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Bulk polycrystalline samples of La0.60Sr0.4MnO3 and La0.60Sr0.25-yNa0.15ΔyMnO3 with 0.00≤y≤0.15 (“Δ” representing cation vacancy) were successfully synthesized using the sol-gel method. The structural, magnetic, and electrical properties of the polycrystalline of the samples were investigated. The results of X-ray powder diffraction patterns show that these compounds crystallize in a distorted rhombohedral structure with the space group R3C. The measurement shows that, with vacancy content y increasing, the unit cell volume V of samples increases, furthermore, the Curie temperature TC decreases. The temperature dependence of resistivity shows that all samples undergo a metal-semiconductor transition accompanying a ferromagnetic to paramagnetic transition with the increase of temperature. Under an applied filed of 1.8 T, a maximum room temperature magnetoresistance (MR) of 20% is obtained at 293 K for the compound La0.60Sr0.1Na0.15Δ0.15MnO3. The MR peak value of La0.60Sr0.1Na0.15Δ0.15MnO3 increases 2 times more than that of La0.60Sr0.40MnO3 (MRP=6.4%, TMR=373 K), and the MR peak is shifted from 373 K to room temperature.
Bulk polycrystalline samples of La0.60Sr0.4MnO3 and La0.60Sr0.25-yNa0.15ΔyMnO3 with 0.00≤y≤0.15 (“Δ” for positive vacancy) were successfully synthesized using the sol-gel method. The structural, magnetic, and electrical properties of the polycrystalline of the samples were investigated. The results of X-ray powder diffraction patterns show that these compounds crystallize in a distorted rhombohedral structure with the space group R3C. The measurement shows that with vacancy content y increasing, the unit cell volume V of samples increases, furthermore, the Curie temperature TC decreases. The temperature dependence of resistivity shows that all samples undergo a metal-semiconductor transition accompanying a ferromagnetic to paramagnetic transition with the increase of temperature. Under an applied filed of 1.8 T, a maximum room temperature magnetoresistance (MR) of 20% is obtained at 293 K for the compound La0.60Sr0.1Na0.15Δ0.15MnO3. The MR peak value of La0.60Sr0.1Na 0.15Δ0.15MnO3 increases 2 times more than that of La0.60Sr0.40MnO3 (MRP = 6.4%, TMR = 373 K), and the MR peak was shifted from 373 K to room temperature.