Short-range magnetic order in La1-xBaxCoO3 cobaltites

Magnetization versus temperature and magnetic-field measurements, M(T, Ha), have been carried out to study the magnetic and critical properties of polycrystalline La1-xBaxCoO3 (x = 0.3 and 0.5) cobaltites. These compounds with the density of ∼6.2 g/cm3 crystallized in the R3¯c rhombohedral and Pm3¯m cubic structures, respectively. With an applied field Ha = 200 Oe, M(T) data have revealed that the samples with x = 0.3 and 0.5 exhibit the ferromagnetic-paramagnetic (FM-PM) phase transition at the Curie temperature points TC = 202 and 157 K, respectively. At 4.2 K, the saturation magnetization (Msat) decreases from 35.9 emu/g for x = 0.3-26.1 emu/g for x = 0.5. Particularly, the critical-behavior analyses in the vicinity of TC reveal all samples undergoing a second-order phase transition, with critical exponent values (β = 0.328 and γ = 1.251 for x = 0.3, and β = 0.331 and γ = 1.246 for x = 0.5) close to those expected for the 3D Ising model. This proves short-range magnetic order existing in La1-xBaxCoO3. We believe that magnetic inhomogeneities due to the mixture of hole-rich FM regions (confined in the trivalent-cobalt hole-poor anti-FM matrix) and uniaxial anisotropy prevent long-range order in La1-xBaxCoO3.