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Field-induced magnetic reorientation and effective anisotropy of a ferromagnetic monolayer within spin wave theory

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

The reorientation of the magnetization of a ferromagnetic monolayer is calculated with the help of many-body Green's function theory. This allows, in contrast to other spin wave theories, a satisfactory calculation of magnetic properties over the entire temperature range of interest since interactions between spin waves are taken into account. A Heisenberg Hamiltonian plus a second-order uniaxial single-ion anisotropy and an external magnetic field is treated by the Tyablikov (Random Phase Approximation: RPA) decoupling of the exchange interaction term and the Anderson-Callen decoupling of the anisotropy term. The orientation of the magnetization is determined by the spin components $\la S^α\ra$ ($α=x,y,z$), which are calculated with the help of the spectral theorem. The knowledge of the orientation angle $Θ_0$ allows a non-perturbative determination of the temperature dependence of the effective second-order anisotropy coefficient. Results for the Green's function theory are compared with those obtained with mean-field theory (MFT). We find significant differences between these approaches.

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P. Fröbrich, P. J. Jensen, P. J. Kuntz. 1999-10-18. Field-induced magnetic reorientation and effective anisotropy of a ferromagnetic monolayer within spin wave theory. https://doi.org/10.1007/s100510050059

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