The temperature dependent bandstructure of a ferromagnetic semiconductor film

TL;DR

This paper investigates how the electronic bandstructure of a ferromagnetic semiconductor film varies with temperature using an extended s-f model, revealing correlation effects influenced by spin, exchange coupling, and temperature.

Contribution

It extends the s-f model to finite temperatures for ferromagnetic semiconductors, providing a continuous theory from the exact zero-temperature limit.

Findings

Correlation effects depend on electron spin, exchange coupling, and temperature.

The theory models materials like EuO and EuS.

Finite temperature influences the quasiparticle spectrum.

Abstract

The electronic quasiparticle spectrum of a ferromagnetic film is investigated within the framework of the s-f model. Starting from the exact solvable case of a single electron in an otherwise empty conduction band being exchange coupled to a ferromagnetically saturated localized spin system we extend the theory to finite temperatures. Our approach is a moment-conserving decoupling procedure for suitable defined Green functions. The theory for finite temperatures evolves continuously from the exact limiting case. The restriction to zero conduction band occupation may be regarded as a proper model description for ferromagnetic semiconductors like EuO and EuS. Evaluating the theory for a simple cubic film cut parallel to the (100) crystal plane, we find some marked correlation effects which depend on the spin of the test electron, on the exchange coupling, and on the temperature of the local-moment system.