Unusual colossal positive magnetoresistance of the n-n heterojunction composed of La0.33Ca0.67MnO3 and Nb-doped SrTiO3

An n-n heterojunction composed of La0.33Ca0.67MnO3 and Nb-doped SrTiO3 was fabricated, and it shows good rectifying property. The temperature variation of junction resistance for high reverse voltage exhibits a metal-insulator-like transition that shifts to high temperatures with further increasing voltage. The heterojunction presents a remarkable positive magnetoresistance under the reverse bias voltage at low temperatures, and the maximum of magnetoresistance can even reach ∼400% under a field of 1T. A qualitative explanation is given based on the analysis of the electron filling near the interface and its tunable feature under the bias voltage and magnetic field. This result can be helpful for both the understanding of the manganites and the future applications of the manganite-based devices.