Magnetic depth profiling and characterization of Fe-oxide films by Kerr rotation and spin polarized photoemission

The site occupancy and the valence valence state of Fe ions in a ferritelike sputtered thin film and its subsequent magnetic properties are well known to critically depend on sample preparation techniques. We show how measuring spin polarization of threshold photoelectrons having a nondestructive depth profiling capability of up to 100 Å can be used to gain detailed insight into site and valency information as a function of depth. In particular, we demonstrate that a reactively sputter deposited Fe-oxide film nominally shown to have crystallography data consistent with bulk Fe3O 4 is uniform throughout, but in fact has no divalent Fe ++ contributing to its overall magnetic properties. Furthermore, post-deposition oxidation of this film to nominally yield the γFe2O3 structure resulted in producing a nonmagnetic top layer followed by a Fe+++ containing magnetic layer very similar to the as-deposited layer, but definitely not γFe2O3. Simple Kerr rotation measurements confirmed the presence of the nonmagnetic top layer to about 200 Å depth consistent with earlier measurements by neutron reflection. The evidence points to film structures with a high concentration of nonbulklike Fe site defects in the as-sputtered and oxidized condition.