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

TL;DR

This study uses soft x-ray magnetic circular dichroism to investigate how Co valency influences magnetism and anisotropy in different LaCoO3-based thin films, revealing valency-dependent spin states and magnetic behaviors.

Contribution

It provides new insights into the valency-dependent spin states and magnetic anisotropy in LaCoO3 films with different doping, using soft x-ray magnetic circular dichroism.

Findings

Higher spin state of Co3+ causes magnetism in LaCoO3.

Co3+ in La0.7Ce0.3CoO3 is low-spin, with ferromagnetism mainly from Co2+.

Magnetism in La0.7Sr0.3CoO3 originates from high-spin Co3+ and Co4+.

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 $T_{\rm{C}}$ $\approx$ 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.