La0.67Sr0.08Na0.25MnO3的奇特输运性质及CMR效应

用固相反应法制备了La_0.67Sr_0.08Na_0.25MnO₃样品.通过磁化强度-温度(M-T)曲线、电阻率-温度(ρ-T)曲线以及ρ-T拟合曲线研究了样品的输运性质及庞磁电阻(colossal magnetoresistance，CMR)效应.结果表明，ρ-T曲线和磁电阻-温度(MR-T)曲线均出现双峰现象；高温峰是伴随顺磁-铁磁(PM-FM)相变出现绝缘体-金属(I-M)相变，低温峰是颗粒界面效应；两个绝缘相输运机理不同：较低温度下(248K<T<274K)，ρ(T)符合极化子的可变程跃迁模型，而在更高温区(330K<T<374K)，ρ(T)符合极化子近邻跃迁模型；两个类金属相输运机理也不同：在低温区(67K<T<186K)，满足ρ-T^2.5关系，输运机理是自旋波散射和电-磁子散射作用，而在高温区(292K<T<304K)，满足ρ-T²关系，输运机理是单磁子散射作用. 关键词： 庞磁电阻 金属-绝缘体转变 晶界效应 输运行为

Peculiar transport properties and CMR effect of La0.67Sr0.08Na0.25MnO3

The La_0.67Sr_0.08Na_0.25MnO₃ sample was prepared by solid-state reaction. The transport properties and CMR effect of the sample were studied through M-T curves, ρ-T curves and ρ-T fitted curves. The results show that: Both the ρ-T curves and the MR-T curve exhibit the double-peak phenomenon; the high-temperature peak corresponds to the I-M transition accompanied by the PM-FM transition, and the low-temperature peak is attributed to grain boundary effect. The two insulator phases have different transport mechanisms: in the low temperature range(248 K<T<274 K),ρ(T) accords with variable-range-hopping model of polaron, while in the high temperature range(330 K<T<374 K),ρ(T) accords with near- neighbor- hopping model of polaron; and the two metal-like phases also have different transport mechanisms: in the low temperature range(67 K<T<186 K), ρ(T) accords with the ρ-T^2.5 relation, and the transport mechanism is the actions of spin wave scattering and electron-magneton scattering, while in the high temperature range(292 K<T<304 K),ρ(T) accords with the ρ-T² relation, and the transport mechanism is single magneton scattering.