Electric-field-induced epitaxial breakdown and emergent magnetoresistance due to strong oxygen reduction in Ca-doped BiFeO3

Abstract

We study the structural and transport properties of a heavily oxygen-reduced region that is formed by electrical injection of a large amount of oxygen vacancies into a ${\mathrm{Bi}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{FeO}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin film. In electroforming, the epitaxial as-grown state is transformed into a disordered, polycrystalline phase. Nonohmic current-voltage relations, which can be interpreted as a space-charge-limited conduction, appear at low temperatures. As temperature increases, the curvature of the current-voltage relationship gradually changes to be nearly ohmic at and above 100 K. The maximum value of magnetoresistance, as large as \ensuremath{-}2.6% at 90 kOe, is attained at the same temperature of \ensuremath{\sim}100 K, which is significantly larger than \ensuremath{-}0.1% at 25 K and \ensuremath{-}1.3% at 300 K.