Influence of global and local distortion on magnetic properties of cubic La0.6Ba0.4–Ca CoO3

Abstract The magnetic and structural study of the La 0.6 Ba 0.4– x Ca x CoO 3 ( x =0.0, 0.1, 0.2, 0.3, and 0.4) compounds with the lowest global or local distortion are studied. The compounds with x =0, 0.1, 0.2 and 0.3 is crystallized in the structure with the space group Pm- 3 m , and that with x =0.4 is Pnma . A ferromagnetic-like transition is observed and the Curie temperature, ranging from 235 K to 220 K, decreases slightly with the increasing Ca 2+ content for x ≤0.3, and the transition temperature is as low as 175 K with x =0.4. A hump, with the hump temperature slightly increase with the Ca 2+ content, is observed in the thermal magnetization curves of all of the compounds at the ZFC state, and it is owing to the magnetic frustration because of the coexistence of the FM and the AFM interaction. Above the transition temperature, the magnetic susceptibility versus the temperature is fitted with the ferromagnetic Curie–Weiss law for the compounds with x ≤0.3, and that with x =0.4 coincides with the ferrimagnetic Weiss-mean-field model. The absolute values of the exchange constants J 1 in the compounds with x ≤0.3 and those of J CO 3 + CO 3 + , J CO 3 + CO 4 + , J CO 4 + CO 4 + of La 0.6 Ca 0.4 CoO 3 are deduced from the fitting. The results indicate that (i) the ferromagnetic exchange constants J 1 increases with the Ca 2+ content x ≤0.3; (ii) the ferromagnetic interaction, J Co 3 + Co 4 + , plays a main role in the magnetic properties of La 0.6 Ca 0.4 CoO 3 ; (iii) the antiferromagnetic interactions, J Co 3 + Co 3 + , J Co 4 + Co 4 + , are not negligible in the compound x =0.4. The unsaturated magnetization at 70 kOe and the high coercive field in the hysteretic magnetization curve supports the existence of the antiferromagnetic interaction, and the percentage of the antiferromagnetic domain is calculated.