FERROMAGNETIC MONOLAYERS

The ferromagnetic properties of ultrathin films grown on non-magnetic substrates provide interesting new insights into the physics of magnet ism. In this report we review experiments in the very low coverage reg ime (- < 2 atomic layers). The Fe monolayer on W plays an outstanding role, because it forms a ferromagnetic and thermodynamically stable mo nolayer. Ferromagnetic Fe monolayers on W can be prepared with a high degree of perfection. We therefore focus on ultrathin Fe films on W(11 0) and W(100) substrates. Experimental results for these in-plane magn etized films, prepared as close as possible to a-dimensional structure s of perfect translational symmetry, are compared with appropriate the oretical models. We also discuss experimental results for the perpendi cularly magnetized Co monolayer on Cu(111). The symmetry of the magnet ic anisotropy is found to play an important role for the understanding of the magnetic phase transition in 2 dimensions. A new aspect is pro vided by finite size effects resulting from the morphology of magnetic ultrathin films. Microscopy with atomic resolution allows a systemati c approach to the understanding of these finite size effects. Starting from the well-known magnetic properties of the extended Fe monolayer on W(110), we focus on ultrathin Fe films on W(110) deviating from the nearly perfect structure.