## Physics - Dissertations

#### Title

Correlation of electronic structure and ferromagnetism at rare earth metal surfaces

1993

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Physics

Peter Dowben

magnetism

#### Subject Categories

Condensed Matter Physics

#### Abstract

The aim of this thesis is to understand surface magnetism from an electronic structure point of view. Specifically, heavy rare earth metal surfaces, especially Gd(0001) surface, were chosen because they provide the extreme examples of surface magnetism. Experimentally, spectroscopy techniques such as photoemission in different modes and spin-polarized photoemission, are utilized to probe the electronic structure and magnetic order of the bulk and surface.

A new surface state near E$\sb{F}$ in the vicinity of $\bar\Gamma$ has been observed, which has 5d$\sb{3z\sp2-r\sp2}$ character and is spatially localized. Our experimental results and a recent theoretical calculation agree with each other on many aspects. The existence of this localized surface state explains the altered magnetic coupling and magnetic moment at the surface, and therefore provides considerable insight into the origin of that enhanced magnetic ordering at the Gd(0001) surface. This surface state is shown to be a magnetic state. There is an imperfect ferromagnetic coupling between the surface and bulk with a perpendicular component of magnetic moment at the surface.

Hydrogen dissociatively chemisorbs onto Gd(0001) surface to form 1 x 1 structure with no surface reconstruction observed. A pair of two-dimensional bands are induced by hydrogen adsorption. The highly localized 5d surface state of the clean surface is "converted" into a dispersive H-induced state. This "conversion" gives us the insight into the origin of the anticipated altered magnetic coupling and magnetic moment at the surface.

For the bulk bands, the exchange splitting changes with temperature while for the surface state, spin mixing is observed. A simple picture which embodies the differences in the relative localization is employed to understand these differences between the surface and the bulk.

The j-J coupling multiplet splittings of the 5p photoemission feature were observed and later calculated with an atomic calculation. The magnetic order is probed from the 5p levels with linearly polarized light. For paramagnetic rare earth metals $\rm (T>T\sb{\it c})$ on a ferromagnetic substrate, magnetic order is induced in the overlayer, which can be modeled with Ginzberg-Landau's theory.

#### Access

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