Two successive magnetic phase transitions in Dy3Pd20Si6 studied by neutron powder diffraction

The low-temperature magnetic structures of Dy3Pd20Si6 have been studied by neutron powder diffraction. In the cubic crystal structure of Dy3Pd20Si6 (space group Fm (3) over bar m), the Dy ions occupy the sites 8c and 4a. They undergo two second-order successive magnetic phase transitions at the Neel temperatures T-N1 approximate to 5.8 K and T-N2 approximate to 1.8 K, respectively. Between T-N1 and T-N2, antiferromagnetic ordering of only the 8e sites occurs with k(1) = [1, 1, 1] whereas the 4a sites are disordered. Below T-N2, an additional ordering of the 4a sites sets in with k(2) = [0, 0, 1]. Unlike the situation found for Tb3Pd20Si6 and Nd3Pd20Ge6, the 4a magnetic Dy moments in Dy3Pd20Si6 point along an intermediate direction close to the high symmetry axis [1, 1, 1]. (C) 2000 Elsevier Science B.V. All rights reserved.