GdMn_2Ge_2化合物的磁性和磁相变的分子场理论研究

Molecular Field Theory Analysis of Magnetic Properties and Magnetic Phase Transitions of Intermetallic Compound

采用交换作用的分子场理论模型对金属间化合物GdMn2 Ge2 的磁性、磁结构和磁相变进行了研究。理论分析和计算结果表明 ,GdMn2 Ge2 中存在 5种不同类型的磁结构 ,外磁场以及温度的变化导致GdMn2 Ge2 从一种磁结构到另一种磁结构的一级或二级磁相变。计算了不同温度时GdMn2 Ge2 单晶的磁化曲线 ,并给出了外磁场沿晶轴a和c方向时的H T磁相图 ,估计了Gd Gd ,Gd Mn ,层面内及层面间Mn Mn的交换耦合参数。结果显示 ,要描述GdMn2 Ge2 的磁性 ,必须考虑晶格常数和温度对层面间Mn Mn交换相互作用的影响。

The molecular field theory of exchange interaction was applied to investigate the magnetic properties, magnetic structure and magnetic phase transition of intermetallic compound GdMn 2Ge 2. Theoretical analysis and calculation show that there are five possible magnetic structures in GdMn 2Ge 2. Variations of external magnetic field and temperature give rise to the first order or second order magnetic transitions from one phase to another. The magnetic curves of GdMn 2Ge 2 single crystal at different temperature were calculated and a good agreement with experimental data were gotten. Based on the calculation the H T magnetic phase diagrams of GdMn 2Ge 2 for the magnetic field perpendicular and parallel to the c axis were depicted. The Gd Gd, Gd Mn, intralayer Mn Mn and interlayer Mn Mn exchange coupling parameters were estimated. It shows that, in order to describe the magnetic properties of GdMn 2Ge 2, the lattice constant and temperature dependence of interlayer Mn Mn exchange interaction must be taken into account.