Correlation between the structural state and magnetoresistive properties of granular CoxAg100-x alloy thin films

Abstract

Extensive investigations into structural, magnetotransport and magnetic properties of granular thin films with a thickness of 20 nm based on Co and Ag in a wide range of component concentrations were carried out: 17 ≤ x ≤ 89 where x is at.% of Co. The samples were obtained by the method of electron beam co-evaporation using two independent electron guns at room temperature. The correlation between the structural-phase state and magnetotransport and magnetic properties was established by TEM method. The threshold of structural percolation in granular films was observed for x ≈ 60%. At lower concentration x < 64%, the films had a phase composition of Ag (fcc) + Co (hcp) and were characterized by an isotropic giant magnetoresistance (GMR). The maximum GMR values of 7.2% and 7.5% in transverse and longitudinal geometry, respectively, were observed at x = 55 at.%. For higher concentrations (x > 70%) the films demonstrated anisotropic magnetoresistance (AMR), which was assumed to be associated with the appearance of ferromagnetic interactions between the cobalt granules.