Magnetization Reversal and Nanoscopic Magnetic Phase Separation in Doped La1-xSrxCoO3

The doped perovskite cobaltite La1-xSrxCoO3 (LSCO) has been advanced as a model system for studying intrinsic magnetic phase separation. We have employed a first-order reversal curve (FORC) method to probe the amount of irreversible switching in bulk polycrystalline LSCO as a function of Sr doping, field cooling procedure, and temperature. The value of the FORC distribution, rho, is used as a measure of the extent of irreversible switching. For x < 0.18, the small values of rho and its ridge-like distribution along local coercivity (Hc) and zero bias (Hb), are characteristic of non-interacting single domain particles. This is consistent with the formation of an array of isolated nanoscopic ferromagnetic clusters, as observed in previous work. For x >= 0.18, the much larger values of rho, the tilting of its distribution towards negative bias field, and the emergence of regions with negative rho, are consistent with increased long-range ferromagnetic ordering. The FORC distributions display little dependence on the cooling procedure. With increasing temperature, the fraction of irreversible switching determined from the FORC distribution follows closely the ferromagnetic phase fraction measured by La nuclear magnetic resonance. Our results furthermore demonstrate that the FORC method is a valuable first-pass characterization tool for magnetic phase separation.