We report the observation of exchange bias phenomena in the hole-doped perovskite cobaltites ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ ($x=0.12$, 0.15, 0.18, and 0.30) in which a spontaneous phase separation occurs. When the ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ samples are cooled in a static magnetic field through a freezing temperature, the magnetization hysteresis loops exhibit both horizontal and vertical shifts. We also observed training effect of the exchange bias, which can be interpreted by a spin configurational relaxation model. Moreover, exchange bias in ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$ is strongly dependent on the measuring field and the cooling field due to the influence of magnetic field on the relative proportion of the coexisting phases. These results suggest that the intrinsic phase inhomogeneity in a spontaneously phase-separated system may induce an interfacial exchange anisotropy.

• Received 26 October 2005

DOI:https://doi.org/10.1103/PhysRevB.73.174419