Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

Abstract

A single phase polycrystalline La0.5Ba0.5CoO3- d sample possessing cubic structure (space group Pm[Formula: see text]m) 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 T C = 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 T C. 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 ( λ par = 265 x 10-6) at 10 K and it decreases with increasing temperature. The smaller value of λ par compared to the available data on La0.5Sr0.5CoO3 ( λ par = 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.