Anisotropic magnetoresistance in Nb:SrTiO₃ thin films under epitaxial strain

We report the effect of epitaxial strain and cationic vacancies on the anisotropic magnetoresistance (AMR) of SrTiO₃ (STO) thin films. Cationic vacancies affect the structural properties of the STO thin films, determining the rotation pattern of the TiO₆ octahedra [1], and produce a characteristic minimum at T* in the temperature dependence of the electrical resistivity of this material. Our results show a change of sign of the AMR, from negative above T*, to positive below this temperature. Seebeck coefficient measurements do not support an interpretation based on the Kondo effect. We will discuss the possible existence and the nature of a magnetic phase below T*. As the effect is only observed in thin films <20 nm, and it is lost in thicker films (»35 nm), this suggests a contribution from accumulated defects close to the interface with the substrate.

[1] L. Iglesias et Al., Phys. Rev. B 95, 165138(2017)