ANTIFERROMAGNETIC ORDERING IN THE NOVEL DY3GE4 AND DYGE1.3 COMPOUNDS STUDIED BY NEUTRON-DIFFRACTION AND MAGNETIC MEASUREMENTS

The magnetic ordering of the novel binary compounds Dy3Ge4 and DyGe13( 1) has been studied by neutron diffraction and magnetic measurements. Dy,Ge, with the Er,Ge, structure type (space group Cmcm) displays a tw o step antiferromagnetic ordering below T-N=19 K. The two Dy sites (Dy -1:8(f) and Dy-2:4(c)) order independently with two distinct order par ameters associated with the same wave vector q = (0, 1, 0). Both subla ttices have a uniaxial antiferromagnetic moment arrangement but with m utually perpendicular orientations. Dy-1 orders below T-N with the mom ents along the a-axis, Dy-2 orders only below T-1=6 K along the c-axis . At 1.4 K the moment values of Dy, and Dy, are 7.31(8) mu(B) and 5.6( 3) mu(B), respectively. Their arrangement leads to a symmetry reductio n described by the monoclinic magnetic space group Cp11 2(1)'/m i'(Sh( 11)(55)). The two-dimensional canted antiferromagnetic structure is th e result of a strong magnetocrystalline anisotropy and the presence of various types of magnetic interactions. The phase of DyGe1.3(1) compo sition with the AIB(2) structure type (space group P6/mmm) was detecte d as an impurity in the studied sample. It orders antiferromagneticall y below T-N=16 K with collinear moment arrangement associated with a 2 c-cell enlargement (q=0,0,1/2) described by the magnetic space group P (2c)11 2'/m' (Sh(11)(56)). At 1.4 K mu(Dy) = 7.2(2) mu B and is confin ed to the (001) plane. (C) 1997 Elsevier Science S.A.