Physical-Properties of Oxygen-Deficient Co-Based Perovskites: Co(Sr 1-x Y x)O 3–δ (0.05 ≤ x ≤ 0.4)

Abstract

In this work, the syntheses and characterization of oxygen deficient perovskite cobalt oxides prepared under ambient pressure conditions with different “x” in the Co(Sr1-xYx)O3–δ; 0.05 ≤ x ≤ 0.4 series are reported. The system studied in the present investigation undergoes structural phase transition at room temperature from cubic to tetragonal symmetry. The samples with x ≥ 0.2 show a tetragonal structure with I4/mmm space group, while the samples with 0.05 ≤ x ≤ 0.15 reveal cubic with pm3m group symmetry. Quite similar to Ho-substituted system [J. Appl. Phys. 103, 07B903 (2008)], the present Y-doped magnetization data clearly show the appearance of an enhanced ferromagnetic component at ~350 K for 0.15 ≤ x ≤ 0.225. Unlike the Ho-substituted system, the present narrow compositions behave as hard ferromagnet with quite high coercive field, Hc = 11.02, 12.25 and 14.0 kOe for x = 0.15, 0.2 and 0.225 compositions, respectively at T = 10 K. All the compositions show a semiconducting-like behaviour and some interesting features of temperature dependence of magnetoresistance (MR) are observed. The Co(Sr1-xYx)O3–δ samples seemly to obey variable range hopping conduction model showing a linear ln ρ versus T–1/4 dependence at the temperature range 80 K ≤ T ≤ 300 K.