Magnetism and Faraday Rotation in Oxygen-Deficient Polycrystalline and Single-Crystal Iron-Substituted Strontium Titanate

Abstract

Both polycrystalline and single-crystal films of iron-substituted strontium titanate, SrðTi 0.65 Fe 0.35 ÞO 3−δ , prepared by pulsed laser deposition, show room-temperature magnetism and Faraday rotation, with the polycrystalline films exhibiting higher saturation magnetization and Faraday rotation. The magnetic properties vary with the oxygen pressure at which the films are grown, showing a maximum at pressures of approximately 4 μ Torr at which the unit-cell volume is largest. The results are discussed in terms of the oxygen stoichiometry and corresponding Fe valence states, the structure and strain state, and the presence of small-volume fractions of metallic Fe in single-crystal films grown at the optimum deposition pressure. Integration of magneto-optical polycrystalline films on an optical-waveguide device demonstrates a nonreciprocal phase shift.

Cluster Expansion Framework for the Sr(Ti1–xFex)O3–x/2 (0 < x < 1) Mixed Ionic Electronic Conductor: Properties Based on Realistic Configurations

“…The absorption coefficient is formulated from the complex dielectric function as where ε (1) (ω) and ε (2) (ω) refer to the real and imaginary parts of dielectric function, respectively, and c is the speed of light. From Figure , absorption becomes gradually enhanced with increasing Fe content as reported in previous studies. , The monotonic variation is consistent with the band gap evolution shown in Figure . Note that the optical absorption spectrum depends on both the band gap and the density of states at the conduction and valence band extrema and the transition oscillator strengths.…”

“…Second, as noted above, V O tends to remain adjacent to Fe instead of Ti atoms and the low-energy configurations contain Fe–V O –Fe structures that locally resemble Sr 2 Fe 2 O 5 , largely consistent with the maintenance of Ti 4+ and Fe 3+ oxidation states. In experiments, Fe 3+ is observed under a wide range of pressures and temperatures. ,,, In the ordered mixture, Fe atoms are introduced periodically in the B-site sublattice and V O is introduced periodically into the oxygen sublattice without regard to the neighboring B-site species. This results in fewer Fe–V O and oxidation states that deviate from Ti 4+ and Fe 3+ .…”

Physics of SrTiO3-based heterostructures and nanostructures: a review

“…The magnetic circular dichroism signal was observed only for the samples annealed under low oxygen partial pressures (to introduce oxygen vacancies), and disappears once the samples were re-oxygenated [410]. The oxygen vacancies also strongly affect the magnetism of Fe-substitute SrTiO 3 (Sr(Ti 1-x Fe x )O 3-δ ) [414]. Several theoretical studies have linked oxygen vacancies (or vacancy clusters) with magnetism.…”

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi1–xFexO3–x/2+δ Considered as a Mixture of SrTiO3 and Sr2Fe2O5

“…20,26 Therefore, with a reasonable amount of Fe, STF exhibits both significant ionic and electronic conductivities. 28,30 Several studies have focused on establishing the mixed conducting properties of STF as a function of Fe concentration, 25,26 and experiments have revealed the material characteristics of STF such as electronic structure and magnetism, 25,26,28,31,32 surface oxygen exchange kinetics, 27,30,33,34 local atomic structure, 25,29,31−33 and oxygen nonstoichiometry. 35,36 There are also a large number of thermodynamic defect chemical models 27,28,36 and computational investigations 25,32,37−41 of the ionic and electronic properties of STF.…”

“…These observations suggest a tendency for short-range ordering of V O around Fe ions, consistent with other computational studies. 32,37,66,67 The presence of V O in the first coordination shell of Fe ion has also been revealed through Fe K-edge X-ray absorption spectroscopy. 29 Therefore, our results are consistent with experiments showing that Fe atoms are largely 5-fold coordinated, whereas Ti atoms remain 6-fold coordinated.…”