Magnetotransport properties of a room temperature rectifying tunnel junction made of electron and hole doped manganites

Abstract

The hole-doped (p) manganite La_0.7Ca_0.3MnO₃ and the electron-doped (n) manganite La_0.7Ce_0.3MnO₃ undergo an insulator-to-metal transition at around 250 K, above which both behave as a polaronic semiconductor. We have fabricated an epitaxial trilayer (La_0.7Ca_0.3MnO₃/SrTiO₃/La_0.7Ce_0.3MnO₃), where SrTiO₃ is an insulator. At room temperature, i.e., in the semiconducting regime, it exhibits asymmetric current–voltage (I–V) characteristics akin to a p–n diode. The observed asymmetry in the I–V characteristics disappear at low temperatures where both the manganite layers are metallic. The I–V curves exhibit an intriguing temperature dependence in the presence of magnetic field. At room temperature, i.e., above the ordering temperature, we have a negative magnetoresistance (MR) and at low temperature we have a positive MR, indicative of a minority spin carrier band in La_0.7Ce_0.3MnO₃. A possible mechanism for the observed effects are discussed.