Soft x-ray magnetic circular dichroism study on Gd-doped $\mathrm{EuO}$ thin films

We report on the growth and magnetic properties of Gd-doped $\mathrm{EuO}$ thin films. We prepared samples with Gd concentrations up to $11\%$ by means of molecular beam epitaxy under distillation conditions. Using soft x-ray magnetic circular dichroism at the Eu and Gd $M_{4,5}$ edges, we found that $T_C$ ranges from $69\mathrm{K}$ for pure stoichiometric $\mathrm{EuO}$ to about $170\mathrm{K}$ for films with the optimal Gd doping of around $4\%$. The doping dependence of $T_C$ has been investigated and compared with available theoretical predictions. We also show that the Gd magnetic moment couples ferromagnetically to that of Eu.

Figure 1

Eu and Gd $M_{4,5}$ $(3d\to 4f)$ XAS spectra of a stoichiometric (undoped) $\mathrm{EuO}$ sample and a $10\%$ Gd-doped $\mathrm{EuO}$ sample.

Figure 2

Eu $M_{4,5}$ XAS spectra of a $3.7\%$ Gd-doped $\mathrm{EuO}$ sample recorded at $20\mathrm{K}$ using circularly polarized x rays with the photon spin parallel (solid line) and antiparallel (dashed line) to the magnetic field direction. The lowest curve shows the difference between both, which is called the XMCD spectrum.

Figure 3

Top panel: XMCD effect as a function of temperature for $\mathrm{EuO}$ samples with different Gd doping levels. Bottom panel: Doping dependence of the Curie temperature $\left(T_C\right)$. The dotted line represents the result of a mean-field calculation.

Figure 4

Eu and Gd $M_{4,5}$ XAS spectra of (a) a $3.7\%$ Gd-doped $\mathrm{EuO}$ sample and (b) an undoped $\mathrm{EuO}$ sample, recorded at $20\mathrm{K}$ using circularly polarized x rays with the photon spin parallel and antiparallel to the magnetic field direction. (c) The net Gd $M_{4,5}$ contribution, obtained by subtracting the $\mathrm{EuO}$ spectra from those of the $3.7\%$ Gd-doped $\mathrm{EuO}$.