High-temperature dynamics of surface magnetism in iron thin films

Finite-temperature magnetic properties of iron thin films are investigated by computer simulation over a broad range of temperatures up to the point of the ferromagnetic-paramagnetic phase transition. The coupled dynamics of atoms and magnetic moments is treated using the large-scale spin-lattice dynamics (SLD) algorithm. We investigate surface and bulk magnetic properties of iron, and how these properties vary as a function of temperature, film thickness and surface crystallography. We find that magnetization at surfaces is enhanced at low temperatures and suppressed at higher temperatures, in agreement with experimental observations. The effective Curie temperature of a film decreases as a function of thickness. Short-range magnetic order and non-vanishing spin-spin spatial correlations are found above the Curie temperature. The spin autocorrelation functions exhibit slower oscillations with longer decoherence times near the surface. We also find that the directional spin disorder has a significant effect on the surface strain.