Spin-polarized tunneling current through a ferromagnetic insulator between two metallic or superconducting leads

N. Sandschneider; W. Nolting

doi:10.1103/PhysRevB.76.115315

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Spin-polarized tunneling current through a ferromagnetic insulator between two metallic or superconducting leads

N. Sandschneider, W. Nolting

DOI 10.1103/PhysRevB.76.115315 · Physical Review B

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Abstract

Using the Keldysh formalism (Zh. Eksp. Teor. Fiz. 47, 1515 (1964) [Sov. Phys. JETP 20, 1018 (1965)]), the tunneling current through a hybrid structure where a confined magnetic insulator (I) is sandwiched between two nonmagnetic leads is calculated. The leads can be either normal metals (M) or superconductors (S). Each region is modeled as a single band in tight-binding approximation in order to understand the formation of the tunneling current as clearly as possible. The tunneling process itself is simulated by a hybridization between the lead and insulator conduction bands. The insulator is assumed to have localized moments which can interact with the tunneling electrons. This is described by the Kondo lattice model and treated within an interpolating self-energy approach. For the superconductor, the mean-field BCS theory is used. The spin polarization of the current shows a strong dependence both on the applied voltage and on the properties of the materials. Even for this idealized three band model, there is a qualitative agreement with experiment.