Structural and unique magnetic properties of PrBa<SUB>2</SUB>Fe<SUB>3</SUB>O<SUB>8</SUB>

Tetragonal PrBa2Fe3O8 exhibits a unique magnetic behavior and behaves differently from both PrBa2Cu3O7 and all RBa2Fe3O8 materials. Magnetic-susceptibility study reveals two anomalies at 23 and 55 K which are sensitive to oxygen concentration, but no specific heat anomaly was observed at either temperature. Mossbauer studies reveal two inequivalent iron sites, which order antiferromagnetically at ~230 K, in contrast to 670 K in RBa2Fe3O8. X-ray absorption spectra indicate that Pr is trivalent. In contrast to PrBa2Cu3O7 [TN(Pr)=17 K] Pr in PrBa2Fe3O8 does not order magnetically. The anomalies at 23 and 55 K are probably related to spin reorientation of Fe moments