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Many-body Green's function theory for the magnetic reorientation of thin ferromagnetic films

P. Fröbrich·P. J. Jensen·P. J. Kuntz·A. Ecker
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Abstract

The field-induced reorientation of the magnetization of ferromagnetic films is treated within the framework of many-body Green's function theory by considering all components of the magnetization. We present a new method for the calculation of expectation values in terms of the eigenvalues and eigenvectors of the equations of motion matrix for the set of Green's functions. This formulation allows a straightforward extension of the monolayer case to thin films with many layers and for arbitrary spin and moreover provides a practicable procedure for numerical computation. The model Hamiltonian includes a Heisenberg term, an external magnetic field, a second-order uniaxial single-ion anisotropy, and the magnetic dipole-dipole coupling. We utilize the Tyablikov (RPA) decoupling for the exchange interaction terms and the Anderson-Callen decoupling for the anisotropy terms. The dipole coupling is treated in the mean-field approximation, a procedure which we demonstrate to be a sufficiently good approximation for realistic coupling strengths. We apply the new method to monolayers with spin $S\geq 1$ and to multilayer systems with S=1. We compare some of our results to those where mean-field theory (MFT) is applied to all interactions, pointing out some significant differences.

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P. Fröbrich, P. J. Jensen, P. J. Kuntz, A. Ecker. 2000-09-01. Many-body Green's function theory for the magnetic reorientation of thin ferromagnetic films. https://doi.org/10.1007/s100510070005

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