Spontaneous behavior and magnetic field and pressure effects on La2/3Ca1/3MnO3 perovskite

The effects of magnetic field and pressure on the unusual spontaneous behavior of La2/3Ca1/3MnO3 have been thoroughly investigated. Resistivity and volume thermal expansion, both under magnetic field and pressure, ac susceptibility under pressure, magnetostriction, magnetoresistance, and neutron diffraction measurements, have allowed us to determine the relevant underlying mechanisms in this system. Above T-c the neutron measurements reveal short-range ferromagnetic correlations and the anomalous volume thermal expansion indicates that local distortions are present. Both experiments support the formation of magnetic polarons above T-c. At T-c the compound undergoes a paramagnetic-ferromagnetic transition accompanied by an insulator-metal-like transition with anomalies in the electrical and volume properties. Above T-c the magnetic field and the pressure favor electrical conduction by enhancing the double-exchange interaction. Below T-c the metallic state is favored by the magnetic field and the pressure in a different way.