General correlation function series: Phase diagram of the anisotropic Heisenberg antiferromagnet in a field
General correlation function series: Phase diagram of the anisotropic Heisenberg antiferromagnet in a field
复制标题
一般相关函数系列：场中各向异性海森堡反铁磁体的相图
DOI：
10.1103/physrevb.22.3256
复制
发表时间：
1980
期刊：
影响因子：
--
通讯作者：
S. Jensen
中科院分区：
文献类型：
--
作者：
O. Mouritsen;E. Hansen;S. Jensen
提出了一种计算包含大量模型参数的哈密顿量自旋系统的自旋算符系综算符系综系综系数的一般方案。该格式以矩方法为基础，给出了级数系数作为模型参数的精确函数，如空间维度、坐标和自旋空间中的耦合分布、与位置有关的场分布和自旋量子数。在具有双线性相互作用的经典哈密顿量和单组分位置相关磁场的情况下，给出了自关联函数和对关联函数级数系数的六阶一般表达式。利用该通式计算了简单立方各向异性经典海森伯反铁磁体在沿易轴的均匀无序磁场中的磁化率级数。级数系数是三个变量的多项式，分别表示场、各向异性以及最近和次最近邻耦合的比率。通过对有序磁化率序列的分析，计算了各向异性参数不同取值时温度和场的相图。计算的相图包括自旋翻转相、反铁磁相和顺磁相，与基于蒙特卡罗和重整化群计算的预测一致。
A general scheme is presented to calculate high-temperature series coefficients for ensemble averages of spin operators for spin systems with Hamiltonians containing a large number of model parameters. The scheme, which is based on the moment method, provides the series coefficients as exact functions of the model parameters, eg, spatial dimensionality, coupling distributions in coordinate and spin space, site-dependent field distributions, and spin quantum number. General expressions for the series coefficients for the auto-and pair-correlation functions are given to sixth order in the case of a classical Hamiltonian with bilinear interactions and a one-component site-dependent magnetic field. The general expressions are used to calculate susceptibility series for the simple cubic anisotropic classical Heisenberg antiferromagnet in a uniform nonordering magnetic field along the easy axis. The series coefficients are polynomials in three variables representing the field, the anisotropy, and the ratio of nearest-and next-nearest-neighbor couplings, respectively. From an analysis of the ordering susceptibility series the phase diagram spanned by the temperature and the field has been calculated for various values of the anisotropy parameter. The calculated phase diagram, which includes a spin-flop phase, an antiferromagnetic phase, and a paramagnetic phase, is in agreement with predictions based on Monte Carlo and renormalization-group calculations.