Abstract
Oxygen vacancies have a profound effect on the magnetic, electronic, and transport properties of transition metal oxide materials. Here, we studied the influence of oxygen vacancies on the magnetoresistance (MR) properties of SrRu1 − xFexO3 - δ epitaxial thin films (x = 0.10, 0.20, and 0.30). For this purpose, we synthesized highly strained epitaxial SrRu1 − xFexO3 − δ thin films with atomically flat surfaces containing different amounts of oxygen vacancies using pulsed laser deposition. Without an applied magnetic field, the films with x = 0.10 and 0.20 showed a metal–insulator transition, while the x = 0.30 thin film showed insulating behavior over the entire temperature range of 2–300 K. Both Fe doping and the concentration of oxygen vacancies had large effects on the negative MR contributions. For the low Fe doping case of x = 0.10, in which both films exhibited metallic behavior, MR was more prominent in the film with fewer oxygen vacancies or equivalently a more metallic film. For semiconducting films, higher MR was observed for more semiconducting films having more oxygen vacancies. A relatively large negative MR (~36.4%) was observed for the x = 0.30 thin film with a high concentration of oxygen vacancies (δ = 0.12). The obtained results were compared with MR studies for a polycrystal of (Sr1 − xLax)(Ru1 − xFex)O3. These results highlight the crucial role of oxygen stoichiometry in determining the magneto-transport properties in SrRu1 − xFexO3 − δ thin films.
Highlights
The electronic and magnetic properties of SrRuO3 (SRO) have received a significant amount of attention, from a fundamental science point of view and due to their potential for device applications [1,2,3]
The crystal structure was characterized by high-resolution X-ray diffraction (HRXRD). (Two thin films were characterized using the Bruker D8 Discover HRXRD system, while the other three films were characterized with the PANalytical X’Pert PRO HRXRD system.) The surface morphology was examined by atomic force microscopy (AFM)
In our previous two reports, we showed that phase-pure high-quality epitaxial SrRu1 − xFexO3 − δ (x = 0.1, 0.2, 0.3) thin films with either high or low oxygen-vacancy content can be grown on STO (001) substrates [13, 14]
Summary
The electronic and magnetic properties of SrRuO3 (SRO) have received a significant amount of attention, from a fundamental science point of view and due to their potential for device applications [1,2,3]. The ferromagnetism in SRO originates from a substantial spin polarization of the low-spin-state configuration of the 4d electrons (S = 1; t42ge0g), producing a saturated magnetic moment of 1.6 μB [7]. The maximum MR (~45%) was reported for (Sr0.7La0.3)(Ru0.7Fe0.3)O3 samples at T = 10 K and H = 9 T. They proposed that the large negative MR was due to the ferromagnetic interaction between the high-spin state of Fe3+ ions and low-spin state of Ru4+ ions. Co-doping of La3+ at the A sites was critical for stabilization of the single phase in their polycrystalline samples.
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