Electric Transport and Magnetoresistance in La_(8/9)Sr_(1/45)Na_(4/45)MnO_3/0.5x(V_2O_5) Composites

The samples of La8/9Sr1/45Na4/45MnO3/0.5x(V2O5)(x = 0,0.04,0.08,0.012,0.16,0.20) were prepared by a solid-state reac-tion method.The temperature stability of magnetoresistance and electric transport property in the system were investigated via X-ray diffraction(XRD),scanning electron microscopy,resistivity–temperature(ρ–T) and magnetoresistance–temperature(RM–T) meas-urements.The results show that for all the samples,there is a insulator-metal transition from high temperature range to low tempera-ture range.The insulator-metal transition temperature(Tp) shifts to high temperature with increasing V2O5 content.Two peaks appear in the ρ–T curves of the samples(x≤0.08) with a low V2O5 content,and they vanish in the samples(x≥0.12) with a high V2O5 con-tent.The magnetoresistance(RM) of the samples increases with decreasing temprerature in the low temperature range,as a character-istic of low-field magnetoresistance effect.The intrinsic magnetoresistance in the high temperature range decreases with increasing V2O5 content.The magnetoresistance of the samples of x = 0.16 and 0.20 in the temperature range of 319–283 K at 0.8 T is 6.4% and 5.8%,respectively.The RM temperature stability may be due to the competition between the tunneling magnetoresistance caused by surface phase and the intrinsic magnetoresistance caused by bulk phase.The intrinsic magnetoresistance in bulk phase caused by dou-ble exchange dominants in the high temperature range,and the tunneling magnetoresistance caused by interface magnetic disorder dominants in the low temperature range.The RM does not change with temperature in the middle temperature range.