The Sr content influence on the positive magnetoresistance in La_1-xSr_xMnO₃/Si heterojunctions

We fabricated La_1-xSr_xMnO₃/Si (LSMO/Si) heterojunctions with different Sr doping concentrations (x = 0.1, 0.2, 0.3) in LSMO and studied the Sr content influence on magnetoresistance (MR) ratio. The heterojunctions show positive MR and high sensitivity of MR ratio in a low applied magnetic field. The MR ratio is dependent on Sr content and the low Sr doping in LSMO causes a large positive MR in LSMO/Si junctions. The MR ratio for 0.1 Sr doping in the LSMO/Si heterostructure is 116% in 100 Oe (1 Oe=79.5775 A/m) at 210 K. The mechanism for the positive MR dependence on the doping density is considered to be the competition between the tunneling rate of electrons in e_g¹ ↑ to t_2g ↓ band and that to e_g² ↑ band at the interface region of LSMO. The experimental results are in agreement with those observed in La_0.9Sr_0.1MnO₃/SrNb_0.01Ti_0.99O₃ p-n junction. The results indicate that choosing low doping concentration to improve the low field sensitivity of the heterojunction deveces is a very efficacious method.