Shigeru Shiomi

Magnetostatic Perpendicular Anisotropy in Iron Films with Columnar Structure

Theoretical calculations are given for the uniaxial perpendicular anisotropy resulting from the magnetostatic energy in magnetic films with a columnar structure; small magnetic cylinders are assumed to form an infinite two-dimensional array with hexagonal symmetry. Experiments have also been done for the dependence of the uniaxial perpendicular anisotropy on the temperature and columnar-structure constants in the iron films prepared by an anodic oxidation method. The experimental results could be well interpreted in terms of the magnetostatic uniaxial anisotropy.

Magnetic properties of CoPt alloy films sputtered on Pt underlayers

CoPt alloy films have been sputtered on room-temperature glass slides. It has been found that effective perpendicular anisotropy K⊥ depends on the film composition and reaches a maximum in films with Ms~850 emu/cm3, and that K⊥ is greatly enhanced by the application of substrate bias and the deposition of a Pt underlayer. K⊥ increases with increasing CoPt layer thickness d(CoPt), becoming almost constant beyond d(CoPt)=100 nm in films sputtered on 100-nm-thick Pt underlayers. It has also been found that sputtering at higher Ar gas pressure without substrate bias greatly enhances coercivity, though K⊥ is somewhat reduced.

Preparation, Magnetic and Magneto-Optic Properties of Small-Crystallite MnBi Films

MnBi composite films were prepared by annealing Bi–Mn multilayers which were deposited in vacuum by repeating an alternate evaporation of Bi and Mn metals. They were found to have a crystallite size of about one thousand angstroms and, moreover, to exhibit an orientation of the C-axis perpendicular to the film plane, as observed in MnBi single layers. A structure analysis by electron microscopy and a significant increase in the coercive force suggest that they have a multilayer structure. Their large coercive force enabled us to write-in reversed magnetic domains (as small as 1.2 µm in diameter) by the irradiation of a single-pulse Baser beam. No significant difference was found in the magnetization, Kerr rotation or reflectivity between composite MnBi films and single-layer MnBi films.

Magnetic properties of carbon nanotubes grown on Fe catalyst layer by microwave plasma enhanced chemical vapor deposition

The magnetic properties of carbon nanotube films grown on an Fe catalyst layer were investigated. The easy magnetization direction of the nanotube films was perpendicular to the film plane when the growth time was more than 2 min. In these films, conical Fe catalyst particles could be found at the tips of the nanotubes. The origin of the perpendicular magnetic anisotropy of these films was considered to be due to the anisotropic shape of the conical Fe catalyst particles at the tips. A large perpendicular coercivity of about 1 kOe was obtained in a nanotube film grown for 10 min.

Synthesis, Crystal Structure and Magnetic Properties of Iron Particles Encaged in Carbon Nanocapsules

Soot containing carbon-coated iron particles was produced by the arc-evaporation of a Fe-packed graphite rod in a modified fullerene generator. X-ray diffraction and electron microscopy revealed that it consisted of carbon nanocapsules encaging α-Fe, γ-Fe and Fe3C particles. Helium gas pressure during arc-evaporation was varied from 1 to 5 atm as well as from 50 to 500 Torr. The fraction of the γ-Fe component increased with helium gas pressure. The fraction of α-Fe, γ-Fe and Fe3C components in the soot prepared in helium gas of 5 atm was estimated to be 45, 25, and 30 wt%, respectively.

Magnetic Properties and Structure of Co/Pt Multilayered Films Evaporated on Heated Substrates

Co/Pt multilayered films were evaporated on glass substrates that were heated up to 500°C. Perpendicular magnetic anisotropy K⊥ was found to increase with the elevation of substrate temperature Ts, reaching a maximum at Ts=300°C. The surface anisotropy component also increased with elevating Ts while the volume component hardly depended on Ts. The coercivity of the perpendicular magnetization curve, Hc⊥, greatly increased with the elevation of Ts, exceeding 4 kOe at Ts=300 and 400°C. The layered structure was found to deteriorate considerably at Ts=300°C, becoming indistinct at Ts=400°C and higher. On the other hand, the (111) preferred orientation normal to the film plane became more pronounced with the elevation of Ts. The average grain size was found to increase with the elevation of Ts. It was also found that Hc⊥ had a close relationship to , reaching a maximum at =250-300 A.

Dynamics of an Isolated Stripe Domain in Bubble Film

The existing horizontal Bloch line (HBL) theory for a planar wall is extended to give explicit expressions for important dynamic properties of the wall such as the translation velocity, the overshoot distance etc. The effect of a static in-plane field applied parallel to the wall is also discussed. When a single straight stripe domain is translated by a pulsed-gradient magnetic field, the dynamic properties of this domain are shown to be directly comparable with those for the planar wall. Experimental results are shown for a single stripe domain in a bubble film with low damping. While the in-plane field is small, the results agree well with the theory. When the in-plane field is increased, however, a phenomenon is found which is hard to explain by the present theory.

Coercivity Enhancement in Co–Pt Alloy Films due to Annealing in Air

Co–Pt alloy films with out-of-plane magnetization were annealed both in air and in vacuum. Annealing in air resulted in a significant increase in coercivity H c, while annealing in vacuum hardly increased H c. Irrespective of Co–Pt alloy layer thickness, the most significant increase in H c was induced when saturation magnetic moment m s was reduced to 0.5–0.7 of that before annealing. The dependence of H c and hysteresis loss on magnetic field direction suggests that the enhancement in H c results from the division of Co–Pt alloy layer into single-domain particles by the oxidation of Co atoms at grain boundaries.

Magnetic and Magneto-Optical Properties of Laser-Annealed PtMnSb Films

Sb, Mn and Pt layers have been sequentially deposited and then annealed using Ar+ laser beam to form PtMnSb alloy film. The crystalline, magnetic and magneto-optical properties of films were found to depend on annealing conditions such as laser power P and beam scan rate R. Adequate combinations of P and R resulted in films which were seemingly of the PtMnSb single phase. In these films, Ms ranged between 300 and 450 emu/cm3 and there was neither perpendicular nor in-plane magnetic anisotropy. At the wavelength of 630 nm, the polar Kerr rotation angle took the peak value, which ranged between -0.8 and -1.7° through the glass substrate.

Effect of Annealing on Magnetic Properties of Sputtered CoPt Alloy Films

CoPt alloy films with perpendicular magnetic anisotropy were sputtered on Pt buffer layers. In spite of rather large perpendicular anisotropy, the coercivity Hc and squareness ratio S of the perpendicular magnetization curve were very low. It was found that annealing at 300°C in air resulted in a drastic increase in Hc and S, while magnetic moment was reduced. The effect of annealing on magnetic properties was more marked in a thinner film. Auger electron spectroscopy and X-ray photoelectron spectroscopy revealed that cobalt atoms were preferentially oxidized to form CoO during annealing.