Electronic and spin states of ${\mathrm{SrRuO}}_3$ thin films: An x-ray magnetic circular dichroism study

We report a study of the local magnetism in thin films of ${\mathrm{SrRuO}}_3$ grown on (111) and (001) oriented ${\mathrm{SrTiO}}_3$ substrates using x-ray magnetic circular dichroism spectroscopy (XMCD) at the Ru-$L_{2,3}$ edges. The application of the sum rules to the XMCD data gives an almost quenched orbital moment and a spin moment close to the value expected for the low spin state $S=1$. Full-multiplet cluster calculations indicate that the low spin state is quite stable and suggest that the occurrence of a transition to the high spin state $S=2$ in strained thin films of ${\mathrm{SrRuO}}_3$ is unlikely as it would be too expensive in energy.

Figure 1

Ru-$L_{2,3}$ XAS spectra of a 27-nm SRO/(111)STO film for linearly polarized light coming in with the electric-field vector $\mathbf{E}$ normal [dark (blue) lines] and parallel [light (red) lines] to the film surface.

Figure 2

Ru-$L_{2,3}$ XAS spectra (a) and XMCD spectra (b) of ${\mathrm{SrRuO}}_3$ films and bulk single crystal measured at $T=50\mathrm{K}$ and $H=6$ T. The spectra are vertically shifted for clarity. The spectra taken at normal $({90}^{\circ })$ and grazing $({20}^{\circ })$ incidence show a small anisotropy. The dashed black curve represents the edge jump.

Figure 3

Setup of the XMCD experiments: the magnetic field $B$ is applied parallel to the Poynting vector of the circularly polarized photons and forms an angle of ${90}^{\circ } ({20}^{\circ })$ in normal (grazing) incidence with the sample surface.

Figure 4

Zoom of Ru-$L_{2,3}$ isotropic XAS and XMCD spectra of a 27-nm thin film of ${\mathrm{SrRuO}}_3$ grown on a (111) oriented ${\mathrm{SrTiO}}_3$ substrate. The vertical dashed lines correspond to the energy position of the maxima in the XAS and XMCD spectra.

Figure 5

Energy-level diagram of the ${\mathrm{Ru}}^{4+}$ ion as a function of the ionic crystal field $10Dq$ in a cubic local symmetry. Black dotted, blue solid, and red dashed lines correspond to levels with $S=$ 0, 1, and 2 spin states, respectively. The inset shows the evolution of the effective crystal field vs ionic crystal field. The vertical brown solid line indicates the $10D{q}_{\text{eff}}$ of ${\mathrm{SrRuO}}_3$ as obtained by the simulation of the XAS and XMCD spectra.

Figure 6

Experimental (top) and simulated (below) XMCD and XAS spectra for different $10D{q}_{\text{eff}}$ values at the $L_3$ (panel a) and $L_2$ (panel b) edges. For a better comparison the spectra were normalized to the peak height and the Ru-$L_3$ XMCD spectrum was reversed. The vertical dotted lines correspond to the energy position of the maxima in the XAS and XMCD spectra.