  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.
