A Study of the Paramagnetic to Ferromagnetic Transition in the Optimally Doped CMR Compound LaCaMnO and Its Dependence on Oxygen Mass

We present a study of the paramagnetic to ferromagnetic transition in the CMR compound LaCaMnO and its dependence on magnetic field and oxygen mass. The transition is characterized by two temperatures, the thermodynamic transition temperature at , obtained from specific heat and thermal expansion data, and the resistive transition obtained from the resistivity maximum. The resistive transition occurs well within the paramagnetic range. The magnetic susceptibility in the paramagnetic range is isotope dependent up to 400 K. The magnitude of the Curie-Weiss constant indicates the presence of small clusters of about 4–5 unit cells. The resistive transition occurs when the percolation limit for these clusters is reached.