A remarkable reduction in coercivity Hc was found in sputtered Fe65Co35(=FeCo) films on Cu, NiFe, Ru, Ta/Cu, Ta/NiFe, or Cu/IrMn underlayers. A decrease in Hc from 120 to 7–12 Oe was observed for Cu, NiFe, and Ru underlayers as thin as 2.5 nm but less for Ta. A Cu underlayer significantly reduced the maximum anisotropy fields from 2 kOe to 40 Oe, resulting in a well-defined in-plane average uniaxial anisotropy field Hk∼30 Oe. The saturation magnetostriction with Cu was (47±4)×10−6, independent of Cu and FeCo thicknesses. In-plane tensile film stress decreased with underlayer thickness tUL from 2 to 0.2 GPa but much less rapidly than the reduction in Hc. All underlayers induced a (110) texture in FeCo, which was strongest with Ta. Transmission electron microscopy of cross-sections showed an unusually long range coherence with low angle grain boundaries in the FeCo without an underlayer. Clear columnar grains were visible with all underlayers with an average grain size of ∼50 nm with Ta dropping to 9–10 nm for Cu, NiFe, and Ru. This alone is sufficient to explain quantitatively the reduction in Hc using Hoffmann’s ripple theory.

A remarkable reduction in the coercivity Hc of sputtered Fe65Co35 films from 9.6 to 0.7 kA/m was observed using a Cu underlayer as thin as 2.5 nm. The FeCo without Cu exhibited a wide distribution of anisotropy fields up to >80 kA/m while the FeCo with Cu showed a well-defined in-plane uniaxial anisotropy field of 2.3 kA/m up to FeCo thicknesses of at least 1 μm. The saturation magnetostriction was (4.7±0.4)×10−5, independent of Cu thickness while the in-plane tensile stress gradually decreased from 2 to 0.2 GPa as the Cu thickness increased to 10 nm. The Cu changed the preferred orientation of the FeCo from (100) to (110) but more significantly reduced the average grain size from ∼50 to ∼9 nm. This alone is sufficient to explain quantitatively the reduction in Hc using Hoffmann’s ripple theory.

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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 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 4 , CoFe alloys with a high uniaxial anisotropy field and a high 4 were investigated. In Co 90 Fe 10 -IrMn(10 nm) multilayer films, a significant increase in the intrinsic pinning field allowed the number of layers to be reduced from 19 to 7 with improved thermal stability. Co 90 Fe 10 -IrMn multilayer using a thinner top layer of (Co 90 Fe 10 )N combined with a Cu-IrMn underlayer showed a unique single domain direction and a low of 108 up to 2 GHz but a low 4 of 15 16 kG. This was improved to 23 kG using Co 35 Fe 65 films in which soft uniaxial anisotropic properties were achieved using a Cu underlayer. Co 35 Fe 65 -IrMn multilayer with the optimized structure of Glass-Cu(20 nm)-IrMn(10 nm)-[Co 35 Fe 65 (50 nm)-IrMn(10 nm)] 4 -Co 35 Fe 65 (25 nm) showed outstanding characteristics for soft underlayers.

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