A neutron diffraction study of HfFe6Ge6-type DyMn6Ge6-xGax compounds (x=0.1, 0.2 and 1.0)

DyMn6Ge6-xGax compounds (x=0.1, 0.2 and 1.0) were studied by magnetization measurements and powder neutron diffraction. DyMn6Ge5.9Ga0.1 and DyMn6Ge5.8Ga0.2 display helical structures between T-N = 427 and 422 K, respectively, and between T-1 = 110 and 147 K, respectively. Below T-1, conical structures with the cone axis close to the c-axis and semi-cone angles of about 50 and 45degrees, respectively, were measured. The moment values measured at 2 K were mu(Mn) = 2.27(10) and 2.26(6) mu(B), respectively, and mu(Dy), = 9.90(20) and 9.73(16) mu(B), respectively. DyMn6Ge5Ga is ferrimagnetic below T-c = 392 K. At 2 K, the moment values are mu(Mn) = 2.22(10) and mu(Dy) = 9.90(17) mu(B). The angle between the moment direction and the c-axis is 0 = 46(2)degrees. This value increases with temperature to 0 = 64(4)degrees at 300 K. The results are discussed and compared with previous neutron diffraction studies on isotypic RMn6Ge6 and RMn6Ge6-xGax compounds (R=Tb-Tm). (C) 2002 Elsevier Science B.V. All rights reserved.