Schwinger boson theory of anisotropic ferromagnetic ultrathin films

Abstract

Ferromagnetic thin films with magnetic single-ion anisotropies are studied within the framework of Schwinger bosonization of a quantum Heisenberg model. Two alternative bosonizations are discussed. We show that qualitatively correct results are obtained even at the mean-field level of the theory, similar to Schwinger boson results for other magnetic systems. In particular, the Mermin-Wagner theorem is satisfied: a spontaneous magnetization at finite temperatures is not found if the ground state of the anisotropic system exhibits a continuous degeneracy. We calculate the magnetization and effective anisotropies as functions of exchange interaction, magnetic anisotropies, external magnetic field, and temperature for arbitrary values of the spin quantum number. Magnetic reorientation transitions and effective anisotropies are discussed. The results obtained by Schwinger boson mean-field theory are compared with the many-body Green's function technique.

14 pages, including 7 EPS figures, minor changes, final version as published

References in corpus (6)

• Collective Excitations, NMR, and Phase Transitions in Skyrme Crystals
• Field-induced magnetic reorientation and effective anisotropy of a ferromagnetic monolayer within spin wave theory
• Reorientation transition of ultrathin ferromagnetic films
• 1/N expansion for two-dimensional quantum ferromagnets
• Monte Carlo study of a two-dimensional quantum ferromagnet
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• A representation of angular momentum (SU(2)) algebra
• Quantum spherical spin models
• Intermediate-statistics spin waves
• Switching the Magnetization in Quantum Antiferromagnets
• Non-standard Schwinger fermionic representation of unitary group