Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

A single phase polycrystalline La0.5Ba0.5CoO3-d sample possessing cubic structure (space group Pm3̄m) was synthesized by microwave irradiation within 20 minutes of processing time and its structural, magnetic, electrical, and magnetostrictive properties were investigated. While the temperature dependence of field-cooled magnetization (M) in a field of H = 0.5 kOe indicates the onset of ferromagnetic transition at TC = 177 K, irreversibility between the zero field-cooled and field cooled M(T) persists even at H = 3 kOe. M(H) at 10 K does not saturate at the maximum available field and has a much smaller value (0.83 μB/Co in a field of 50 kOe) than 1.9 μB/Co expected for spin only contribution from intermediate Co3+ and Co4+ spins. Resistivity shows insulating behavior down to 10 K and only a small magnetoresistance (∼ -2% for H = 70 kOe) occurs around TC. All these results suggest a magnetically heterogeneous ground state with weakly interacting ferromagnetic clusters coexisting with a non-ferromagnetic phase. The length of the sample expands in the direction of the applied magnetic field (positive magnetostriction) and does not show saturation even at 50 kOe. The magnetostriction has a maximum value (λpar = 265 x 10-6) at 10 K and it decreases with increasing temperature. The smaller value of λpar compared to the available data on La0.5Sr0.5CoO3 (λpar = 900 x 10-6) suggests that the non-ferromagnetic matrix is most likely antiferromagnetic and it restrains the field-induced expansion of ferromagnetic clusters in the microwave synthesized La0.5Ba0.5CoO3-d sample.