Magnetic Structure of RCuIn (R = Nd, Tb, Ho, Er)

Magnetic and neutron diffraction measurements of RCuIn (R = Nd, Tb, Ho, Er) are reported. The compounds crystallize in the hexagonal ZrNiAl-type structure. The ZrNiAl lattice originates from a distortion of a kagomélattice. The studied compounds are antiferromagnets with the Néel temperature equal to 4.9 K for R = Nd, 14.5 K for R = Tb, 4.5 K for R = Ho and 3.5 K for R = Er. The magnetic ordering is described by the propagation vectorwe k = (1/2, 1/2, $k_z$) with $k_z$ equal to 0.161(6) for R = Nd, 0.2213(5) for R = Tb, 0.2510(3) for R = Ho and 0 for R = Er. The magnetic structure is noncollinear with magnetic moments in the basal plane for R = Nd, Tb and Ho and collinear with magnetic moments parallel to the c-axis for R = Er. The observed magnetic ordering results from the competition between exchange interactions of the Ruderman-Kittel-Kasuya-Yosida type, the geometrical frustration of the rare-earth magnetic moments and the influence of the crystal electric field. The latter affects the direction of magnetic moments and is responsible for the magnetic crystalline anisotropy.