Condensed Matter Physics Seminar

2 p.m., Thursday, March 18, 2004
Room 1201, Physics Building

Theory of Ferromagnetism in Double Perosvkites

Luis Brey

(Instituto de Ciencia de Materiales de Madrid (CSIC))

Abstract: We study the magnetic phase diagram of double perovskites of the type Sr_2-xLa_xFeMoO₆. These materials are good candidates for magnetoelectronics as they have a high Curie temperature and are thought to be half metallic. The magnetism arises from the Fe³⁺ S=5/2 cores spins, whereas the electrons move in a Fe-Mo conduction band. The antiferromagnetic coupling between the carriers and the Fe spins produces a ferromagnetic coupling of the core Fe spins. We develop a mean field theory describing the ferromagnetism in double perovskite materials. We describe the band motion of the carriers using a realistic (parametrized) tight binding Hamiltonian. We study the dependence of the Curie temperature on the band structure parameters, the exchange coupling, and the carrier density, and we compare the mean field results with that obtained using the Dynamical Mean Field Theory and Monte Carlo simulations. We also analyze the effect that the electron electron interaction has on the value of the Curie temperature. We include a Hubbard on-site Coulomb repulsion U, and study the effect of this interaction on the phase diagram. We comment on the experimental situation, and also compare the ferromagnetic mechanism in double perovskites with that in diluted magnetic semiconductors and manganese oxides.

Host: Das Sarma
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