01
A bi-layer system consisting of layers of spins (7/2, 3) in a ferromagnetic dendrimer structure, separated by a non-magnetic spacer, is studied by Monte Carlo simulations. The effect of the RKKY interactions is investigated and discussed for such system. It is shown that the magnetic properties in the two magnetic layers depend strongly on the thickness of the magnetic and non-magnetic layers. The total magnetizations and susceptibilities are studied as a function of the reduced temperature. The effect of the reduced exchange interactions as well as the reduced crystal field is outlined. On other hand, the critical temperature is discussed as a function of the magnetic layer values. To complete this study we presented and discussed the magnetic hysteresis cycles.
Covariant quantization of infinite spin particle models, and higher order gauge theories
International Nuclear Information System (INIS)
Edgren, Ludde; Marnelius, Robert
2006-01-01
Further properties of a recently proposed higher order infinite spin particle model are derived. Infinitely many classically equivalent but different Hamiltonian formulations are shown to exist. This leads to a condition of uniqueness in the quantization process. A consistent covariant quantization is shown to exist. Also a recently proposed supersymmetric version for half-odd integer spins is quantized. A general algorithm to derive gauge invariances of higher order Lagrangians is given and applied to the infinite spin particle model, and to a new higher order model for a spinning particle which is proposed here, as well as to a previously given higher order rigid particle model. The latter two models are also covariantly quantized
van't Erve, Olaf
2014-03-01
New paradigms for spin-based devices, such as spin-FETs and reconfigurable logic, have been proposed and modeled. These devices rely on electron spin being injected, transported, manipulated and detected in a semiconductor channel. This work is the first demonstration on how a single layer of graphene can be used as a low resistance tunnel barrier solution for electrical spin injection into Silicon at room temperature. We will show that a FM metal / monolayer graphene contact serves as a spin-polarized tunnel barrier which successfully circumvents the classic metal / semiconductor conductivity mismatch issue for electrical spin injection. We demonstrate electrical injection and detection of spin accumulation in Si above room temperature, and show that the corresponding spin lifetimes correlate with the Si carrier concentration, confirming that the spin accumulation measured occurs in the Si and not in interface trap states. An ideal tunnel barrier should exhibit several key material characteristics: a uniform and planar habit with well-controlled thickness, minimal defect / trapped charge density, a low resistance-area product for minimal power consumption, and compatibility with both the FM metal and semiconductor, insuring minimal diffusion to/from the surrounding materials at temperatures required for device processing. Graphene, offers all of the above, while preserving spin injection properties, making it a compelling solution to the conductivity mismatch for spin injection into Si. Although Graphene is very conductive in plane, it exhibits poor conductivity perpendicular to the plane. Its sp2 bonding results in a highly uniform, defect free layer, which is chemically inert, thermally robust, and essentially impervious to diffusion. The use of a single monolayer of graphene at the Si interface provides a much lower RA product than any film of an oxide thick enough to prevent pinholes (1 nm). Our results identify a new route to low resistance-area product spin
Diffusionless phase transition with two order parameters in spin-crossover solids
Energy Technology Data Exchange (ETDEWEB)
Gudyma, Iurii, E-mail: yugudyma@gmail.com; Ivashko, Victor [Department of General Physics, Chernivtsi National University, 58012 Chernivtsi (Ukraine); Linares, Jorge [Groupe d' Etude de la Matière Condensée (GEMAC), UMR 8635, CNRS, Université de Versailles Saint Quentin, 45 avenue des Etats-Unis, 78035 Versailles (France)
2014-11-07
The quantitative analysis of the interface boundary motion between high-spin and low-spin phases is presented. The nonlinear effect of the switching front rate on the temperature is shown. A compressible model of spin-crossover solid is studied in the framework of the Ising-like model with two-order parameters under statistical approach, where the effect of elastic strain on interaction integral is considered. These considerations led to examination of the relation between the order parameters during temperature changes. Starting from the phenomenological Hamiltonian, entropy has been derived using the mean field approach. Finally, the phase diagram, which characterizes the system, is numerically analyzed.
International Nuclear Information System (INIS)
Akazaki, T.; Munekata, H.; Yokoyama, T.; Tanaka, Y.; Takayanagi, H.
2011-01-01
Spin-polarized carrier transport across Nb/p-(In,Mn)As junctions has been studied. Suppressions of conductance in the superconductor sub-gap region and conductance peaks at the bias voltage around the edge of the sub-gap are observed. These features are well reproduced by a newly modified BTK model including both spin polarization and the inverse proximity effect. The value of spin polarization in p-(In,Mn)As extracted by the calculation is P = 0.725 at 0.5 K with Z = 0.25
Ferroelectricity with Ferromagnetic Moment in Orthoferrites
Tokunaga, Yusuke
2010-03-01
Exotic multiferroics with gigantic magnetoelectric (ME) coupling have recently been attracting broad interests from the viewpoints of both fundamental physics and possible technological application to next-generation spintronic devices. To attain a strong ME coupling, it would be preferable that the ferroelectric order is induced by the magnetic order. Nevertheless, the magnetically induced ferroelectric state with the spontaneous ferromagnetic moment is still quite rare apart from a few conical-spin multiferroics. To further explore multiferroic materials with both the strong ME coupling and spontaneous magnetization, we focused on materials with magnetic structures other than conical structure. In this talk we present that the most orthodox perovskite ferrite systems DyFeO3 and GdFeO3 have ``ferromagnetic-ferroelectric,'' i.e., genuinely multiferroic states in which weak ferromagnetic moment is induced by Dzyaloshinskii-Moriya interaction working on Fe spins and electric polarization originates from the striction due to symmetric exchange interaction between Fe and Dy (Gd) spins [1] [2]. Both materials showed large electric polarization (>0.1 μC/cm^2) and strong ME coupling. In addition, we succeeded in mutual control of magnetization and polarization with electric- and magnetic-fields in GdFeO3, and attributed the controllability to novel, composite domain wall structure. [4pt] [1] Y. Tokunaga et al., Phys. Rev. Lett. 101, 097205 (2008). [0pt] [2] Y. Tokunaga et al., Nature Mater. 8, 558 (2009).
Jahn-Teller effect and ferromagnetic ordering in La0.875Sr0.125MnO3: A reentrant behaviour
International Nuclear Information System (INIS)
Pinsard, L.; Revcolevschi, A.; Anane, A.; Dupas, C.
1997-01-01
The compound La 0.875 Sr 0.125 MnO 3 undergoes a series of structural phase transitions in which different physical effects are involved. The compound is rhombohedral above T RO ∝400 K. On cooling, a phase transition to an orthorhombic Pbnm O-phase takes place at T RO , no significant orbital ordering is observed. At T OO' ∝270 K a structural phase transition to another orthorhombic (O') form takes place, and an orbital ordering appears due to a cooperative JT effect. For this temperature range the compound is a paramagnetic semiconductor. Upon cooling it becomes ferromagnetic at T C ∝180 K and the orbital ordering is partially suppressed. Below a temperature T O'O '' ∝150 K at which the average Mn magnetic moment is about 2μ B the orbital ordering is completely suppressed by a first order structural transition to another orthorhombic phase (O '' ) similar to the O-phase. Between T C and T O'O '' the compound is metallic and becomes a ferromagnetic insulator below T O'O '' where a canting of the ferromagnetic order appears. (orig.)
Directory of Open Access Journals (Sweden)
Chong Wang
2013-12-01
Full Text Available We report on a spin-polarized inelastic neutron-scattering study of spin waves in the antiferromagnetically ordered state of BaFe_{2}As_{2}. Three distinct excitation components are identified, with spins fluctuating along the c axis, perpendicular to the ordering direction in the ab plane and parallel to the ordering direction. While the first two “transverse” components can be described by a linear spin-wave theory with magnetic anisotropy and interlayer coupling, the third “longitudinal” component is generically incompatible with the local-moment picture. It points toward a contribution of itinerant electrons to the magnetism that is already in the parent compound of this family of Fe-based superconductors.
Energy Technology Data Exchange (ETDEWEB)
Horley, Paul P., E-mail: paul.horley@cimav.edu.mx [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Kushnir, Mykola Ya. [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine); Morales-Meza, Mishel [Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua (Mexico); Sukhov, Alexander [Institut für Physik, Martin-Luther Universität Halle-Wittenberg, 06120 Halle (Saale) (Germany); Rusyn, Volodymyr [Yuri Fedkovych Chernivtsi National University, 2 Kotsyubynsky str., 58012 Chernivtsi (Ukraine)
2016-04-01
We report on complex magnetization dynamics in a forced spin valve oscillator subjected to a varying magnetic field and a constant spin-polarized current. The transition from periodic to chaotic magnetic motion was illustrated with bifurcation diagrams and Hausdorff dimension – the methods developed for dissipative self-organizing systems. It was shown that bifurcation cascades can be obtained either by tuning the injected spin-polarized current or by changing the magnitude of applied magnetic field. The order–chaos transition in magnetization dynamics can be also directly observed from the hysteresis curves. The resulting complex oscillations are useful for development of spin-valve devices operating in harmonic and chaotic modes.
High-order moments of spin-orbit energy in a multielectron configuration
Na, Xieyu; Poirier, M.
2016-07-01
In order to analyze the energy-level distribution in complex ions such as those found in warm dense plasmas, this paper provides values for high-order moments of the spin-orbit energy in a multielectron configuration. Using second-quantization results and standard angular algebra or fully analytical expressions, explicit values are given for moments up to 10th order for the spin-orbit energy. Two analytical methods are proposed, using the uncoupled or coupled orbital and spin angular momenta. The case of multiple open subshells is considered with the help of cumulants. The proposed expressions for spin-orbit energy moments are compared to numerical computations from Cowan's code and agree with them. The convergence of the Gram-Charlier expansion involving these spin-orbit moments is analyzed. While a spectrum with infinitely thin components cannot be adequately represented by such an expansion, a suitable convolution procedure ensures the convergence of the Gram-Charlier series provided high-order terms are accounted for. A corrected analytical formula for the third-order moment involving both spin-orbit and electron-electron interactions turns out to be in fair agreement with Cowan's numerical computations.
Saeed, Yasir
2010-10-01
We report a first-principles study of structural, electronic and magnetic properties of crystalline alloys Zn1-xTMxS (TM = Fe, Co and Ni) at x = 0.25. Structural properties are computed from the total ground state energy convergence and it is found that the cohesive energies of Zn 1-xTMxS are greater than that of zincblende ZnS. We also study the spin-polarized electronic band structures, total and partial density of states and the effect of TM 3d states. Our results exhibit that Zn 0.75Fe0.25S, Zn0.75Co0.25S and Zn0.75Ni0.25S are half-metallic ferromagnetic with a magnetic moment of 4μB, 3μB and 2μB, respectively. Furthermore, we calculate the TM 3d spin-exchange-splitting energies Δx (d), Δx (x-d), exchange constants N0α and N0β, crystal field splitting (ΔEcrystEt2g-Eeg), and find that p-d hybridization reduces the local magnetic moment of TM from its free space charge value. Moreover, robustness of Zn1-xTMxS with respect to the variation of lattice constants is also discussed. © 2010 Elsevier B.V. All rights reserved.
Monir, M. El Amine.; Baltache, H.; Murtaza, G.; Khenata, R.; Ahmed, Waleed K.; Bouhemadou, A.; Omran, S. Bin; Seddik, T.
2015-01-01
Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn1-xVxSe (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the "d" electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N0α (conduction band) and N0β (valence band) due to Se(4p)-V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 μB and the minor atomic magnetic moment on Zn and Se are generated.
Spin dynamics and magnetic ordering in mixed valence systems
International Nuclear Information System (INIS)
Shapiro, S.M.; Moller, H.B.; Axe, J.D.; Birgeneau, R.J.; Bucher, E.
1977-01-01
Neutron scattering measurements are reported on the mixed valence compounds Ce/sub 1-x/Th/sub x/ and TmSe. The Chi''(Q,ω) as derived from the inelastic spectra of Ce 0 . 74 Th 0 . 26 shows a peak in the γ phase near 20.0 meV and shifts abruptly to greater than 70.0 meV at the transition to the α phase. The temperature independence of the susceptibility within the γ phase cannot be simply reconciled with the temperature dependence of the valence within the γ phase. TmSe is shown to order in a type I antiferromagnetic structure below T/sub N/ approx. 3.2 K. The magnetic phase diagram is understood as a successive domain reorientation and a metamagnetic phase transition for T 3+ orders in a type II structure but never achieves long range order
Energy Technology Data Exchange (ETDEWEB)
Keskin, Mustafa [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)], E-mail: keskin@erciyes.edu.tr; Canko, Osman [Department of Physics, Erciyes University, 38039 Kayseri (Turkey)
2008-01-15
We study the thermal variations of the ferromagnetic spin-3/2 Blume-Emery-Griffiths (BEG) model with repulsive biquadratic coupling by using the lowest approximation of the cluster variation method (LACVM) in the absence and presence of the external magnetic field. We obtain metastable and unstable branches of the order parameters besides the stable branches and phase transitions of these branches are investigated extensively. The classification of the stable, metastable and unstable states is made by comparing the free energy values of these states. We also study the dynamics of the model by using the path probability method (PPM) with the point distribution in order to make sure that we find and define the metastable and unstable branches of the order parameters completely and correctly. We present the metastable phase diagrams in addition to the equilibrium phase diagrams in the (kT/J, K/J) and (kT/J, D/J) planes. It is found that the metastable phase diagrams always exist at the low temperatures, which are consistent with experimental and theoretical works.
International Nuclear Information System (INIS)
Keskin, Mustafa; Canko, Osman
2008-01-01
We study the thermal variations of the ferromagnetic spin-3/2 Blume-Emery-Griffiths (BEG) model with repulsive biquadratic coupling by using the lowest approximation of the cluster variation method (LACVM) in the absence and presence of the external magnetic field. We obtain metastable and unstable branches of the order parameters besides the stable branches and phase transitions of these branches are investigated extensively. The classification of the stable, metastable and unstable states is made by comparing the free energy values of these states. We also study the dynamics of the model by using the path probability method (PPM) with the point distribution in order to make sure that we find and define the metastable and unstable branches of the order parameters completely and correctly. We present the metastable phase diagrams in addition to the equilibrium phase diagrams in the (kT/J, K/J) and (kT/J, D/J) planes. It is found that the metastable phase diagrams always exist at the low temperatures, which are consistent with experimental and theoretical works
International Nuclear Information System (INIS)
Baishya, R.; Jamil, U.; Sarma, J. K.
2009-01-01
In this paper the spin-dependent singlet and nonsinglet structure functions have been obtained by solving Dokshitzer, Gribov, Lipatov, Altarelli, Parisi evolution equations in leading order and next to leading order in the small x limit. Here we have used Taylor series expansion and then the method of characteristics to solve the evolution equations. We have also calculated t and x evolutions of deuteron structure functions, and the results are compared with the SLAC E-143 Collaboration data.
Fracton topological order from nearest-neighbor two-spin interactions and dualities
Slagle, Kevin; Kim, Yong Baek
2017-10-01
Fracton topological order describes a remarkable phase of matter, which can be characterized by fracton excitations with constrained dynamics and a ground-state degeneracy that increases exponentially with the length of the system on a three-dimensional torus. However, previous models exhibiting this order require many-spin interactions, which may be very difficult to realize in a real material or cold atom system. In this work, we present a more physically realistic model which has the so-called X-cube fracton topological order [Vijay, Haah, and Fu, Phys. Rev. B 94, 235157 (2016), 10.1103/PhysRevB.94.235157] but only requires nearest-neighbor two-spin interactions. The model lives on a three-dimensional honeycomb-based lattice with one to two spin-1/2 degrees of freedom on each site and a unit cell of six sites. The model is constructed from two orthogonal stacks of Z2 topologically ordered Kitaev honeycomb layers [Kitaev, Ann. Phys. 321, 2 (2006), 10.1016/j.aop.2005.10.005], which are coupled together by a two-spin interaction. It is also shown that a four-spin interaction can be included to instead stabilize 3+1D Z2 topological order. We also find dual descriptions of four quantum phase transitions in our model, all of which appear to be discontinuous first-order transitions.
Spin injection and spin accumulation in all-metal mesoscopic spin valves
Jedema, FJ; Nijboer, MS; Filip, AT; van Wees, BJ
2003-01-01
We study the electrical injection and detection of spin accumulation in lateral ferromagnetic-metal-nonmagnetic-metal-ferromagnetic-metal (F/N/F) spin valve devices with transparent interfaces. Different ferromagnetic metals, Permalloy (Py), cobalt (Co), and nickel (Ni), are used as electrical spin
International Nuclear Information System (INIS)
Moura, A.R.; Pereira, A.R.; Moura-Melo, W.A.; Pires, A.S.T.
2008-01-01
We develop an effective theory to study the skyrmion dynamics in the presence of a hole (removed spins from the lattice) in Neel ordered two-dimensional antiferromagnets with arbitrary spin value S. The general equation of motion for the 'mass center' of this structure is obtained. The frequency of small amplitude oscillations of pinned skyrmions around the defect center is calculated. It is proportional to the hole size and inversely proportional to the square of the skyrmion size
A next-to-leading order QCD analysis of the spin structure function $g_1$
AUTHOR|(CDS)2067425; Arik, E; Badelek, B; Bardin, G; Baum, G; Berglund, P; Betev, L; Birsa, R; De Botton, N R; Bradamante, Franco; Bravar, A; Bressan, A; Bültmann, S; Burtin, E; Crabb, D; Cranshaw, J; Çuhadar-Dönszelmann, T; Dalla Torre, S; Van Dantzig, R; Derro, B R; Deshpande, A A; Dhawan, S K; Dulya, C M; Eichblatt, S; Fasching, D; Feinstein, F; Fernández, C; Forthmann, S; Frois, Bernard; Gallas, A; Garzón, J A; Gilly, H; Giorgi, M A; von Goeler, E; Görtz, S; Gracia, G; De Groot, N; Grosse-Perdekamp, M; Haft, K; Von Harrach, D; Hasegawa, T; Hautle, P; Hayashi, N; Heusch, C A; Horikawa, N; Hughes, V W; Igo, G; Ishimoto, S; Iwata, T; Kabuss, E M; Kageya, T; Karev, A G; Kessler, H J; Ketel, T; Kiryluk, J; Kiselev, Yu F; Krämer, Dietrich; Krivokhizhin, V G; Kröger, W; Kukhtin, V V; Kurek, K; Kyynäräinen, J; Lamanna, M; Landgraf, U; Le Goff, J M; Lehár, F; de Lesquen, A; Lichtenstadt, J; Litmaath, M; Magnon, A; Mallot, G K; Marie, F; Martin, A; Martino, J; Matsuda, T; Mayes, B W; McCarthy, J S; Medved, K S; Meyer, W T; Van Middelkoop, G; Miller, D; Miyachi, Y; Mori, K; Moromisato, J H; Nassalski, J P; Naumann, Lutz; Niinikoski, T O; Oberski, J; Ogawa, A; Ozben, C; Pereira, H; Perrot-Kunne, F; Peshekhonov, V D; Piegia, R; Pinsky, L; Platchkov, S K; Pló, M; Pose, D; Postma, H; Pretz, J; Puntaferro, R; Rädel, G; Rijllart, A; Reicherz, G; Roberts, J; Rodríguez, M; Rondio, Ewa; Sabo, I; Saborido, J; Sandacz, A; Savin, I A; Schiavon, R P; Schiller, A; Sichtermann, E P; Simeoni, F; Smirnov, G I; Staude, A; Steinmetz, A; Stiegler, U; Stuhrmann, H B; Szleper, M; Tessarotto, F; Thers, D; Tlaczala, W; Tripet, A; Ünel, G; Velasco, M; Vogt, J; Voss, Rüdiger; Whitten, C; Windmolders, R; Willumeit, R; Wislicki, W; Witzmann, A; Ylöstalo, J; Zanetti, A M; Zaremba, K; Zhao, J
1998-01-01
We present a next-to-leading order QCD analysis of the presently available data on the spin structure function $g_1$ including the final data from the Spin Muon Collaboration (SMC). We present resu lts for the first moments of the proton, deuteron and neutron structure functions, and determine singlet and non-singlet parton distributions in two factorization schemes. We also test the Bjor ken sum rule and find agreement with the theoretical prediction at the level of 10\\%.
Wu, Zhenhua; Luo, Kun; Yu, Jiahan; Wu, Xiaobo; Lin, Liangzhong
2018-02-01
Electron tunneling through a single magnetic barrier in a HgTe topological insulator has been theoretically investigated. We find that the perpendicular magnetic field would not lead to spin-flip of the edge states due to the conservation of the angular moment. By tuning the magnetic field and the Fermi energy, the edge channels can be transited from switch-on states to switch-off states and the current from unpolarized states can be filtered to fully spin polarized states. These features offer us an efficient way to control charge/spin transport in a HgTe/CdTe quantum well, and pave a way to construct the nanoelectronic devices utilizing the topological edge states.
Massless second-order tetradic spin-3 and higher-helicity bosons
Energy Technology Data Exchange (ETDEWEB)
Aragone, C; La Roche, H [Universidad Simon Bolivar, Caracas (Venezuela) Dept. de Fisica
1982-11-21
The unique, uniform, second-order formulation of massless bosons of helicity >=3 is presented here in terms of tetradic fields. The actions we find are shown to coincide both with the first-order (tetradic) formulation of Vasiliev and with the symmetric second-order description of Fronsdal. We carefully analyse the gravitational coupling of the spin-3 field and find that tetradic spin-3 matter presents the same translational consistency problem as symmetric matter does. Furthermore, in the curved tetradic case the generalized Lorentz invariance can be restored by the addition of nominimal terms.
Equivalence of two formalisms for calculating higher order synchrotron sideband spin resonances
International Nuclear Information System (INIS)
Mane, S.R.
1988-01-01
Synchrotron sideband resonances of a first order spin resonance are generally regarded as the most important higher order spin resonances in a high-energy storage ring. Yokoya's formula for these resonances is rederived, including some extra terms, which he neglected, but which turn out to be of comparable magnitude to the terms retained. Including these terms, Yokoya's formalism and the SMILE algorithm are shown to be equivalent to leading order in the resonance strengths. The theoretical calculations are shown to agree with certain measurements from SPEAR
Spin Dynamics and Magnetic Ordering in Mixed Valence Systems
DEFF Research Database (Denmark)
Shapiro, S. M.; Bjerrum Møller, Hans; Axe, J. D.
1978-01-01
. 0 meV at the transition to the alpha phase. The temperature independence of the susceptibility within the gamma phase cannot be simply reconciled with the temperature dependence of the valence within the gamma phase. TmSe is shown to order in a type I antiferromagnetic structure below T//N similar 3....... 2 K. The magnetic phase diagram is understood as a successive domain reorientation and a metamagnetic phase transition for T less than 3 K with increasing field. The mixed valence nature manifests itself in a reduced moment and a markedly altered crystal field. Another sample of TmSe with a lattice...
Energy Technology Data Exchange (ETDEWEB)
Levi, Michele [Institut d' Astrophysique de Paris, Université Pierre et Marie Curie, CNRS-UMR 7095, 98 bis Boulevard Arago, 75014 Paris (France); Steinhoff, Jan, E-mail: michele.levi@upmc.fr, E-mail: jan.steinhoff@ist.utl.pt [Centro Multidisciplinar de Astrofisica, Instituto Superior Tecnico, Universidade de Lisboa, Avenida Rovisco Pais 1, 1049-001 Lisboa (Portugal)
2014-12-01
The next-to-next-to-leading order spin1-spin2 potential for an inspiralling binary, that is essential for accuracy to fourth post-Newtonian order, if both components in the binary are spinning rapidly, has been recently derived independently via the ADM Hamiltonian and the Effective Field Theory approaches, using different gauges and variables. Here we show the complete physical equivalence of the two results, thereby we first prove the equivalence of the ADM Hamiltonian and the Effective Field Theory approaches at next-to-next-to-leading order with the inclusion of spins. The main difficulty in the spinning sectors, which also prescribes the manner in which the comparison of the two results is tackled here, is the existence of redundant unphysical spin degrees of freedom, associated with the spin gauge choice of a point within the extended spinning object for its representative worldline. After gauge fixing and eliminating the unphysical degrees of freedom of the spin and its conjugate at the level of the action, we arrive at curved spacetime generalizations of the Newton-Wigner variables in closed form, which can also be used to obtain further Hamiltonians, based on an Effective Field Theory formulation and computation. Finally, we make use of our validated result to provide gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to fourth post-Newtonian order, including all known sectors up to date.
Excitonic magnet in external field: Complex order parameter and spin currents
Geffroy, D.; Hariki, A.; Kuneš, J.
2018-04-01
We investigate spin-triplet exciton condensation in the two-orbital Hubbard model close to half-filling by means of dynamical mean-field theory. Employing an impurity solver that handles complex off-diagonal hybridization functions, we study the behavior of excitonic condensate in stoichiometric and doped systems subject to external magnetic field. We find a general tendency of the triplet order parameter to lie perpendicular with the applied field and identify exceptions from this rule. For solutions exhibiting k -odd spin textures, we discuss the Bloch theorem, which, in the absence of spin-orbit coupling, forbids the appearance of spontaneous net spin current. We demonstrate that the Bloch theorem is not obeyed by the dynamical mean-field theory.
DEFF Research Database (Denmark)
Enevoldsen, Thomas; Oddershede, Jens; Sauer, Stephan P. A.
1998-01-01
We present correlated calculations of the indirect nuclear spin-spin coupling constants of HD, HF, H2O, CH4, C2H2, BH, AlH, CO and N2 at the level of the second-order polarization propagator approximation (SOPPA) and the second-order polarization propagator approximation with coupled-cluster sing...
International Nuclear Information System (INIS)
Pedro, I de; Rojo, J M; Pizarro, J L; Fernandez, J RodrIguez; Marcos, J Sanchez; Fernandez-DIaz, M T; Arriortua, M I; Rojo, T
2006-01-01
Compounds of the general formula Co 2-x Ni x (OH)PO 4 (x = 0.1, 0.3) have been synthesized under mild hydrothermal conditions. Neutron powder diffraction, susceptibility and heat capacity measurements were carried out on polycrystalline samples. The cobalt-nickel compounds are ordered as three-dimensional antiferromagnets with ordering temperatures of 70 and 64 K for x = 0.1 and x = 0.3, respectively. The magnetic study shows a spin glass-like state below 11 and 5 K for Co 1.9 Ni 0.1 (OH)PO 4 and Co 1.7 Ni 0.3 (OH)PO 4 , respectively. Specific heat data present peaks at 68 and 61 K for Co 1.9 Ni 0.1 and Co 1.7 Ni 0.3 , respectively. These peaks show broad shoulders between approximately 15 and 40 K. The lack of any distinguishable anomaly below 10 K supports the spin glass nature of the low temperature transitions. Refinement of room temperature neutron diffraction data indicates that the Ni(II) ions are in octahedral co-ordination with the practical absence of these ions in the trigonal bipyramidal sites. The magnetic structures of Co 2-x Ni x (OH)PO 4 consist of ferromagnetic arrangements between the octahedral chains and trigonal bipyramidal dimers within the xz plane with the magnetic moments along the z axis. The ferromagnetic layers are disposed antiparallel to one another along the y direction establishing the three-dimensional antiferromagnetic order (T N ∼70 K for Co 1.9 Ni 0.1 and ∼64 K for Co 1.7 Ni 0.3 ). The different exchange pathways, the anisotropy of the Co(II) ions and the frustration of the magnetic moments in the trigonal bipyramidal geometry could be responsible for the freezing process
Energy Technology Data Exchange (ETDEWEB)
Salazar Mejía, C., E-mail: Catalina.Salazar@cpfs.mpg.de; Mydeen, K.; Naumov, P.; Medvedev, S. A.; Wang, C.; Schwarz, U.; Felser, C.; Nicklas, M., E-mail: nicklas@cpfs.mpg.de [Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Hanfland, M. [ESRF, BP220, 38043 Grenoble (France); Nayak, A. K. [Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Germany)
2016-06-27
We report on the effect of hydrostatic pressure on the magnetic and structural properties of the shape-memory Heusler alloy Ni{sub 50}Mn{sub 35}In{sub 15}. Magnetization and x-ray diffraction experiments were performed at hydrostatic pressures up to 5 GPa using diamond anvil cells. Pressure stabilizes the martensitic phase, shifting the martensitic transition to higher temperatures, and suppresses the ferromagnetic austenitic phase. Above 3 GPa, where the martensitic-transition temperature approaches the Curie temperature in the austenite, the magnetization shows no longer indications of ferromagnetic ordering. We further find an extended temperature region with a mixture of martensite and austenite phases, which directly relates to the magnetic properties.
Hoi, Bui Dinh; Yarmohammadi, Mohsen; Mirabbaszadeh, Kavoos; Habibiyan, Hamidreza
2018-03-01
In this work, based on the Kubo-Greenwood formalism and the k . p Hamiltonian model, the impact of Rashba spin-orbit coupling on electronic band structure and electrical conductivity of spin-up and spin-down subbands in counterparts of graphene, including silicene, stanene, and germanene nanosheets has been studied. When Rashba coupling is considered, the effective mass of Dirac fermions decreases significantly and no significant change is caused by this coupling for the subband gaps. All these nanosheets are found to be in topological insulator quantum phase at low staggered on-site potentials due to the applied perpendicular external electric field. We point out that the electrical conductivity of germanene increases gradually with Rashab coupling, while silicene and stanene have some fluctuations due to their smaller Fermi velocity. Furthermore, some critical temperatures with the same electrical conductivity values for jumping to the higher energy levels are observed at various Rashba coupling strengths. For all structures, a broad peak appears at low temperatures in electrical conductivity curves corresponding to the large entropy of systems when the thermal energy reaches to the difference between the energy states. Finally, we have reported that silicene has the larger has the larger electrical conductivity than two others.
Energy Technology Data Exchange (ETDEWEB)
Monir, M. El Amine.; Baltache, H. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Ahmed, Waleed K. [ERU, Faculty of Engineering, United Arab Emirates University, Al Ain (United Arab Emirates); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Seddik, T. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria)
2015-01-15
Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn{sub 1−x}V{sub x}Se (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the “d” electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) due to Se(4p)–V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 µ{sub B} and the minor atomic magnetic moment on Zn and Se are generated. - Highlights: • Half metallicity origins by doping V in ZnSe. • PBE-GGA+U approximation is employed to treat the “d” electrons properly. • s(p)-d Exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) are due to Se(4p)-V(3d) hybridization.
International Nuclear Information System (INIS)
Choutri, H.; Ghebouli, M.A.; Ghebouli, B.; Bouarissa, N.; Uçgun, E.; Ocak, H.Y.
2014-01-01
The structural, elastic, electronic and magnetic properties of the diluted magnetic semiconductors Mn x Ca 1−x S in the rock-salt phase have been investigated using first-principles calculations with both LDA and LDA + U functional. Features such as lattice constant, bulk modulus, elastic constants, spin-polarized band structure, total and local densities of states have been computed. We predict the values of the exchange constants and the band edge spin splitting of the valence and conduction bands. The hybridization between S-3p and Mn-3d produces small local magnetic moment on the nonmagnetic Ca and S sites. The ferromagnetism is induced due to the exchange splitting of S-3p and Mn-3d hybridized bands. The total magnetic moment per Mn of Mn x Ca 1−x S is 4.4μ B and 4.5μ B for LDA and LDA + U functional and is independent of the Mn concentration. The unfilled Mn-3d levels reduce the local magnetic moment of Mn from its free space charge value of 5μ B –4.4μ B and4.5μ B for LDA and LDA + U functional due to 3p–3d hybridization. - Highlights: • Fundamental properties of magnetic semiconductors Mn x Ca 1−x S. • Rock-salt phase of Mn x Ca 1−x S. • Magnetic properties of the diluted magnetic semiconductors Mn x Ca 1−x S. • The use of LDA + U functionals
Energy Technology Data Exchange (ETDEWEB)
Choutri, H.; Ghebouli, M.A. [LMSE Laboratory, University of Bachir Ibrahimi, 34265 Bordj-Bou-Arréridj (Algeria); Ghebouli, B. [Laboratory of Surface and Interface Studies of Solid Materials, Department of Physics, Faculty of Science, Setif University 1, Setif 19000 (Algeria); Bouarissa, N., E-mail: n_bouarissa@yahoo.fr [Department of Physics, Faculty of Science, University of M' sila, 28000 M' sila (Algeria); Uçgun, E.; Ocak, H.Y. [Department of Physics, Faculty of Arts and Sciences, Dumlupinar University, Kutahya (Turkey)
2014-12-15
The structural, elastic, electronic and magnetic properties of the diluted magnetic semiconductors Mn{sub x}Ca{sub 1−x}S in the rock-salt phase have been investigated using first-principles calculations with both LDA and LDA + U functional. Features such as lattice constant, bulk modulus, elastic constants, spin-polarized band structure, total and local densities of states have been computed. We predict the values of the exchange constants and the band edge spin splitting of the valence and conduction bands. The hybridization between S-3p and Mn-3d produces small local magnetic moment on the nonmagnetic Ca and S sites. The ferromagnetism is induced due to the exchange splitting of S-3p and Mn-3d hybridized bands. The total magnetic moment per Mn of Mn{sub x}Ca{sub 1−x}S is 4.4μ{sub B} and 4.5μ{sub B} for LDA and LDA + U functional and is independent of the Mn concentration. The unfilled Mn-3d levels reduce the local magnetic moment of Mn from its free space charge value of 5μ{sub B}–4.4μ{sub B} and4.5μ{sub B} for LDA and LDA + U functional due to 3p–3d hybridization. - Highlights: • Fundamental properties of magnetic semiconductors Mn{sub x}Ca{sub 1−x}S. • Rock-salt phase of Mn{sub x}Ca{sub 1−x}S. • Magnetic properties of the diluted magnetic semiconductors Mn{sub x}Ca{sub 1−x}S. • The use of LDA + U functionals.
Magnetic ordering and spin excitations in Mn(dca) sub 2 (pyz) [dca=N(CN) sub 2 sup - , pyz=pyrazine
Manson, J L; Argyriou, D N; Bordallo, H N; Lynn, J W; Huang, Q; Feyerherm, R; Loose, A
2002-01-01
We have studied the T- and H-dependent magnetism in Mn(dca) sub 2 (pyz) [dca=N(CN) sub 2 sup - , pyz=pyrazine] using neutron-scattering methods. The crystal structure can be viewed as a molecular analog of ReO sub 3 , where 1D Mn-pyz-Mn chains connect 2D Mn(dca) sub 2 square sheets to form a 3D network. In zero field, the Mn sup 2 sup + moments order antiferromagnetically below 2.53(2) K along the ac diagonal with a magnitude of 4.15(6) mu B at 1.35 K. The field-dependent response of the [111] magnetic reflection is consistent with spin-flop and induced ferromagnetic phase transitions as previously observed in magnetization measurements. Diffuse-scattering studies indicated no evidence for low-dimensional spin correlations. Using quasielastic neutron scattering, a low-energy spin-wave excitation was observed at propor to 0.23 meV, which is propor to 1/6 the momentum transfer observed in Mn(dca) sub 2 owing to a reduced number of magnetic nearest neighbors. (orig.)
International Nuclear Information System (INIS)
Synoradzki, K.; Toliński, T.
2016-01-01
We report on the CeNi_4Mn (ferromagnet FM) - CeCu_4Mn (spin-glass SG) transformation leading to a complex magnetic phase diagram (MPD). It is verified that all the Ce(Cu_1_-_xNi_x)_4Mn alloys are isostructural and the transformation is governed only by the Cu-Ni substitution. MPD is built based on the magnetic dc/ac susceptibility measurements and reveals SG formation as well as the region of the coexistence of the FM and SG state in the middle range of the Ni concentration. The complex MPD is explained by clusters formation and a competition of interactions between various crystallographic sites of the hexagonal CaCu_5-type structure, mainly the 3g-3g and 3g-2c interactions. The predominance of the SG state is confirmed by the analysis of the frequency dependence of the ac magnetic susceptibility components and the relaxation of the remanent magnetization. Additionally, the presence of two multicritical points is observed. - Highlights: • We fully characterized the magnetic properties of Ce(Cu_1_-_xNi_x)_4Mn alloys. • We show the presence of complex magnetic behaviour due to atomic-site disorder. • Magnetic phase diagram revels mixed-phase ground state. • Two multicritical points on magnetic phase diagram occurs.
International Nuclear Information System (INIS)
Pu Qiurong; Chen Yuan
2013-01-01
Green's function method is applied to investigate the two-dimensional spin-1 ferromagnetic Heisenberg model with the exchange and single-ion anisotropies. In the presence of the magnetic field, the effects of the anisotropies and field on the thermodynamic properties are obtained within the random phase approximation combining with Anderson-Callen approximation. The field-induced laws are found for the thermodynamic properties. Field dependences of heights of the susceptibility maximum and specific heat maximum fit well to power laws. The linear increase at high fields is shown for positions of the susceptibility maximum and specific heat maximum. A power law at low fields occurs for the position of the susceptibility maximum. At the positions of the maxima, the magnetization and internal energy display the power-law increase and linear decrease with the field, respectively. The exponents of the power laws are dependent of the anisotropies, as well as the slopes of the linear laws. Our results do not support the 2/3 power law which was obtained by the Landau theory.
Itinerant ferromagnetism in the narrow band limit
Liu, S H
2000-01-01
It is shown that in the narrow band, strong interaction limit the paramagnetic state of an itinerant ferromagnet is described by the disordered local moment state. As a result, the Curie temperature is orders of magnitude lower than what is expected from the large exchange splitting of the spin bands. An approximate analysis has also been carried out for the partially ordered state, and the result explains the temperature evolvement of the magnetic contributions to the resistivity and low-energy optical conductivity of CrO sub 2.
Absence of Long-Range Order in a Triangular Spin System with Dipolar Interactions
Keleş, Ahmet; Zhao, Erhai
2018-05-01
The antiferromagnetic Heisenberg model on the triangular lattice is perhaps the best known example of frustrated magnets, but it orders at low temperatures. Recent density matrix renormalization group (DMRG) calculations find that the next nearest neighbor interaction J2 enhances the frustration, and it leads to a spin liquid for J2/J1∈(0.08 ,0.15 ). In addition, a DMRG study of a dipolar Heisenberg model with longer range interactions gives evidence for a spin liquid at a small dipole tilting angle θ ∈[0 ,1 0 ° ). In both cases, the putative spin liquid region appears to be small. Here, we show that for the triangular lattice dipolar Heisenberg model, a robust quantum paramagnetic phase exists in a surprisingly wide region, θ ∈[0 ,5 4 ° ) , for dipoles tilted along the lattice diagonal direction. We obtain the phase diagram of the model by functional renormalization group (RG), which treats all magnetic instabilities on equal footing. The quantum paramagnetic phase is characterized by a smooth continuous flow of vertex functions and spin susceptibility down to the lowest RG scale, in contrast to the apparent breakdown of RG flow in phases with stripe or spiral order. Our finding points to a promising direction to search for quantum spin liquids in ultracold dipolar molecules.
Effects of hydrostatic pressure on spin-lattice coupling in two-dimensional ferromagnetic Cr2Ge2Te6
Sun, Y.; Xiao, R. C.; Lin, G. T.; Zhang, R. R.; Ling, L. S.; Ma, Z. W.; Luo, X.; Lu, W. J.; Sun, Y. P.; Sheng, Z. G.
2018-02-01
Spin-lattice coupling plays an important role in both formation and understanding of the magnetism in two-dimensional magnetic semiconductors (2DMS). In this paper, the steady pressure effects on the lattice structure, Raman resonances, and magnetization of a 2DMS Cr2Ge2Te6 have been studied by both experiments and first principles calculations. It is found that the bond length of Cr-Cr decreases, the angle of Cr-Te-Cr diverges from 90°, and the Raman modes Eg3 and Ag1 show an increase with the application of external pressure. Consequently, the magnetic phase transition temperature TC decreases from 66.6 K to 60.6 K (˜9%) as the pressure increases from 0 to 1 GPa. These pressure effects not only confirm the existence of strong spin-lattice coupling but also reveal the detailed information about the lattice deformation effect on the magnetic properties in such 2DMS, which would be a benefit for the further understanding and manipulation of the magnetism in 2D materials.
Aperiodic spin state ordering of bistable molecules and its photoinducede erasing
Czech Academy of Sciences Publication Activity Database
Collet, E.; Watanabe, H.; Bréfuel, N.; Palatinus, Lukáš; Roudaut, L.; Toupet, L.; Tanaka, K.; Tuchagues, J.-P.; Fertey, P.; Ravy, S.; Toudic, B.; Cailleau, H.
2012-01-01
Roč. 109, č. 25 (2012), "257206-1"-"257206-5" ISSN 0031-9007 Institutional research plan: CEZ:AV0Z10100521 Keywords : photocrystallography * aperiodic structure * spin-state ordering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.943, year: 2012
Inhomogeneous superconductivity in a ferromagnet
International Nuclear Information System (INIS)
Kontos, T.; Aprili, M.; Lesueur, J.; Genet, F.; Boursier, R.; Grison, X.
2003-01-01
We have studied a new superconducting state where the condensate wave function resulting from conventional pairing, is modified by an exchange field. Superconductivity is induced into a ferromagnetic thin film (F) by the proximity effect with a superconducting reservoir (S). We observed oscillations of the superconducting order parameter induced in F as a function of the distance from the S/F interface. They originate from the finite momentum transfer provided to Cooper pairs by the splitting of the spin up and down bands. We measured the superconducting density of states in F by tunneling spectroscopy and the Josephson critical current when F is coupled with a superconducting counter-electrode. Negative values of the superconducting order parameter are revealed by capsized tunneling spectra in F and a negative Josephson coupling (π-junction)
Kaplan, C. Nadir; Hinczewski, Michael; Berker, A. Nihat
2009-06-01
For a variety of quenched random spin systems on an Apollonian network, including ferromagnetic and antiferromagnetic bond percolation and the Ising spin glass, we find the persistence of ordered phases up to infinite temperature over the entire range of disorder. We develop a renormalization-group technique that yields highly detailed information, including the exact distributions of local magnetizations and local spin-glass order parameters, which turn out to exhibit, as function of temperature, complex and distinctive tulip patterns.
Coupling between Spin and Charge Order Driven by Magnetic Field in Triangular Ising System LuFe2O4+δ
Directory of Open Access Journals (Sweden)
Lei Ding
2018-02-01
Full Text Available We present a study of the magnetic-field effect on spin correlations in the charge ordered triangular Ising system LuFe2O4+δ through single crystal neutron diffraction. In the absence of a magnetic field, the strong diffuse neutron scattering observed below the Neel temperature (TN = 240 K indicates that LuFe2O4+δ shows short-range, two-dimensional (2D correlations in the FeO5 triangular layers, characterized by the development of a magnetic scattering rod along the 1/3 1/3 L direction, persisting down to 5 K. We also found that on top of the 2D correlations, a long range ferromagnetic component associated with the propagation vector k1 = 0 sets in at around 240 K. On the other hand, an external magnetic field applied along the c-axis effectively favours a three-dimensional (3D spin correlation between the FeO5 bilayers evidenced by the increase of the intensity of satellite reflections with propagation vector k2 = (1/3, 1/3, 3/2. This magnetic modulation is identical to the charge ordered superstructure, highlighting the field-promoted coupling between the spin and charge degrees of freedom. Formation of the 3D spin correlations suppresses both the rod-type diffuse scattering and the k1 component. Simple symmetry-based arguments provide a natural explanation of the observed phenomenon and put forward a possible charge redistribution in the applied magnetic field.
Mean fields and self consistent normal ordering of lattice spin and gauge field theories
International Nuclear Information System (INIS)
Ruehl, W.
1986-01-01
Classical Heisenberg spin models on lattices possess mean field theories that are well defined real field theories on finite lattices. These mean field theories can be self consistently normal ordered. This leads to a considerable improvement over standard mean field theory. This concept is carried over to lattice gauge theories. We construct first an appropriate real mean field theory. The equations determining the Gaussian kernel necessary for self-consistent normal ordering of this mean field theory are derived. (orig.)
Glavic, Artur; Summers, Brock; Dahal, Ashutosh; Kline, Joseph; Van Herck, Walter; Sukhov, Alexander; Ernst, Arthur
2018-01-01
Abstract The nature of magnetic correlation at low temperature in two‐dimensional artificial magnetic honeycomb lattice is a strongly debated issue. While theoretical researches suggest that the system will develop a novel zero entropy spin solid state as T → 0 K, a confirmation to this effect in artificial honeycomb lattice of connected elements is lacking. This study reports on the investigation of magnetic correlation in newly designed artificial permalloy honeycomb lattice of ultrasmall elements, with a typical length of ≈12 nm, using neutron scattering measurements and temperature‐dependent micromagnetic simulations. Numerical modeling of the polarized neutron reflectometry data elucidates the temperature‐dependent evolution of spin correlation in this system. As temperature reduces to ≈7 K, the system tends to develop novel spin solid state, manifested by the alternating distribution of magnetic vortex loops of opposite chiralities. Experimental results are complemented by temperature‐dependent micromagnetic simulations that confirm the dominance of spin solid state over local magnetic charge ordered state in the artificial honeycomb lattice with connected elements. These results enable a direct investigation of novel spin solid correlation in the connected honeycomb geometry of 2D artificial structure. PMID:29721429
First-order phase transition in the quantum spin glass at T=0
Energy Technology Data Exchange (ETDEWEB)
Viana, J. Roberto; Nogueira, Yamilles; Sousa, J. Ricardo de
2003-05-26
The van Hemmen model with transverse and random longitudinal field is studied to analyze the tricritical behavior in the quantum Ising spin glass at T=0. The free energy and order parameter are calculated for two types of probability distributions: Gaussian and bimodal. We obtain the phase diagram in the {omega}-H plane, where {omega} and H are the transverse and random longitudinal fields, respectively. For the case of Gaussian distribution the phase transition is of second order, while the bimodal distribution we observe second-order transition for high-transverse field and first-order transition for small transverse field, with a tricritical point in the phase diagram.
First-order phase transition in the quantum spin glass at T=0
International Nuclear Information System (INIS)
Viana, J. Roberto; Nogueira, Yamilles; Sousa, J. Ricardo de
2003-01-01
The van Hemmen model with transverse and random longitudinal field is studied to analyze the tricritical behavior in the quantum Ising spin glass at T=0. The free energy and order parameter are calculated for two types of probability distributions: Gaussian and bimodal. We obtain the phase diagram in the Ω-H plane, where Ω and H are the transverse and random longitudinal fields, respectively. For the case of Gaussian distribution the phase transition is of second order, while the bimodal distribution we observe second-order transition for high-transverse field and first-order transition for small transverse field, with a tricritical point in the phase diagram
Improved corrosion resistance of spin-valve film
International Nuclear Information System (INIS)
Tetsukawa, H.; Hommura, H.; Okabe, A.; Soda, Y.
2007-01-01
We investigated the corrosion behavior and magnetoresistance of spin-valve film in order to improve the corrosion resistance of the spin-valve head for a tape recording system. The conventional spin-valve head (sub./Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta) with no diamond-like carbon (DLC) protective layer showed poor corrosion resistance. This is because the CoFe for ferromagnetic layer and Cu for spacer in the spin-valve film exhibited poor corrosion resistance. The corrosion resistance of the CoFe film and Cu film improved with the addition of Ni and Au, respectively. The spin-valve film (sub./Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) showed higher pitting potential than the conventional spin-valve film by +0.45 V. This presents a significant improvement over the conventional spin-valve film. We also investigated the effect of the composition of ferromagnetic layer and spacer on the magnetoresistance of the spin-valve film. The magnetoresistance of the spin-valve film by substitution of CoNiFe for CoFe in ferromagnetic layer decreased slightly. The magnetoresistance of the spin-valve film decreased as the addition of Au of the spacer increased. The diffusion at CoNiFe/CuAu interface has not been observed in annealing process. The quantitative relation between corrosion resistance and magnetoresistance of spin-valve film, and its ferromagnetic layer and spacer's compositions have been clarified. The output voltage at 50 Oe of the corrosion-resistant spin-valve head with CoNiFe ferromagnetic layer and CuAu spacer was about 50% of that of the conventional spin-valve head
Improved corrosion resistance of spin-valve film
Energy Technology Data Exchange (ETDEWEB)
Tetsukawa, H. [Sony Corporation, 6-7-35 Kitashinagawa, Shinagawa-ku, Tokyo 141-0001 (Japan)]. E-mail: tetsukaw@arc.sony.co.jp; Hommura, H. [Sony Corporation, 6-7-35 Kitashinagawa, Shinagawa-ku, Tokyo 141-0001 (Japan); Okabe, A. [Sony Corporation, 6-7-35 Kitashinagawa, Shinagawa-ku, Tokyo 141-0001 (Japan); Soda, Y. [Sony Corporation, 6-7-35 Kitashinagawa, Shinagawa-ku, Tokyo 141-0001 (Japan)
2007-06-15
We investigated the corrosion behavior and magnetoresistance of spin-valve film in order to improve the corrosion resistance of the spin-valve head for a tape recording system. The conventional spin-valve head (sub./Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta) with no diamond-like carbon (DLC) protective layer showed poor corrosion resistance. This is because the CoFe for ferromagnetic layer and Cu for spacer in the spin-valve film exhibited poor corrosion resistance. The corrosion resistance of the CoFe film and Cu film improved with the addition of Ni and Au, respectively. The spin-valve film (sub./Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) showed higher pitting potential than the conventional spin-valve film by +0.45 V. This presents a significant improvement over the conventional spin-valve film. We also investigated the effect of the composition of ferromagnetic layer and spacer on the magnetoresistance of the spin-valve film. The magnetoresistance of the spin-valve film by substitution of CoNiFe for CoFe in ferromagnetic layer decreased slightly. The magnetoresistance of the spin-valve film decreased as the addition of Au of the spacer increased. The diffusion at CoNiFe/CuAu interface has not been observed in annealing process. The quantitative relation between corrosion resistance and magnetoresistance of spin-valve film, and its ferromagnetic layer and spacer's compositions have been clarified. The output voltage at 50 Oe of the corrosion-resistant spin-valve head with CoNiFe ferromagnetic layer and CuAu spacer was about 50% of that of the conventional spin-valve head.
Towards spin injection into silicon
Energy Technology Data Exchange (ETDEWEB)
Dash, S.P.
2007-08-15
Si has been studied for the purpose of spin injection extensively in this thesis. Three different concepts for spin injection into Si have been addressed: (1) spin injection through a ferromagnet-Si Schottky contact, (2) spin injection using MgO tunnel barriers in between the ferromagnet and Si, and (3) spin injection from Mn-doped Si (DMS) as spin aligner. (1) FM-Si Schottky contact for spin injection: To be able to improve the interface qualities one needs to understand the atomic processes involved in the formation of silicide phases. In order to obtain more detailed insight into the formation of such phases the initial stages of growth of Co and Fe were studied in situ by HRBS with monolayer depth resolution.(2) MgO tunnel barrier for spin injection into Si: The fabrication and characterization of ultra-thin crystalline MgO tunnel barriers on Si (100) was presented. (3) Mn doped Si for spin injection: Si-based diluted magnetic semiconductor samples were prepared by doping Si with Mn by two different methods i) by Mn ion implantation and ii) by in-diffusion of Mn atoms (solid state growth). (orig.)
Majumder, Arpi; Choudhury, Chirantan Roy; Mitra, Samiran; Rosair, Georgina M; El Fallah, M Salah; Ribas, Joan
2005-04-28
Atmospheric CO2 fixation by an aqueous solution containing Cu(ClO4)2.6H2O and 4-aminopyridine (4-apy) yields a novel example of a two-dimensional mu3-CO3 bridged copper(II) complex {[Cu(4-apy)2]3(mu3-CO3)2(ClO4)2.(1/2)CH3OH}n that has been characterized by IR, UV and X-ray crystallography; preliminary magnetic measurements show that complex exhibits long-range ordered ferromagnetic coupling.
Microscopic description of orbital-selective spin ordering in BaMn2As2
Craco, L.; Carara, S. S.
2018-05-01
Using generalized gradient approximation+dynamical mean-field theory, we provide a microscopic description of orbital-selective spin ordering in the tetragonal manganese pnictide BaMn2As2 . We demonstrate the coexistence of local moments and small band-gap electronic states in the parent compound. We also explore the role played by electron/hole doping, showing that the Mott insulating state is rather robust to small removal of electron charge carriers similar to cuprate oxide superconductors. Good qualitative accord between theory and angle-resolved photoemission as well as electrical transport provides support to our view of orbital-selective spin ordering in BaMn2As2 . Our proposal is expected to be an important step to understanding the emergent correlated electronic structure of materials with persisting ordered localized moments coexisting with Coulomb reconstructed nonmagnetic electronic states.
Spin model for nontrivial types of magnetic order in inverse-perovskite antiferromagnets
Mochizuki, Masahito; Kobayashi, Masaya; Okabe, Reoya; Yamamoto, Daisuke
2018-02-01
Nontrivial magnetic orders in the inverse-perovskite manganese nitrides are theoretically studied by constructing a classical spin model describing the magnetic anisotropy and frustrated exchange interactions inherent in specific crystal and electronic structures of these materials. With a replica-exchange Monte Carlo technique, a theoretical analysis of this model reproduces the experimentally observed triangular Γ5 g and Γ4 g spin-ordered patterns and the systematic evolution of magnetic orders. Our Rapid Communication solves a 40-year-old problem of nontrivial magnetism for the inverse-perovskite manganese nitrides and provides a firm basis for clarifying the magnetism-driven negative thermal expansion phenomenon discovered in this class of materials.
Superconducting Ferromagnetic Nanodiamond
Czech Academy of Sciences Publication Activity Database
Zhang, G.; Samuely, T.; Xu, Z.; Jochum, J. K.; Volodin, A.; Zhou, S. Q.; May, P. W.; Onufriienko, O.; Kacmarik, J.; Steele, J. A.; Li, J.; Vanacken, J.; Vacík, Jiří; Szabo, P.; Yuan, H. F.; Roeffaers, M. B. J.; Cerbu, D.; Samuely, P.; Hofkens, J.; Moshchalkov, V.V.
2017-01-01
Roč. 11, č. 6 (2017), s. 5358-5366 ISSN 1936-0851 R&D Projects: GA ČR(CZ) GBP108/12/G108; GA MŠk LM2015056 Institutional support: RVO:61389005 Keywords : nanodiamond * superconductivity and ferromagnetism * spin fluctuations * giant positive magnetoresistance * anamalous Hall effect Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders OBOR OECD: Nano-materials (production and properties ) Impact factor: 13.942, year: 2016
International Nuclear Information System (INIS)
Epstein, A.J.
1990-01-01
This past year has been one of substantial advancement in both the physics and chemistry of molecular and polymeric ferromagnets. The specific heat studies of (DMeFc)(TCNE) have revealed a cusp at the three-dimensional ferromagnetic transition temperature with a crossover to primarily 1-D behavior at higher temperatures. This paper discusses these studies
Sengupta, Abhronil; Shim, Yong; Roy, Kaushik
2016-12-01
Non-Boolean computing based on emerging post-CMOS technologies can potentially pave the way for low-power neural computing platforms. However, existing work on such emerging neuromorphic architectures have either focused on solely mimicking the neuron, or the synapse functionality. While memristive devices have been proposed to emulate biological synapses, spintronic devices have proved to be efficient at performing the thresholding operation of the neuron at ultra-low currents. In this work, we propose an All-Spin Artificial Neural Network where a single spintronic device acts as the basic building block of the system. The device offers a direct mapping to synapse and neuron functionalities in the brain while inter-layer network communication is accomplished via CMOS transistors. To the best of our knowledge, this is the first demonstration of a neural architecture where a single nanoelectronic device is able to mimic both neurons and synapses. The ultra-low voltage operation of low resistance magneto-metallic neurons enables the low-voltage operation of the array of spintronic synapses, thereby leading to ultra-low power neural architectures. Device-level simulations, calibrated to experimental results, was used to drive the circuit and system level simulations of the neural network for a standard pattern recognition problem. Simulation studies indicate energy savings by ∼ 100× in comparison to a corresponding digital/analog CMOS neuron implementation.
Spectral Properties, Generation Order Parameters, and Luminosities for Spin-powered X-Ray Pulsars
Wang, Wei; Zhao, Yongheng
2004-02-01
We show the spectral properties of 15 spin-powered X-ray pulsars, and the correlation between the average power-law photon index and spin-down rate. Generation order parameters (GOPs) based on polar cap models are introduced to characterize the X-ray pulsars. We calculate three definitions of generation order parameters arising from the different effects of magnetic and electric fields on photon absorption during cascade processes, and study the relations between the GOPs and spectral properties of X-ray pulsars. There exists a possible correlation between the photon index and GOP in our pulsar sample. Furthermore, we present a method stemming from the concept of GOPs to estimate the nonthermal X-ray luminosity for spin-powered pulsars. Then X-ray luminosity is calculated in the context of our polar cap accelerator model, which is consistent with most observed X-ray pulsar data. The ratio between the X-ray luminosity estimated by our method and the pulsar's spin-down power is consistent with the LX~10-3Lsd feature.
Energy Technology Data Exchange (ETDEWEB)
Kaur, Palvinder [Department of Physics, Punjabi University, Patiala, Punjab, 147002 (India); Kumar, Sanjeev, E-mail: sanjeev04101977@gmail.com [Applied Science Department, PEC University of Technology, Chandigarh, 160012 (India); Chen, Chi-Liang, E-mail: chen.cl@nsrrc.org.tw [National Synchrotron Radiation Research Center (NSRRC), Hsinchu, 30076, Taiwan (China); Yang, Kai-Siang [National Synchrotron Radiation Research Center (NSRRC), Hsinchu, 30076, Taiwan (China); Department of Mechanical Engineering, National Taipei University of Technology, Taipei, Taiwan (China); Wei, Da-Hua [Department of Mechanical Engineering, National Taipei University of Technology, Taipei, Taiwan (China); Dong, Chung-Li [Department of Physics, Tamkang University, Tamsui, Taiwan (China); Srivastava, C. [Materials Engineering Department, Indian Institute of Science, Bangalore, 560012 (India); Rao, S.M. [Department of Physics, Punjabi University, Patiala, Punjab, 147002 (India); Institute of Physics, Academia Sinica, Taipei, 11529, Taiwan (China)
2017-01-15
Zn{sub 1−x}Gd{sub x}S nanoparticles with Gd concentration x = 0.00, 0.02 and 0.04 were synthesized by the chemical co-precipitation technique using thioglycerol as capping agent. X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy, X-ray absorption near-edge structure (XANES) and vibrating sample magnetometer (VSM) were employed to characterize the as synthesized Gd doped ZnS nanoparticles. XRD and TEM studies show the formation of cubic ZnS nanoparticles with an average size in the range 5–10 nm. The doping did not alter the phase of the ZnS. The PL spectra of doped ZnS nanoparticles showed the presence of sulphur vacancies in the lattice. XANES of Gd doped ZnS nanoparticles depicts spectral changes may arise from charge transfer between host Zn and dopant Gd ions. A VSM study shows that the weak ferromagnetic behaviour increases with increase in Gd doping ZnS nanoparticles. - Highlights: • Gd doped ZnS nanoparticles synthesized using co-precipitation technique. • PL studies depict sulphur and zinc vacancies in Gd doped ZnS nanoparticles. • XANES studies depict the charge transfer between host Zn and dopant Gd ions. • Room temperature weak ferromagnetism is observed in Gd doped ZnS nanoparticles.
International Nuclear Information System (INIS)
Kaur, Palvinder; Kumar, Sanjeev; Chen, Chi-Liang; Yang, Kai-Siang; Wei, Da-Hua; Dong, Chung-Li; Srivastava, C.; Rao, S.M.
2017-01-01
Zn_1_−_xGd_xS nanoparticles with Gd concentration x = 0.00, 0.02 and 0.04 were synthesized by the chemical co-precipitation technique using thioglycerol as capping agent. X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy, X-ray absorption near-edge structure (XANES) and vibrating sample magnetometer (VSM) were employed to characterize the as synthesized Gd doped ZnS nanoparticles. XRD and TEM studies show the formation of cubic ZnS nanoparticles with an average size in the range 5–10 nm. The doping did not alter the phase of the ZnS. The PL spectra of doped ZnS nanoparticles showed the presence of sulphur vacancies in the lattice. XANES of Gd doped ZnS nanoparticles depicts spectral changes may arise from charge transfer between host Zn and dopant Gd ions. A VSM study shows that the weak ferromagnetic behaviour increases with increase in Gd doping ZnS nanoparticles. - Highlights: • Gd doped ZnS nanoparticles synthesized using co-precipitation technique. • PL studies depict sulphur and zinc vacancies in Gd doped ZnS nanoparticles. • XANES studies depict the charge transfer between host Zn and dopant Gd ions. • Room temperature weak ferromagnetism is observed in Gd doped ZnS nanoparticles.
Magnetic and electric order in the spin-1/2 XX model with three-spin interactions
Energy Technology Data Exchange (ETDEWEB)
Thakur, Pradeep; Durganandini, P. [Department of Physics, University of Pune, Ganeshkhind, Pune - 411007 (India)
2016-05-23
We study the spin-1/2 XX model in the presence of three-spin interactions of the XZX+YZY and XZY-YZX types. We solve the problem exactly and show that there is both finite magnetization and electric polarization for low non-zero strengths of the three-spin interactions.
Spin current through quantum-dot spin valves
International Nuclear Information System (INIS)
Wang, J; Xing, D Y
2006-01-01
We report a theoretical study of the influence of the Coulomb interaction on the equilibrium spin current in a quantum-dot spin valve, in which the quantum dot described by the Anderson impurity model is coupled to two ferromagnetic leads with noncollinear magnetizations. In the Kondo regime, electrons transmit through the quantum dot via higher-order virtual processes, in which the spin of either lead electrons or a localized electron on the quantum dot may reverse. It is found that the magnitude of the spin current decreases with increasing Coulomb interactions due to spin flip effects on the dot. However, the spatial direction of the spin current remains unchanged; it is determined only by the exchange coupling between two noncollinear magnetizations
Mixed-order phase transition in a minimal, diffusion-based spin model.
Fronczak, Agata; Fronczak, Piotr
2016-07-01
In this paper we exactly solve, within the grand canonical ensemble, a minimal spin model with the hybrid phase transition. We call the model diffusion based because its Hamiltonian can be recovered from a simple dynamic procedure, which can be seen as an equilibrium statistical mechanics representation of a biased random walk. We outline the derivation of the phase diagram of the model, in which the triple point has the hallmarks of the hybrid transition: discontinuity in the average magnetization and algebraically diverging susceptibilities. At this point, two second-order transition curves meet in equilibrium with the first-order curve, resulting in a prototypical mixed-order behavior.
International Nuclear Information System (INIS)
Monthus, Cécile
2015-01-01
For the quantum Ising chain, the self-dual block renormalization procedure of Fernandez-Pacheco (1979 Phys. Rev. D 19 3173) is known to reproduce exactly the location of the zero-temperature critical point and the correlation length exponent ν = 1. Recently, Miyazaki and Nishimori (2013 Phys. Rev. E 87 032154) have proposed to study the disordered quantum Ising model in dimensions d > 1 by applying the Fernandez-Pacheco procedure successively in each direction. To avoid the inequivalence of directions of their approach, we propose here an alternative procedure where the d directions are treated on the same footing. For the pure model, this leads to the correlation length exponents ν ≃ 0.625 in d = 2 (to be compared with the 3D classical Ising model exponent ν ≃ 0.63) and ν ≃ 0.5018 (to be compared with the 4D classical Ising model mean-field exponent ν = 1/2). For the disordered model in dimension d = 2, either ferromagnetic or spin-glass, the numerical application of the renormalization rules to samples of linear size L = 4096 yields that the transition is governed by an Infinite Disorder Fixed Point, with the activated exponent ψ ≃ 0.65, the typical correlation exponent ν typ ≃ 0.44 and the finite-size correlation exponent ν FS ≃ 1.25. We discuss the similarities and differences with the Strong Disorder Renormalization results. (paper)
Spin Orbit Interaction Engineering for beyond Spin Transfer Torque memory
Wang, Kang L.
Spin transfer torque memory uses electron current to transfer the spin torque of electrons to switch a magnetic free layer. This talk will address an alternative approach to energy efficient non-volatile spintronics through engineering of spin orbit interaction (SOC) and the use of spin orbit torque (SOT) by the use of electric field to improve further the energy efficiency of switching. I will first discuss the engineering of interface SOC, which results in the electric field control of magnetic moment or magneto-electric (ME) effect. Magnetic memory bits based on this ME effect, referred to as magnetoelectric RAM (MeRAM), is shown to have orders of magnitude lower energy dissipation compared with spin transfer torque memory (STTRAM). Likewise, interests in spin Hall as a result of SOC have led to many advances. Recent demonstrations of magnetization switching induced by in-plane current in heavy metal/ferromagnetic heterostructures have been shown to arise from the large SOC. The large SOC is also shown to give rise to the large SOT. Due to the presence of an intrinsic extraordinarily strong SOC and spin-momentum lock, topological insulators (TIs) are expected to be promising candidates for exploring spin-orbit torque (SOT)-related physics. In particular, we will show the magnetization switching in a chromium-doped magnetic TI bilayer heterostructure by charge current. A giant SOT of more than three orders of magnitude larger than those reported in heavy metals is also obtained. This large SOT is shown to come from the spin-momentum locked surface states of TI, which may further lead to innovative low power applications. I will also describe other related physics of SOC at the interface of anti-ferromagnetism/ferromagnetic structure and show the control exchange bias by electric field for high speed memory switching. The work was in part supported by ERFC-SHINES, NSF, ARO, TANMS, and FAME.
International Nuclear Information System (INIS)
Popov, A.P.
2012-01-01
Simple phenomenological model of ferromagnetic film characterized by equal energies of surface anisotropies at two sides of a film (symmetric film) is considered. The model is used to describe a two-step spin reorientation transition (SRT) in Au/Co/Au sandwich with Co film thickness: the SRT from perpendicular to canted noncollinear (CNC) state at N ⊥ =6.3 atomic layers and the subsequent SRT from CNC to in-plane state at N ∥ =10.05 atomic layers. Analytic expressions for the stability criterion of collinear perpendicular and in-plane states of a film are derived with account of discrete location of atomic layers. The dependence of borders that separate regions corresponding to various magnetic states of a film in the (k B ,k S )-diagram on film thickness N is established. k S (k B ) is surface (bulk) reduced anisotropy constant. The comparison of theory with experiment related to Au/Co/Au sandwich shows that there is a whole region in the (k B ,k S )-diagram corresponding to experimentally determined values of threshold film thicknesses N ⊥ =6.3 and N ∥ =10.05. The comparison of this region with similar region determined earlier for a bare Co/Au film within the same model of asymmetric film and characterized by N ⊥ =3.5, N ∥ =5.5 shows that the intersection of these regions is not empty. Hence, both the SRT in Au/Co/Au sandwich and in bare Co/Au film with Co film thickness can be described within the same model using the same magnitudes of model parameters k S , k B . Based on this result we conclude that the energy of Neel surface anisotropy at free Co surface is negligible compared to the energy of Co–Au interface anisotropy. It is demonstrated that the destabilization of collinear states in symmetric film leads to occurrence of the ground CNC state and two novel metastable CNC states. These three CNC states exhibit different kinds of symmetry. In case of asymmetric film only ground CNC state occurs on destabilization of collinear states of a film
Antiferromagnetic spin phase transition in nuclear matter with effective Gogny interaction
International Nuclear Information System (INIS)
Isayev, A.A.; Yang, J.
2004-01-01
The possibility of ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the effective Gogny interaction. It is shown that at some critical density nuclear matter with the D1S effective force undergoes a phase transition to the antiferromagnetic spin state (opposite directions of neutron and proton spins). The self-consistent equations of spin polarized nuclear matter with the D1S force have no solutions corresponding to ferromagnetic spin ordering (the same direction of neutron and proton spins) and, hence, the ferromagnetic transition does not appear. The dependence of the antiferromagnetic spin polarization parameter as a function of density is found at zero temperature
Formation of ordered microphase-separated pattern during spin coating of ABC triblock copolymer.
Huang, Weihuan; Luo, Chunxia; Zhang, Jilin; Han, Yanchun
2007-03-14
In this paper, the authors have systematically studied the microphase separation and crystallization during spin coating of an ABC triblock copolymer, polystyrene-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) (PS-b-P2VP-b-PEO). The microphase separation of PS-b-P2VP-b-PEO and the crystallization of PEO blocks can be modulated by the types of the solvent and the substrate, the spinning speed, and the copolymer concentration. Ordered microphase-separated pattern, where PEO and P2VP blocks adsorbed to the substrate and PS blocks protrusions formed hexagonal dots above the P2VP domains, can only be obtained when PS-b-P2VP-b-PEO is dissolved in N,N-dimethylformamide and the films are spin coated onto the polar substrate, silicon wafers or mica. The mechanism of the formation of regular pattern by microphase separation is found to be mainly related to the inducement of the substrate (middle block P2VP wetting the polar substrate), the quick vanishment of the solvent during the early stage of the spin coating, and the slow evaporation of the remaining solvent during the subsequent stage. On the other hand, the probability of the crystallization of PEO blocks during spin coating decreases with the reduced film thickness. When the film thickness reaches a certain value (3.0 nm), the extensive crystallization of PEO is effectively prohibited and ordered microphase-separated pattern over large areas can be routinely prepared. When the film thickness exceeds another definite value (12.0 nm), the crystallization of PEO dominates the surface morphology. For films with thickness between these two values, microphase separation and crystallization can simultaneously occur.
Magneto-elastic resonant phenomena at the motion of the domain wall in weak ferromagnets
International Nuclear Information System (INIS)
Kuz'menko, A.P.; Zhukov, E.A.; Dobromyslov, M.B.; Kaminsky, A.V.
2007-01-01
Dynamics of domain walls (DWs) in transparent thin orthoferrite samples with weak ferromagnetic ordering is investigated at sub- and supersonic velocities. A resonant increase of Lamb waves and the formation of magnetoelastic solitons under resonant conditions in both an elastic and between a spin and elastic subsystems were observed
Magnetic excitations in ferromagnetic semiconductors
International Nuclear Information System (INIS)
Furdyna, J.K.; Liu, X.; Zhou, Y.Y.
2009-01-01
Magnetic excitations in a series of GaMnAs ferromagnetic semiconductor films were studied by ferromagnetic resonance (FMR). Using the FMR approach, multi-mode spin wave resonance spectra have been observed, whose analysis provides information on magnetic anisotropy (including surface anisotropy), distribution of magnetization precession within the GaMnAs film, dynamic surface spin pinning (derived from surface anisotropy), and the value of exchange stiffness constant D. These studies illustrate a combination of magnetism and semiconductor physics that is unique to magnetic semiconductors
Spin diffusion and torques in disordered antiferromagnets
Manchon, Aurelien
2017-02-01
We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.
Spin diffusion and torques in disordered antiferromagnets
Manchon, Aurelien
2017-01-01
We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.
DEFF Research Database (Denmark)
Larsen, J.; Schäffer, T. K.; Hansen, U. B.
2017-01-01
We present experimental evidence for a quantum phase transition in the easy-axis S = 3/2 anisotropic quasione-dimensional ferromagnet CoCl2 · 2D2O in a transverse field. Elastic neutron scattering shows that the magnetic order parameter vanishes at a transverse critical field μ0Hc = 16.05(4) T......, while inelastic neutron scattering shows that the gap in the magnetic excitation spectrum vanishes at the same field value, and reopens for H>Hc. The field dependence of the order parameter and the gap are well described by critical exponents β = 0.45 ± 0.09 and zν close to 1/2, implying...... that the quantum phase transition in CoCl2 · 2D2O differs significantly from the textbook version of a S = 1/2 Ising chain in a transverse field. We attribute the difference to weak but finite three-dimensionality of the magnetic interactions....
Giant magneto-spin-Seebeck effect and magnon transfer torques in insulating spin valves
Cheng, Yihong; Chen, Kai; Zhang, Shufeng
2018-01-01
We theoretically study magnon transport in an insulating spin valve (ISV) made of an antiferromagnetic insulator sandwiched between two ferromagnetic insulator (FI) layers. In the conventional metal-based spin valve, the electron spins propagate between two metallic ferromagnetic layers, giving rise to giant magnetoresistance and spin transfer torque. Here, the incoherent magnons in the ISV serve as angular momentum carriers and are responsible for the angular momentum transport between two FI layers across the antiferromagnetic spacer. We predict two transport phenomena in the presence of the temperature gradient: a giant magneto-spin-Seebeck effect in which the output voltage signal is controlled by the relative orientation of the two FI layers and magnon transfer torque that can be used for switching the magnetization of the FI layers with a temperature gradient of the order of 0.1 Kelvin per nanometer.
Kreissl, M; Stephens, T; Ziebeck, K R A
2003-01-01
The effect of atomic order on the martensitic phase transition and magnetic properties of stoichiometric Ni sub 2 MnGa has been investigated in a sample quenched from 1000 deg C. Magnetization, resistivity and x-ray diffraction measurements indicate that the structural phase transition occurs at approx 103 K, substantially lower than the value reported for samples quenched from 800 deg C and ordered in the Heusler L2 sub 1 structure. A small reduction in the ferromagnetic moment was also observed, although the Curie temperature remained largely unaffected. The electronic Sommerfeld coefficient obtained from heat capacity measurements is enhanced but smaller than that observed for the 800 deg C quenched sample. The results are consistent with band structure calculations and the electronic changes brought about by atomic disorder.
Frequency-domain reduced order models for gravitational waves from aligned-spin compact binaries
International Nuclear Information System (INIS)
Pürrer, Michael
2014-01-01
Black-hole binary coalescences are one of the most promising sources for the first detection of gravitational waves. Fast and accurate theoretical models of the gravitational radiation emitted from these coalescences are highly important for the detection and extraction of physical parameters. Spinning effective-one-body models for binaries with aligned-spins have been shown to be highly faithful, but are slow to generate and thus have not yet been used for parameter estimation (PE) studies. I provide a frequency-domain singular value decomposition-based surrogate reduced order model that is thousands of times faster for typical system masses and has a faithfulness mismatch of better than ∼0.1% with the original SEOBNRv1 model for advanced LIGO detectors. This model enables PE studies up to signal-to-noise ratios (SNRs) of 20 and even up to 50 for total masses below 50 M ⊙ . This paper discusses various choices for approximations and interpolation over the parameter space that can be made for reduced order models of spinning compact binaries, provides a detailed discussion of errors arising in the construction and assesses the fidelity of such models. (paper)
Energy Technology Data Exchange (ETDEWEB)
Levi, Michele [Université Pierre et Marie Curie, CNRS-UMR 7095, Institut d' Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris (France); Steinhoff, Jan, E-mail: michele.levi@upmc.fr, E-mail: jan.steinhoff@aei.mpg.de [Max-Planck-Institute for Gravitational Physics (Albert-Einstein-Institute), Am Mühlenberg 1, 14476 Potsdam-Golm (Germany)
2016-01-01
The next-to-next-to-leading order spin-squared interaction potential for generic compact binaries is derived for the first time via the effective field theory for gravitating spinning objects in the post-Newtonian scheme. The spin-squared sector is an intricate one, as it requires the consideration of the point particle action beyond minimal coupling, and mainly involves the spin-squared worldline couplings, which are quite complex, compared to the worldline couplings from the minimal coupling part of the action. This sector also involves the linear in spin couplings, as we go up in the nonlinearity of the interaction, and in the loop order. Hence, there is an excessive increase in the number of Feynman diagrams, of which more are higher loop ones. We provide all the Feynman diagrams and their values. The beneficial ''nonrelativistic gravitational'' fields are employed in the computation. This spin-squared correction, which enters at the fourth post-Newtonian order for rapidly rotating compact objects, completes the conservative sector up to the fourth post-Newtonian accuracy. The robustness of the effective field theory for gravitating spinning objects is shown here once again, as demonstrated in a recent series of papers by the authors, which obtained all spin dependent sectors, required up to the fourth post-Newtonian accuracy. The effective field theory of spinning objects allows to directly obtain the equations of motion, and the Hamiltonians, and these will be derived for the potential obtained here in a forthcoming paper.
Energy Technology Data Exchange (ETDEWEB)
Levi, Michele [Université Pierre et Marie Curie, CNRS-UMR 7095, Institut d' Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris (France); Steinhoff, Jan, E-mail: michele.levi@upmc.fr, E-mail: jan.steinhoff@aei.mpg.de [Max-Planck-Institute for Gravitational Physics (Albert-Einstein-Institute), Am Mühlenberg 1, 14476 Potsdam-Golm (Germany)
2016-01-01
We implement the effective field theory for gravitating spinning objects in the post-Newtonian scheme at the next-to-next-to-leading order level to derive the gravitational spin-orbit interaction potential at the third and a half post-Newtonian order for rapidly rotating compact objects. From the next-to-next-to-leading order interaction potential, which we obtain here in a Lagrangian form for the first time, we derive straightforwardly the corresponding Hamiltonian. The spin-orbit sector constitutes the most elaborate spin dependent sector at each order, and accordingly we encounter a proliferation of the relevant Feynman diagrams, and a significant increase of the computational complexity. We present in detail the evaluation of the interaction potential, going over all contributing Feynman diagrams. The computation is carried out in terms of the ''nonrelativistic gravitational'' fields, which are advantageous also in spin dependent sectors, together with the various gauge choices included in the effective field theory for gravitating spinning objects, which also optimize the calculation. In addition, we automatize the effective field theory computations, and carry out the automated computations in parallel. Such automated effective field theory computations would be most useful to obtain higher order post-Newtonian corrections. We compare our Hamiltonian to the ADM Hamiltonian, and arrive at a complete agreement between the ADM and effective field theory results. Finally, we provide Hamiltonians in the center of mass frame, and complete gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to third and a half post-Newtonian order. The derivation presented here is essential to obtain further higher order post-Newtonian corrections, and to reach the accuracy level required for the successful detection of gravitational radiation.
Ferromagnetism in Cr-doped passivated AlN nanowires
Kanoun, Mohammed; Goumri-Said, Souraya; Schwingenschlö gl, Udo
2014-01-01
We apply first principles calculations to predict the effect of Cr doping on the electronic and magnetic properties of passivated AlN nanowires. We compare the energetics of the possible dopant sites and demonstrate the favorable configuration ferromagnetic ordering. The charge density of the pristine passivated AlN nanowires is used to elucidate the bonding character. Spin density maps demonstrate an induced spin polarization for N atoms next to dopant atoms, though most of the magnetism is carried by the Cr atoms. Cr-doped AlN nanowires turn out to be interesting for spintronic devices. © 2014 the Partner Organisations.
Intrinsic and spatially nonuniform ferromagnetism in Co-doped ZnO films
Tseng, L. T.; Suter, A.; Wang, Y. R.; Xiang, F. X.; Bian, P.; Ding, X.; Tseng, A.; Hu, H. L.; Fan, H. M.; Zheng, R. K.; Wang, X. L.; Salman, Z.; Prokscha, T.; Suzuki, K.; Liu, R.; Li, S.; Morenzoni, E.; Yi, J. B.
2017-09-01
Co doped ZnO films have been deposited by a laser-molecular beam epitaxy system. X-ray diffraction and UV spectra analysis show that Co effectively substitutes the Zn site. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy analysis indicate that there are no clusters. Co dopants are uniformly distributed in ZnO film. Ferromagnetic ordering is observed in all samples deposited under an oxygen partial pressure, PO2=10-3 , 10-5, and 10-7 torr, respectively. However, the magnetization of PO2=10-3 and 10-5 is very small at room temperature. At low temperature, the ferromagnetic ordering is enhanced. Muon spin relaxation (μ SR ) measurements confirm the ferromagnetism in all samples, and the results are consistent with magnetization measurements. From μ SR and TEM analysis, the film deposited under PO2=10-7 torr shows intrinsic ferromagnetism. However, the volume fraction of the ferromagnetism phase is approximately 70%, suggesting that the ferromagnetism is not carrier mediated. Resistivity versus temperature measurements indicate Efros variable range hopping dominates the conductivity. From the above results, we can confirm that a bound magnetic polaron is the origin of the ferromagnetism.
Sahoo, R. C.; Paladhi, D.; Nath, T. K.
2017-08-01
Single-phase polycrystalline La1.5Ca0.5CoMnO6 double perovskite nanoparticles (∼25 nm) have been synthesized by chemical sol-gel method. We report here the structural, magnetic and transport properties using X-ray diffraction, dc magnetization, ac susceptibility, exchange bias and dc resistivity measurements. The Rietveld refinement of X-ray diffraction pattern reveals that the La1.5Ca0.5CoMnO6 (LCCMO) system crystallizes in orthorhombic structure with pbnm space group. Mn and Co ions are not completely ordered on the B sites due to the presence of about 30% antisite-disorder in the system. The ordering of Co2+ and Mn4+ gives rise to the ferromagnetism below 145 K. A spin glass like ground state has also been observed near 37.6(4) K, arising mainly due to the presence of competing magnetic interactions and antisite-disorder in the LCCMO nanoparticles. The frequency dependence peak shift of the Ac-susceptibility peak in the glassy state follows the critical slowing down model. The observed memory effect in ac susceptibility data reveals the existence of interacting clusters in a competing magnetic interactions state. The presence of noticeable exchange bias effect can be best explained on the basis of uncompensated interface (ferromagnetic/spin-glass) spins of antisite-disordered LCCMO system. This anti-site disordered nanocompound exhibits semiconducting behavior with variable range hopping kind of electronic conduction mechanism in the temperature range of 200-300 K. We have also observed large negative magnetoresistance (-30% at 100 K and 60 kOe) mainly due to the spin-polarized transport across the grain boundaries.
Spin ice Thin Film: Surface Ordering, Emergent Square ice, and Strain Effects
Jaubert, L. D. C.; Lin, T.; Opel, T. S.; Holdsworth, P. C. W.; Gingras, M. J. P.
2017-05-01
Motivated by recent realizations of Dy2 Ti2 O7 and Ho2 Ti2 O7 spin ice thin films, and more generally by the physics of confined gauge fields, we study a model spin ice thin film with surfaces perpendicular to the [001] cubic axis. The resulting open boundaries make half of the bonds on the interfaces inequivalent. By tuning the strength of these inequivalent "orphan" bonds, dipolar interactions induce a surface ordering equivalent to a two-dimensional crystallization of magnetic surface charges. This surface ordering may also be expected on the surfaces of bulk crystals. For ultrathin films made of one cubic unit cell, once the surfaces have ordered, a square ice phase is stabilized over a finite temperature window. The square ice degeneracy is lifted at lower temperature and the system orders in analogy with the well-known F transition of the 6-vertex model. To conclude, we consider the addition of strain effects, a possible consequence of interface mismatches at the film-substrate interface. Our simulations qualitatively confirm that strain can lead to a smooth loss of Pauling entropy upon cooling, as observed in recent experiments on Dy2 Ti2 O7 films.
Spin thermoelectric effects in organic single-molecule devices
Energy Technology Data Exchange (ETDEWEB)
Wang, H.L.; Wang, M.X.; Qian, C.; Hong, X.K.; Zhang, D.B.; Liu, Y.S.; Yang, X.F., E-mail: xfyang@cslg.edu.cn
2017-05-25
Highlights: • A stronger spin thermoelectric performance in a polyacetylene device is observed. • For the antiferromagnetic (AFM) ordering, a transport gap is opened. Thus the thermoelectric effects are largely enhanced. - Abstract: The spin thermoelectric performance of a polyacetylene chain bridging two zigzag graphene nanoribbons (ZGNRs) is investigated based on first principles method. Two different edge spin arrangements in ZGNRs are considered. For ferromagnetic (FM) ordering, transmission eigenstates with different spin indices distributed below and above Fermi level are observed, leading directly to a strong spin thermoelectric effect in a wide temperature range. With the edge spins arranged in the antiferromagnetic (AFM) ordering, an obvious transport gap appears in the system, which greatly enhances the thermoelectric effects. The presence of a small spin splitting also induces a spin thermoelectric effect greater than the charge thermoelectric effect in certain temperature range. In general, the single-molecule junction exhibits the potential to be used for the design of perfect thermospin devices.
International Nuclear Information System (INIS)
Wei Guozhu; Miao Hailing
2009-01-01
The magnetic properties of a mixed spin-3/2 and spin-2 and a mixed spin-3/2 and spin-5/2 Ising ferromagnetic system with different anisotropies are studied by means of mean-field theory (MFT). The dependence of the phase diagram on single-ion anisotropy strengths is studied too. In the mixed spin-3/2 and spin-2 Ising model, besides the second-order phase transition, the first order-disorder phase transition and the tricritical line are found. In the mixed spin-3/2 and spin-5/2 Ising model, there is no first-order transition and tricritical line. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Energy Technology Data Exchange (ETDEWEB)
Tatara, Gen, E-mail: gen.tatara@riken.jp [RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198 Japan (Japan); Nakabayashi, Noriyuki [RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198 Japan (Japan); Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 Japan (Japan)
2014-05-07
Emergent electromagnetic field which couples to electron's spin in ferromagnetic metals is theoretically studied. Rashba spin-orbit interaction induces spin electromagnetic field which is in the linear order in gradient of magnetization texture. The Rashba-induced effective electric and magnetic fields satisfy in the absence of spin relaxation the Maxwell's equations as in the charge-based electromagnetism. When spin relaxation is taken into account besides spin dynamics, a monopole current emerges generating spin motive force via the Faraday's induction law. The monopole is expected to play an important role in spin-charge conversion and in the integration of spintronics into electronics.
Dynamical response of vibrating ferromagnets
Gaganidze, E; Ziese, M
2000-01-01
The resonance frequency of vibrating ferromagnetic reeds in a homogeneous magnetic field can be substantially modified by intrinsic and extrinsic field-related contributions. Searching for the physical reasons of the field-induced resonance frequency change and to study the influence of the spin glass state on it, we have measured the low-temperature magnetoelastic behavior and the dynamical response of vibrating amorphous and polycrystalline ferromagnetic ribbons. We show that the magnetoelastic properties depend strongly on the direction of the applied magnetic field. The influence of the re-entrant spin glass transition on these properties is discussed. We present clear experimental evidence that for applied fields perpendicular to the main area of the samples the behavior of ferromagnetic reeds is rather independent of the material composition and magnetic state, exhibiting a large decrease of the resonance frequency. This effect can be very well explained with a model based on the dynamical response of t...
Silicon spintronics with ferromagnetic tunnel devices
International Nuclear Information System (INIS)
Jansen, R; Sharma, S; Dash, S P; Min, B C
2012-01-01
In silicon spintronics, the unique qualities of ferromagnetic materials are combined with those of silicon, aiming at creating an alternative, energy-efficient information technology in which digital data are represented by the orientation of the electron spin. Here we review the cornerstones of silicon spintronics, namely the creation, detection and manipulation of spin polarization in silicon. Ferromagnetic tunnel contacts are the key elements and provide a robust and viable approach to induce and probe spins in silicon, at room temperature. We describe the basic physics of spin tunneling into silicon, the spin-transport devices, the materials aspects and engineering of the magnetic tunnel contacts, and discuss important quantities such as the magnitude of the spin accumulation and the spin lifetime in the silicon. We highlight key experimental achievements and recent progress in the development of a spin-based information technology. (topical review)
Spin Torques in Systems with Spin Filtering and Spin Orbit Interaction
Ortiz Pauyac, Christian
2016-01-01
ﬁltering. In Chap. 3 we discuss the Rashba torque in ferromagnetic ﬁlms, and in Chap. 4 we study spin Hall eﬀect and spin swapping in ferromagnetic ﬁlms, exploring the nature of spin-orbit torques based on these mechanisms. Conclusions and perspectives
Molecular order and T1-relaxation, cross-relaxation in nitroxide spin labels
Marsh, Derek
2018-05-01
Interpretation of saturation-recovery EPR experiments on nitroxide spin labels whose angular rotation is restricted by the orienting potential of the environment (e.g., membranes) currently concentrates on the influence of rotational rates and not of molecular order. Here, I consider the dependence on molecular ordering of contributions to the rates of electron spin-lattice relaxation and cross relaxation from modulation of N-hyperfine and Zeeman anisotropies. These are determined by the averages and , where θ is the angle between the nitroxide z-axis and the static magnetic field, which in turn depends on the angles that these two directions make with the director of uniaxial ordering. For saturation-recovery EPR at 9 GHz, the recovery rate constant is predicted to decrease with increasing order for the magnetic field oriented parallel to the director, and to increase slightly for the perpendicular field orientation. The latter situation corresponds to the usual experimental protocol and is consistent with the dependence on chain-labelling position in lipid bilayer membranes. An altered dependence on order parameter is predicted for saturation-recovery EPR at high field (94 GHz) that is not entirely consistent with observation. Comparisons with experiment are complicated by contributions from slow-motional components, and an unexplained background recovery rate that most probably is independent of order parameter. In general, this analysis supports the interpretation that recovery rates are determined principally by rotational diffusion rates, but experiments at other spectral positions/field orientations could increase the sensitivity to order parameter.
Quantum spin-glass transition in the two-dimensional electron gas
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 58; Issue 2 ... Spin glasses; quantum phase transition; ferromagnetism; electron gas. ... We argue that a quantum transition involving the destruction of the spin-glass order in an applied in-plane magnetic ﬁeld offers a natural explanation of some features of recent ...
Energy Technology Data Exchange (ETDEWEB)
Loong, Li Ming; Kwon, Jae Hyun; Deorani, Praveen; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, 117576 Singapore (Singapore); Tung Yu, Chris Nga [Department of Physics, The University of York, York YO10 5DD (United Kingdom); Hirohata, Atsufumi, E-mail: atsufumi.hirohata@york.ac.uk [Department of Electronics, The University of York, York YO10 5DD (United Kingdom)
2014-06-09
Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (CFAS) is a Heusler compound that is of interest for spintronics applications, due to its high spin polarization and relatively low Gilbert damping constant. In this study, the behavior of ferromagnetic resonance as a function of temperature was investigated in CFAS, yielding a decreasing trend of damping constant as the temperature was increased from 13 to 300 K. Furthermore, we studied spin waves in CFAS using both frequency domain and time domain techniques, obtaining group velocities and attenuation lengths as high as 26 km/s and 23.3 μm, respectively, at room temperature.
Sound dispersion in a spin-1 Ising system near the second-order phase transition point
International Nuclear Information System (INIS)
Erdem, Ryza; Keskin, Mustafa
2003-01-01
Sound dispersion relation is derived for a spin-1 Ising system and its behaviour near the second-order phase transition point or the critical point is analyzed. The method used is a combination of molecular field approximation and Onsager theory of irreversible thermodynamics. If we assume a linear coupling of sound wave with the order parameter fluctuations in the system, we find that the dispersion which is the relative sound velocity change with frequency behaves as ω 0 ε 0 , where ω is the sound frequency and ε the temperature distance from the critical point. In the ordered region, one also observes a frequency-dependent velocity or dispersion minimum which is shifted from the corresponding attenuation maxima. These phenomena are in good agreement with the calculations of sound velocity in other magnetic systems such as magnetic metals, magnetic insulators, and magnetic semiconductors
International Nuclear Information System (INIS)
Bednarski, Henryk; Spałek, Józef
2014-01-01
We extend the theory of the bound magnetic polaron (BMP) in diluted paramagnetic semiconductors to the situation with a ferromagnetic phase transition. This is achieved by including the classical Gaussian fluctuations of magnetization from the quartic (non-Gaussian) term in the effective Ginzburg–Landau Hamiltonian for the spins. Within this approach, we find a ferromagnetically ordered state within the BMP in the temperature range well above the Curie temperature for the host magnetic semiconductor. Numerical results are compared directly with the recently available experimental data for the ferromagnetic semiconductor GdN. The agreement is excellent, given the simplicity of our model, and is because the polaron size (≃1.4 nm) encompasses a relatively large but finite number (N≈400) of quasiclassical spins S=7/2 coming from Gd 3+ ions. The presence of BMP invalidates the notion of critical temperature and thus makes the incorporation of classical Gaussian fluctuations sufficient to realistically describe the situation. (paper)
Neutron diffraction study of the pressure-induced magnetic ordering in the spin gap system TlCuCl3
International Nuclear Information System (INIS)
Oosawa, Akira; Osakabe, Toyotaka; Kakurai, Kazuhisa; Tanaka, Hidekazu
2003-01-01
Neutron elastic scattering measurements have been performed under a hydrostatic pressure in order to investigate the spin structure of the pressure-induced magnetic ordering in the spin gap system TlCuCl 3 . Below the ordering temperature T N = 16.9 K for the hydrostatic pressure P = 1.48 GPa, magnetic Bragg reflections were observed at reciprocal lattice points Q = (h, 0, l) with integer h and odd l, which are equivalent to those points with the lowest magnetic excitation energy at ambient pressure. This indicates that the spin gap close due to the applied pressure. The spin structure of the pressure-induced magnetic ordered state for P = 1.48 GPa was determined. (author)
Low to High Spin-State Transition Induced by Charge Ordering in Antiferromagnetic YBaCo2O5
International Nuclear Information System (INIS)
Vogt, T.; Woodward, P. M.; Karen, P.; Hunter, B. A.; Henning, P.; Moodenbaugh, A. R.
2000-01-01
The oxygen-deficient double perovskite YBaCo 2 O 5 , containing corner-linked CoO 5 square pyramids as principal building units, undergoes a paramagnetic to antiferromagnetic spin ordering at 330 K. This is accompanied by a tetragonal to orthorhombic distortion. Below 220 K orbital ordering and long-range Co 2+ /Co 3+ charge ordering occur as well as a change in the Co 2+ spin state from low to high spin. This transition is shown to be very sensitive to the oxygen content of the sample. To our knowledge this is the first observation of a spin-state transition induced by long-range orbital and charge ordering. (c) 2000 The American Physical Society
Microscopic studies of nonlocal spin dynamics and spin transport (invited)
Energy Technology Data Exchange (ETDEWEB)
Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris, E-mail: hammel@physics.osu.edu [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States)
2015-05-07
Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.
Microscopic studies of nonlocal spin dynamics and spin transport (invited)
Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris
2015-05-01
Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.
Microscopic studies of nonlocal spin dynamics and spin transport (invited)
International Nuclear Information System (INIS)
Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris
2015-01-01
Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems
Jiang, Yuan
2015-01-01
© The Royal Society of Chemistry 2015. The controlled organization of high-spin complexes into 1D coordination polymers is a challenge in molecular magnetism. In this work, we report a ferromagnetic Mn trimer Mn3(HL)2(CH3OH)6(Br)4·Br·(CH3OH)21 (H2L = 2-[(9H-fluoren-9-yl)amino]propane-1,3-diol) with the ground spin state of ST = 7 that can be assembled into a one-dimensional coordination chain [Mn3(HL)2(CH3OH)2(Br)4(N3)(H2O)·CH3OH]∞2 using azido bridging ligands. Interestingly, the ferromagnetic nature of 1 is well retained in 2. However, due to the negligible magnetic anisotropy in 1, both 1 and 2 do not show slow-relaxation of magnetization, which indicates that during the process of molecular assembly not only the intratrimer magnetic interaction but also the magnetic anisotropy of the trimer can be reserved.
International Nuclear Information System (INIS)
Asulin, I.; Yuli, O.; Millo, O.; Koren, G.
2005-01-01
Full Text:Since the ferromagnetic side of a superconductor-ferromagnet junction is spin polarized, Andreev reflections are suppressed. Consequently, the proximity induced superconductor order parameter in the ferromagnet is expected to decay rapidly, on the order of a nm, the typical coherence length in a ferromagnet. Our scanning tunneling spectroscopy measurements on thin epitaxial (100)YBa 2 Cu 3 O 7+ δ-SrRuO 3 (YBaCuO-SrO) bilayers, where SrO is a ferromagnet, indeed show that on most of the junction area the superconductor order parameter vanishes in the SrO layers thicker than 8 nm. However, we find localized regions, arranged along narrow (< 10 nm) stripes, where the order parameter (superconductor-like gap structure) penetrates the ferromagnet over more than 20 nm. This is attributed to 'Crossed Andreev Reflections,' taking place at domain boundaries, where an electron from one magnetic domain is retro reflected as a hole with opposite spin in an adjacent domain. Our observation may account for the (not abundant) cases where a long-range proximity effect was found in superconductor-ferromagnet proximity systems
Spin freezing in the re-entrant spin glass FeNiMn close to the frustration limit
Energy Technology Data Exchange (ETDEWEB)
Pappas, Catherine [Hahn-Meitner-Institut, Glienickerstr. 100, 14109 Berlin (Germany); Klenke, Jens [Hahn-Meitner-Institut, Glienickerstr. 100, 14109 Berlin (Germany); Hesse, Juergen [Institut fuer Metallphysik und Nukleare Festkoerperphysik, Technische Universitaet Braunschweig, 38106 Braunschweig (Germany); Wagner, Volker [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)]. E-mail: volker.wagner@ptb.de
2007-07-15
In the invar alloy (Fe{sub 0.65}Ni{sub 0.35}){sub 1-} {sub x} Mn {sub x} we measured the magnetic form factor s(Q) and the intermediate scattering function s(Q,t) for a sample close to the critical Mn concentration (x {sub c}=0.139), at which the sample turns to a re-entrant spin glass phase. The aim was to check whether the magnetic behaviour would approach the Q-independent relaxation behaviour of a classical spin glass when x=x {sub c}. The experiment showed a quite similar spin freezing as for a more ferromagnetic sample with x=0.113. The intermediate scattering function and the form factor were determined by paramagnetic NSE. The normalized scattering function S(Q,t)=s(Q,t)/s(Q)=exp[(-{gamma}t) {sup n}] was fitted by stretched exponential decay. As a function of temperature T<200 K the inverse time constant {gamma} showed the change of more than four orders of magnitude from frozen spin glass (T=60 K to T=100 K), where the ferromagnetic phase occurred. In general, the inverse time constant is higher than in the more ferromagnetic sample as the frustration of the spins became larger. In the ferromagnetic phase S(Q,t) depended on 0.3spin diffusive behaviour remained in the re-entrant spin glass down to at least 60 K.
Liu, Xiangyu; Chen, Sanping; Grancha, Thais; Pardo, Emilio; Ke, Hongshan; Yin, Bing; Wei, Qing; Xie, Gang; Gao, Shengli
2014-11-07
A new azido-Cu(II) compound, [Cu(4-fba)(N3)(C2H5OH)] (4-fba = 4-fluorobenzoic acid) (1), has been synthesized and characterized. The X-ray crystal structure analysis demonstrates that only one crystallographically independent Cu(II) ion in the asymmetric unit of 1 exhibits a stretched octahedral geometry in which two azido N atoms and two carboxylic O atoms locate in the equatorial square, while two ethanol O atoms occupy the apical positions, forming a 1D Cu(II) chain with an alternating triple-bridge of EO-azido, syn,syn-carboxylate, and μ2-ethanol. The title compound consists of ferromagnetically interacting ferromagnetic chains, which exhibit ferromagnetic order (T(c) = 7.0 K). The strong ferromagnetic coupling between adjacent Cu(II) ions within each chain is due to the countercomplementarity of the super-exchange pathways, whereas the ferromagnetic interchain interactions--responsible for the long-range magnetic ordering--are most likely due to the presence of coordinated ethanol molecules establishing hydrogen bonds with neighboring chains. DFT calculations have been performed on compound 1 to offer a qualitative theoretical explanation of the magnetic behavior.
Transport through hybrid superconducting/ferromagnetic double-path junction
Energy Technology Data Exchange (ETDEWEB)
Facio, T.J.S. [Departamento de Física e Química, Universidade Estadual Paulista – UNESP, 15385-000, Ilha Solteira, SP (Brazil); Orellana, P.A. [Departamento de Física, Universidad Técnica Federico Santa Maria, Av. Vicuña Mackenna, 3939, Santiago (Chile); Jurelo, A.R. [Departamento de Física, Universidade Estadual de Ponta Grossa – UEPG, 84030-000, Ponta Grossa, PR (Brazil); Figueira, M.S. [Instituto de Física, Universidade Federal Fluminense, 24210-340, Niterói, RJ (Brazil); Cabrera, G.G. [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas – UNICAMP, 13083-859, Campinas, SP (Brazil); Siqueira, E.C., E-mail: ecosta@utfpr.edu.br [Departamento de Física, Universidade Tecnológica Federal do Paraná – UTFPR, 84016-210, Ponta Grossa, PR (Brazil)
2017-02-05
In this paper we study a double-path junction formed by a ferromagnetic and a superconductor lead. The first path connects the superconductor and ferromagnet directly while the second path connects these metals through a quantum dot. The whole system works as an Aharonov–Bohm interferometer allowing the study of the interference between these two paths under the presence of spin imbalance and Andreev bound states. We considered the effect of Fano interference on the electronic transmittance through the quantum dot and observed two regimes of conduction depending on the strength of the direct coupling. For the weak coupling regime, the transmittance presented the usual four resonances due to the Andreev bound states whereas for the strong coupling regime the profile was inverted and resonances became anti-resonances. However, even in the strong coupling regime it was possible to observe a central resonance due to the interference between the Andreev bound states. We have also studied the signatures of Fano interference on the average occupation within the quantum dot. The spin accumulation was analyzed and how it depends on the direct coupling and an external magnetic field applied to the system. The results obtained may be used in a possible experimental implementation of this system in order to probe spin related effects in ferromagnetic superconductor nanostructures. - Highlights: • An Aharonov–Bohm interferometer composed by a quantum-dot coupled to a superconductor and ferromagnetic lead is studied. • The transmittance through the QD is determined by the interplay between Andreev and Fano interference. • Spin accumulation within the quantum dot is studied as a function of bias/gate voltages and an external magnetic flux.
International Nuclear Information System (INIS)
Singh, S. C.; Gopal, R.; Kotnala, R. K.
2015-01-01
Intrinsic Room Temperature Ferromagnetism (RTF) has been observed in undoped/uncapped zinc oxide and titanium dioxide spherical nanoparticles (NPs) obtained by a purely green approach of liquid phase pulsed laser ablation of corresponding metal targets in pure water. Saturation magnetization values observed for zinc oxide (average size, 9 ± 1.2 nm) and titanium dioxide (average size, 4.4 ± 0.3 nm) NPs are 62.37 and 42.17 memu/g, respectively, which are several orders of magnitude larger than those of previous reports. In contrast to the previous works, no postprocessing treatments or surface modification is required to induce ferromagnetism in the case of present communication. The most important result, related to the field of intrinsic ferromagnetism in nonmagnetic materials, is the observation of size dependent ferromagnetism. Degree of ferromagnetism in titanium dioxide increases with the increase in particle size, while it is reverse for zinc oxide. Surface and volume defects play significant roles for the origin of RTF in zinc oxide and titanium dioxide NPs, respectively. Single ionized oxygen and neutral zinc vacancies in zinc oxide and oxygen and neutral/ionized titanium vacancies in titanium dioxide are considered as predominant defect centres responsible for observed ferromagnetism. It is expected that origin of ferromagnetism is a consequence of exchange interactions between localized electron spin moments resulting from point defects
Charge, spin and orbital order in the candidate multiferroic material LuFe2O4
International Nuclear Information System (INIS)
Groot, Joost de
2012-01-01
This thesis is a detailed study of the magnetic, structural and orbital order parameters of the candidate multiferroic material LuFe 2 O 4 . Multiferroic oxides with a strong magnetoelectric coupling are of high interest for potential information technology applications, but they are rare because the traditional mechanism of ferroelectricity is incompatible with magnetism. Consequently, much attention is focused on various unconventional mechanisms of ferroelectricity. Of these, ferroelectricity originating from charge ordering (CO) is particularly intriguing because it potentially combines large electric polarizations with strong magneto-electric coupling. However, examples of oxides where this mechanism occurs are exceedingly rare and none is really well understood. LuFe 2 O 4 is often cited as the prototypical example of CO-based ferroelectricity. In this material, the order of Fe valences has been proposed to render the triangular Fe/O bilayers polar by making one of the two layers rich in Fe 2+ and the other rich in Fe 3+ , allowing for a possible ferroelectric stacking of the individual bilayers. Because of this new mechanism for ferroelectricity, and also because of the high transition temperatures of charge order (T CO ∝320K) and ferro magnetism (T N ∝240 K) LuFe 2 O 4 has recently attracted increasing attention. Although these polar bilayers are generally accepted in the literature for LuFe 2 O 4 , direct proof is lacking. An assumption-free experimental determination of whether or not the CO in the Fe/O bilayers is polar would be crucial, given the dependence of the proposed mechanism of ferroelectricity from CO in LuFe 2 O 4 on polar bilayers. This thesis starts with a detailed characterization of the macroscopic magnetic properties, where growing ferrimagnetic contributions observed in magnetization could be ascribed to increasing oxygen off-stoichiometry. The main focus is on samples exhibiting a sharp magnetic transition to long-range spin order
Spin-fluctuation mechanism of high-Tc superconductivity and order-parameter symmetry
International Nuclear Information System (INIS)
Izyumov, Yurii A
1999-01-01
The notion that electrons in high-T c cuprates pair via antiferromagnetic spin fluctuations is discussed and the symmetry of the superconducting order parameter is analyzed. Three approaches to the problem, one phenomenological (with an experimental dynamic magnetic susceptibility) and two microscopic (involving, respectively, the Hubbard model and the tJ-model) are considered and it is shown that in each case strong-coupling theory leads to a d-wave order parameter with zeros at the Fermi surface. The review then proceeds to consider experimental techniques in which the d-symmetry of the order parameter may manifest itself. These include low-temperature thermodynamic measurements, measurements of the penetration depth and the upper critical field, Josephson junction experiments to obtain the phase of the superconducting order parameter, and various spectroscopic methods. The experimental data suggest that the order parameter in cuprates is d x 2 -y 2 -wave. Ginzburg-Landau theory for a superconductor with a d-wave order parameter is outlined and both an isolated vortex and a vortex lattice are investigated. Finally, some theoretical aspects of the effects of nonmagnetic impurities on a d-wave superconductor are considered. (reviews of topical problems)
Magnetic ordering and spin-reorientation transitions in TbCo3B2
International Nuclear Information System (INIS)
Dubman, Moshe; Caspi, El'ad N.; Ettedgui, Hanania; Keller, Lukas; Melamud, Mordechai; Shaked, Hagai
2005-01-01
The magnetic structure of the compound TbCo 3 B 2 has been studied in the temperature range 1.5 K≤T≤300 K by means of neutron powder diffraction, magnetization, magnetic ac susceptibility, and heat capacity measurements. The compound is of hexagonal symmetry and is paramagnetic at 300 K, undergoes a magnetic Co-Co ordering transition at ∼170 K, and a second magnetic Tb-Tb ordering transition at ∼30 K. The latter induces a spin-reorientation transition, in which the magnetic axis rotates from the c axis toward the basal plane. Below this transition a symmetry decrease (γ magnetostriction) sets in, leading to an orthorhombic distortion of the crystal lattice. The crystal and magnetic structures and interactions and their evolution with temperature are discussed using a microscopic physical model
Spin-glass behavior in the S=1/2 fcc ordered perovskite Sr2CaReO6
International Nuclear Information System (INIS)
Wiebe, C.R.; Greedan, J.E.; Luke, G.M.; Gardner, J.S.
2002-01-01
The ordered perovskite Sr 2 CaReO 6 of monoclinic symmetry [space group P2 1 /n,a=5.7556(3) A,b=5.8534(3) A,c=8.1317(4) A,β=90.276(5) deg. at T=4 K] has been synthesized using standard solid-state chemistry techniques. The difference in the size and charge of the cations induces an ordering of the B site Ca 2+ and Re 6+ ions which leads to a distorted fcc lattice of spin-(1/2) Re 6+ (5d 1 ) moments. dc magnetic susceptibility measurements indicate a maximum at T G ∼14 K and an irreversibility in the field-cooled and zero-field-cooled data at ∼22 K that is believed to be caused by the geometric frustration inherent in the fcc structure. Neutron-scattering measurements confirm the absence of magnetic long-range order, and muon spin relaxation experiments indicate the presence of an abrupt spin freezing at T G . Specific heat measurements reveal a broad anomaly typical of spin glasses and no sharp feature. 65% of the spin entropy is released at low temperatures. The low-temperature data do not show the expected linear temperature dependence, but rather a T 3 relationship, as is observed, typically, for antiferromagnetic spin waves. The material is characterized as an unconventional, essentially disorder-free, spin glass
Spin pumping and inverse spin Hall effects in heavy metal/antiferromagnet/Permalloy trilayers
Saglam, Hilal; Zhang, Wei; Jungfleisch, M. Benjamin; Jiang, Wanjun; Pearson, John E.; Hoffmann, Axel
Recent work shows efficient spin transfer via spin waves in insulating antiferromagnets (AFMs), suggesting that AFMs can play a more active role in the manipulation of ferromagnets. We use spin pumping and inverse spin Hall effect experiments on heavy metal (Pt and W)/AFMs/Py (Ni80Fe20) trilayer structures, to examine the possible spin transfer phenomenon in metallic AFMs, i . e . , FeMn and PdMn. Previous work has studied electronic effects of the spin transport in these materials, yielding short spin diffusion length on the order of 1 nm. However, the work did not examine whether besides diffusive spin transport by the conduction electrons, there are additional spin transport contributions from spin wave excitations. We clearly observe spin transport from the Py spin reservoir to the heavy metal layer through the sandwiched AFMs with thicknesses well above the previously measured spin diffusion lengths, indicating that spin transport by spin waves may lead to non-negligible contributions This work was supported by US DOE, OS, Materials Sciences and Engineering Division. Lithographic patterning was carried out at the CNM, which is supported by DOE, OS under Contract No. DE-AC02-06CH11357.
A qualitative study of spin polarization effect in defect tuned Co/graphene/Co nanostructures
Mandal, Sumit; Saha, Shyamal K.
2014-10-01
Theoretical reports predict that in contact with a ferromagnetic giant spin, spin polarization evolves in defective graphene since defects in graphene act as local spin moments. We have synthesized different Co/graphene/Co nano spin valve like structures tuning the degree of defect applying ultrasonic vibration and characterized them by Raman spectroscopy. Initially with increasing ID/IG ratio in Raman spectra, antiferromagnetic coupling between the Co nanosheets on either sides of graphene enhances leading to betterment in spin transport through graphene. But for highest ID/IG, a totally new phenomenon called antiferro quadrupolar ordering (AFQ) takes place which eventually reduces the spin polarization effect.
Takeda, Yukiharu; Saitoh, Yuji; Okane, Tetsuo; Yamagami, Hiroshi; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Haga, Yoshinori; Ōnuki, Yoshichika
2018-05-01
We have performed soft x-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U 4 d -5 f (N4 ,5) and Co 2 p -3 d (L2 ,3) absorption edges in order to investigate the magnetic properties of the U 5 f and Co 3 d electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co 3 d electrons is unusually large. Through the systematic temperature (T )- and magnetic field (H )-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of H and T (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was clearly observed under 15 K at HM. The value of the HM and its T dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings clearly show that the role of the Co 3 d electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.
Magnetic ordering in tetragonal FeS: Evidence for strong itinerant spin fluctuations
Energy Technology Data Exchange (ETDEWEB)
Kwon, K.D.; Refson, K.; Bone, S.; Qiao, R.; Yang, W.; Liu, Z.; Sposito, G.
2010-11-01
Mackinawite is a naturally occurring layer-type FeS mineral important in biogeochemical cycles and, more recently, in the development of microbial fuel cells. Conflicting results have been published as to the magnetic properties of this mineral, with Moessbauer spectroscopy indicating no magnetic ordering down to 4.2 K but density functional theory (DFT) predicting an antiferromagnetic ground state, similar to the Fe-based high-temperature superconductors with which it is isostructural and for which it is known that magnetism is suppressed by strong itinerant spin fluctuations. We investigated this latter possibility for mackinawite using photoemission spectroscopy, near-edge x-ray absorption fine structure spectroscopy, and DFT computations. Our Fe 3{sub s} core-level photoemission spectrum of mackinawite showed a clear exchange-energy splitting (2.9 eV) consistent with a 1 {micro}{sub B} magnetic moment on the Fe ions, while the Fe L-edge x-ray absorption spectrum indicated rather delocalized Fe 3{sub d} electrons in mackinawite similar to those in Fe metal. Our DFT computations demonstrated that the ground state of mackinawite is single-stripe antiferromagnetic, with an Fe magnetic moment (2.7 {micro}{sub B}) that is significantly larger than the experimental estimate and has a strong dependence on the S height and lattice parameters. All of these trends signal the existence of strong itinerant spin fluctuations. If spin fluctuations prove to be mediators of electron pairing, we conjecture that mackinawite may be one of the simplest Fe-based superconductors.
Magnetic order, magnetic correlations, and spin dynamics in the pyrochlore antiferromagnet Er2Ti2O7
Dalmas de Réotier, P.; Yaouanc, A.; Chapuis, Y.; Curnoe, S. H.; Grenier, B.; Ressouche, E.; Marin, C.; Lago, J.; Baines, C.; Giblin, S. R.
2012-09-01
Er2Ti2O7 is believed to be a realization of an XY antiferromagnet on a frustrated lattice of corner-sharing regular tetrahedra. It is presented as an example of the order-by-disorder mechanism in which fluctuations lift the degeneracy of the ground state, leading to an ordered state. Here we report detailed measurements of the low-temperature magnetic properties of Er2Ti2O7, which displays a second-order phase transition at TN≃1.2 K with coexisting short- and long-range orders. Magnetic susceptibility studies show that there is no spin-glass-like irreversible effect. Heat capacity measurements reveal that the paramagnetic critical exponent is typical of a 3-dimensional XY magnet while the low-temperature specific heat sets an upper limit on the possible spin-gap value and provides an estimate for the spin-wave velocity. Muon spin relaxation measurements show the presence of spin dynamics in the nanosecond time scale down to 21 mK. This time range is intermediate between the shorter time characterizing the spin dynamics in Tb2Sn2O7, which also displays long- and short-range magnetic order, and the time scale typical of conventional magnets. Hence the ground state is characterized by exotic spin dynamics. We determine the parameters of a symmetry-dictated Hamiltonian restricted to the spins in a tetrahedron, by fitting the paramagnetic diffuse neutron scattering intensity for two reciprocal lattice planes. These data are recorded in a temperature region where the assumption that the correlations are limited to nearest neighbors is fair.
High frequency spin torque oscillators with composite free layer spin valve
International Nuclear Information System (INIS)
Natarajan, Kanimozhi; Arumugam, Brinda; Rajamani, Amuda
2016-01-01
We report the oscillations of magnetic spin components in a composite free layer spin valve. The associated Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation is studied by stereographically projecting the spin on to a complex plane and the spin components were found. A fourth order Runge–Kutta numerical integration on LLGS equation also confirms the similar trajectories of the spin components. This study establishes the possibility of a Spin Torque Oscillator in a composite free layer spin valve, where the exchange coupling is ferromagnetic in nature. In-plane and out-of-plane precessional modes of magnetization oscillations were found in zero applied magnetic field and the frequencies of the oscillations were calculated from Fast Fourier Transform of the components of magnetization. Behavior of Power Spectral Density for a range of current density is studied. Finally our analysis shows the occurrence of highest frequency 150 GHz, which is in the second harmonics for the specific choice of system parameters.
High frequency spin torque oscillators with composite free layer spin valve
Energy Technology Data Exchange (ETDEWEB)
Natarajan, Kanimozhi; Arumugam, Brinda; Rajamani, Amuda
2016-07-15
We report the oscillations of magnetic spin components in a composite free layer spin valve. The associated Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation is studied by stereographically projecting the spin on to a complex plane and the spin components were found. A fourth order Runge–Kutta numerical integration on LLGS equation also confirms the similar trajectories of the spin components. This study establishes the possibility of a Spin Torque Oscillator in a composite free layer spin valve, where the exchange coupling is ferromagnetic in nature. In-plane and out-of-plane precessional modes of magnetization oscillations were found in zero applied magnetic field and the frequencies of the oscillations were calculated from Fast Fourier Transform of the components of magnetization. Behavior of Power Spectral Density for a range of current density is studied. Finally our analysis shows the occurrence of highest frequency 150 GHz, which is in the second harmonics for the specific choice of system parameters.
PREFACE: Half Metallic Ferromagnets
Dowben, Peter
2007-08-01
Since its introduction by de Groot and colleagues in the early 1980s [1], the concept of half metallic ferromagnetism has attracted great interest. Idealized, half-metals have only one spin channel for conduction: the spin-polarized band structure exhibits metallic behavior for one spin channel, while the other spin band structure exhibits a gap at the Fermi level. Due to the gap for one spin direction, the density of states at the Fermi level has, theoretically, 100 & spin polarization. This gap in the density of states in one spin at the Fermi level, for example ↓ so N↓ (EF) = 0, also causes the resistance of that channel to go to infinity. At zero or low temperatures, the nonquasiparticle density of states (electron correlation effects), magnons and spin disorder reduce the polarization from the idealized 100 & polarization. At higher temperatures magnon-phonon coupling and irreversible compositional changes affect polarization further. Strategies for assessing and reducing the effects of finite temperatures on the polarization are now gaining attention. The controversies surrounding the polarization stability of half metallic ferromagnets are not, however, limited to the consideration of finite temperature effects alone. While many novel half metallic materials have been predicted, materials fabrication can be challenging. Defects, surface and interface segregation, and structural stability can lead to profound decreases in polarization, but can also suppress long period magnons. There is a 'delicate balance of energies required to obtain half metallic behaviour: to avoid spin flip scattering, tiny adjustments in atomic positions might occur so that a gap opens up in the other spin channel' [2]. When considering 'spintronics' devices, a common alibi for the study of half metallic systems, surfaces and interfaces become important. Free enthalpy differences between the surface and the bulk will lead to spin minority surface and interface states, as well as
2011-11-03
... contained 1,4-butylene glycol (``TMG''). TMG is a chemical that, upon ingestion, metabolizes to gamma... that TMG is harmful if swallowed, and that, upon ingestion, it targets the kidneys and central nervous... containing TMG. 11. On November 2, 2007, Spin Master received a report that a child became ill after...
Energy Technology Data Exchange (ETDEWEB)
Sahoo, R.C.; Paladhi, D.; Nath, T.K., E-mail: tnath@phy.iitkgp.ernet.in
2017-08-15
Highlights: • SG has been observed due to antisite disorder and different magnetic interactions. • The observed EB can be best explained on the basis of uncompensated interface spins. • −30% MR has been observed due to the spin-polarized transport at grain boundaries. - Abstract: Single-phase polycrystalline La{sub 1.5}Ca{sub 0.5}CoMnO{sub 6} double perovskite nanoparticles (∼25 nm) have been synthesized by chemical sol-gel method. We report here the structural, magnetic and transport properties using X-ray diffraction, dc magnetization, ac susceptibility, exchange bias and dc resistivity measurements. The Rietveld refinement of X-ray diffraction pattern reveals that the La{sub 1.5}Ca{sub 0.5}CoMnO{sub 6} (LCCMO) system crystallizes in orthorhombic structure with pbnm space group. Mn and Co ions are not completely ordered on the B sites due to the presence of about 30% antisite-disorder in the system. The ordering of Co{sup 2+} and Mn{sup 4+} gives rise to the ferromagnetism below 145 K. A spin glass like ground state has also been observed near 37.6(4) K, arising mainly due to the presence of competing magnetic interactions and antisite-disorder in the LCCMO nanoparticles. The frequency dependence peak shift of the Ac-susceptibility peak in the glassy state follows the critical slowing down model. The observed memory effect in ac susceptibility data reveals the existence of interacting clusters in a competing magnetic interactions state. The presence of noticeable exchange bias effect can be best explained on the basis of uncompensated interface (ferromagnetic/spin-glass) spins of antisite-disordered LCCMO system. This anti-site disordered nanocompound exhibits semiconducting behavior with variable range hopping kind of electronic conduction mechanism in the temperature range of 200–300 K. We have also observed large negative magnetoresistance (−30% at 100 K and 60 kOe) mainly due to the spin-polarized transport across the grain boundaries.
Srivastava, C M; Gundurao, T K; Nigam, A K; Bahadur, D
2003-01-01
The transport and magnetic studies of a series of compounds having the general formula La sub 0 sub . sub 7 Ca sub 0 sub . sub 3 Mn sub 1 sub - sub x Co sub x O sub 3 (0.1 = 0.25 there is a clear spin transition at low temperature from the high to the low spin state of trivalent cobalt and this leads to change in ferromagnetic (FM) and antiferromagnetic (AFM) phases. For x >= 0.25 there are two transitions for each value of x: the upper one gives the FM and AFM spin arrangement depending upon whether the DE or the SE dominates; the lower one is obtained due to the transition from the high to the low spin state of the trivalent cobalt ion.
Tsafrir, D; Tsafrir, I; Ein-Dor, L; Zuk, O; Notterman, D A; Domany, E
2005-05-15
We introduce a novel unsupervised approach for the organization and visualization of multidimensional data. At the heart of the method is a presentation of the full pairwise distance matrix of the data points, viewed in pseudocolor. The ordering of points is iteratively permuted in search of a linear ordering, which can be used to study embedded shapes. Several examples indicate how the shapes of certain structures in the data (elongated, circular and compact) manifest themselves visually in our permuted distance matrix. It is important to identify the elongated objects since they are often associated with a set of hidden variables, underlying continuous variation in the data. The problem of determining an optimal linear ordering is shown to be NP-Complete, and therefore an iterative search algorithm with O(n3) step-complexity is suggested. By using sorting points into neighborhoods, i.e. SPIN to analyze colon cancer expression data we were able to address the serious problem of sample heterogeneity, which hinders identification of metastasis related genes in our data. Our methodology brings to light the continuous variation of heterogeneity--starting with homogeneous tumor samples and gradually increasing the amount of another tissue. Ordering the samples according to their degree of contamination by unrelated tissue allows the separation of genes associated with irrelevant contamination from those related to cancer progression. Software package will be available for academic users upon request.
Czech Academy of Sciences Publication Activity Database
Kudrnovský, Josef; Drchal, Václav; Turek, Ilja
2015-01-01
Roč. 92, č. 22 (2015), "224421-1"-"224421-8" ISSN 1098-0121 R&D Projects: GA ČR GA15-13436S Institutional support: RVO:68378271 ; RVO:68081723 Keywords : anomalous Hall effect * anisotropis magnetoresistance * first-principles * effect of ordering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014
Graphene spin capacitor for magnetic field sensing
Semenov, Y. G.; Zavada, J. M.; Kim, K. W.
2010-01-01
An analysis of a novel magnetic field sensor based on a graphene spin capacitor is presented. The proposed device consists of graphene nanoribbons on top of an insulator material connected to a ferromagnetic source/drain. The time evolution of spin polarized electrons injected into the capacitor can be used for an accurate determination at room temperature of external magnetic fields. Assuming a spin relaxation time of 100 ns, magnetic fields on the order of $\\sim 10$ mOe may be detected at r...
Effect of quenched disorder on charge-orbital-spin ordering in single-layer manganites
International Nuclear Information System (INIS)
Uchida, Masaya; Mathieu, Roland; He, Jinping; Kaneko, Yoshio; Tokura, Yoshinori; Asamitsu, Atsushi; Kumai, Reiji; Tomioka, Yasuhide; Matsui, Yoshio
2006-01-01
Structural and magnetic properties have been investigated for half-doped single-layer manganites RE 0.5 Sr 1.5 MnO 4 [RE=La, (La, Pr), Pr, Nd, Sm, and Eu]. Analyses of electron diffraction and ac susceptibility measurements have revealed that the long-range charge-orbital ordering (CO-OO) state as observed in La 0.5 Sr 1.5 MnO 4 is suppressed for the other materials: the CO-OO transition temperature, as well as the correlation length decreases with a decrease in the cation size of RE. Such a short-range CO-OO state shows a spin-glass behavior at low temperatures. A new electronic phase diagram is established with quenched disorder as the control parameter. (author)
Shlyk, L.; Strobel, S.; Farmer, B.; De Long, L. E.; Niewa, R.
2018-02-01
Single-crystal x-ray diffraction refinements indicate SrS n2F e4O11 crystallizes in the hexagonal R -type ferrite structure with noncentrosymmetric space group P 63m c and lattice parameters a =5.9541 (2 )Å , c =13.5761 (5 )Å , Z =2 (R (F )=0.034 ). Octahedrally coordinated 2 a [M (1) and M (1a)] and 6 c sites [M (2 )] have random, mixed occupation by Sn and Fe; whereas the tetrahedrally coordinated 2 b sites [Fe(3) and Fe(3a)] are exclusively occupied by Fe, whose displacement from the ideal position with trigonal-bipyramidal coordination causes the loss of inversion symmetry. Our dc and ac magnetization data indicate SrS n2F e4O11 single crystals undergo a ferro- or ferri-magnetic transition below a temperature TC=630 K with very low coercive fields μoHc ⊥=0.27 Oe and μoHc ∥=1.5 Oe at 300 K, for applied field perpendicular and parallel to the c axis, respectively. The value for TC is exceptionally high, and the coercive fields exceptionally low, among the known R-type ferrites. Time-dependent dc magnetization and frequency-dependent ac magnetization data indicate the onset of short-range, spin-glass freezing below Tf=35.8 K , which results from crystallographic disorder of magnetic F e3 + and nonmagnetic S n4 + ions on a frustrated Kagome sublattice. Anomalous ac susceptibility and thermomagnetic relaxation behavior in the short-range-ordered state differs from that of conventional spin glasses. Optical measurements in the ultraviolet to visible frequency range in a diffuse reflectance geometry indicate an overall optical band gap of 0.8 eV, consistent with observed semiconducting properties.
Gani, Terry Z H; Kulik, Heather J
2017-11-14
Accurate predictions of spin-state ordering, reaction energetics, and barrier heights are critical for the computational discovery of open-shell transition-metal (TM) catalysts. Semilocal approximations in density functional theory, such as the generalized gradient approximation (GGA), suffer from delocalization error that causes them to overstabilize strongly bonded states. Descriptions of energetics and bonding are often improved by introducing a fraction of exact exchange (e.g., erroneous low-spin GGA ground states are instead correctly predicted as high-spin with a hybrid functional). The degree of spin-splitting sensitivity to exchange can be understood based on the chemical composition of the complex, but the effect of exchange on reaction energetics within a single spin state is less well-established. Across a number of model iron complexes, we observe strong exchange sensitivities of reaction barriers and energies that are of the same magnitude as those for spin splitting energies. We rationalize trends in both reaction and spin energetics by introducing a measure of delocalization, the bond valence of the metal-ligand bonds in each complex. The bond valence thus represents a simple-to-compute property that unifies understanding of exchange sensitivity for catalytic properties and spin-state ordering in TM complexes. Close agreement of the resulting per-metal-organic-bond sensitivity estimates, together with failure of alternative descriptors demonstrates the utility of the bond valence as a robust descriptor of how differences in metal-ligand delocalization produce differing relative energetics with exchange tuning. Our unified description explains the overall effect of exact exchange tuning on the paradigmatic two-state FeO + /CH 4 reaction that combines challenges of spin-state and reactivity predictions. This new descriptor-sensitivity relationship provides a path to quantifying how predictions in transition-metal complex screening are sensitive to the
Ba2NiOsO6 : A Dirac-Mott insulator with ferromagnetism near 100 K
International Nuclear Information System (INIS)
Feng, Hai L.; Calder, Stuart
2016-01-01
In this study, the ferromagnetic semiconductor Ba 2 NiOsO 6 (T mag ~ 100 K) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m; a = 8.0428 (1) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a > 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (T mag < 180 K), the spin-gapless semiconductor Mn 2 CoAl (T mag ~ 720 K), and the ferromagnetic insulators EuO (T mag ~ 70 K) and Bi 3 Cr 3 O 11 (T mag ~ 220 K). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2 NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.
International Nuclear Information System (INIS)
Yamanoi, Kazuto; Yokotani, Yuki; Kimura, Takashi
2015-01-01
The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated
Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures
Savero Torres, W.; Sierra, J. F.; Benítez, L. A.; Bonell, F.; Costache, M. V.; Valenzuela, S. O.
2017-12-01
Spin Hall effects have surged as promising phenomena for spin logics operations without ferromagnets. However, the magnitude of the detected electric signals at room temperature in metallic systems has been so far underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the signal in monolayer graphene/Pt devices when compared to their fully metallic counterparts. The enhancement stems in part from efficient spin injection and the large spin resistance of graphene but we also observe 100% spin absorption in Pt and find an unusually large effective spin Hall angle of up to 0.15. The large spin-to-charge conversion allows us to characterise spin precession in graphene under the presence of a magnetic field. Furthermore, by developing an analytical model based on the 1D diffusive spin-transport, we demonstrate that the effective spin-relaxation time in graphene can be accurately determined using the (inverse) spin Hall effect as a means of detection. This is a necessary step to gather full understanding of the consequences of spin absorption in spin Hall devices, which is known to suppress effective spin lifetimes in both metallic and graphene systems.
Defect-band mediated ferromagnetism in Gd-doped ZnO thin films
Venkatesh, S.; Franklin, J. B.; Ryan, M. P.; Lee, J.-S.; Ohldag, Hendrik; McLachlan, M. A.; Alford, N. M.; Roqan, Iman S.
2015-01-01
. %) at low oxygen deposition pressure (<25 mTorr) were ferromagnetic at room temperature. Negative magnetoresistance, electric transport properties showed that the ferromagnetic exchange is mediated by a spin-split defect band formed due to oxygen deficiency
Shlyk, Larysa; Strobel, S.; Farmer, B.; De Long, L. E.; Niewa, R.
2018-05-01
Single-crystal x-ray diffraction refinements indicate SrSn2Fe4O11 crystallizes in the hexagonal R-type ferrite structure with non-centrosymmetric space group P63mc and lattice parameters a = 5.9541(2) Å, c = 13.5761(5) Å, Z = 2 (R(F) = 0.034). Octahedrally coordinated sites are randomly occupied by Sn and Fe; whereas tetrahedrally coordinated sites are exclusively occupied by Fe, whose displacement from ideal trigonal-bipyramidal coordination causes the loss of inversion symmetry. DC magnetization data indicate SrSn2Fe4O11 single crystals undergo ferro- or ferri-magnetic order below a transition temperature TC = 630 K with very low coercive fields Hc ⊥ = 0.27 Oe and Hc// = 1.5 Oe at 300 K, for applied fields perpendicular and parallel to the c-axis, respectively. The value for TC is exceptionally high, and the coercive fields exceptionally low, among the known R-type ferrites. Enhanced coercivity and thermomagnetic hysteresis suggest the onset of short-range, spin glass order occurs below Tf = 35 K. Optical measurements indicate a band gap of 0.8 eV, consistent with wide-gap semiconducting behavior and a previously established empirical correlation between the semiconducting gap and TC for R-type ferrites based upon Ru.
Microscopic theoretical study of Raman spectra in charge and spin ordered cuprate systems
International Nuclear Information System (INIS)
Raj, B.K.; Panda, S.K.; Rout, G.C.
2013-01-01
Highlights: • The model calculation treats CDW interaction as pseudogap for cuprates. • The interplay of Raman active CDW-SDW mixed modes are investigated. • Independent CDW and SDW gap values can be determined from experimental data. -- Abstract: Raman scattering is one of the most powerful methods to investigate the electron as well as the phonon excitations in the systems. In this communication, we present a theoretical study of Raman scattering in the normal state of the high-T C systems in the under-doped region displaying the interplay of the spin-density-wave (SDW) and charge-density-wave (CDW) interactions. The SDW order arises from the repulsive Coulomb interaction of electrons, while the CDW order arises due to strong electron–phonon interaction giving rise to Fermi surface instability. We calculate phonon response function in order to examine the possibility of observing the SDW excitation mode in presence of the CDW interaction present in the same conduction band. The Raman scattering intensity is calculated from the imaginary part of the phonon Green’s function assigning an arbitrary spectral width. The spectral density function displays two mixed modes of excitation peaks at energies 2(Δ c ± Δ s ). The evolution of excitation peaks are investigated by varying CDW coupling, SDW coupling and the phonon momentum transfer energy
Microscopic theoretical study of Raman spectra in charge and spin ordered cuprate systems
Energy Technology Data Exchange (ETDEWEB)
Raj, B. K. [Dept. of Physics, Govt. Autonomous College, Angul, Orissa (India); Panda, S. K. [KD Science College, Pochilima, Hinjilicut, 761 101 Ganjam, Orissa (India); Rout, G.C., E-mail: gcr@iopb.res.in [Condensed Matter Physics Group, PG Dept. of Applied Physics and Ballistics, FM University, Balasore 756 019 (India)
2013-09-15
Highlights: • The model calculation treats CDW interaction as pseudogap for cuprates. • The interplay of Raman active CDW-SDW mixed modes are investigated. • Independent CDW and SDW gap values can be determined from experimental data. -- Abstract: Raman scattering is one of the most powerful methods to investigate the electron as well as the phonon excitations in the systems. In this communication, we present a theoretical study of Raman scattering in the normal state of the high-T{sub C} systems in the under-doped region displaying the interplay of the spin-density-wave (SDW) and charge-density-wave (CDW) interactions. The SDW order arises from the repulsive Coulomb interaction of electrons, while the CDW order arises due to strong electron–phonon interaction giving rise to Fermi surface instability. We calculate phonon response function in order to examine the possibility of observing the SDW excitation mode in presence of the CDW interaction present in the same conduction band. The Raman scattering intensity is calculated from the imaginary part of the phonon Green’s function assigning an arbitrary spectral width. The spectral density function displays two mixed modes of excitation peaks at energies 2(Δ{sub c} ± Δ{sub s}). The evolution of excitation peaks are investigated by varying CDW coupling, SDW coupling and the phonon momentum transfer energy.
Spin Filters as High-Performance Spin Polarimeters
International Nuclear Information System (INIS)
Rougemaille, N.; Lampel, G.; Peretti, J.; Drouhin, H.-J.; Lassailly, Y.; Filipe, A.; Wirth, T.; Schuhl, A.
2003-01-01
A spin-dependent transport experiment in which hot electrons pass through a ferromagnetic metal / semiconductor Schottky diode has been performed. A spin-polarized free-electron beam, emitted in vacuum from a GaAs photocathode, is injected into the thin metal layer with an energy between 5 and 1000 eV above to the Fermi level. The transmitted current collected in the semiconductor substrate increases with injection energy because of secondary - electron multiplication. The spin-dependent part of the transmitted current is first constant up to about 100 eV and then increases by 4 orders of magnitude. As an immediate application, the solid-state hybrid structure studied here leads to a very efficient and compact device for spin polarization detection
International Nuclear Information System (INIS)
Stamopoulos, D; Manios, E; Pissas, M
2007-01-01
It is generally believed that superconductivity and magnetism are two antagonistic long-range phenomena. However, as was preliminarily highlighted in Stamopoulos et al (2007 Phys. Rev. B 75 014501), and extensively studied in this work, under specific circumstances these phenomena instead of being detrimental to each other may even become cooperative so that their synergy may promote the superconducting properties of a hybrid structure. Here, we have studied systematically the magnetic and transport behavior of such exchange biased hybrids that are comprised of ferromagnetic (FM) Ni 80 Fe 20 and low-T c superconducting (SC) Nb for the case where the magnetic field is applied parallel to the specimens. Two structures have been studied: FM-SC-FM trilayers (TLs) and FM-SC bilayers (BLs). Detailed magnetization data on the longitudinal and transverse magnetic components are presented for both the normal and superconducting states. These data are compared to systematic transport measurements including I-V characteristics. The comparison of the exchange biased BLs and TLs that are studied here with the plain ones studied in Stamopoulos et al (2007 Phys. Rev. B 75 184504) enable us to reveal an underlying parameter that may falsify the interpretation of the transport properties of relevant FM-SC-FM TLs and FM-SC BLs investigated in the recent literature: the underlying mechanism motivating the extreme magnetoresistance peaks in the TLs relates to the suppression of superconductivity mainly due to the magnetic coupling of the two FM layers as the out-of-plane rotation of their magnetizations takes place across the coercive field where stray fields emerge in their whole surface owing to the multidomain magnetic state that they acquire. The relative in-plane magnetization configuration of the outer FM layers exerts a secondary contribution on the SC interlayer. Since the exchange bias directly controls the in-plane magnetic order it also controls the out-of-plane rotation of
Spin Hall magnetoresistance in antiferromagnet/normal metal bilayers
Manchon, Aurelien
2017-01-01
We investigate the emergence of spin Hall magnetoresistance in a magnetic bilayer composed of a normal metal adjacent to an antiferromagnet. Based on a recently derived drift diffusion equation, we show that the resistance of the bilayer depends on the relative angle between the direction transverse to the current flow and the Néel order parameter. While this effect presents striking similarities with the spin Hall magnetoresistance recently reported in ferromagnetic bilayers, its physical origin is attributed to the anisotropic spin relaxation of itinerant spins in the antiferromagnet.
Nuclear Spin Nanomagnet in an Optically Excited Quantum Dot
Korenev, V. L.
2007-12-01
Linearly polarized light tuned slightly below the optical transition of the negatively charged exciton (trion) in a single quantum dot causes the spontaneous nuclear spin polarization (self-polarization) at a level close to 100%. The effective magnetic field of spin-polarized nuclei shifts the optical transition energy close to resonance with photon energy. The resonantly enhanced Overhauser effect sustains the stability of the nuclear self-polarization even in the absence of spin polarization of the quantum dot electron. As a result the optically selected single quantum dot represents a tiny magnet with the ferromagnetic ordering of nuclear spins—the nuclear spin nanomagnet.
Larbi, T.; Ouni, B.; Gantassi, A.; Doll, K.; Amlouk, M.; Manoubi, T.
2017-12-01
Chromium oxide (Cr2O3) thin films have been synthesized on glass substrates by the spray pyrolysis technique. The structural, morphological and optical properties of the sample have been studied by X-ray diffraction (XRD), Raman spectroscopy, FTIR spectroscopy, scanning probe microscopy and UV-vis spectroscopy respectively. X-ray diffraction results reveal that as deposited film is polycrystalline with a rhombohedral corundum structure and a preferential orientation of the crystallites along the (1 0 4) direction. IR and Raman spectra were recorded in the 100-900 cm-1 range and the observed modes were analysed and assigned to different normal modes of vibration. The direct optical band gap energy value calculated from the transmittance spectra of as-deposited thin film is about 3.38 eV. We employ first principles calculations based on density functional theory (DFT) with the B3LYP hybrid functional and a coupled perturbed Hartree-Fock/Kohn-Sham approach (CPHF/KS). We study the electronic structure, optimum geometry, and IR and Raman spectra of ferromagnetically and antiferromagnetically ordered Cr2O3. The computed results are consistent with the experimental measurements, and provide complete vibrational assignment, for the characterization of Cr2O3 thin film materials which can be used in photocatalysis and gas sensors.
Microscopic coexistence of ferromagnetism and superconductivity in single-crystal UCoGe
International Nuclear Information System (INIS)
Ohta, Tetsuya; Hattori, Taisuke; Ishida, Kenji; Nakai, Yusuke; Osaki, Eisuke; Deguchi, Kazuhiko; Sato, Noriaki K.; Satoh, Isamu
2010-01-01
Unambiguous evidence for the microscopic coexistence of ferromagnetism and superconductivity in UCoGe (T Curie -2.5 K and T SC -0.6 K) is reported from 59 Co nuclear quadrupole resonance (NQR). The 59 Co-NQR signal below 1 K indicates ferromagnetism throughout the sample volume, while the nuclear spin-lattice relaxation rate 1/T 1 in the ferromagnetic (FM) phase decreases below T SC due to the opening of the superconducting (SC) gap. The SC state is found to be inhomogeneous, suggestive of a self-induced vortex state, potentially realizable in a FM superconductor. In addition, the 59 Co-NQR spectrum around T Curie shows that the FM transition in UCoGe possesses a first-order character, which is consistent with the theoretical prediction that the low-temperature FM transition in itinerant magnets is generically of first-order. (author)
Energy Technology Data Exchange (ETDEWEB)
Melnikov, N.B., E-mail: melnikov@cs.msu.su [Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Reser, B.I., E-mail: reser@imp.uran.ru [Miheev Institute of Metal Physics, Ural Branch of Russian Academy of Sciences, Ekaterinburg 620990 (Russian Federation); Paradezhenko, G.V., E-mail: gparadezhenko@cs.msu.su [Lomonosov Moscow State University, Moscow 119991 (Russian Federation)
2016-08-01
To study the spin-density correlations in the ferromagnetic metals above the Curie temperature, we relate the spin correlator and neutron scattering cross-section. In the dynamic spin-fluctuation theory, we obtain explicit expressions for the effective and local magnetic moments and spatial spin-density correlator. Our theoretical results are demonstrated by the example of bcc Fe. The effective and local moments are found in good agreement with results of polarized neutron scattering experiment over a wide temperature range. The calculated short-range order is small (up to 4 Å) and slowly decreases with temperature.
Low temperature properties of spin filter NbN/GdN/NbN Josephson junctions
Energy Technology Data Exchange (ETDEWEB)
Massarotti, D., E-mail: dmassarotti@na.infn.it [Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, via Roma 29, 81031 Aversa (CE) (Italy); CNR-SPIN UOS Napoli, Complesso Universitario di Monte Sant’Angelo, via Cinthia, 80126 Napoli (Italy); Caruso, R. [Dipartimento di Fisica, Università degli Studi di Napoli Federico II, Via Cinthia, 80126 Napoli (Italy); CNR-SPIN UOS Napoli, Complesso Universitario di Monte Sant’Angelo, via Cinthia, 80126 Napoli (Italy); Pal, A. [Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS (United Kingdom); Rotoli, G. [Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, via Roma 29, 81031 Aversa (CE) (Italy); Longobardi, L. [Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, via Roma 29, 81031 Aversa (CE) (Italy); American Physical Society, 1 Research Road, Ridge, New York 11961 (United States); Pepe, G.P. [Dipartimento di Fisica, Università degli Studi di Napoli Federico II, Via Cinthia, 80126 Napoli (Italy); CNR-SPIN UOS Napoli, Complesso Universitario di Monte Sant’Angelo, via Cinthia, 80126 Napoli (Italy); Blamire, M.G. [Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS (United Kingdom); Tafuri, F. [Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università di Napoli, via Roma 29, 81031 Aversa (CE) (Italy); CNR-SPIN UOS Napoli, Complesso Universitario di Monte Sant’Angelo, via Cinthia, 80126 Napoli (Italy)
2017-02-15
Highlights: • We study the phase dynamics of ferromagnetic NbN/GdN/NbN Josephson junctions. • The ferromagnetic insulator GdN barrier generates spin-filtering properties. • Spin filter junctions fall in the underdamped regime. • MQT occurs with the same phenomenology as in conventional Josephson junctions. • Dissipation is studied in a wide range of critical current density values. - Abstract: A ferromagnetic Josephson junction (JJ) represents a special class of hybrid system where different ordered phases meet and generate novel physics. In this work we report on the transport measurements of underdamped ferromagnetic NbN/GdN/NbN JJs at low temperatures. In these junctions the ferromagnetic insulator gadolinium nitride barrier generates spin-filtering properties and a dominant second harmonic component in the current-phase relation. These features make spin filter junctions quite interesting also in terms of fundamental studies on phase dynamics and dissipation. We discuss the fingerprints of spin filter JJs, through complementary transport measurements, and their implications on the phase dynamics, through standard measurements of switching current distributions. NbN/GdN/NbN JJs, where spin filter properties can be controllably tuned along with the critical current density (J{sub c}), turn to be a very relevant term of reference to understand phase dynamics and dissipation in an enlarged class of JJs, not necessarily falling in the standard tunnel limit characterized by low J{sub c} values.
Charge and current orders in the spin-fermion model with overlapping hot spots
Volkov, Pavel A.; Efetov, Konstantin B.
2018-04-01
Experiments carried over the last years on the underdoped cuprates have revealed a variety of symmetry-breaking phenomena in the pseudogap state. Charge-density waves, breaking of C4 rotational symmetry as well as time-reversal symmetry breaking have all been observed in several cuprate families. In this regard, theoretical models where multiple nonsuperconducting orders emerge are of particular interest. We consider the recently introduced [Volkov and Efetov, Phys. Rev. B 93, 085131 (2016), 10.1103/PhysRevB.93.085131] spin-fermion model with overlapping `hot spots' on the Fermi surface. Focusing on the particle-hole instabilities we obtain a rich phase diagram with the chemical potential relative to the dispersion at (0 ,π );(π ,0 ) and the Fermi surface curvature in the antinodal regions being the control parameters. We find evidence for d-wave Pomeranchuk instability, d-form factor charge density waves, as well as commensurate and incommensurate staggered bond current phases similar to the d-density wave state. The current orders are found to be promoted by the curvature. Considering the appropriate parameter range for the hole-doped cuprates, we discuss the relation of our results to the pseudogap state and incommensurate magnetic phases of the cuprates.
Energy Technology Data Exchange (ETDEWEB)
Hauke, Philipp [ICFO-Institut de Ciencies Fotoniques, Meditarranean Technology Park, E-08860 Castelldefels, Barcelona (Spain); Roscilde, Tommaso [Laboratoire de Physique, Ecole Normale Superieure de Lyon, 46 Allee d' Italie, F-69007 Lyon (France); Murg, Valentin; Ignacio Cirac, J; Schmied, Roman, E-mail: Philipp.Hauke@icfo.e [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany)
2010-05-15
We investigate a system of frustrated hardcore bosons, modeled by an XY antiferromagnet on the spatially anisotropic triangular lattice, using Takahashi's modified spin-wave (MSW) theory. In particular, we implement ordering vector optimization on the ordered reference state of MSW theory, which leads to significant improvement of the theory and accounts for quantum corrections to the classically ordered state. The MSW results at zero temperature compare favorably to exact diagonalization (ED) and projected entangled-pair state (PEPS) calculations. The resulting zero-temperature phase diagram includes a one-dimensional (1D) quasi-ordered phase, a 2D Neel ordered phase and a 2D spiraling ordered phase. Strong indications coming from the ED and PEPS calculations, as well as from the breakdown of MSW theory, suggest that the various ordered or quasi-ordered phases are separated by spin-liquid phases with short-range correlations, in analogy to what has been predicted for the Heisenberg model on the same lattice. Within MSW theory, we also explore the finite-temperature phase diagram. In agreement with the Berezinskii-Kosterlitz-Thouless (BKT) theory, we find that zero-temperature long-range-ordered phases turn into quasi-ordered phases (up to a BKT transition temperature), while zero-temperature quasi-ordered phases become short-range correlated at finite temperature. These results show that, despite its simplicity, MSW theory is very well suited to describing ordered and quasi-ordered phases of frustrated XY spins (or, equivalently, of frustrated lattice bosons) both at zero and finite temperatures. While MSW theory, just as other theoretical methods, cannot describe spin-liquid phases, its breakdown provides a fast and reliable method for singling out Hamiltonians that may feature these intriguing quantum phases. We thus suggest a tool for guiding our search for interesting systems whose properties are necessarily studied with a physical quantum simulator
Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates
Bonilla, Manuel; Kolekar, Sadhu; Ma, Yujing; Diaz, Horacio Coy; Kalappattil, Vijaysankar; Das, Raja; Eggers, Tatiana; Gutierrez, Humberto R.; Phan, Manh-Huong; Batzill, Matthias
2018-04-01
Reduced dimensionality and interlayer coupling in van der Waals materials gives rise to fundamentally different electronic1, optical2 and many-body quantum3-5 properties in monolayers compared with the bulk. This layer-dependence permits the discovery of novel material properties in the monolayer regime. Ferromagnetic order in two-dimensional materials is a coveted property that would allow fundamental studies of spin behaviour in low dimensions and enable new spintronics applications6-8. Recent studies have shown that for the bulk-ferromagnetic layered materials CrI3 (ref. 9) and Cr2Ge2Te6 (ref. 10), ferromagnetic order is maintained down to the ultrathin limit at low temperatures. Contrary to these observations, we report the emergence of strong ferromagnetic ordering for monolayer VSe2, a material that is paramagnetic in the bulk11,12. Importantly, the ferromagnetic ordering with a large magnetic moment persists to above room temperature, making VSe2 an attractive material for van der Waals spintronics applications.
Possible evidence for spin-transfer torque induced by spin-triplet supercurrent
Li, Lailai; Zhao, Yuelei; Zhang, Xixiang; Sun, Young
2017-01-01
Cooper pairs in superconductors are normally spin singlet. Nevertheless, recent studies suggest that spin-triplet Cooper pairs can be created at carefully engineered superconductor-ferromagnet interfaces. If Cooper pairs are spin
An order-by-disorder process in the cyclic phase of spin-2 condensate with a weak magnetic field
International Nuclear Information System (INIS)
Zheng, Gong-Ping; Xu, Lei-Kuan; Qin, Shuai-Feng; Jian, Wen-Tian; Liang, J.-Q.
2013-01-01
We present in this paper a model study on the “order-by-disorder” process in the cyclic phase of spin-2 condensate, which forms a family of incommensurable, spiral degenerate ground states. On the basis of the ordering mechanism of entropic splitting, it is demonstrated that the energy corrections resulting from quantum fluctuations of disorder lift the accidental degeneracy of the cyclic configurations and thus lead to an eventual spiral order called the cyclic order. The order-by-disorder phenomenon is then realized even if the magnetic field exists. Finally, we show that our theoretic observations can be verified experimentally by direct detection of the cyclic order in the 87 Rb condensate of a spin-2 manifold with a weak magnetic field. -- Highlights: •A model for the order-by-disorder process in the cyclic phase of spin-2 condensate is presented. •The second-order quantum fluctuations of the mean-field states are studied. •The energy corrections lift the accidental degeneracy of the cyclic configurations. •The order-by-disorder phenomenon is realized even if a magnetic field exists. •The theoretic observations can be verified experimentally for 87 Rb condensate
Effects of electric field and magnetic induction on spin injection into organic semiconductors
International Nuclear Information System (INIS)
Wang, Y.M.; Ren, J.F.; Yuan, X.B.; Dou, Z.T.; Hu, G.C.
2011-01-01
Spin-polarized injection and transport into ferromagnetic/organic semiconductor structure are studied theoretically in the presence of the external electric field and magnetic induction. Based on the spin-drift-diffusion theory and Ohm's law, we obtain the charge current polarization, which takes into account the special carriers of organic semiconductors. From the calculation, it is found that the current spin polarization is enhanced by several orders of magnitude by tuning the magnetic induction and electric fields. To get an apparent current spin polarization, the effects of spin-depended interfacial resistances and the special carriers in the organic semiconductor, which are polarons and bipolarons, are also discussed. -- Research highlights: → Current polarization in ferromagnetic/organic semiconductor structure is obtained. → Calculations are based on spin-drift-diffusion theory and Ohm's law. → Current polarization is enhanced by tuning magnetic induction and electric fields. → Effects of interfacial resistances and the special carriers are also discussed.
Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb₂Ti₂O₇.
Chang, Lieh-Jeng; Onoda, Shigeki; Su, Yixi; Kao, Ying-Jer; Tsuei, Ku-Ding; Yasui, Yukio; Kakurai, Kazuhisa; Lees, Martin Richard
2012-01-01
In a class of frustrated magnets known as spin ice, magnetic monopoles emerge as classical defects and interact via the magnetic Coulomb law. With quantum-mechanical interactions, these magnetic charges are carried by fractionalized bosonic quasi-particles, spinons, which can undergo Bose-Einstein condensation through a first-order transition via the Higgs mechanism. Here, we report evidence of a Higgs transition from a magnetic Coulomb liquid to a ferromagnet in single-crystal Yb(2)Ti(2)O(7). Polarized neutron scattering experiments show that the diffuse [111]-rod scattering and pinch-point features, which develop on cooling are suddenly suppressed below T(C)~0.21 K, where magnetic Bragg peaks and a full depolarization of the neutron spins are observed with thermal hysteresis, indicating a first-order ferromagnetic transition. Our results are explained on the basis of a quantum spin-ice model, whose high-temperature phase is effectively described as a magnetic Coulomb liquid, whereas the ground state shows a nearly collinear ferromagnetism with gapped spin excitations.
Magnetic excitations in amorphous ferromagnets
International Nuclear Information System (INIS)
Continentino, M.A.
The propagation of magnetic excitations in amorphous ferromagnets is studied from the point of view of the theory of random frequency modulation. It is shown that the spin waves in the hydrodynamic limit are well described by perturbation theory while the roton-like magnetic excitations with wavevector about the peak in the structure factor are not. A criterion of validity of perturbation theory is found which is identical to a narrowing condition in magnetic resonance. (author) [pt
Quantifying Spin Hall Angles from Spin Pumping : Experiments and Theory
Mosendz, O.; Pearson, J.E.; Fradin, F.Y.; Bauer, G.E.W.; Bader, S.D.; Hoffmann, A.
2010-01-01
Spin Hall effects intermix spin and charge currents even in nonmagnetic materials and, therefore, ultimately may allow the use of spin transport without the need for ferromagnets. We show how spin Hall effects can be quantified by integrating Ni80Fe20|normal metal (N) bilayers into a coplanar
Ferromagnet / superconductor oxide superlattices
Santamaria, Jacobo
2006-03-01
The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa2Cu3O7 (YBCO) and La0.7Ca0.3MnO3 (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Peña^1, Z. Sefrioui^1, J. Garcia-Barriocanal^1, C. Visani^1, D. Arias^1, C. Leon^1 , N. Nemes^2, M. Garcia Hernandez^2, S. G. E. te Velthuis^3, A. Hoffmann^3, M. Varela^4, S. J. Pennycook^4. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic
Heterogeneous bilayer films NiFe (Fe)-Dy: magnetic circular dichroism and Dy spin ordering
Energy Technology Data Exchange (ETDEWEB)
Markov, V.V. E-mail: ise@iph.krasn.ruise@iph.krasnoyarsk.su; Kesler, V.G.; Khudyakov, A.E.; Edelman, I.S.; Bondarenko, G.V
2001-08-01
Results of the magnetic circular dichroism (MCD) and Auger electron spectroscopy (AES) investigations in the 3d transition metal-Dy bi-layer films are presented. It is shown that even at room temperature the Dy layer makes a contribution to MCD of the bi-layer film, which corresponds to the MCD value in the single-layer Dy film measured below T{sub C}=85 K. According to the AES data there is no sharp interface between 3d and Dy layers in these films. Some amount of Ni and Fe atoms is dispersed in the Dy layer and some amount of Dy atoms is dispersed in the 3d layer. The comparison of the MCD and AES data allows one to suppose the Dy layer in the bi-layer films to be magnetically ordered at room temperature under the influence of the 3d-layer spin system. The influence spreads to long distances inside Dy layer through the 3d-ions dispersed in it.
Heterogeneous bilayer films NiFe (Fe)-Dy: magnetic circular dichroism and Dy spin ordering
International Nuclear Information System (INIS)
Markov, V.V.; Kesler, V.G.; Khudyakov, A.E.; Edelman, I.S.; Bondarenko, G.V.
2001-01-01
Results of the magnetic circular dichroism (MCD) and Auger electron spectroscopy (AES) investigations in the 3d transition metal-Dy bi-layer films are presented. It is shown that even at room temperature the Dy layer makes a contribution to MCD of the bi-layer film, which corresponds to the MCD value in the single-layer Dy film measured below T C =85 K. According to the AES data there is no sharp interface between 3d and Dy layers in these films. Some amount of Ni and Fe atoms is dispersed in the Dy layer and some amount of Dy atoms is dispersed in the 3d layer. The comparison of the MCD and AES data allows one to suppose the Dy layer in the bi-layer films to be magnetically ordered at room temperature under the influence of the 3d-layer spin system. The influence spreads to long distances inside Dy layer through the 3d-ions dispersed in it
Blue shift of the plasma edge of a ferromagnetic semimetal
International Nuclear Information System (INIS)
Wachter, P.; Bommeli, F.; Degiorgi, L.; Burlet, P.; Bourdarot, F.
1998-01-01
Full text: In general rare earth pnictides are semimetals and antiferromagnets. Only some nitrides are quoted as ferri or ferromagnetic. However, it has been shown when prepared stoichiometrically and in single crystalline form the free carrier concentration is only in the percent per cation range, thus they are typical low carrier systems. Under these conditions the nitrides are all canted antiferromagnets and metamagnets, i.e. they show Abstract only. The full magnetic moment only with an applied magnetic field. However, when prepared as single crystals but with excess of the rare earths they become spontaneously ferromagnets due to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in addition to the superexchange mechanisms. On such ferromagnetic compositions of TbN and GdN and also in EuB 6 a new magneto-optic effect has been discovered, a spontaneous blue shift of the plasma edge upon magnetic order. The plasma edge is measured with optical reflectivity and it depends on the free carrier concentration. In other words the free carrier concentration increases upon ferromagnetic order. This effect can be understood with the spontaneous exchange splitting of mainly the 5d conduction band, lowering the bottom of the spin up 5d band, thus increasing the indirect overlap with the valence p band of the anions and thus enhancing the carrier concentration. This blue shift of the plasma edge follows a spin correlation function. An external magnetic field applied near TC enhances the blue shift since the magnetization is not yet saturated. For T→0 a magnetic field has no effect since the magnetization is spontaneously saturated
Magnetization Reversal through Soliton in a Site-Dependent Weak Ferromagnet
International Nuclear Information System (INIS)
Kavitha, L.; Sathishkumar, P.; Saravanan, M.; Gopi, D.
2010-06-01
Switching the magnetization of a magnetic bit through flipping of soliton offers the possibility of developing a new innovative approach for data storage technologies. The spin dynamics of a site-dependent ferromagnet with antisymmetric Dzyaloshinskii-Moriya interaction is governed by a generalized inhomogeneous higher order nonlinear Schroedinger equation. We demonstrate the magnetization reversal through flipping of soliton in the ferromagnetic medium by solving the two coupled evolution equations for the velocity and amplitude of the soliton using the fourth order Runge-Kutta method numerically. We propose a new approach to induce the flipping behaviour of soliton in the presence of inhomogeneity by tuning the parameter associated with Dzyaloshinskii-Moriya interaction which causes the soliton to move with constant velocity and amplitude along the spin lattice. (author)
International Nuclear Information System (INIS)
An Xingtao; Liu Jianjun
2008-01-01
Based on the scattering approach, we investigate transport properties of electrons in a one-dimensional waveguide that contains a ferromagnetic/semiconductor/ferromagnetic heterojunction and tunnel barriers in the presence of Rashba and Dresselhaus spin-orbit interactions. We simultaneously consider significant quantum size effects, quantum coherence, Rashba and Dresselhaus spin-orbit interactions and noncollinear magnetizations. It is found that the tunnel barrier plays a decisive role in the transmission coefficient and shot noise of the ballistic spin electron transport through the heterojunction. When the small tunnel barriers are considered, the transport properties of electrons are quite different from those without tunnel barriers