Impact of size mismatch induced quenched disorder on phase fluctuation and low field magnetotransport in polycrystalline Nd0.58-xGdxSr0.42MnO3.

We report the magnetic and transport properties of polycrystalline Nd0.58-xGdxSr0.42MnO3 (x~0.0, 0.04, 0.08, 0.12, 0.16, 0.20, 0.25, 0.30, 0.35, and 0.42). All the samples are single phase and have grain size ~1-2 μm. As the variance σ2 increases, the paramagnetic-ferromagnetic transition shows a gradual decrease and broadening, while the decrease in insulator metal transition is sharpened. However, near equality of TC and TIM at intermediate values of σ2 could be understood in terms of the competing quenched and the grain boundary disorder. The variation in peak magnetoresistance (MR) (maximum MR around TC/TIM) with σ2 shows that maximum low field MR≈35% at H=3 kOe) 68% at H=10 kOe) is centered around σ2=0.009 857 Å2 (x=0.25). This shows that huge intrinsic MR can be obtained at relatively higher temperatures and lower magnetic fields in the region of enhanced phase fluctuations. [ABSTRACT FROM AUTHOR]