Teruaki Takeuchi

Ferromagnetic Mn/C/Si films

Ferromagnetism at room temperature has been found in Mn/C/Si films prepared by sequential deposition of these elements at a substrate temperature about 360 °C by vacuum evaporation. The saturation magnetization increases rapidly with the carbon quantity, and it is about 250 emu/cc for a film with a nominal structure of Mn(6 nm)/C(0.5 nm)/Si(6 nm). The magnetization measurements at low temperatures show that the magnetic moment per ferromagnetic Mn atom corresponds to more than 1.2 Bohr magnetons.

Epitaxial growth and enhanced saturation magnetization of single crystal Co/sub 1-x/Cr/sub x/ media suitable for perpendicular magnetic recording

Highly c-axis oriented, single crystal films of Co/sub 1-x/Cr/sub x/ have been grown epitaxially on mica substrates by e-beam evaporation. The method, using a Ru underlayer, is simple and applicable to similar c-axis oriented, large area growth of the wide range of Co alloys suitable for perpendicular recording. The films show narrow peak widths in X-ray diffraction (/spl Delta//spl Theta//sub 00.2//spl sim/1.0-1.5/spl deg/) and their magnetic properties are composition dependent. Moreover, for any given Cr concentration, these single crystal films exhibit the largest saturation magnetization when compared with either sputtered/evaporated samples or films grown under identical conditions on glass/silicon substrates. It is shown that this enhanced M/sub s/ is directly correlated with the dispersion of the c-axis about the film normal and their narrowest values are observed for these epitaxially grown films. X-ray microanalysis shows some inter/intra-granular variation in Cr content, but systematic segregation trends appropriate for explaining these results have not yet been observed. >

Determination of strain distributions in ion‐implanted magnetic bubble garnets applying x‐ray dynamical theory

X‐ray dynamical theory has been applied to determine strain distributions caused by ion implantation into magnetic bubble garnets. Experimental rocking curves obtained by a double‐crystal x‐ray diffractometer were compared with theoretical curves for assumed strain distributions, and after several trials, good fittings were obtained. It is shown that slight change in the assumed strain distribution leads to appreciable change in the theoretical rocking curve. Comparison between dynamical and kinematical treatments shows that dynamical treatment is more accurate. Applying the method, it was confirmed that strain by multiple ion implantation was basically the sum of those by single ion implantation.

Ion-implanted and permalloy hybrid magnetic bubble memory devices

Hybrid bubble memory devices have been proposed and operated with the memory density of 4 Mbit/cm2. In the hybrid bubble memory devices, minor loops are composed of ion-implanted tracks with 4-µm period, and major lines and functional parts including block-replicate and swap gates are composed of Permalloy tracks with a longer period of 12 µm. Passive junctions between ion-implanted and Permalloy tracks have been developed, introducing the tapered ion-implantation technique. Improving the characteristics of the functional parts composed of Permalloy tracks, the hybrid bubble memory devices with block-replicate and swap gates have been operated, and the feasibility of the devices has been confirmed. In addition, the possibility of higher memory density has been shown.

Method of making magnetic bubble memory device by implanting hydrogen ions and annealing

A method of implanting a magnetic garnet film with ions is disclosed in which a covering film is provided on a monocrystalline magnetic garnet film for magnetic bubbles, and hydrogen ions are implanted in a desired portion of a surface region in the magnetic garnet film through the covering film. According to this method, it is possible to form an ion-implanted layer in which the ion concentration distribution in the direction of depth is uniform, and moreover the inplane anisotropy field in the ion-implanted layer decreases only a little with time in an annealing process.

Structure and magnetic properties of Mn‐Al multilayered films

Correlation between the structure and the magnetic properties of Mn‐Al multilayered films prepared by vacuum evaporation have been investigated. Films on MgO(100) substrates with layer thicknesses of 100 A or more were found to have structures with flat layers and (100) orientation of α‐Mn, while a film on a glass substrate and a film with a layer thickness of 50 A on a MgO(100) substrate were seen to have variations in layer thicknesses and no crystal orientation of α‐Mn. Saturation magnetizations for the former two films are more than several times greater than those for the latter two films. From these properties, it is judged that stacking of α‐Mn layers with (100) surfaces and Al layers is an important factor for the evolution of ferromagnetic properties in Mn‐Al multilayered films.

Magnetic Properties of Mn-Al Multilayered Films

The magnetic properties of Mn-Al multilayered films prepared by alternate deposition of Mn and Al in a vacuum evaporation system are investigated. Such films are found to show ferromagnetic properties when the substrate temperature during deposition is around 300°C. The saturation magnetization is seen to depend on the kind of substrate: the values for MgO(100) substrates are greater than those for MgO(111) and glass substrates. The obtained saturation magnetization of 50 emu/cm3 is expected to increase.

Characteristics of junctions between ion-implanted and permalloy tracks in hybrid bubble devices

The characteristics of junctions between ion-implanted and Permalloy tracks are described for hybrid bubble memory devices. It has been found that the junctions which have a sharply formed edge of the ion-implanted layer have a problem in reproducibility of bias field margins. It is caused by the potential barrier due to the stress change and free poles which appear at the edge as well as the attractive poles in the ion-implanted tracks which tend to keep the bubbles in the ion-implanted tracks. To reduce their influence, we have introduced the tapered edge. A good bias field margin has been obtained for the tapered junctions with the modified pickax Permalloy pattern from the ion-implanted to Permalloy tracks. In the junctions from the Permalloy to ion-implanted tracks, the bias field margin strongly depends on the orientation of the edge of the ion-implanted layer with respect to the easy magnetization directions of the garnet. The edge should not be parallel to the easy magnetization direction, and the Permalloy pattern should be made larger near the edge. The improved junctions have a good bias field margin with reproducibility.

Temperature dependence of magnetization reversal in TbFeCo films

The magnetization reversal process has been studied in a series of four TbFeCo films over the temperature range 300–460 K. The films were characterized by time decay, dynamic coercivity, Kerr imaging, and torque measurements. For a film with a sputter-etched SiN underlayer, the reversal process at low temperatures was dominated by nucleation followed by rapid domain wall motion. The low temperature relaxation curves for this sample were analyzed using a Fatuzzo model. At high temperatures, the Fatuzzo model did not apply. For the other films, with no etching, relaxation curves were logarithmic at all temperatures. All activation volumes increased with increasing temperature and decreased with increasing sputtering pressure. The magnetic anisotropy direction changed from perpendicular to in-plane as the argon sputtering pressure was increased.

Origin of effective anisotropy field change induced by ion implantation in magnetic garnet films

The origin of effective anisotropy field change induced by ion implantation in magnetic garnet films has been investigated using films with uniform strains. Uniform strains were produced by ion implantation into very thin (600 A) garnet films. Using such ion-implanted samples, strain, saturation induction 4πMs, magnetostriction coefficient λ 111 and effective anisotropy field change Δ(Hk-4πMs) were measured. It was found that Δ(Hk-4πMs) is mainly brought about by the magnetostriction effect for both H 2 + and Ne+ implantations. Different dependences of Δ(Hk-4πMs) on strain between H 2 + and Ne+ implantations are attributed to different dependences of λ 111 and 4πMs. A large value of Δ(Hk-4πMs) for H 2 + implantation originates from a large magnitude of λ 111 .