Surface and interface phase transitions in thin magnetic films with frustrated exchange interactions

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Abstract
Detailed studies of magnetic phase transitions in thin magnetic films with frustrated exchange interactions on nonmagnetic surfaces are presented. In the first part of the work we use a self-consistent real-space tight-binding linear-muffin-tin orbital approach to determine the magnetic structure of face-centered cubic Fe films on Cu(100) substrates and a Green’s-function technique to calculate the exchange pair interactions. The results demonstrate a ferromagnetic coupling at the free surface and antiferromagnetic coupling in the interior of the films. The competition between ferro- and antiferromagnetism leads to a pronounced enhancement of the exchange coupling at the surface and at the interface with the nonmagnetic substrate and a strong reduction (frustration) in the inner layers. In the second part we use these results to formulate an Ising model for magnetic films with frustrated exchange interactions and to perform extended Monte Carlo simulations of magnetic phase transitions. The results demonstrate a rich scenario of two-dimensional surface and interface phase transitions, coupled through weak magnetic fluctuations in the interior of the film. In addition, spin-reorientation transitions (reversible and irreversible) between high- and low-moment states are observed.