Field dependent specific-heat of rare earth manganites

The low-temperature specific heat C(H) of several rare-earth manganites (La_0.7Sr_0.3MnO₃, Nd_0.5Sr_0.5MnO₃, Pr_0.5Sr_0.5MnO₃, La_0.67Ca_0.33MnO₃, La_0.5Ca_0.5MnO₃, La_0.45Ca_0.55MnO₃ and La_0.33Ca_0.67MnO₃) was measured as a function of magnetic field. We observed behavior consistent with thermodynamic expectations, i.e., C(H) decreases with field for ferromagnetic metallic compounds by an amount which is in quantitative agreement with spin-wave theory. We also find that C(H) increases with field in most compounds with a charge-ordered antiferromagnetic ground state. In compounds which show evidence of a coexistence of ferromagnetic metallic and antiferromagnetic charge-ordered states, C(H) displays some unusual non-equilibrium effects presumably associated with the phase-separation of the two states. We also observe a large anomalous low-temperature specific heat at the doping-induced metal-insulator transition (at x = 0.50) in La_1-xCa_xMnO₃.