J. Holroyd

Effect of electrode and EuO thickness on EuO-electrode interface in tunneling spin filter

The effect of electrode material and EuO film thickness on the interface between the two was studied. Of the electrodes examined, yttrium was found to decrease the formation of the nonmagnetic oxide Eu2O3. By decomposing the x-ray absorption spectroscopy (XAS) spectra of the samples with different electrodes against the reference EuO and Eu2O3 spectra, the relative fraction of these two species was quantified. Multilayers with silver electrodes had the highest amount of Eu2O3, about 41%, whereas aluminum had 28% compared to the less than 5% observed for the multilayers with yttrium electrodes. A slight decrease in the fraction of Eu2O3 with increasing EuO thickness was found. Angle dependent XAS measurements, done on 80A EuO film, indicated the presence of Eu2O3 at high grazing angles which then decreased drastically with decreasing grazing angle. This indicated that the Eu2O3 was localized at the EuO-electrode interface.

Site determination of Zn doping in protein encapsulated ZnxFe3−xO4 nanoparticles

The x-ray absorption spectra of the Fe and Zn L edges for 6.7nm Fe3O4 nanoparticles grown inside 12nm ferritin protein cages with 10%, 15%, 20%, and 33% zinc doping show that Zn is substitutional as Zn2+ within the iron oxide host structure. A Neel–Arrhenius plot of the blocking temperature in frequency dependent ac-susceptibility measurements shows that the particles are noninteracting and that the anisotropy energy barrier is reduced with Zn loading. X-ray magnetic circular dichroism of the Fe displays a linear decrease with Zn doping in sharp contrast to the initial increase present in the bulk system. The most plausible explanation for the decrease in moment is that Zn substitutes preferentially into the tetrahedral A site as a Zn2+ cation, generating a mixed spinel.

Properties of thin film europium oxide by x-ray magnetic circular dichroism

Magnetic circular dichroism was measured as function of temperature for the Eu M5 and M4 absorption edges in single crystal EuO thin films. The M5 edge is resolved into two major features, one with the same helicity dependence as the M4 edge, and one with opposite helicity dependence. While the ratio of the absorption peaks with similar helicity dependence remains constant as a function of temperature, the ratio of those with opposite dependence is found to change linearly with temperature below 75 K. The physical mechanism for this linear behavior in the absorption peak intensity is not well understood.