Field-induced crossover in La0.7Pb0.3MnO3

A field-induced crossover is observed both resistively and magnetically in a single crystal of La0.7Pb0.3MnO3, a compound that exhibits colossal magne toresistance (CMR) and has a second-order ferromagnetic transition. The res istivity (rho) data observed in high magnetic fields show a universal decre ase with the magnetization (M) and little dependence on temperature. In con trast, rho is independent of M for lower fields. An analysis of the magneti zation data finds that the critical exponents have different values dependi ng on whether the high held data or the low field data are analyzed. The re sults are consistent with the interpretation that at low fields, the compou nd behaves as a collection of magnetic clusters with mean-field-like inter- cluster interactions, and at high fields the compound behaves as a system o f individual spins with short-range interactions.