Impact of size mismatch induced quenched disorder on phase fluctuation and low field magnetotransport in polycrystalline [formula omitted]

Abstract

We report the magnetic and transport properties of polycrystalline [formula omitted] ([formula omitted], 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 [formula omitted]. As the variance [formula omitted] increases, the paramagnetic-ferromagnetic transition shows a gradual decrease and broadening, while the decrease in insulator metal transition is sharpened. However, near equality of [formula omitted] and [formula omitted] at intermediate values of [formula omitted] could be understood in terms of the competing quenched and the grain boundary disorder. The variation in peak magnetoresistance (MR) (maximum MR around [formula omitted]) with [formula omitted] shows that maximum low field [formula omitted] at [formula omitted] (68% at [formula omitted]) is centered around [formula omitted] [formula omitted]. This shows that huge intrinsic MR can be obtained at relatively higher temperatures and lower magnetic fields in the region of enhanced phase fluctuations. © 2010, American Institute of Physics. All rights reserved.