A neutron diffraction study of magnetic ordering in DyMn6-xCrxGe6 compounds (II)

We have studied the effect of Cr substitution on the magnetic structures of the hexagonal pseudoternary DyMn6-xCrxGe6 compounds by neutron diffraction for various compositions in the range x less than or equal to 2 at temperatures between 1.5 K and 300 K. In all these cases the low-temperature structure corresponds to a distorted cone structure as it comprises an in-plane ferrimagnetic component (mu(xy)) whose value varies with x. The high-temperature phase corresponds to a flat spiral. We have shown that the substitution of almost non-magnetic Cr decreases drastically the ordering temperatures and modifies the thermal behaviour of all relevant physical quantities of the cone and spiral structures observed in the low-and the high-temperature regions (mu(S)=spiral moment, mu(F)=ferromagnetic component, q(z)=spiral wave vector, Phi(c)=cone angle Phi(Mn)=phase angle). A discussion of the magnetic structural changes is given in terms of an exchange induced 3d sublattice anisotropy and a crystal-field induced Dy sublattice anisotropy. (C) 1998 Elsevier Science S.A.