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Li L.,Anhui Key Laboratory of Spin Electronic and Nanometric Materials Cultivating Base | Li L.,Suzhou University | Wang G.,Anhui Key Laboratory of Spin Electronic and Nanometric Materials Cultivating Base | Wang G.,Suzhou University | And 6 more authors.
Xiyou Jinshu/Chinese Journal of Rare Metals | Year: 2013

Ag was introduced into the surface of La0.7Ca0.3MnO3 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) photograph and SEM spectroscopy (EDS), ρ-T curves ρ-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); ρ-T curves of the samples of x=0.00, 0.10 could be reasonably fitted by the ρ-T2 formula, which belonged to single magneton scattering function; ρ-T curves of the samples of x=0.20, 0.25 could be reasonably fitted by the ρ-T2.5 formula, which belonged to spin wave scattering function; ρ-T curves of the samples of x=0.30, 0.35 could be reasonably fitted by the ρ-T4.5 formula above 97 and 93 K respectively, which belonged to electron-magneton scattering function; for all the samples with composite Ag, MR showed very good temperature stability in the temperature 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. Source


Wang G.-Y.,Anhui Key Laboratory of Spin Electronic and Nanometric Materials Cultivating Base | Wang G.-Y.,Suzhou University | Tang Y.-G.,Anhui Key Laboratory of Spin Electronic and Nanometric Materials Cultivating Base | Tang Y.-G.,Suzhou University | And 7 more authors.
Chinese Rare Earths | Year: 2013

Non-stoichiometric samples of (La0.6Dy0.1Sr0.3)1-x MnO3 (x = 0.00, 0.10, 0.20, 0.30, 0.35) were pre-pared by the traditional solid-state reaction method. The mechanism of electric transport and of temperature stability of mag-netoresistance (MR) was studied through the measurements of XRD, ρ-T curves and MR-T curves. The XRD detection indicates that non-stoichiometric (La0.6Dy0.1Sr0.3)1-x MnO3 sintered at 1200°C for 24 h are the two-phase composites between La0.6Dy0.1Sr0.3MnO3 perovskite phase and Mn2O3 phase. The electrical transport properties indicate that all the samples exhibit insulator-metal transition, a sharp peak shows in high temperature zone and a shoulder peak shows in lower temperature zone for ρ-T curves. The phenomenon is caused by the common function of double exchange interaction within the body phase of the perovskite and electron spin-polarized tunneling at the grain boundaries. The MR-T curves show that a magnetoresistance peak appears in high temperature zone, magnetoresistance increases continuously with temperature decreasing in low temperature zone, which is the characteristic of low-field magnetoresistance, and the temperature stability of magnetoresistance appears in intermediate temperature zone. These results can be explained by the superposition of the intrinsic magnetoresistance induced by the grain phase of La0.6Dy0.1Sr0.3MnO3 and the tunneling magnetoresistance induced by grain boundary effect. The magnetoresistance of the sample with x = 0.30 is (6.3 ± 0.2) % at the magnetic field of 0.8 T in the temperature zone of 258-198 K. Source

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