CoFe-IrMn exchange-coupled soft underlayers for perpendicular media

FeTaN-IrMn exchange-coupled multilayer films have shown outstanding characteristics as soft underlayers for perpendicular media but 19 layers including the IrMn layer were required to meet the target permeability μ of ∼100 and ferromagnetic thickness of 200 nm. In order to decrease the number of layers, to improve thermal stability, and to increase the saturation flux density 4πM_s, CoFe alloys with a high uniaxial anisotropy field H_k and a high 4πM_s were investigated. In Co₉₀Fe₁₀-IrMn(10 nm) multilayer films, a significant increase in the intrinsic pinning field H_po allowed the number of layers to be reduced from 19 to 7 with improved thermal stability. Co₉₀Fe₁₀-IrMn multilayer using a thinner top layer of (Co₉₀Fe₁₀)N combined with a Cu-IrMn underlayer showed a unique single domain direction and a low μ of 108 up to 2 GHz but a low 4πM_s of 15∼16 kG. This was improved to ∼23 kG using Co₃₅Fe₆₅ films in which soft uniaxial anisotropic properties were achieved using a Cu underlayer. Co₃₅Fe₆₅-IrMn multilayer with the optimized structure of Glass-Cu(20 nm)-IrMn(10 nm)-[Co₃₅Fe₆₅(50 nm)-IrMn(10 nm)]₄-Co₃₅Fe₆₅(25 nm) showed outstanding characteristics for soft underlayers.