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

• RNi4B (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 ErNi4B.
• The RNi4B (R=Nd, Tb, Ho) display a spin re-orientation below Tc.
• Their easy axis tilts from the c-axis at Tc to ~30 deg above the basal plane at 1.5 K.

Neutron diffraction has been performed on RNi4B (R=Nd, Tb, Ho, Er) polycrystals. The orthorhombic structure for NdNi4B and the CeCo4B structure type (hexagonal) for TbNi4B and HoNi4B are confirmed. Our data also show that this last structure is currently the best approximant for ErNi4B. The RNi4B (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 RNi4B (R=Nd, Tb, Ho) and parallel to the c-axis in ErNi4B at 1.6 K. The RNi4B (R=Nd, Tb, Ho) display a spin re-orientation below Tc which arises from a competition between the second order term and the higher order terms of the CEF hamiltonian.

Simplified magnetic structure in NdNi4B and full magnetic structure in RNi4B (R=Tb, Ho). Variation with temperature of the easy magnetization axis direction (angle with c-axis) showing a spin re-orientation. Figure optionsDownload as PowerPoint slide