Sign reversal of junction magnetoresistance in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure: a possibility in spintronics application.

We have fabricated a p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure, consisting of a p-type manganite (La0.7Ca0.3MnO3) and n-type Si with a interfacial layer of SiO2 with typical thickness of about 9 nm using pulsed laser deposition technique. The junction exhibits rectifying behavior over the temperature range of 10-300 K with rectification factor 52 at room temperature. Investigation on the electrical properties of p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure exhibits nonlinear J-V characteristics in a wide temperature range. A crossover from negative to positive junction magnetoresistance (JMR) is observed in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure in current perpendicular to film plane (CPP) geometry. The temperature dependent sign of junction magnetoresistance of the heterojunction has been investigated carefully in details. It is found that the junction exhibits the positive junction magnetoresistance when the temperature is greater than the ferromagnetic to paramagnetic transition temperature (Tc) of the top highly spin-polarized half-metallic ferromagnetic La0.7Ca0.3MnO3 manganite film layer. The relation between junction magnetoresistance and external magnetic field is found to be of (delta rho/rho approximately equal alphaHbeta) type having both alpha and beta temperature dependent. We attribute the emergence of negative JMR at lower temperature (< Tc) and positive JMR at higher temperature (> Tc) to the quantum mechanical tunneling transport mechanism across the heterojunction. Our results might be very useful to fabricate artificial devices using the manganite-based heterojunction grown on single crystalline n-Si (100) in spintronics device applications.