An XMCD study of magnetism and valence state in iron-substituted strontium titanate

Abstract

Room temperature ferromagnetism was characterized for thin films of SrTi${}_{0.6}$Fe${}_{0.4}$O${}_{3-\delta }$ grown by pulsed laser deposition on SrTiO${}_3$ and Si substrates under different oxygen pressures and after annealing under oxygen and vacuum conditions. X-ray magnetic circular dichroism demonstrated that the magnetization originated from Fe${}^{2+}$ cations, whereas Fe${}^{3+}$ and Ti${}^{4+}$ did not contribute. Films with the highest magnetic moment (0.8 μB per Fe) had the highest measured Fe${}^{2+}$:Fe${}^3+$ ratio of 0.1 corresponding to the largest concentration of oxygen vacancies (δ = 0.19). Post-growth annealing treatments under oxidizing and reducing conditions demonstrated quenching and partial recovery of magnetism respectively, and a change in Fe valence states. The study elucidates the microscopic origin of magnetism in highly Fe-substituted SrTi${}_{1-x}$Fe${}_x$O${}_{3-\delta }$ perovskite oxides and demonstrates that the magnetic moment, which correlates with the relative content of Fe${}^{2+}$ and Fe${}^{3+}$, can be controlled via the oxygen content, either during growth or by post-growth annealing.