Structure and magnetic properties of TbMn6−xAlxSn6 compounds

In the present work, the influence of the substitution of Al for Mn on the structure and magnetic properties of ${\mathrm{TbMn}}_{\text{6−x}}{\mathrm{Al}}_x{\mathrm{Sn}}_6$ compounds was investigated. With increasing Al concentration the lattice constants $a$ , $c$ , and the unit-cell volume $V$ decrease monotonically. The ${\mathrm{TbMn}}_{\text{6−x}}{\mathrm{Al}}_x{\mathrm{Sn}}_{\mathrm{6}}$ compounds exhibit ferrimagnetic ordering. The magnetic ordering temperature first decreases with increasing Al content up to $x$ =1.5, then increases with further increasing Al content. As for the unsubstituted material, it was found that this series of compounds exhibits a second magnetic transition at lower temperature that is attributed to spin reorientation. The spin-reorientation temperature and the magnetic anisotropy field first decrease with increasing Al content, go through a minimum at $x$ =0.5, then increase with further increasing Al content. The saturation magnetization decreases monotonically with increasing Al content. Two metamagnetic transitions are found in Tb${\mathrm{Mn}}_{\mathrm{6}}{\mathrm{Sn}}_{\mathrm{6}}$ compounds, one at 0.44 T, and the other at about 0.16 T. With increasing Al content only one metamagnetic transition remains.