Thermodynamic modelling of phase separated manganites

JOAQUIN SACANELL; FRANCISCO PARISI; JUAN CAMPOY; LUIS GHIVELDER

Mar del Plata, Argentina

Otro; PASI 2006 “From disordered systems to complex systems”; 2006

Universidad Nacional de Mar del Plata - CONICET

The low temperature thermodynamics (below 60K) of a phase separated manganite is studied. The phase separated state (PS) is characterized by the coexistence of ferromagnetic metallic (FM) and charge ordered insulator (COI) phases. We propose a procedure to obtain the Gibbs free energies of both phases in La5/8-yPryCa3/8MnO3 with y=0.4 (LPCMO(0.4)), which display PS features. The method is based on specific heat (Cp) and magnetization measurements under magnetic fields. Through a particular protocol it is possible to obtain the temperature dependence of Cp for each one of the coexisting phases.  The PS state can be further obtained under the hypothesis that chemical and structural disorder gives rise to an inhomogeneous distribution transition temperatures, resulting in a non uniform distribution of the free energy density. Through this procedure we were able to reproduce the equilibrium state of the system. As the response of the system in the phase separated state is characterized by important out of equilibrium features, we have developed a global model for a complete description of the inbreeded dynamic and static properties. A good agreement has been found between calculated and experimental data.