Magnetic ordering in TbMn6-xCrxSn6 (x=1, 2) compounds studied by neutron diffraction and magnetic measurements

The magnetic behaviour of the TbMn6-xCrxSn6 (x=1, 2) compounds has been stu died by neutron diffraction and magnetic measurements. Both compounds exhib it a uniaxial ferromagnetic moment arrangement for both magnetic (R and Mn) sublattices, which order simultaneously and are coupled antiferromagnetica lly over the entire ordered regime below T-C. A spin reorientation transiti on 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 spannin g 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) mu(B) and 8.9(1) mu(B) per Tb atom and 2.09(2) mu(B) and 1.88(3) mu(B) per (Mn/Cr) atom for the two compounds TbMn5CrSn6 and TbMn4Cr2Sn6, respectively. Alloying with t he almost non-magnetic Cr leads to a linear decrease of the ordering and of the spin reorientation temperatures. (C) 2000 Elsevier Science S.A. All ri ghts reserved.