关键词: 电输运, 小极化子模型, 变程跳跃模型, 磁电阻

Abstract: As a colossal magnetoresistance material, the perovskite manganese oxide La_1-xSr_xMnO₃ has broad application prospects in magnetic sensors and other fields. However, it is difficult to obtain a significant colossal magnetoresistance effect at a low magnetic field and room temperature. In order to improve its magnetoresistance effect and transition temperature, La_0.8Sr_0.2Mn_1-xAl_xO₃ (0≤x≤0.25) (LSMAO) polycrystalline samples were prepared by the traditional solid-state reaction method in this study. The effects of Al doping on the electrical transport property and magnetoresistance effects of LSMO were systematically analyzed. The X-ray diffraction (XRD) results indicate that all the samples crystallize in a single rhombohedral structure with the space group of R3̅C. The study of electrical transport property shows that the resistivity of the samples increases exponentially with the doping of Al³⁺, and the metal-insulator transition temperature is increased by an external magnetic field. This may be due to the dilution of the Mn³⁺/Mn⁴⁺ ions network by Al³⁺, which increases the magnetic disorder while reducing the number of carriers. In addition, the conduction mechanism of LSMAO ceramics changes from the small polaron hopping model (SPH) to the variable range hopping model (VRH) with the doping of Al³⁺, reflecting that the non-magnetic Al³⁺ suppress the carrier exchange between the ferromagnetic clusters. As a result, the thermally activated neighbor transition process of small polarons is suppressed. The magnetoresistance value of LSMAO is enhanced from 21.03% to 59.71% with x increasing from 0 to 0.25, which proves that the doping of Al³⁺ can effectively enhance the magnetoresistance effect of LSMAO.

Key words: electrical transport, small polaron hopping model, variable range hopping model, magnetoresistance