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] which keeping bare (radical) carbons on one side zigzag edge, whereas mono hydrogenated carbons on another side. Optimizing atomic configuration, self-consistent calculation demonstrated that a total energy of the highest spin state is more stable than that of the lower one, which origin comes from the exchange coupling between carbons. This analysis suggested a capability of designing magnetic data track utilizing such asymmetric graphene ribbon. In order to increase areal magnetization density, bi-layer and quadric layer model were analyzed. Detailed calculation resulted that also the highest spin state is the most stable one. Increasing layer numbers is an effective way to enhance strong magnetism.

The multiple spin states of zigzag edge modified graphene molecules were analyzed to study the possibility of carbon based magnetic materials by using first principles density functional theory to select suitable elements for modification. Radical carbon modified C64H17 and dihydrogenated carbon C64H27 demonstrated that the highest spin state is most stable, which arises from the tetrahedral molecular orbital configuration in two up-spins at the zigzag edge. In contrast, oxygen modified C59O5H17 exhibited the lowest spin state to be most stable due to the cancellation of four spins at the oxygen site. Boron modified C59B5H22 had no π-orbit at the boron site, which meant the lowest spin state was most stable, whereas, C59N5H22 had two π-electrons, where spins cancelled each other out to yield the lowest stable spin state. Silicon modified C59Si5H27 and phosphorous modified C59P5H22 had a curved molecular geometry due to large atom insertion at the zigzag site, which also brought about a complex spin distribution. Radical carbon and dihydrogenated carbon modification were identified as promising candidates for designing carbon based magnetic materials.

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., 6 pages, 7 figures

Using first principles calculations within the generalized gradient approximation, the structural stability of compound Mo-S clusters at subnanometer level is discussed based on results obtained for various Mo5Sn isomers with n ¼ 5{15. The symmetrical Mo-S bonds generally lead to higher stability, while the formation of S-S bond and the observation of magnetism in these clusters lower the structural stability. Mo5Sn isomers with n ¼ 6, 8, and 11 are found to be most stable. The addition of sulfur atoms is quite favorable in the edge capped square pyramid and face capped trigonal bipyramid isomers. [doi:10.2320/matertrans.48.658]

Atomic structures of Mo n O 2 n , n = 1–6 clusters are studied using first principles calculations and are compared with those obtained for Mo n S 2 n clusters. The lowest energy isomers of Mo n O 2 n differ significantly from those of Mo n S 2 n for n > 3. Oxygen atoms favor to bind with two Mo atoms, while S atoms are bonded with three Mo atoms. However, the clustering of Mo atoms is generally favored xin both cases due to the partially occupied d-orbitals. The lowest energy isomers of Mo n O 2 n have larger HOMO–LUMO gaps than the values for Mo n S 2 n clusters and for n = 1 and 4 the clusters are magnetic.

We have fabricated a new layered structure, named "U-mag," for perpendicular magnetic recording media, in terms of stacked films including a very thin (2 nm) ferromagnetic (Co) intermediate layer and lattice spacing control layers. The formed medium having a 100-nm soft magnetic underlayer with high coercivity over 6 kOe and sufficient nucleation field (-1.5 kOe) shows higher signal-to-noise ratio (SNR) than a medium with a conventional Ru underlayer. The detailed microstructures of the U-mag medium were also revealed by a transmission electron microscope with an energy dispersive spectrometer. A double Co intermediate layer gave a significant improvement in the SNR compared to a single Co layer.

Thermally assisted or hybrid magnetic recording system is expected to be a data storage device with high areal density beyond 1 Tb/in2. Several features of the hybrid recording are treated, such as high resolution recording capability by sharp thermal gradient, and pico-second order high-speed magnetization reversal. Since the hybrid recording solves the head field limit problem, the high magnetic anisotropy (Ku) materials with order of 107 erg/cm3 are used for the hybrid recording media. We discuss the candidates of the high Ku materials, FePt and CoPt L10 ordered alloy, Tb-Fe-Co amorphous, and Co/Pd multilayer thin films.

With consideration to the Curie-Weiss law, we investigate magnetization reversal beyond the Curie temperature, from theoretical to experimental. This paper outlines a theoretical model in accordance with the Curie-Weiss law and also presents a new criterion for the shape stability of recorded domains using magneto-optical recording or hybrid recording. Fairly good agreement was obtained between the theoretical and experimental investigations.

We have investigated Co-Pd multilayers deposited on a Pd-SiN granular seed layer and a FeTaC soft magnetic underlayer (SUL) for perpendicular magnetic recording. The Pd-SiN granular seed layer of 3 nm was found to be very effective for good magnetic properties with coercivity of 3.9 kOe, a negative nucleation field of -2.1 kOe, and a M-H loop slope parameter 4/spl pi/ (dM/dH)/sub H=Hc/ of 1.3. The average column diameter of 13.7 nm with a dispersion of 21.7% was evaluated from the transmission electron microscopy image of well-separated columns with a clear boundary. This Co-Pd medium gave better playback performances by a merged ring giant magnetoresistive head compared to the medium with a Pd seed layer. The effect of Ar plasma etching on the SUL was also investigated to improve playback performance.

Ultrafast 100 femtosecond laser light was irradiated on an amorphous GdFeCo film under a DC magnetic field. Complete magnetization reversal and rewritable response were observed in a less than 1 picosecond time period. This experiment reveals the intrinsic capability of ultrafast high-speed rewitable storage under the thermomagnetic switching scheme. Current pure magnetic recording such as that in the case of hard disk storage has a serious spin reversal time problem limited by the ferromagnetic resonance (FMR) frequency. Such frequency is ordinarily 1 to 3 GHz, which means that the recording speed limit is of a similar order. A one-picosecond response enables a very attractive future information storage scheme realizing 10 to 1000 Gbps ultrafast devices.

We investigated head-to-head domain walls in nanostrips of epitaxial $\mathrm{Fe}_4\mathrm{N}(001)$ thin films, displaying a fourfold magnetic anisotropy. Magnetic force microscopy and micromagnetic simulations show that the domain walls have specific properties, compared to soft magnetic materials. In particular, strips aligned along a hard axis of magnetization are wrapped by partial flux-closure concertina domains below a critical width, while progressively transforming to zigzag walls for wider strips. Transverse walls are favored upon initial application of a magnetic field transverse to the strip, while transformation to a vortex walls is favored upon motion under a longitudinal magnetic field. In all cases the magnetization texture of such fourfold anisotropy domain walls exhibits narrow micro-domain walls, which may give rise to peculiar spin-transfer features.

An activated Nd:YAG fiber tip using fiber-tip enhanced device (FTED) makes an activated and scattered irradiation beam. The enhanced (activated) fiber tip could be irradiated parallel to the target surface. The purpose of this study was to determine the effect of the activated laser fiber tip for calculus removal compared with other techniques. Specimens of extracted teeth with or without calculus were prepared. Nd:YAG laser power pulse 1 (SLT Japan, Tokyo, Japan) was used. The diameter of the optimal fiber was 400 μm. The enhanced condition was firstly examined using irradiation power from 100 to 900 mJ, 1 to 10 pps, in order to verify which is the best condition for calculus removal with scattering irradiation beam. Four types of calculus removal methods were compared: (1) hand curette; (2) ultrasonic scaler; (3) laser irradiation through a normal optimal fiber tip at 900 mJ, 10 pps, using a perpendicular irradiation mode with water coolant; (4) laser irradiation through the active fiber tip at 900 mJ, 10 pps, using a parallel irradiation mode with water coolant. After the roughness of the surfaces was clinically measured, the specimens were then prepared for scanning electron microscopy (SEM) observation. These results indicated that the best enhanced condition of the FTED for calculus removal with scattering irradiation beam was 800 mJ, 10 pps. The FTED was more useful for calculus removal than the normal fiber tip. However, it was less effective than hand and ultrasonic scaling considering the treatment time.

Recent experiments indicate room-temperature ferromagnetism in graphite-like materials. This paper offers multiple spin state analysis applied to asymmetric graphene molecule to find out mechanism of ferromagnetic nature. First principle density functional theory is applied to calculate spin density, energy and atom position depending on each spin state. Molecules with dihydrogenated zigzag edges like C64H27, C56H24, C64H25, C56H22 and C64H23 show that in every molecule the highest spin state is the most stable one with over 3000 K energy difference with next spin state. This result suggests a stability of room temperature ferromagnetism in these molecules. In contrast, nitrogen substituted molecules like C59N5H22, C52N4H20, C61N3H22, C54N2H20 and C63N1H22 show opposite result that the lowest spin state is the most stable. Magnetic stability of graphene molecule can be explained by three key issues, that is, edge specified localized spin density, parallel spins exchange interaction inside of a molecule and atom position optimization depending on spin state. Those results will be applied to design a carbon-base ferro-magnet, an ultra high density 100 tera bit /inch2 class information storage and spintronic devices., 6 pages, 8 figures

SVOD (Stacked Volumetric Optical Disk) can realize 0.94-5TB capacity cartridge using 100 ultra thin disks and commercialized drive. This paper presents the mechanism of aerodynamic stabilizer and several types of thin discs.

We grow a 15-nm-thick ferromagnetic Fe4N epitaxial film on a SrTiO3(001) substrate by molecular beam epitaxy, and process it into approximately 0.5-µm-wide and 24-µm-long L-shaped ferromagnetic narrow wires by electron-beam lithography and Cl2 reactive ion etching. Their longitudinal directions are set in parallel to the magnetic easy axes, Fe4N[100] and [010]. With applying external magnetic field in the direction parallel to Fe4N[100] or [010], the position of domain wall is controlled either on the upper side or lower side of the corner. This experiment is the preliminary step toward current-driven domain wall motion in Fe4N having a negative spin polarization.

The magnetization and spin transport of asymmetric zigzag-edge graphene nanoribbons, terminated by hydrogen on one edge while unterminated on the other edge, were investigated by a combination of first-principles calculations and a tight-binding approach. At the unterminated edge, a spin-polarized σ edge state of minority spin appears near the Fermi level and contributes to spin transport. This state enters the band gap for ribbon widths of less than 15 chains, dominating the spin-polarized current. This indicates the importance of the σ edge states in the design of spintronic devices using graphene nanoribbons. We also examined the case where the ‘unterminated’ edge is partially terminated by hydrogen.

Magnetic recording will face very serious problems beyond Tera bit/in/sup 2/, such as: recorded bit thermal stability in a size range of less than 20 nm×30 nm; very strong magnetic field necessary to write on a high coercive media, estimated over 15 kOe; write frequency limited to a few GHz, depending on the natural resonance of the magnetic material. In a hybrid recording scheme, writing is done at a high temperature around 150-230 °C, while archiving at room temperature. Such a simple concept brings solutions to solve the above difficulties. This paper outlines various hybrid recording device configurations and checks out the applicability of several materials for this type of application.

Advantages of Hybrid recording and material candidates like CoCrPt,TbFeCo.Pd/Co and FePt are discussed targeting the recording density beyond Tera bit/in2.

We present a magneto-optical recording head designed for a 400 nm laser with a 0.85 numerical aperture doublet objective lens and a thin film Magnetic Field Modulation coil integrated in a flying slider.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Magnetic Amplifying Magneto-Optical System (MAMMOS) shows human brain like memory behavior. Magnetic field and laser power have threshold to recover the stored memory like the human response of remembering. MAMMOS also has a feature to amplify very small recorded signals like our recovery of memory, e.g. fifty years ago episode.By adding the meaningful information on the magnetic field pattern, we can get some correlation between our memory and external stimulation. Such scheme is named as “the Active readout MAMMOS” which is analogues to the human process of remembering the memory.If the applied field pattern and timing phase just coincide with stored information, there occurs the coherent amplification of MAMMOS signal. We can utilize such phenomena as the trigger of “Memory Association”.

A stacked volumetric optical disks (SVOD) system has been developed to achieve an over 1 Tbytes cartridge capacity using a commercialized drive and conventional recording layers. To confirm the reliability of thin optical disks in SVOD, several feasibility tests were conducted. The recording power margin, tilt margin and read stability of the thin optical disks were measured, and the lifetime of the thin optical disks was estimated. The results were similar to those of conventional 1.2-mm-thick optical disks regardless of the disk thickness.

We present results of first-surface blue zero-field magnetic amplifying magneto-optical system (MAMMOS) recording of isolated marks of 60 nm and a single tone carrier of 90 nm. The signals are recorded by laser-pulsed magnetic field modulation using a blue laser, a recording head with numerical aperture (NA) = 0.7 with integrated thin film coil and a free working distance of 12 µm from the disc. The media are covered with a 3 µm thin cover layer to prevent heating induced contamination of the optics.

High-speed and high-density recording on magneto-optical disks has been achieved with accurate edge control. The Highest transfer rate of 64 Mb/s is obtained.

We study hexagonal assemblies of M6X6 (M=Mo and W and X=S, Se, and Te) nanowires from first-principles calculations to understand their structural stability, electronic properties, and the effects of Li intercalation. It is shown that due to van der Waals interactions between the nanowires, the intercalation is achieved without a significant change in their atomic structure. With an increase in Li concentration, we predict a new phase for Li3Mo6S6 compound, in which the hexagonal assembly transforms to a monoclinic structure by a change in the orientation of nanowires. The LixMo6S6 assemblies are electrically conductive and can be potentially used as cathode materials in Li-ion batteries for nanoscale applications. The voltage of such a battery, calculated to be 1.7V, can be manipulated such as by iodine doping without a significant change in the atomic structure.

This article presents a theoretical model for the temperature dependent magnetic properties for a Co∕Pd multilayer thin film medium assuming virtual interface (VIF). We assume that the exchange integral for the Co-VIF interaction is 1.38 times the exchange integral for the Co-Co interaction. Based on the mean field theory, temperature dependences of the average Co spin, the virtual interface spin, saturation magnetization Ms and exchange stiffness constant A are presented for the [Co(0.2nm)∕Pd(0.8nm)]12 multilayer thin film. Fairly good agreement in Ms between the simulations and the experiments suggests validity in the temperature dependence of A.

We have investigated the Co/Pd multilayer media with a Pd–SiN granular seed layer as perpendicular recording media. The Pd–SiN granular seed layer and the Co(0.2 nm)/Pd(0.8 nm) multilayer were formed by dc and rf sputtering at room temperature on a FeTaC soft magnetic underlayer. The Pd–SiN granular seed layer of 3 nm was very effective to get good magnetic properties with coercivity of 3.9 kOe, a nucleation field of −2.1 kOe, and a M–H slope parameter 4π(dM/dH)H=Hc of 1.4. In addition, it was found that growth of multilayer grains is sensitive to surface conditions of the soft magnetic underlayer. The average column diameter of 13.7 nm with a dispersion of 21.7% was evaluated from the plan-view transmission electron microscope image of well-separated Co/Pd columns with a boundary, which was grown on the Pd–SiN seed layer and the soft magnetic underlayer with Ar plasma etching. Atomic force microscope measurements showed that mean roughness (Ra) of the FeTaC surface decreased from 0.46 to 0.39 nm by the p...

Crystal growth of ZnS by a new type of MBE apparatus having a H2S gas source has been performed. The basic characteristics of the H2S gas source have been examined and an attempt to determine the optimum growth conditions has been made. In our present experiments, single crystalline films having fairly high quality have been obtained under suitable conditions, i.e., Tsub (substrate temperature) = 360°C, PH2S (inlet gas pressure of H2S) = 3×10−5 Torr, Tcr(H2S)(cracking temperature of H2S) = 920°C and JZn (Zn beam intensity) = (6−9)X1015 mol/cm2·s.