The spin reorientation transition and first-order magnetization process of TbMn6Sn6 compound

The molecular field theory has been applied to investigate the spin-reorientation transition and first-order magnetization process (FOMP) of intermetallic compound TbMn6Sn6. The temperature dependence of easy magnetization direction, the magnetocrystalline anisotropy constants K1R and K2R of Tb ion and the total magnetocrystalline anisotropy constants K1 and K2 of compound have been calculated. The theoretical calculations have good agreement with the experimental data. Results show that K1R keeps positive, while K2R remains negative, in the whole magnetically ordered temperature range. K1 + K2 changes its sign at 310 K, indicating the occurrence of spin reorientation transition. The magnetization curves for the field perpendicular to the c-axis at different temperatures have also been calculated, which give a good description of FOMP. Our studies show that the second-order magnetic anisotropy constant K2 (in other words, the fourth-order crystalline field parameter B40 of Tb ions) must be taken into account in order to giving a full description of the spin reorientation and FOMP of TbMn6Sn6 compound.