Properties of the ferrimagnetic double-perovskites A{sub}2FeReO{sub}6 (A = Ba and Ca)

摘要

We have synthesized ceramics of A{sub}2FeReO{sub}6 double-perovskites A{sub}2FeReO{sub}6 (A=Ba, Ca), Structural characterizations indicate a cubic structure with a=8.0854(1) A for Ba{sub}2FeReO{sub}6 and a distorted monoclinic symmetry with a=5.396(1) A, b=5.522(1) A, c=7.688(2) A and β=90.4° for Ca{sub}2FeReO{sub}6. The barium compound is metallic from 5K to 385K, i.e. no metal-insulator transition has been seen up to 385K, and the calcium compound is semiconducting from 5K to 385K. Magnetization measurements show a ferrimagnetic behavior for both materials, with T{sub}c=315 K for Ba{sub}2FeReO{sub}6 and above 385K for Ca{sub}2FeReO{sub}6. At 5K we observed, only for Ba{sub}2FeReO{sub}6, a negative magnetoresistance of 10% in a magnetic field of ST. Electrical, magnetic and thermal properties are discussed and compared to those of the analogous compounds Sr{sub}2Fe(Mo,Re)O{sub}6 recently studied.