Magnetic ordering in TbMn 6− xCr xSn 6 ( x=1, 2) compounds studied by neutron diffraction and magnetic measurements

Abstract

The magnetic behaviour of the TbMn 6− x Cr x Sn 6 ( x=1, 2) compounds has been studied by neutron diffraction and magnetic measurements. Both compounds exhibit a uniaxial ferromagnetic moment arrangement for both magnetic (R and Mn) sublattices, which order simultaneously and are coupled antiferromagnetically over the entire ordered regime below T C. A spin reorientation transition occurs at lower temperatures ( T t). The magnetic phase diagram comprises three regions. In the high temperature range T t– T C the magnetic moments are confined to the basal plane. In the intermediate region T t– T i spanning about 40–50 K the moments rotate smoothly by 90 K. In the low temperature range 1.5 K– T i the magnetic moments of both sublattices point into the c-direction. The ordered moment values at 1.5 K are 8.62(5) μ B and 8.9(1) μ B per Tb atom and 2.09(2) μ B and 1.88(3) μ B per (Mn/Cr) atom for the two compounds TbMn 5CrSn 6 and TbMn 4Cr 2Sn 6, respectively. Alloying with the almost non-magnetic Cr leads to a linear decrease of the ordering and of the spin reorientation temperatures.