Spin-Polarized Tunnelling Magnetoresistance Effects in La 0.833 K 0.167 MnO 3 /SrTiO 3 Polycrystalline Perovskite Manganites

A sample of La0.833K0.167MnO3–SrTiO3 (LKMO/STO) is fabricated by the sol-gel method. The microstructure, magnetic and transportation properties have been studied. X-ray diffraction patterns indicate that the structure of LKMO/STO is a homogeneous solid solution phase. The resistivity of LKMO/STO shows the insulator behaviour, which is different from La0.833K0.167MnO3 (LKMO) whose resistivity shows metal–insulator transition with decreasing temperature. The low-field (m0H = 0.02 T) magnetoresistance decreases from 11% to 0.2% with the increasing temperature from 4 K to 220 K for the LKMO/STO sample. The magnitude of magnetoresistance in a strong field (μ0H = 5.5 T) almost increases linearly with decreasing temperature and reaches the maximum of 65% at the low temperature of 4.2 K, which is much higher than that of LKMO (40%). The enhanced low-field magnetoresistance effects are quantitatively explained by the spin-polarized tunnelling at grain boundaries.