Ferromagnetism and Temperature-Driven Reorientation Transition in Thin Itinerant-Electron Films

TL;DR

This paper investigates temperature-driven magnetic reorientation transitions in thin itinerant-electron films using an extended Hubbard model, revealing both Fe- and Ni-type transitions influenced by temperature, film thickness, and band occupation.

Contribution

It introduces a novel approach applying an itinerant-electron Hubbard model with layer-dependent anisotropy to study reorientation transitions, extending beyond traditional Heisenberg models.

Findings

Both Fe- and Ni-type reorientation transitions are possible.

Surface magnetization reduction drives the transition.

Transition depends on temperature, film thickness, and band filling.

Abstract

The temperature-driven reorientation transition which, up to now, has been studied by use of Heisenberg-type models only, is investigated within an itinerant-electron model. We consider the Hubbard model for a thin fcc(100) film together with the dipole interaction and a layer-dependent anisotropy field. The isotropic part of the model is treated by use of a generalization of the spectral-density approach to the film geometry. The magnetic properties of the film are investigated as a function of temperature and film thickness and are analyzed in detail with help of the spin- and layer-dependent quasiparticle density of states. By calculating the temperature dependence of the second-order anisotropy constants we find that both types of reorientation transitions, from out-of-plane to in-plane (``Fe-type'') and from in-plane to out-of-plane (``Ni-type'') magnetization are possible within our model. In the latter case the inclusion of a positive volume anisotropy is vital. The reorientation transition is mediated by a strong reduction of the surface magnetization with respect to the inner layers as a function of temperature and is found to depend significantly on the total band occupation.