Magnetic structures in RNi4B (R=Nd, Tb, Ho, Er)

Abstract

Neutron diffraction has been performed on R Ni 4 B ( R =Nd, Tb, Ho, Er) polycrystals. The orthorhombic structure for NdNi4B and the CeCo 4 B structure type (hexagonal) for TbNi 4 B and HoNi 4 B are confirmed. Our data also show that this last structure is currently the best approximant for ErNi 4 B. The R Ni 4 B ( R =Nd, Tb, Ho, Er) order ferromagnetically at respectively 11.0, 18.1, 6.2 and 10.0 K. The crystal electric field (CEF) interaction controls the magnetic anisotropy in this series leading to an easy axis ~30 deg above the basal plane in R Ni 4 B ( R =Nd, Tb, Ho) and parallel to the c -axis in ErNi 4 B at 1.6 K. The R Ni 4 B ( R =Nd, Tb, Ho) display a spin re-orientation below T c which arises from a competition between the second order term and the higher order terms of the CEF hamiltonian. Simplified magnetic structure in NdNi 4 B and full magnetic structure in R Ni 4 B ( R =Tb, Ho). Variation with temperature of the easy magnetization axis direction (angle with c -axis) showing a spin re-orientation. • R Ni 4 B ( R =Nd, Tb, Ho, Er) polycrystals were inductively melted. • Neutron diffraction confirms they all order ferromagnetically. • The magnetization easy axis is parallel to the c -axis in ErNi 4 B. • The R Ni 4 B ( R =Nd, Tb, Ho) display a spin re-orientation below T c . • Their easy axis tilts from the c -axis at T c to ~30 deg above the basal plane at 1.5 K.