α-Fe2O3单离子磁晶各向异性的计算及Morin转变的解释

本文根据晶场理论计算了α-Fe₂O₃的单离子磁晶各向异性。采用点电荷模型,计及近邻及次近邻对晶场的贡献,并考虑到近邻O^2-离子对次近邻Fe³⁺离子的电屏蔽效应,在六级微扰近似下,得到单离子各向异性场H_si=102.3×10²Oe。这一结果结合Artman等人对磁偶极各向异性的计算,导出了α-Fe₂O₃的Morin转变温度T _关键词：

CALCULATION OF MAGNETIC SINGLE-ION ANISOTROPY AND THE MORIN TRANSITION IN HEMATITE

A calculation of magnetic single-ion anisotropy in hematite (α-Fe₂O₃) has been made, based on point-charge model in crystalline field. The nearest-neighbor O^2- ions and the nexi-nearest-neighbor Fe³⁺ ions were chosen as ligands and the effect of electrostatic shield provided by the O^2- ions was taken into account. Considering the sixth order perturbation, we ob-tained an equivalent single-ion anisotropy field H_si=102.3×10² Oe. Making use of this results in conjunction with the computed equivalent dipolar anisotropy field by Artmen et al,. the Morin transition temperature in hematite T_M=261 K was obtained, which is in good agreement with the experimental value. Based on the linear approximation principle, we got the T_M-n relation for low n value in α-(Fe_-1nAl_n)₂O₃. With this relation the dependence of the-Morin transition temperature, T_M, on n in low n value range could be explained quite well.