Influence of particle size distribution in cermet nanocomposites on magnetoresistance sensitivity

Abstract

Summary form only given. Granular (in particular -cermet) nanocomposites and thin films attract much attention due to their unique physical properties and potential applications for magnetic sensors, magnetic recording media etc. Easy preparation procedure and high stability are the striking features of the granular structures. At the same time low magnetoresistance (MR) sensitivity comparing layered structures can be considered as an imperfection. Recently it has been shown that formation of specific granular structures (layered granular films or discontinuous multilayers) lead to increase in MR sensitivity. However the influence of the topology on magnetic and MR properties of granular nanocomposites is not completely clear. We report the influence of particle size distribution (PSD) on magneto-transport properties of (Co/sub 50/Fe/sub 50/)/sub x/-(Al/sub 2/O/sub 3/)/sub 1-x/ granular films prepared by dual electron beam evaporation (x -is the volume fraction). Magnetic susceptibility, magnetization hysteresis loops and magnetotransport properties were studied in the temperature range 5-300K and in the fields (H) up to 50 kOe. PSD was obtained from the approximation of M(H) curves at different temperatures. The average particle size, also estimated from ZFC-FC high temperature susceptibility, varies from 1 nm (x=0.07) to 3 nm (x=0.24) and the PSD become broader. The correlation between magnetization and MR was studied. It has been found that MR(M) curves does not follow (M/M/sub g/)/sup 2/ dependence (M/sub g/ is saturation magnetization), predicted for uniform size spherical particles with uncorrelated magnetic moments. The derivation from square-law is determined by PSD and is maximal for the films with the broadest distribution of superparamagnetic particles. In this region the highest values of MR were also observed. The effect of PSD could be used for enhancement of MR sensitivity in granular nanocomposites.