Coexisting tunable fractions of glassy and equilibrium long-range-order phases in manganites

Abstract

Antiferromagnetic-insulating (AF-I) and ferromagnetic-metallic (FM-M) phases coexist in various half-doped manganites over a range of temperature and magnetic field, and this is often believed to be an essential ingredient of their colossal magnetoresistance. We present magnetization and resistivity measurements on Pr_0.5Ca_0.5Mn_0.975Al_0.025O₃ and Pr_0.5Sr_0.5MnO₃ showing that the fraction of the two coexisting phases at low temperature in any specified measuring field, H, can be continuously controlled by following designed protocols traversing field-temperature space; for both materials the FM-M fraction rises under similar cooling paths. Constant-field temperature variations, however, show that the former sample undergoes a first-order transition from AF-I to FM-M with decreasing T, while the latter undergoes the reverse transition. We suggest that the observed path-dependent phase-separated states result from the low-T equilibrium phase coexisting with supercooled glass-like high-temperature phase, where the low-T equilibrium phases are actually homogeneous FM-M and AF-I phases respectively for the two materials.