Abnormal electric transport property and magnetoresistance stability of La–Sr–K–Mn–O system

The perovskite samples La_1−x (Sr_1−y K _y ) _x MnO₃ (y = 0.0, 0.2, 04, 0.6, 0.8) were prepared by the solid-state reaction method with comparatively low sintering temperature and with comparatively short sintering time, and the electric transport property and temperature stability of MR of this system were studied. The ρ–T curves show the abnormal phenomenon that with the increase of K doping amount, resistivity increases, and the insulator–metal transition temperature decreases, which is because the influence of the occupation disorder degree of A-site ions σ ² on the electric transport property of perovskite manganites is larger than that of the radius of A-site ions 〈r _A〉. In the temperature range below 225 K, MR increases continuously with the decrease of temperature, which is the characteristic of low-field magnetoresistance; in the comparatively wide temperature range near 250 K, the MR–T curves of all the samples are comparatively flat, and the value of MR almost does not change with temperature, which shows the temperature stability of magnetoresistance, and can be explained by the competition between the low-field magnetoresistance induced by spin-dependent tunneling of surface phase and the intrinsic magnetoresistance of grain phase. The magnetoresistance value of the sample with y = 0.8 keeps at (7.92 ± 0.36) % in the very wide temperature range of 225–275 K, and this is a good reference for the preparation of this kind of sample with practical application value in the future.