Magnetic properties, oxygen content and metal valences in BaRE(Cu 0.5Fe 0.5) 2O 5+ δ with RE=Lu, Yb, Y, Eu, Sm, Nd and Pr

Abstract

Oxygen-deficient double-perovskite samples of BaRE(Cu 0.5Fe 0.5) 2O 5+ δ (RE=Lu, Yb, Y, Eu, Sm, Nd and Pr; 0≤ δ≤0.45) have been characterized for their magnetic properties. For the samples with RE=Lu–Sm, the oxygen content could be raised above δ≈0 only by means of high-pressure heat treatment. In the case of the larger rare earth elements, i.e. Nd and Pr, excess oxygen was easily introduced under normal pressure as well. The (Cu 0.5Fe 0.5)O 2 planes were found to exhibit antiferromagnetism at or below room temperature and weak spontaneous magnetization below ∼80 K. The Néel temperature decreases with increasing amount of excess oxygen. Based on the charge-neutrality principle and the 57Fe Mössbauer data, the average valences of Fe and Cu were deduced. The ratio of six-coordinated Fe 3+ to Fe 5+ depends on both the choice of RE and the sample preparation process. The excess oxygen introduced into the RE layer upon the high-pressure heat treatment increases not only the valence of Fe but also the valence of Cu. The behavior of an observed susceptibility anomaly around 80 K was studied upon varying δ.