High coercivity and giant magnetoresistance of CoAg, CoCu granular films

Abstract

We report our study on the structure, magnetic and giant magnetoresistance properties of two systems: CoxAg1-x (x=33, 48, 49, 52 at%) and CoyCu1-y (y=11, 13, 15, 17 at%) granular films prepared by RF sputtering. The thermal transition measured by the SDT 2960 apparatus revealed exothermal peaks at 400 ?C, corresponding to the crystallization of FCC-Co crystallites. The studied films were annealed in a temperature range of 300-450 ?C for 1 h. The structure and particle size were determined from the X-ray diffraction data. Superparamagnetic state was shown in as-deposited films. After appropriate heat treatment, coercivity increased up to 1100 Oe in the Co52Ag48 film annealed at 350 ?C, and 690 Oe in the Co13Cu87 film annealed at 400 ?C. Maximum magnetoresistance up to 4.25% in the Co48Ag52 film, and 5.4% in the Co15Cu85 film annealed at 400 ?C was obtained. Our values for magnetoresistance are quite high compared with recent studies. ?? 2006 Elsevier B.V. All rights reserved.