Enhanced room temperature magnetoresistance in maganites La0.60Sr0.25−yNa0.15Δy MnO31

Bulk polycrystalline samples of La0.60Sr0.4MnO3 and La0.60Sr0.25−yNa0.15Δy MnO3 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 R C. 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.