The Curie temperature of a spin-one Heisenberg ferromagnet with biquadratic exchange and uniaxial anisotropy

With the pair model approximation, the Curie temperature of a spin-one Heisenberg ferromagnet with biquadratic exchange interaction J' and uniaxial anisotropy term D is calculated for both positive as well as negative values of J' and D.     

Critical spin dynamics in the ordered phase of a uniaxial ferromagnet

We report the results of a study of the critical hydrodynamics of an easy axis ferromagnet with weak anisotropic exchange. Self-consistent equations based on the mode coupling hypothesis are solved for the decay rates of the longitudinal and transverse spin fluctuations in the region below the Curie point.     

On the curie temperature of an anisotropic Heisenberg-Ising ferromagnet with crystal-field anisotropy

The effect of crystal-field anisotropy on the Curie temperature is studied in an S = 1 anisotropic Heisenberg-Ising ferromagnet. The Green function technique with a Callen-type approximation is used. The results show that, when the correlations between spins of nearest neighbouring sites are taken into account, the change in the Curie temperature with crystal-field anisotropy is not so great as that calculated in the random phase approximation.     

具有Dzyaloshinskii-Moriya相互作用的一维随机量子XY模型中的纠缠特性

研究了一维随机量子XY自旋链中中心两量子位的纠缠特性,在该系统中引入了自旋间的交换耦合杂质、磁杂质和Dzyaloshinskii-Moriya相互作用,并且杂质满足高斯分布关系.通过数值计算,求出了自旋的关联函数和平均磁化强度,给出了Concurrence的解析表达式.结果表明：高斯分布和Dzyaloshinskii-Moriya相互作用对两量子位的纠缠有重要的影响,选择合适的交换耦合、外界磁场和Dzyaloshinskii-Moriya相互作用参数,可以控制和提高中心两量子位的纠缠. 关键词： 纠缠 XY模型')" href="#">随机量子XY模型 高斯分布 Dzyaloshinskii-Moriya相互作用     

Current controlled spin reversal of nanomagnets with giant uniaxial anisotropy

Since a giant magnetic anisotropy of 9 meV per atom has been realized on a Pt surface, we use the kinetic Monte Carlo method to study the spin dynamics of a nanomagnet that is made by putting a line of such adatoms on a thin metallic strip so that the fixed spins are coupled very weakly and a spin-polarized current can be injected into the strip. There is a magnetization hysteresis versus the current because of the giant anisotropy. The hysteresis loop is diminished exponentially with the temperature increasing. The magnetization can be controlled by injecting a spin-polarized current.     

Effects of the uniaxial anisotropy on the Curie temperature of the anisotropic Heisenberg ferromagnet with mixed spins S = 12 and S = 1

With the use of the pair model approximation, the effects of the D-term on the Curie temperature of the anisotropic Heisenberg ferromagnet with mixed spins $\text{S =}\text{1}\text{2}$ have been investigated and shown to be significant for D > 0.     

Effect of a random crystalline field on the Curie temperature of an anisotropic crystalline ferromagnet

We examine how substitution of nonmagnetic atoms of one species by another that leads to the emergence of a random crystalline field affects the Curie temperature T _C of an anisotropic crystalline ferromagnet. We study the case of low concentrations, in which individual substitutional impurities create isolated clusters of perturbed magnetic ions with additional easy-or hard-magnetization axes. Finally, we analyze the various sign relations among the parameters D and d of regular and impurity second-order anisotropies with Kramers (J=1) and non-Kramers (J=3/2) angular momenta, and show that usually the effects of a random crystalline field lower the Curie temperature as the concentration of the nonmagnetic impurity atoms increases. Zh. éksp. Teor. Fiz. 111, 127–143 (January 1997)     

Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbouring interactions

By using the method of density-matrix renormalization-group to solve the different spin spin correlation functions, the nearest-neighbouring entanglement （NNE） and the next-nearest-neighbouring entanglement （NNNE） of one-dimensional alternating Heisenberg XY spin chain are investigated in the presence of alternating the-nearestneighbouring interaction of exchange couplings, external magnetic fields and the next-nearest neighbouring interaction. For a dimerised ferromagnetic spin chain, the NNNE appears only above a critical dimerized interaction, meanwhile, the dimerized interaction a effects a quantum phase transition point and improves the NNNE to a large extent. We also study the effect of ferromagnetic or antiferromagnetic next-nearest neighbouring （NNN） interaction on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction increases and shrinks the NNE below and above a critical frustrated interaction respectively, while the antiferromagnetic NNN interaction always reduces the NNE. The antiferromagnetic NNN interaction results in a large value of NNNE compared with the case where the NNN interaction is ferromagnetic.     

Local spin excitations and Curie temperature of iron

The expression for the Curie temperature of ferromagnetic metals in the mean field approximations is obtained for arbitrary types of exchange interactions. In the framework of local spin density functional approach an exact formula for the effective exchange parameter J₀ is derived. The numerical calculations for ferromagnetic iron illustrate the possibilities of the method.     

具有长程相互作用S-1/2 XY链的研究

采用平均场Jordan - Wigner 变换分析方法,研究了外场中且具有Z方向均匀长程相互作用自旋－1/2 XY链的热力学性质,得到了系统格点的亥姆赫兹自由能、内能、比热、磁化强度、磁化率等热力学量的解析表达式及其数值解,讨论了系统的一级和两级相变,数值结果在退化条件下与其他文献的结果符合很好. 关键词： XY链')" href="#">XY链 平均场Jordan-Wigner变换 长程相互作用     

铁磁/半导体/铁磁结构的双量子环自旋输运的特性

研究了与铁磁/半导体/铁磁结构相关的双量子环自旋输运的规律,研究结果表明：总磁通为零条件下,铁磁电极磁化方向反平行时,双量子环与单量子环相比提高了自旋电子透射概率的平均值.铁磁电极磁化方向平行时,双量子环对提高自旋向下电子平均透射概率的效果更明显;双量子环受到Rashba自旋轨道耦合作用影响时,自旋电子的平均透射概率明显高于单量子环,即使再加上外加磁场的影响,透射概率较高这一特征依然存在;双量子环所含的δ势垒具有阻碍自旋电子输运的作用,随δ势垒强度Z的增大透射概率 关键词： 双量子环 Rashba自旋轨道耦合 透射概率 δ势垒')" href="#">δ势垒     

High temperature spin wave dynamics of the uniaxial antiferromagnets

In the framework of the spin operators diagram technique the dynamical properties of the easy-axis type antiferromagnets at high temperatures are considered. The diagonalization procedure generalizing the Bogoliubov u-v transformation on the spin operators is presented. The spin wave (SW) spectrum allowing for the temperature and the magnetic field dependence of the sublattice magnetizations at T～T_～ is obtained. The SW relaxation frequencies due to the processes of SW scattering on the thermal spin fluctuations are calculated. The latter are in agreement with the data obtained on MnF₂ near the spin-flop transition¹⁰.     

Thermodynamics of a quasi-two-dimensional heisenberg ferromagnet with single-ion anisotropy

A quasi-two-dimensional ferromagnet (S = 1) with easy axis type anisotropy and interplanar exchange J and intraplanar exchange K is examined within the framework of the spin-wave approximation. An expression for the Curie temperature that is dependent on both the anisotropy parameter D (D/J 1) and on the exchange parameter ratio =K/J is obtained from the self-consistent equations. The important role of the single-ion anisotropy in the formation of the long-range magnetic order in two-dimensional systems is shown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 94–101, March, 1988.The authors are grateful to S. S. Aplesnin for performing all the numerical computations and to I. S. Sandalov and A. F. Sadreev for useful discussions.     

Thermal entanglement in a two-qubit Heisenberg XY chain with the Dzyaloshinskii--Moriya interaction

This paper investigates thermal entanglements of a two-qubit Heisenberg XY chain in the presence of the Dzyaloshinskii-Moriya anisotropic antisymmetric interaction. By the concept of concurrence, it is found that the effects of spin-orbit coupling on the entanglement are different from those of spin-spin model. The analytical expressions of concurrence are obtained for this model.