Schwinger-boson mean-field theory of an anisotropic ferrimagnetic spin chain

By using the Schwinger-boson mean-field theory, the Heisenberg ferrimagnetic spin chain with the single-ion anisotropy D is explored. Based on the effect of the single-ion anisotropy D, we obtain four branches of the low-lying excitation and calculate the anisotropy dependence of spin reduction and the longitudinal correlation at zero temperature. We also discuss the free energy, magnetic susceptibility and specific heat at finite temperature with different anisotropy D.     

阻挫诱导的亚铁磁性Heisenberg系统中的量子相变

利用密度矩阵重整化群(DMRG)方法研究磁性阻挫对一种S=1/2准一维反铁磁自旋链但却具有亚铁磁性的Heisenberg系统基态的影响.计算了单个晶胞的基态能、自旋关联函数以及自旋能隙.研究表明这种Heisenberg自旋系统的基态随着阻挫α的增强将从磁有序相变化到自旋无序相，并且伴随着自旋能隙的出现，量子相变点为α≈0.412.同时线形链上格点间自旋长程关联值的计算结果表明在磁有序区间体系的磁有序性质随着α的增强而减弱，阻挫在0≤α<     

The ferrimagnetic phase of the Blume-Emery-Griffiths model on the cellular automaton

The Blume-Emery-Griffiths model is simulated using the cooling algorithm which is improved from the Creutz cellular automaton (CCA) under periodic boundary conditions. The simulations are carried out on a simple cubic lattice at K/J = −1.5 in the range of −3.5 < D/J < 0.5, with J and K representing the nearestneighbour bilinear and biquadratic interactions, D being the single-ion anisotropy parameter. The phase diagram characterizing phase transition of the model is obtained. We found different kinds of phase transitions between the ferromagnetic, quadrupolar, staggered quadrupolar and ferrimagnetic phases for K/J = −1.5. In particular, the region of the phase diagram containing a ferrimagnetic phase is explored and compared to those obtained by other methods. The simulations confirm that the ferrimagnetic phase occurs in the narrow interval −3.006 ≤ D/J < −3. This result is in a good agreement with Monte Carlo renormalization group and closer to the cluster variation method result than the mean field approximation result.      

阻挫诱导的亚铁磁性Heisenberg系统中的量子相变

利用密度矩阵重整化群(DMRG)方法研究磁性阻挫对一种S=1/2准一维反铁磁自旋链但却具有亚铁磁性的Heisenberg系统基态的影响.计算了单个晶胞的基态能、自旋关联函数以及自旋能隙.研究表明这种Heisenberg自旋系统的基态随着阻挫α的增强将从磁有序相变化到自旋无序相,并且伴随着自旋能隙的出现,量子相变点为α≈0.412.同时线形链上格点间自旋长程关联值的计算结果表明在磁有序区间体系的磁有序性质随着α的增强而减弱,阻挫在0≤α< 关键词： 准一维反铁磁自旋链 亚铁磁性 密度矩阵重整化群 自旋能隙     

低温下自旋为1/2的一维亚铁磁棱型链系统的元激发谱

利用不变本征算符法计算了低温下自旋为1/2的一维亚铁磁棱型链系统的元激发谱,并讨论了在此系统中不同的特殊情形下的元激发能量及不变本征算符法的优点与不足.     

Schwinger-boson approach to anisotropy ferrimagnetic chain with bond alternation

We use the Schwinger-boson approach to study the anisotropy ferrimagnetic spin-(1/2,1) chain with bond alternation.Based on the effect of bond alternation δ,we obtain energy gap,free energy,and specific heat,respectively.The specific heat with larger bond alternation(δ 0.7) displays a peak at low temperature.Based on the effect of XXZ anisotropy parameter δ,we present excited spectrums,free energy,and specific heat,respectively.     

Spin current transmission in Co1-xTbx films

We investigate the spin to charge conversion phenomena in Y₃Fe₅O₁₂/Pt/Co_1-xTb_x/Pt multilayers by both the spin pumping and spin Seebeck effects.We find that the spin transport efficiency is irrelevant to magnetization states of the perpendicular magnetized Co;Tb;films,which can be attributed to the symmetry requirement of the inverse transverse spin Hall effect.Furthermore,the spin transmission efficiency is significantly affected by the film concentration,revealing the dominant role of extrinsic impurity scattering caused by Tb impurity.The present results provide further guidance for enhancing the spin transport efficiency and developing spintronic devices.     

Degenerate ferrimagnetic ground state of frustrated kagome lattice

The frustrated Ising model on kagome lattice with nearest-neighboring antiferromagnetic interaction is investigated by using Monte Carlo simulation of the Wang-Landau algorithm and Glauber dynamics. The geometrical frustration leads to a particularly high degeneracy of ground states in this system. A small magnetic field applied can lift the degeneracy partially, and produce the magnetization plateau of 1/3 saturate value (Ms), which is analogous to the magnetic behavior in triangular antiferromagnetic system. However, different from the long-range ferrimagnetic state responsible for 1/3 Ms plateau in triangular lattice, the ferrimagnetic ground state corresponding to 1/3 Ms plateau in kagome lattice is short-ranged and still highly degenerate. Furthermore, the spin configuration of these degenerate ferrimagnetic ground states show an inherent characteristic that the spins along the magnetic field must be aligned on the closed loops, which can be well understood in terms of geometrical frustration.     

固态格点自旋体系中的量子关联

量子态的关联特性是量子通信和量子计算的重要资源。文章首先回顾了经典关联、量子关联的概念以及常用的度量方法,随后简要介绍了作者最近对固态格点自旋体系中量子关联的研究成果。最后对未来量子关联的研究指出了几个方向。     

固态格点自旋体系中的量子关联*

量子态的关联特性是量子通信和量子计算的重要资源。文章首先回顾了经典关联、量子关联的概念以及常用的度量方法,随后简要介绍了作者最近对固态格点自旋体系中量子关联的研究成果。最后对未来量子关联的研究指出了几个方向。     

The Physical Property of Susceptibility for One-Dimensional Ferrimagnetic Chain with Alternating Spins 1 and 1/2 in Finite Magnetic Field

We further calculate the dependence of xT on T in high magnetic fields,where X denotes susceptibility and T is temperature,using our previous research work - Green function‘s decoupling approximate approach,for the one-dimensional ferrimagnetic chain with alternating spins 1 and 1/2.We find a linear correlation in certain range of magnetic field between the temperature of xT maximum and the magnetic field.Moreover,we simply analyze its physical meaning by our approach.``     

The Physical Property of Susceptibility for One-Dimensional Ferrimagnetic Chain with Alternating Spins 1 and 1/2 in Finite Magnetic Field

We further calculate the dependence of χT on T in high magnetic fields,where χ denotes susceptibility and T is temperature,using our previous research work - Green function's decoupling approximate approach,for the one-dimensional ferrimagnetic chain with alternating spins 1 and 1/2.We find a linear correlation in certain range of magnetic field between the temperature of χT maximum and the magnetic field.Moreover,we simply analyze its physical meaning by our approach.     

A fixed-point equation for the high-temperature phase of discrete lattice spin systems

A fixed-point equation on an infinite-dimensional space is proposed as an alternative to the usual definition of the infinite-volume limit in discrete lattice spin systems in the high-temperature phase. It is argued heuristically that the free energy and correlation functions one obtains by solving this equation agree with the usual definitions of these quantities. A theorem is then proved that says that if a certain finite-volume condition is satisfied, then this fixed-point equation has a solution and the resulting free energy is analytic in the parameters in the Hamiltonian. For particular values of the temperature this finite-volume condition may be checked with the help of a computer. The two-dimensional Ising model is considered as a test case, and it is shown that the finite-volume condition is satisfied for0.77 _critical.     

Ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies

We develop a model for ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies. This model applies to (i) magnetic materials with both uniaxial and cubic anisotropies, and (ii) magnetic nanoparticles with effective core and surface anisotropies; We numerically compute the resonance frequency as a function of the field and the resonance field as a function of the direction of the applied field for an arbitrary ratio of cubic-to-uniaxial anisotropy. We also provide some approximate analytical expressions in the case of weak cubic anisotropy. We propose a method that uses these expressions for estimating the uniaxial and cubic anisotropy constants, and for determining the relative orientation of the cubic anisotropy axes with respect to the crystal principle axes. This method is applicable to the analysis of experimental data of resonance type measurements for which we give a worked example of an iron thin film with mixed anisotropy.     

自旋为1/2的XY模型亚铁磁棱型链的物性和有序-无序竞争

利用不变本征算符法, 计算低温下自旋为1/2的XY模型一维亚铁磁棱型链系统的元激发谱, 讨论在此系统中不同的特殊情形下的元激发能量, 从而给出体系的三个临界磁场强度的解析解H_C1, H_C2, H_peak. 分析不同外磁场下 体系的磁化强度随温度的变化规律, 发现三个临界磁场强度的解析解H_C1, H_C2, H_peak是正确的, 并从三个元激发对磁化强度的贡献进行了说明. 低温下磁化强度随外磁场的变化呈现1/3磁化平台. 体系的磁化率随温度或者外磁场的变化都出现了双峰现象. 这说明双峰源于二聚体分子内电子自旋平行排列的铁磁交换作 用能和二聚体与单基体分子间电子自旋反平行排列的反铁磁交换作用能, 热无序能, 外磁场强度相关的自旋磁矩势能之间的竞争.     

On the asymptotic behaviour of Spitzer's model for evolution of one-dimensional point systems

A nearest-neighbor gradient dynamics of one-dimensional infinite particle systems is considered; the model admits a two-parameter family of stationary configurations. Some domains of attraction of stationary configurations are described, and the continuum (hydrodynamical) limit of the system is investigated. It is shown that the mean density of points satisfies a nonlinear diffusion equation in the hydrodynamical limit.Research supported by I.H.E.S., Bures-sur-Yvette, France.     

相分离体系Nd1-xSrxCoO3的亚铁磁行为

研究了Nd1-xSrxCoO3(0.1≤x≤0.5)系列多晶样品在低温时的亚铁磁行为.通过传统的固相反应法合成了Nd1-xSrxCoO3多晶样品,应用物理性质测试系统对样品进行了直流磁化强度、磁滞回线的测试.磁化强度的研究表明,随掺杂量增加,团簇的数目和尺寸都在增加,铁磁性增强.同时,多晶样品在低温时形成亚铁磁序.磁滞回线的研究表明,Nd离子与Co离子之间存在磁性耦合.由于Co与Nd的反平行排列,Nd1-xSrxCoO3体系低温时出现亚铁磁序.     

Linear response and relaxation in quantum lattice systems

For spin-lattice systems, the Kubo formula, expressing the relaxation function in terms of the linear response function, is found to be exact in the thermodynamic limit. In addition, analyticity properties are obtained.