(1-x)La_(0.7)Ca_(0.3)MnO_3/xAg磁电阻的温度稳定性

Temperature Stability of Magnetoresistance in (1-x)La_(0.7)Ca_(0.3)MnO_3/xAg

用固相反应法将Ag引入La0.7Ca0.3MnO3颗粒表面,形成(1-x)La0.7Ca0.3MnO3/xAg(x=0.00,0.10,0.20,0.25,0.30,0.35)。通过XRD谱、扫描电子显微镜(SEM)照片及SEM能谱(EDS)、ρ-T曲线、ρ-T拟合曲线、MR-T曲线,研究电输运性质及MR温度稳定性。结果表明:随复Ag量增大,电阻率急剧下降,高复Ag(x≥0.3)的电阻率比低复Ag(x≤0.10)的电阻率下降2个数量级;发现x=0.00,0.10用ρ-T2公式拟合比较合理,是单磁子散射作用;x=0.20,0.25用ρ-T2.5公式拟合比较合理,是自旋波散射作用;x=0.30,0.35,分别在97,93 K以上用ρ-T4.5公式拟合比较合理,说明是电子-磁子散射作用;所有复Ag样品,在250～20 K温区MR表现出很好的温度稳性,特别是x=0.10的样品,在220～150 K温区MR保持(13.8±0.2)%。提出磁电阻稳定性的机制:Ag与钙钛矿颗粒形成电输运二元通道,钙钛矿颗粒通道产生的低场磁电阻与Ag通道产生的正常磁电阻共同作用,产生MR温度稳定性。

Ag was introduced into the surface of La0.7 Ca0.3 MnO3 grains by the solid-state reaction method, and the samples （ 1 - x） La0.7Ca0.3MnO3/xAg （x =0. 00, 0.10, 0.20, 0.25, 0.30, 0.35） were prepared. The electric transport property and the temperature stability of MR in the system were studied through the measurements of XRD spectrum, scanning electron microscope （SEM） photo- graph and SEM spectroscopy （EDS）, p-T curves p-T fitted curves, and MR-T curves. The results indicated that with the increase of composite Ag amount, resistivity decreased sharply, and the resistivity of the samples with high composite Ag amount （ x ≥0.3 ） was two orders of magnitude lower than that of the samples with low composite Ag amount（x≤0. 10） ; p-T curves of the samples of x = 0. 00, 0.10 could be reasonably fitted by the p-T2 formula, which belonged to single magneton scattering function; p-T curves of the samples of x = 0.20, 0.25 could be reasonably fitted by the p-T^2. 5 formula, which belonged to spin wave scattering function; p-T curves of the samples of x = 0.30, 0.35 could be reasonably fitted by the p-T^4 5 formula above 97 and 93 K respectively, which belonged to e- lectron-magneton scattering function; for all the samples with composite Ag, MR showed very good temperature stability in the tempera- ture range of 250 - 20 K, especially MR of the sample of x = 0.10 kept at （ 13.8 ± 0.2） % in the temperature range of 220 -150 K. The mechanism of magnetoresistance stability was put forward as below： Ag and the perovskite grains formed two channels for electric transport, and the temperature stability of MR came from the common effect of low-field magnetoresistance induced by the channel of perovskite grains and ordinary magnetoresistance induced by the channel of Ag.