Size evolution of nanomagnetic particles and magnetotransport properties of (Co 90Fe 10) 20Ag 80 nanogranular films: Influence of Cu 80Ag 15Au 5 underlayer

Abstract

The influence of (Co 90Fe 10) 20Ag 80 film thickness and of Cu 80Ag 15Au 5 underlayer on nanomagnetic, magnetotransport and structural properties of (Co 90Fe 10) 20Ag 80 nanogranular films prepared by ultra-high vacuum ion beam sputtering technique have been investigated using X-ray diffraction, X-ray reflectivity and vibrating sample magnetometer. Films indicate a superparamagnetic behavior. The evolution of the magnetic particle size in (Co 90Fe 10) 20Ag 80 film with different thicknesses was calculated by fit of magnetization curves using Langevin equation. A parallel resistance model has been used to determine particle size distribution. The average (mean) particle sizes range from 1.6 to 2.1 nm. A linear dependence of giant magnetoresistance (GMR) on the particle size has been found. This result is also supported by the observed linear correlation between the square root of the effective magnetization and the particle size. Furthermore, a linear correlation between the square of GMR and the distance between particles has been found. This remains unchanged also in (Co 90Fe 10) 20Ag 80 films with Cu 80Ag 15Au 5 underlayer. Using of the underlayer leads to an enhancement of the mean particle size (1.8-2.5 nm) and GMR; however, to a reduction of distances between particles accompanied by the destruction of the <111> texture in the Ag matrix structure. The reason of the GMR effect in the nanogranular films is discussed by means of the obtained results.