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

The hole-doped (p) manganite La0.7Ca0.3MnO3 and the electron-doped (n) manganite La0.7Ce0.3MnO3 undergo an insulator-to-metal transition at around 250 K, above which both behave as a polaronic semiconductor. We have fabricated an epitaxial trilayer (La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3), 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 La0.7Ce0.3MnO3. A possible mechanism for the observed effects are discussed. (C) 2002 American Institute of Physics.