Structural and magnetic studies on PrBa2Fe3O8

It is known that Fe moments order antiferromagnetically with Néel temperature, TN, above 700 K in RBa2Fe3O7-δ with R=Y and Eu, and Pr moments order antiferromagnetically in PrBa2Cu3,O7-δ, with TN of 17 K. We have synthesized PrBa2Fe3O8 to study the ordering of Pr and Fe moments. From X-ray and neutron diffraction studies, this compound is found to crystallize in the tetragonal structure (space group P4/mmm). 57Fe Mössbauer studies show a complex hyperfine split pattern at 77 K, but a doublet superimposed on a six-line pattern at 300 K implying that some of the Fe moments order magnetically between 77 and 300 K while others may have ordering temperature of more than 300 K. Magnetization measurements reveal discontinuities in the susceptibility data around 80 and 20 K, probably an indication of magnetic ordering of the Fe and Pr moments. Neutron diffraction studies at 300 K suggest the presence of additional oxygen in the Pr plane and a magnetic structure very different from that of YBa2Fe3O8