CoPt-TiO₂ granular-type media with extremely thin Ru intermediate layer of 1.9 nm were prepared on a highly oriented high-B_s FeCo soft underlayer (SUL) pinned by an IrMn antiferromagnetic layer. The FeCo SUL thickness was changed to reduce the medium noise. CoPt clusters surrounded by relatively wide boundaries were formed for the medium with the FeCo SUL of 40 nm. As the FeCo SUL thickness was decreased, the cluster size and the number of the CoPt grains was decreased. The CoPt grains were mostly isolated for the medium with the FeCo SUL of 20 nm. The average cluster size was 7.4 nm in diameter. The recording performance was evaluated by using a single-pole-type head. This new-designed medium has high writability and large reproduced output compared to an old-designed medium with an amorphous SUL of 80 nm and an intermediate layer of 30 nm. As the FeCo SUL thickness was decreased down to 10 nm, the medium noise was greatly decreased at the recording densities of more than 200 kfci. As a result, the S/N was increased as the FeCo SUL thickness was decreased down to 10 nm at the recording densities of more than 200 kfci. The film thickness of the FeCo SUL could be reduced down to 10-20 nm.

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  Reducing the thickness of the Ru intermediate layer (IML) is one of the most effective ways of realizing high-density hard disk drives and magnetic tapes. Use of a crystalline soft magnetic underlayer (SUL) has the advantage of reducing the IML thickness and results in better (001) orientations in both Ru IML and CoPtCr-SiO₂ recording layer (RLs). Ru or Si/NiFe seed layers improve the degree of FeCo(110) orientation in the SUL and the c-axis orientation of the RL. An Ru/FeCoB layer and an Si/NiFe/FeCoB layer were compared for crystalline orientation and magnetic properties. The integrated intensity of the (002) diffraction peak of CoPtCr had an almost constant value even when the thickness of the Ru IML was changed from 30 nm to 2 nm. The coercivity and squareness ratio in the direction perpendicular to the of recording layer maintained the same value even when reducing the thickness of the Ru IML was reduced from 30 nm to 5 nm.

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  We propose a technique for low-gas-pressure (0.6 Pa) deposition of a granular film consisting of Co-based metallic grains and stoichiometric SiO₂ grain boundaries by using reactive sputtering. As a typical example, we experimented in forming Co-SiO₂ granular films by using dc magnetron sputtering with Ar+O₂ mixed gas with a Co_92.3Si_7.7 (at%) alloy target. Detailed analyses of the composition, microstructure, and magnetic properties of the granular films revealed that: (1) a high deposition rate of 3.4 nm/s was realized under a Si-selective oxidization condition of the surface of the CoSi alloy target. (2) The granular film with an O/Si composition ratio of 2 was successfully achieved under the selective oxidization conditions. (3) c-plane-oriented Co grains with SiO₂ grain boundaries were formed on a Ru underlayer. (4) The low-gas-pressure process made it possible to enhance the columnar grown of Co grains without tapering off. These results suggest that the low-gas-pressure process will be effective in improving corrosion and impact resistance even for the current mass-produced perpendicular magnetic recording media with CoPtCr (-SiO₂, -TiO₂) granular materials.

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  We investigated how a Ru underlayer contributed to the in-plane magnetic anisotropy of an FeCoB upper layer. The Ru underlayer with a higher degree of Ru (001) orientation induced higher in-plane magnetic anisotropy in the FeCoB upper layer. A Si/NiFe seed layer, which was located beneath the Ru underlayer, changed the Ru crystalline orientation from random to (001) preferential orientation and induced a remarkably high in-plane anisotropy field of 540 Oe. The in-plane anisotropy of Ru crystallites in the Ru underlayer is discussed in the paper. The Ru (002) pole_figure indicated isotropic in-plane alignment of Ru crystallites. Si/NiFe/Ru/FeCoB film was prepared using two methods, i.e., with unturned and turned underlayer deposition. The direction of anisotropic alignment of FeCo crystallites and in-plane magnetic anisotropy of the FeCoB layer was not influenced by the direction of the Ru underlayer; therefore, the Ru underlayer was not a dominant factor, and the oblique incidence effect caused by the configuration of Facing Targets Sputtering system (FTS) was a dominant factor that induced in-plane magnetic anisotropy in the FeCoB layer. The Ru underlayer may have contributed to an increment of the oblique incidence effect.

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  Several experiments have recently found room-temperature ferromagnetism in graphite-like carbon based materials. This paper offers a model explaining such ferromagnetism by using an asymmetric nano-graphene. Our first typical model is C₄₈H₂₄ graphene molecule, which has three dihydrogenated (-CH₂) zigzag edges. There are several multiple spin states competing for stable minimum energy in the same atomic topology. Both molecular orbital and density function theory methods indicate that the quartet state (S=3/2) is more stable than that of doublet (S=1/2), which means that larger saturation magnetization will be achieved. We also enhanced this molecule to an infinite length ribbon having many (-CH₂) edges. Similar results were obtained where the highest spin state was more stable than lower spin state. In contrast, a nitrogen substituted (-NH) molecule C₄₅N₃H₂₁ demonstrated opposite results. that is, the lowest spin state (S=1/2) is more stable than that of highest one (S=3/2), which arises from the slight change in atom position.

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