Pressure enhanced ferromagnetism and suppressed exchange bias in La _0.9Ba_0.1CoO₃ cobaltite

Pressure effect on magnetic properties of La_0.9Ba _0.1CoO₃ cobaltite, exhibiting the ferromagnetic (FM) cluster-glass behavior and exchange bias (EB) effect at low temperatures, was investigated up to 10 kbar. It was found that an applied pressure increases the temperature T_C^cl ≈ 190 K, below which the FM clusters appear, and enlarges the FM phase volume in the sample. Positive value of dT_C^cl/dP coefficient suggests a wide e_g- electron bandwidth for Co ions sited inside the Ba-rich regions (FM clusters). The EB field H_E increases sharply with decreasing temperature below the spin-glass (SG) like transition temperature T_f ≈ 38 K, in a consequence of the exchange coupling at the FM/SG interfaces. Applied pressure was found to suppress strongly the EB, in particular, H_E reduces by a factor of ∼3 under pressure of 10 kbar at 30 K. It appears that under pressure, H_E varies oppositely to the changes in FM phase volume that is very similar to the behavior observed for phase-separated FM/antiferromagnetic manganites. Overall, the pressure-induced diminution in H_E is explained by considering an increase of the FM cluster size and by concomitant decrease of distance between clusters. The results show that for phase-separated FM/SG cobaltites, the EB effect may be controlled by external pressure.