Effective Co-rich ternary CoFeNi alloys for spintronics application

Abstract

The dependence of crystal structure, hysteresis properties and magnetoresistance on composition of ternary CoFeNi alloy has been studied for glass/Ta/(Ni80Fe20)60Cr40/[CoFeNi/Cu(2.2 nm)]n/Ta multilayers. Two series of Co-rich CoFeNi alloys were used. In series (I) the Co content decreases from 90 to 67 at. %, Fe content increases from 10 to 20 at.% and Ni content – from 0 to 13 at.%. Series (II) includes alloys with a fixed Co content: Co70Fe30-xNix (x = 5, 10, 15 and 20). For each type of ternary alloys the multilayer composition was optimized in order to obtain maximum giant magnetoresistance (GMR). The highest GMR ratios of 30–33% at room temperature are revealed in multilayers of series (I) alloys. It has been established that the most effective CoFeNi alloys, using which the GMR multilayers have a high GMR ratio in combination with low coercivity, are located in a narrow region of the ternary diagram near the Co70Fe20Ni10 composition. A deviation of the ternary alloy composition from this optimal one leads either to a decrease in the GMR ratio, or to a significant increase of coercivity.