https://doi.org/10.1007/s100510070005
Many-body Green's function theory for the magnetic reorientation of thin ferromagnetic films
1
Hahn-Meitner-Institut Berlin, Glienicker Straße 100, 14109 Berlin,
Germany
2
Institut für Theoretische Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
Corresponding author: a froebrich@hmi.de
Received:
19
June
2000
Revised:
2
August
2000
Published online: 15 December 2000
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
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.
PACS: 75.10.Jm – Quantized spin models / 75.30.Ds – Spin waves / 75.70.Ak – Magnetic properties of monolayers and thin films
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000