Magnetic ordering of neodymium monopnictides determined by neutron diffraction

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Abstract
The magnetic structures and ordered moments of NdN, NdP, NdAs, and NdSb with NaCl structure have been determined by means of line profile analysis of neutron diffraction powder patterns. NdN orders ferromagnetically at 4.2 K, which is characteristic of most 4f nitrides. The other neodymium monopnictides in contrast to the type II magnetic structures of heavy rare earths show FCC (BCT) type I antiferromagnetism at low temperatures. Except for NdBi and NdSb the ordered magnetic moments are reduced considerably below the free ion value because of crystal field effects and due to comparably weaker magnetic exchange interactions. The experimental and calculate neutron magnetic form factors of Nd3+ (dipole and MJ=J approximations) are in reasonable agreement. The measured powder intensities do not show conclusive evidence for anisotropy of the form factor related to the asymmetry of the magnetization distribution. The observed magnetic structures are discussed in the context of molecular field theory, and exchange constants have been determined. The neutron scattering amplitude of neodymium was refined to bNd=0.75(1)*10-12cm.