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

Room-temperature ferromagnetism was characterized for thin films of SrTi0.6Fe0.4O3-delta grown by pulsed laser deposition on SrTiO3 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 Fe2+ cations, whereas Fe3+ and Ti4+ did not contribute. Films with the highest magnetic moment (0.8 mu(B) per Fe) had the highest measured Fe2+:Fe3+ ratio of 0.1 corresponding to the largest concentration of oxygen vacancies (delta = 0.19). Postgrowth 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 SrTi1-xFexO3-delta perovskite oxides and demonstrates that the magnetic moment, which correlates with the relative content of Fe2+ and Fe3+, can be controlled via the oxygen content, either during growth or by postgrowth annealing.