Structure and magnetic order in the series BixRE1―xFe0.5Mn0.5O3 (RE=La,Nd)

The influence of Bi3+ on the structure and magnetic properties of the rare-earth containing perovskites REFe0.5Mn0.5O3 (RE= La,Nd) was studied, and the limit of bismuth substitution was determined to be x 0.5 in BixRE1-xFe0.5Mn0.5O3+ (RE= La,Nd) at ambient pressure. Both X-ray and Neutron powder diffraction data were used to determine the crystal structures. Crystal structures in both La and Nd series were determined to be GdFeO3-type Pnma with the exception of the Bi0.3La0.7Fe0.5Mn0.5O3+ sample, which is monoclinic I2/a in the a-b-b- tilt scheme. Bond valence results suggest that the oxidation states are most consistent with Fe3+ and Mn3+, with some oxidation to form Mn4+ suggested by Rietveld refinement of oxygen excess and bismuth deficiency from neutron powder diffraction data. The samples undergo a transition to G-type antiferromagnetic order along with a weak ferromagnetic component, mixed with cluster-glass type behavior. Long range ordering temperatures TN in the range of 240-255K were also observed, with a significantly lower ordered magnetic moment in the case of lanthanum (M ~ 1.7-1.9 B) than in the case of neodymium (M ~ 2.1 B). The substitution of bismuth into the lattice results with a drop in T N relative to the lanthanide end-members, but exhibits no clear correlation with the magnitude of the ordered moment on the B-site.