Magnetic structures of RCuGe (R=Pr, Nd, Tb, Dy, Ho and Er) compounds from neutron diffraction and magnetic measurements

The crystal and magnetic structures of RCuGe (R = Pr, Nd, Tb, Dy, Ho and Er) compounds were determined by neutron diffraction on polycrystalline samples. Their magnetic data, including also GdCuGe, are reported. The compounds with R = Pr and Nd have hexagonal AlB2-type crystal structure, while other compounds show hexagonal LiGaGe-type. All compounds are antiferromagnetic at low temperatures. The Neel temperatures change from 2.2 K for R = Pr to 17 K for R = Gd. The magnetic structures of these compounds (excluding NdCuGe) are sine modulated with wavevector k = (1/3,0,0). For heavy lanthanide compounds a change in direction of the magnetic moments, from perpendicular to the c-axis (R = Tb and Dy) to parallel to the c-axis (R = Ho and Er), has been found. For ErCuGe a change in magnetic structure is observed at low temperatures. NdCuGe exhibits a collinear antiferromagnetic structure with unit cell dimensions a(m) = root(3a(h)), b(m) = a(h), c(m) = c(h) and magnetic moments parallel to the a-axis.