Magnetic structures of R 3Cu 4Ge 4 (R=Tb, Dy, Ho, Er)

Abstract

Neutron diffraction studies of polycrystalline R 3Cu 4Ge 4 (R=Tb, Dy, Ho, Er) intermetallic compounds with the orthorhombic Gd 3Cu 4Ge 4-type crystal structure indicate complex magnetic structures. In these compounds the rare earth atoms occupy two nonequivalent 2d and 4e sublattices. For R=Tb and Er with decreasing temperature the magnetic moments in the 2d sublattice order first; the 4e sublattice magnetic moments order at lower temperatures. For R=Dy, Ho both sublattices order simultaneously although the magnetic moment values are different for each of them. In the compounds with R=Tb and Er a change of the magnetic structure, connected with the 2d sublattice, is observed near the Néel temperature. This is a transition from the commensurate structure, described by the propagation vector k =(0, 1 2 ,0) at low temperatures to the incommensurate structure with k =(0, 1 2 +δ,0) at higher temperatures (still below the Néel temperature).