Nd ordering, cluster formation, and the origin of negative magnetization in NdMn0.8Fe0.2O3+δ

Abstract

The orthorhombic pseudo-perovskite series NdMn1-xFexO3+δ has negative magnetization, i.e. magnetization directed opposite to an applied field under certain conditions, for x = 0.2 and x = 0.25. We have investigated the microscopic origin of this phenomenon for x = 0.2 by using elastic and inelastic scattering techniques including neutron backscattering, X-ray magnetic circular dichroism at the Mn K and Nd L2 edges, neutron powder diffraction, and powder inelastic neutron scattering. We find that Nd3+ ions possess zero field ordered moments of 1.6 μB per ion at 1.5 K oriented parallel to the Mn moments. Based upon the neutron diffraction, there is a freezing of magnetic clusters before the long-range order sets in. The Nd crystal field levels shift with temperature due to a molecular field that is 1.1 meV at 1.5 K. These findings are consistent with a magnetic domain/cluster model for the negative magnetization in NdMn0.8Fe0.2O3+δ.