Soft x-ray magnetic circular dichroism of LaCoO${}_3$, La${}_{0.7}$Ce${}_{0.3}$CoO${}_3$, and La${}_{0.7}$Sr${}_{0.3}$CoO${}_3$ films: Evidence for Co valency-dependent magnetism and magnetic anisotropy

Abstract

Epitaxial thin films of undoped LaCoO${}_3$\@, of electron-doped La${}_{0.7}$Ce${}_{0.3}$CoO${}_3$\@, and of hole-doped La${}_{0.7}$Sr${}_{0.3}$CoO${}_3$\@ exhibit ferromagnetic order with a transition temperature $T_{\mathrm{C}}$ $\approx$ 85 K, 22 K, and 240 K, respectively. The spin-state structure for these compounds was studied by soft x-ray magnetic circular dichroism at the Co $L_{2,3}$ and O $K$ edges. It turns out that a higher spin state of the Co${}^{3+}$ ions is responsible for the magnetism in LaCoO${}_3$\@ while for La${}_{0.7}$Ce${}_{0.3}$CoO${}_3$ the Co${}^{3+}$ ions are in a low-spin state and the ferromagnetism is predominantly determined by Co${}^{2+}$\@. For La${}_{0.7}$Sr${}_{0.3}$CoO${}_3$\@, on the other hand, the magnetism originates from higher spin states of Co${}^{3+}$ and Co${}^{4+}$\@. Moreover, a strong magnetic anisotropy is observed for all systems.

submitted