Magnetic ordering in DyMn6-xCrxSn6 (x=1,2) compounds studied by neutron diffraction and magnetic measurements

We have studied the effect of Cr substitution on the magnetic ordering of t he hexagonal pseudoternary DyMn6-xCrxSn6 (x = 1, 2) compounds by neutron di ffraction and magnetic measurements at temperatures between 1.5 and 360 K. Below T-C each of the magnetic sublattices displays a ferromagnetic moment arrangement. The moments of the two sublattices are coupled antiferromagnet ically with a temperature-dependent moment orientation at lower temperature s (T-t). For the compound with x = 1 magnetic ordering occurs below 355K an d T-t= 260 K. For the compound with x = 2 magnetic ordering occurs below 24 5 K and T-t = 220 K. Between T-t and T-C both compounds display planar anis otropy. Below T-t a partial rotation of the moment angle (phi(e)) with c se ts in. The value of phi(c) decreases smoothly with temperature from 90 degr ees to about 45-50 degrees between T-t and T-i approximate to 100-120K and retains the same angle down to 1.5K. The ordered moment values at 1.5 K are 8.28(9) and 8.13(8)mu(B) per Dy atom and 3.12(5) and 1.79(4)mu(B), per (Mn /Cr) atom for the two compounds DyMn5CrSn6 and DyMn4Cr2Sn6, respectively. A lloying with the almost non-magnetic Cr leads to a substantial decrease of the ordering and of the spin reorientation temperatures as well as a reduct ion of the ordered Dy moment value compared to the compound DyMn6Sn6. (C) 2 000 Elsevier Science B.V. All rights reserved.