Numerical Analysis of Heat Transport Behavior in the Ferromagnetic Metallic State of La0.80Ca0.20MnO3 Manganites

Abstract

The lattice contribution to the thermal conductivity (κph) in La0.80Ca0.20 MnO3 manganites is discussed within the Debye-type relaxation rate approximation in terms of the acoustic phonon frequency and relaxation time. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries, charge carriers, and phonons. The lattice thermal conductivity dominates in La–Ca–MnO manganites and is an artifact of strong phonon-impurity and -phonon scattering mechanisms in the ferromagnetic metallic state. The electronic contribution to the thermal conductivity (κe) is estimated following the Wiedemann–Franz law. This estimate sets an upper bound on κe, and in the vicinity of the Curie temperature (240 K) κe is about 1% of total heat transfer of manganites. Another important contribution in the metallic phase should come from spin waves (κm). It is noticed that κm increases with a T2 dependence on the temperature. These channels for heat transfer are algebraically added and κtot develops a broad peak at about 55 K, before falling off at lower temperatures. The behavior of the thermal conductivity in manganites is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron, magnon, and phonon contributions. The numerical analysis of heat transfer in the ferromagnetic metallic phase of manganites shows similar results as those revealed from experiments.