Structural, magnetization, and magnetotransport measurements have been performed for anion deficient La 0.5 Ba 0.5 Co 1Àx Fe x O 3Àd (x 0:4) and La 1Ày Ba y CoO 3Àd (0:5 y 0:6) perovskites. It has been found that the iron doped compositions with x 0:23 are predominantly ferromagnetic. The Curie point and magnetization are slightly larger in insulating phase (x ¼ 0.1) than in metallic one (x ¼ 0.05). Magnetoresistance ratio rises with lowering temperature and increasing iron content reaching three orders of magnitude in predominantly antiferromagnetic state (x ! 0:2 5) .T h er i s eo ft h eb a r i u m content in La 1Ày Ba y CoO 3Àd series above y ¼ 0.5 leads to stabilization of antiferromagnetic phase and strong enhancement of the magnetoresistance. Antiferromagnetic ordering is accompanied by increase in resistivity. The lack of the low field intergrain magnetoresistance is in agreement with a weak spin polarization of the charge carriers. Magnetoresistance is associated with antiferromagnet-ferromagnet (from mixed high/low into intermediate spin state) transition induced by magnetic field. It is suggested that ferromagnetism is originated from superexchange interaction via oxygen. V

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Stress-induced local polarization reversal was studied in La doped BiFeO 3 ceramics under the action of Berkovich-type prism indentation. Piezoresponse force microscopy was used for detailed study of domain structure before and after local polarization reversal. Two mechanisms of domain formation under the action of the mechanical loading were revealed: (1) direct stress-induced and (2) stress mediated by grain clamping. Critical stress value for local polarization reversal was extracted from the dependence of the switched area on the applied loading force.

Stress-induced local polarization reversal was studied in La doped BiFeO 3 ceramics under the action of Berkovich-type prism indentation. Piezoresponse force microscopy was used for detailed study of domain structure before and after local polarization reversal. Two mechanisms of domain formation under the action of the mechanical loading were revealed: (1) direct stress-induced and (2) stress mediated by grain clamping. Critical stress value for local polarization reversal was extracted from the dependence of the switched area on the applied loading force.

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