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 $TbMn6−xAlxSn6$ compounds was investigated. With increasing Al concentration the lattice constants $a$⁠, $c$⁠, and the unit-cell volume $V$ decrease monotonically. The $TbMn6−xAlxSn6$ 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$Mn6Sn6$ compounds, one at 0.44 T, and the other at about 0.16 T. With increasing Al content only one metamagnetic transition remains.