Magnetoresistance enhancement and temperature stability of magnetoresistance in La 1− x (Sr 1− y Na y ) x MnO 3

A series of the samples La 1− x (Sr 1− y Na y ) x MnO 3 ( y =0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by the solid-state reaction method. Magnetoresistance enhancement and temperature stability of magnetoresistance in the system La 1− x (Sr 1− y Na y ) x MnO 3 with unchanged Mn 3+ /Mn 4+ ratio through the doping of both monovalent and divalent elements at A site were studied through the measurements of X-ray diffraction (XRD) patterns, resistivity-temperature ( ρ-T ) curves and magnetoresistance-temperature ( MR-T ) curves. The results indicate that with the increase of Na doping amount, the peak value of MR increases, and it increases from 12.4% for y =0.2 to 50.6% for y =1.0 in the magnetic field B =0.8 T; ρ-T curves exhibit the double-peak phenomenon, which comes from the competition between the resistivity of surface phase and that of body phase; for the sample of y =0.8, MR increases slowly from 8.3% to 9.4% in the temperature range from 259 to 179 K, and MR is so stable in such a wide temperature range, which provides reference for the research on the temperature stability of MR .