The magnetic coupling of an elemental local moment 4f magnetic system

The relationship between magnetic behavior and the electronic structure of a 4f local moment ferromagnet, gadolinium, has been explored. The spin-polarized electronic structure of gadolinium is an admixture of rigid band magnetism and Stoner-like ferromagnetism. The admixture is dependent upon electron localization, band structure, wave vector, film thickness and coordination number. The work presented in this dissertation focuses on the interplay between rigid band and Stoner magnetism of strained thin films gadolinium in comparison to that of unstrained gadolinium. A spin-polarized band mapping of strained Gd(0001) reveals the first direct experimental evidence for wave vector dependent magnetic coupling in an elemental local moment ferromagnet. The influence of the surface on the magnetic behavior of ultra-thin films is extremely important, as evidenced by the increasing dominance of the surface magnetic ordering in increasingly thinner films. With decreasing film thickness, the bulk bands of strained Gd exhibit increasingly more passive magnetic behavior resembling a paramagnet over an increasing volume of the bulk Brillouin zone. This results in a deviation from the finite size scaling behavior. Strained thin films of gadolinium with an increased lattice constant of more than 1% as compared to Gd(0001) have been obtained for the first time by growing Gd on the corrugated surface of Mo(112). Ultra-thin $\rm (3\ ML \u3c d \u3c 10\ ML)$ and thin $\rm (d \u3e 10\ ML)$ films of Gd order in well defined rectangular and hexagonal surface unit cells, that resemble strained Gd(1012) and strained Gd(0001), respectively. Expansive strain of approximately 4% within the hexagonal closed packed system results in increased electron localization of the itinerant valence electrons and is seen to have a profound effect on both the magnetic properties of gadolinium and the attendent band structure. Expansive strain enhances both bulk and surface magnetization, leading to large Gd 5d exchange splittings and enhanced (higher) Curie temperatures