Magnetic properties of ultrathin epitaxial films of iron

Abstract

Ultrathin Fe films epitaxially grown on Cu(100), Au(100), Pd(100) and Ru(0001) substrates are used to study monolayer magnetism, surface magnetic anisotropy and two-dimensional (2D) critical behavior, by means of in-situ surface magneto-optical Kerr-effect measurements. Epitaxial structures and growth modes are characterized by auxiliary low-energy electron diffraction and Auger electron studies. The magnetic properties of the films depend on the growth temperature. For 100 K growth, all films exhibit a universal behavior of perpendicular spin orientations in the monolayer regime, while for 300 K growth, Fe/Pd(100) and Fe/Au(100) have in-plane easy-axis of magnetization for all thickness. Fe/Ru(0001) lacks a ferromagnetic response for thickness less than two monolayers (ML). Fe/Pd(100) has remarkable thermal stability in the monolayer and submonolayer range. Reversible magnetization data are obtained for 0.6 to 3.0 ML thick films, which show second-order phase transitions at thickness-dependent Curie temperatures ( T c ). An effective magnetization exponent β eff of 0.127 ± 0.004 is obtained for a 1.2 ML Fe/Pd (100) film, in agreement with the theoretical value of β c = 0.125 for an ideal 2D Ising model. The T c trend with film thickness for Fe/Pd(100) is also in agreement with Monte Carlo calculations for Ising films.