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We have investigated the soft magnetic characteristics of an ultrathin Co-rich CoFeNi free layer in spin-valve films. By addition of Ni to a Co-rich CoFe free layer, magnetostriction ( λ ) of the films increased positively with Ni concentration, in contrast to which a Co90Fe10 free layer showed a negatively large λ . However, Ni addition also caused an increase in coercivity of the easy axis direction (Hce.a.). To avoid this problem, a slight decrease in the Co contents of a CoFeNi free layer was found to be effective for decreasing Hce.a.. In order to satisfy both the small λ and Hce.a., a free layer of (Co86Fe14)88−94Ni12−6 proved to be an optimum composition in spin-valve films. Moreover, the zero λ composition of the CoFeNi free layer was changed by a high-conductance Cu layer deposited on the free layer, which was considered to come from the lattice strain of a free layer.

To confirm the origin of the exchange coupling through the nano-oxide layer (NOL), the detailed analyses of the magnetization curve and the temperature dependence on magnetization for the Co 1− x Fe x -NOL samples with various oxidation processes are investigated. The field cooling effect is observed for NOL-inserted samples, which suggests the existence of the antiferromagnetic (AFM) component in the NOL. The characteristic temperature (blocking temperature) increases with increase in the Fe content for Co 1− x Fe x ( x =0.08,0.17,0.26)-NOL. These results support that NOL pinning appears higher than room temperature. Further, the twisted coupling through the NOL observed for the Co 0.50 Fe 0.50 -NOL is discussed from the viewpoint of the magnetic roughness due to the ferrimagnetic nature of the very thin NOL in specular spin valve (SPSV).

A novel method is proposed for increasing the giant magnetoresistance (GMR) of dual spin valves of the CoFe/Cu/CoFe/Cu/CoFe type by inserting nano-oxide layers (NOLs) into the pinned layers. Using this method, MR ratio of 23.5% was obtained, a value equal to those of specular spin valves with antiferromagnetic oxide, e.g., NiO. This method allows the selection of metallic materials for the antiferromagnetic layer. In addition, we obtained the specularity factor of upper NOLs, 0.8, and that of lower NOLs, 0.7, by calculating Boltzmann equations taking into account the roughness of each interlayer. This model shows that the MR ratio would be 27.5% for dual spin valves with ideal NOLs.

This paper reports the film and head performance of specular spin valves with nano-oxide layer (NOL-SPSV). A large MR ratio of 17% was obtained by using an ultrathin CoFe free layer with a high conductance Cu layer, which decreases the sense current field of a free layer and brings good soft magnetic characteristics. Prototype heads with a read track width of 0.47–0.61 μm were fabricated by using NOL-SPSV films with an MR ratio of 14–15%, H ua ∼400 Oe, and H c ∼5 Oe. High output signal voltage of 8–11 mV/μm was realized in the NOL-SPSV heads.

The B2 structure Fe50Co50 alloy is very attractive material as a large spin conductance asymmetry. In this study, we have tried to fabricate epitaxial Fe/Co superlattice with B2 structure. In order to investigate the relationship between the film structure and the substrate temperature, the films were prepared at different substrate temperature. The film structure of Fe/Co was evaluated by reflection high energy electron diffraction (RHEED). The in-plane lattice spacing gradually decreased to that of a bulk Fe50Co50 as increase in the number of layers. The B2 structure ordered phase of Fe/Co superlattice was successfully confirmed by RHEED and X-ray diffraction (XRD).

The anisotropic magnetostrictions of the cubic Laves phase compounds Gd(Fe1−xCox)2 and Dy(Fe1−xCox)2 pseudobinary system have been measured from 8 to 130 K below their ordering temperatures. The concentration dependence of anisotropic magnetostriction for these two systems has been observed. An attempt is made to find the reason for the high magnetostriction in DyCo2 and GdCo2. The results obtained suggest that the high anisotropic magnetostriction of RCo2 (R:Gd, Dy) relates to the strong magnetocrystalline anisotropy caused by cobalt.

The Ni nano constriction dots embedded in the Ta-nano-oxide layer (NOL) was prepared by the ion beam sputtering (IBS) method. After the various conditions of the oxidations, the structural analyses of the NOL were performed by RHEED, AES and in situ STM/AFM observations. From the current image of the conductive AFM for NOL, the periodically aligned metallic dots with the size around 5–10 nm were successfully observed. The mechanism of the formation of the self-organized aligned Ni nano constriction dots is discussed from the standpoint of the grain size, the crystal orientation, the preferred oxidation of Ta at the diffused interface.

Crystal structure of high temperature phase has been investigated as functions of Cu, Fe, Ti content in Sm(Co, Cu, Fe, Ti)7 alloys. These alloys are shown to crystallize in three polymorphic forms. It has been found that Cu and Ti stabilize TbCu7, but Fe stabilizes Th2Zn17. The relationship is discussed between TbCu7 stability and hard magnetic properties.