共查询到20条相似文献,搜索用时 15 毫秒
1.
Joonyeon Chang Hyunjung Yi Hyun Cheol Koo V.L. Mironov B.A. Gribkov A.A. Fraerman S.A. Gusev S.N. Vdovichev 《Journal of magnetism and magnetic materials》2007
We investigated remagnetization processes in ferromagnetic nanoparticles under inhomogeneous magnetic field induced by the tip of magnetic force microscope (MFM) in both theoretical and empirical ways. Systematic MFM observations were carried out on arrays of submicron-sized elliptical ferromagnetic particles of Co and FeCr with different sizes and periods. It clearly reveals the distribution of remanent magnetization and processes of local remagnetization of individual ferromagnetic particles. Modeling of remagnetization processes in ferromagnetic nanoparticles under magnetic field induced by MFM probe was performed on the base of Landau–Lifshitz–Gilbert equation for magnetization. MFM-induced inhomogeneous magnetic field is very effective to control the magnetic state of individual ferromagnetic nanoparticles as well as to create different distribution of magnetic field in array of ferromagnetic nanoparticles. 相似文献
2.
Heterostructures that integrate conventional semiconductors with ferromagnetic semiconductors and ferromagnetic metals are important for developing a framework for semiconductor spintronics. We describe recent efforts to study ‘hybrid’ ferromagnetic/semiconductor heterostructures that combine conventional III-V and II-VI semiconductors with the ferromagnetic semiconductor (Ga,Mn)As and the ferromagnetic metal MnAs. We focus on the characteristics of two novel classes of heterostructures: (a) (Ga,Mn)As/AlAs/MnAs magnetic tunnel junctions (MTJs) that provide an all-electrical scheme for probing spin injection from metals into GaAs and (b) n-ZnSe/(Ga,Mn)As heterojunction diodes that surprisingly exhibit a magnetically-driven photoconductivity. 相似文献
3.
A. Yu. Zyuzin 《JETP Letters》2002,76(8):495-497
We consider a mechamism of exchange coupling based on interaction between electrons in a nonmagnetic layer. Depending on the ratio of inverse time of diffusion of electrons between ferromagnetic layers and ferromagnetic splitting of conducting electrons, this mechanism describes the transition from ferromagnetic to noncollinear ordering of magnetizations of ferromagnetic layers. 相似文献
4.
采用铁磁共振方法,研究了铁磁/反铁磁双层膜系统中,因交换耦合以及磁晶各向异性而产生的有效各向异性场.结果表明:被测系统有无交换偏置场以及其正负号性质等均能在共振谱中得到辨析.结果还显示:沿着不同结晶方向施加外磁场,共振场的行为与磁晶各向异性以及铁磁/反铁磁交换耦合作用而诱发的单向各向异性等密切相关.将共振频率的变化看成外磁场(包括其方向和大小)的函数,研究得到了单向各向异性,立方各向异性等对共振频率的影响,并同实验结果做了很好的比较.
关键词:
铁磁/反铁磁双层膜
交换耦合
铁磁共振
单向各向异性 相似文献
5.
The magneto-volume effect is discussed in terms of the recent unified theory of ferromagnetic metals based on general spin fluctuations. Explanations are given for the large negative thermal expansion observed in weakly ferromagnetic metals and for the invar effect in some f.c.c. alloys. Large thermal expansion in nearly ferromagnetic metals is also pointed out. 相似文献
6.
M. Wilczyński 《Journal of magnetism and magnetic materials》2011,323(11):1529-1536
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. 相似文献
7.
Using the recursion method, we study the phase transitions of the
Ashkin-Teller model on the Bethe lattice, restricting ourselves to the case of ferromagnetic interactions. The isotropic Ashkin-Teller model and the
anisotropic one are respectively investigated, and exact expressions for the free energy and the magnetization are obtained. It can be found that each of the three varieties of phase diagrams, for the anisotropic Ashkin-Teller model, consists of four phases, i.e., the fully disordered paramagnetic
phase Para, the fully ordered ferromagnetic phase Ferro, and two
partially ordered ferromagnetic phases 〈σ〉and 〈σs〉, while the phase diagram, for the
isotropic Ashkin-Teller model, contains three phases, i.e., the fully
disordered paramagnetic phase Para, the fully ordered ferromagnetic phase
Baxter Phase, and the partially ordered ferromagnetic phase 〈σs〉. 相似文献
8.
K. O. Khutsishvili N. P. Fokina 《Journal of Experimental and Theoretical Physics》2009,109(5):794-804
It is shown that antiferromagnetic ordering in doped manganites with strong double-exchange interaction is transformed into
ferromagnetic canted ordering with residual antiferromagnetic behavior in the basal plane as a result of hopping of mobile
electron. The canting angle between the core magnetiztions is controlled by the competition of the Heisenberg antiferromagnetic
exchange and double exchange. The temperatures of the paramagnet-antiferromagnet and paramagnet-canted ferromagnetic phase
transitions are calculated. The results on the dependence of the magnetization in the canted phase and critical temperatures
on the doping degree are in qualitative agreement with experiment. The form of uniform oscillations of core magnetiztions
in the canted ferromagnetic phase of a doped manganite sample with hopping conduction is analyzed with and without allowance
for relaxation of mobile electrons to the lattice. We propose a mechanism for the ferromagnetic resonance broadening and its
resonance frequency shift in a ferromagnetic conducting sample (hopping conduction) of doped manganite due to double exchange.
The resonance frequency shift and the ferromagnetic resonance damping constant (linewidth) are calculated in this model. In
contrast to other relaxation mechanisms, the model is based on the fact that mobile electrons rapidly relax to the lattice
(over a time on the order of the precession period). 相似文献
9.
通过求解磁性d波超导中的能隙和磁交换能的自洽方程, 研究磁性d波超导/铁磁/磁性d波超导结中的约瑟夫森电流. 计算结果表明: 1)临界电流随中间的铁磁层厚度呈现出两种不同周期的振荡混合, 通过增强铁磁层中的磁交换能q0和铁磁/磁性d波超导界面处的势垒强度z0, 短周期分量可从长周期中分离出来, 反之, 通过降低q0和z0, 长周期分量可从短周期中分离出来; 2)在两边磁性d波超导的磁化方向取平行时, 在取一些特定的铁磁层厚度下, 磁性d波超导中的磁交换能可增强系统的临界电流.
关键词:
磁性d波超导体
铁磁体
约瑟夫森电流 相似文献
10.
We study spin dependent transport through a magnetic bilayer graphene nanojunction configured as a two-dimensional normal/ferromagnetic/normal structure where the gate voltage is applied on the layers of ferromagnetic graphene. Based on the four-band Hamiltonian, conductance is calculated by using the Landauer-Buttiker formula at zero temperature. For a parallel configuration of the ferromagnetic layers of bilayer graphene, the energy band structure is metallic and spin polarization reaches its maximum value close to the resonant states, while for an antiparallel configuration the nanojunction behaves as a semiconductor and there is no spin filtering. As a result, a huge magnetoresistance is achievable by altering the configurations of ferromagnetic graphene around the band gap. 相似文献
11.
《Photonics and Nanostructures》2014,12(5):398-418
In this paper a theoretical study of the band structure of collective modes of binary ferromagnetic systems formed by a submicrometric periodic array of cylindrical cobalt nanodots partially or completely embedded into a permalloy ferromagnetic film is performed. The binary ferromagnetic systems studied are two-dimensional periodic, but they can be regarded as three-dimensional, since the magnetization is non uniform also along the z direction due to the contrast between the saturation magnetizations of the two ferromagnetic materials along the thickness. The dynamical matrix method, a finite-difference micromagnetic approach, formulated for studying the dynamics in one-component periodic ferromagnetic systems is generalized to ferromagnetic systems composed by F ferromagnetic materials. It is then applied to investigate the spin dynamics in four periodic binary ferromagnetic systems differing each other for the volume of cobalt dots and for the relative position of cobalt dots within the primitive cell. The dispersion curves of the most representative frequency modes are calculated for each system for an in-plane applied magnetic field perpendicular to the Bloch wave vector. The dependence of the dispersion curves on the cobalt quantity and position is discussed in terms of distribution of effective “surface magnetic charges” at the interface between the two ferromagnetic materials. The metamaterial properties in the propagative regime are also studied (1) by introducing an effective magnetization and effective “surface magnetic charges” (2) by describing the metamaterial wave dispersion of the most representative mode in each system within an effective medium approximation and in the dipole-exchange regime. It is also shown that the interchange between cobalt and permalloy does not necessarily lead to an interchange of the corresponding mode dispersion. Analogously to the case of electromagnetic waves in two-dimensional photonic crystals, the degree of localization of the localized collective modes is expressed in terms of an energy concentration factor. 相似文献
12.
With the help of the generalized static replica symmetric spin-glass theory, a quantum Heisenberg S = 112 spin-glass model with the infinite-ranged random Dzyaloshinskii-Moriya (DM) interactions and ferromagnetic coupling is investigated. The dependence of the local susceptibility and the corresponding order parameters on temperature is calculated numerically for different ferromagnetic interactions and fixed anisotropy It has been found that the local susceptibility exhibits double-cusp features for different ferromagnetic coupfings (Jo). In addition, the dependence of the spontaneous moment on temperature is studied numerically, too. 相似文献
13.
A. Kotani S. Takahashi M. Tachiki H. Matsumoto H. Umezawa 《Solid State Communications》1981,37(8):619-624
Anomalous magnetic and superconducting behavior which originates from the electromagnetic interaction between the persistent current and the rare earth magnetic moments is theoretically predicted in thin films of ferromagnetic superconductors. It is shown that the ferromagnetic ordering can coexist with superconductivity for films of thickness smaller than the London penetration depth. The ferromagnetic phase transition is of the second order and its critical temperature depends on the thickness of the film. 相似文献
14.
The possible ferromagnetic ground state of π-conjugated alternant hydrocarbon chains with unequal number of atoms on two sublattices is studied by the peierls-Hubbard model. Allowing for full lattice relaxation, a set of self-consistent iterative equations are established to study this system. The stabilities of the possible ferromagnetic ground states with respect to two kinds of unsymmetric site energies are also studied. We find that the ground state of the system is a stable ferromagnetic state as a result of the topological structure of the network and the electron-electron interaction. And the unsymmetric site energies, induced by substitutions, will severely weaken the stability of the ferromagnetic ground state. 相似文献
15.
We present a new scenario for the breakdown of ferromagnetic order in a two-dimensional quantum magnet with competing ferromagnetic and antiferromagnetic interactions. In this, dynamical effects lead to the formation of two-magnon bound states, which undergo Bose-Einstein condensation, giving rise to bond-centered nematic order. This scenario is explored in some detail for an extended Heisenberg model on a square lattice. In particular, we present numerical evidence confirming the existence of a state with d-wave nematic correlations but no long-range magnetic order, lying between the saturated ferromagnetic and collinear antiferromagnetic phases of the ferromagnetic model J1-J2. We argue by continuity of spectra that this phase is also present in a model with 4-spin cyclic exchange. 相似文献
16.
采用铁磁共振理论研究了自旋阀体系中交换各向异性场和两铁磁薄膜厚度对体系性质的影响,得到系统色散关系的解析表达式.研究表明:体系中存在的交换各向异性场H_E对声学模和光学模的共振场均有影响(其对声学模的影响较大).而且还发现声学模共振场随A,B层铁磁薄膜厚度的变化关系依赖于系统中交换各项异性场的强弱;相反,光学模共振场随两铁磁层厚度的增加始终增强. 相似文献
17.
铁磁和反铁磁双层膜中铁磁共振的研究 总被引:2,自引:0,他引:2
采用微磁学理论研究了铁磁/反铁磁双层膜中的铁磁共振现象.本模型将铁磁薄层抽象为一个单晶,具有立方磁晶各向异性和单轴磁晶各向异性,而反铁磁层视为厚度趋近于半无穷,且只有单轴磁晶各向异性.推导出了该系统的铁磁共振频率和频率谱宽度的解析式.数值计算表明,铁磁共振模式分两支,取决于立方磁晶各向异性.而界面的交换耦合,是磁易轴具有单向性的起因. 相似文献
18.
Y. -S. Xiong L. Yi K. -L. Yao Z. -G. Li 《Zeitschrift für Physik B Condensed Matter》1994,96(2):261-265
By means of the generalized static replica symmetric spin glass theory, a quantum HeisenbergS=1/2 spin glass model with the infinite-ranged random Dzyaloshinskii-Moriya (DM) interaction and ferromagnetic coupling is investigated. The dependence of entropy, specific heat, susceptibility and the corresponding order parameters on temperature is studied numerically for different ferromagnetic interactions and fixed anisotropy. Two spin glass phases has been found including transverse and mixed spin glass phases. It has been shown that the local susceptibility exhibits double-cusp features for different ferromagnetic coupling (J
0). Phase transition poins are found in the specific heat-temperature plane at various ferromagnetic coupling values. Additionally, the dependence of the spontaneous moment on temperature is calculated. 相似文献
19.
杨森 鲍慧新 周超 王宇 任晓兵 宋晓平 Yoshitaka Matsushita Yoshio Katsuya Masahiko Tanaka Keisuke Kobayashi 《中国物理 B》2013,(4):1-16
Ferromagnetic transition has generally been considered to involve only an ordering of magnetic moment with no change in the host crystal structure or symmetry, as evidenced by a wealth of crystal structure data from conventional X-ray diffractometry (XRD). However, the existence of magnetostriction in all known ferromagnetic systems indicates that the magnetic moment is coupled to the crystal lattice; hence there is a possibility that magnetic ordering may cause a change in crystal structure. With the development of high-resolution synchrotron XRD, more and more magnetic transitions have been found to be accompanied by simultaneous structural changes. In this article, we review our recent progress in understand- ing the structural change at a ferromagnetic transition, including synchrotron XRD evidence of structural changes at the ferromagnetic transition, a phenomenological theory of crystal structure changes accompanying ferromagnetic transitions, new insight into magnetic morphotropic phase boundaries (MPB) and so on. Two intriguing implications of non-centric symmetry in the ferromagnetic phase and the first-order nature of ferromagnetic transition are also discussed here. In short, this review is intended to give a self-consistent and logical account of structural change occurring simultaneously with a ferromagnetic transition, which may provide new insight for developing highly magneto-responsive materials. 相似文献
20.
The magnetic susceptibility of neutron matter was calculated by means of Owen's LOCV method. The results showed that a transition to a ferromagnetic state can exist for HJ, IY and M-S potentials, but there is no transition for Reid soft-core potential .By analyses, we concluded that the ferromagnetic state is a possible origin of strong magnetic field within the neutron star. We also considered an influence of the ferromagnetic state on the mass, radius and moment of inertia of the neutron star.Finally we discussed the effect of magnetization on physical state in the neutron star. 相似文献