Probing magnetic phase separation in manganites by nonlinear susceptibility

At low frequencies ν≤300Hz, nonlinear magnetic susceptibility of polycrystalline La0.7Pb0.3Mn0.8(Co, Ni)0.2O3 samples near the ferromagnetic (FM)–paramagnetic (PM) phase transition reinforces the earlier observation, based on linear ac susceptibility, that these systems behave as a three-dimensional isotropic dipolar ferromagnet in the asymptotic critical regime and exhibit an isotropic dipolar to isotropic Heisenberg crossover. In addition, the nonlinear susceptibility results reveal the phase segregation of the conducting and insulating FM phases (clusters) within the conducting FM regime and existence of conducting FM clusters in the insulating PM matrix at high frequencies.