AES/XPS studies of oxidized R 2Fe 4B alloys

Abstract

Auger and X-ray photoelectron spectroscopies have been used to study the compositional and chemical nature of air-exposed R 2Fe 14B (R = Y, Nd and Gd) magnet alloys. Rare earth segregation correlates with the extent of surface oxidation and moderately oxidized surfaces show either stoichiometric rare earth concentrations or slight enrichment over near-surface values while heavily oxidized surfaces show rare earth depletion. The depleted surfaces contain significant amounts of iron oxides and it is proposed that, after initial oxidation of the near-surface rare-earth component, iron segregates to the surface driven by the formation of iron oxides. Boron segregation is also observed, although migration results in alloy-like surface boron species. However, once at the surface, boron oxidation is possible and boron oxides are identified by their characteristic 171 eV AES signal. Preferential sputtering of the boron component prevents meaningful depth analysis of this component of the rare-earth alloys.