MAGNETIC-PROPERTIES OF ULTRATHIN EPITAXIAL-FILMS OF IRON

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 thicknesses. Fe/Ru(0001) lacks a ferromagnetic response for thicknesses 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 beta-eff of 0.127 +/- 0.004 is obtained for a 1.2 ML Fe/Pd (100) film, in agreement with the theoretical value of beta-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.