Morio Masuda

Perpendicular Magnetic Anisotropy of TbCo Films

An experimental study has been made on the magnetic anisotropy of amorphous TbCo films prepared by rf co-sputtering. TbCo films prepared at a substrate bias voltage of –100 V exhibit a large uniaxial anisotropy of 2×106 erg/cm3 with its easy axis perpendicular to the film plane, whereas films prepared without the substrate bias exhibit the anisotropy with its easy axis in the film plane. The planar stress due to the substrate constraint considerably influences the perpendicular anisotropy through the large magnetostriction of about 2×10-4. When films with perpendicular anisotropy are removed from the substrate, the anisotropy energy decreases to 65–80 percent of its initial value. Annealing for one hour at 300°C destroys the perpendicular anisotropy almost completely.

Measurement of Anisotropy Dispersion by means of Ferromagnetic Resonance

It is reported that the magnitude dispersion and the angular dispersion of the anisotropy energy in permalloy films can be measured by means of the ferromagnetic absorption measurement at a radio frequency of about 0.5 Mc/s. Principles of the method for dispersion measurement are developed here on the basis of a particle domain model. The experimental setup as well as the results obtained are also shown.

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.

Magnetostriction and Perpendicular Magnetic Anisotropy of Amorphous GdFeCo Thin Films

The saturation magnetostriction constant λs, and the perpendicular magnetic anisotropy Ku of amorphous Gdx(Fe100-yCoy)100-x(9.5<x<50) films prepared by dc-biased rf sputtering have been measured at room temperature. In films with high Co concentration, λs showed strong dependence on Gd content, whereas in Fe-rich films, λs showed weak dependence. Furthermore, it was confirmed that λs was not affected by the substrate bias voltage Vb, although Ku strongly depended on Vb.

On the origin of uniaxial anisotropy in permalloy thin films

Variation of H k during isothermal magnetic annealing has been systematically investigated to make clear the origin of the induced anisotropy in evaporated Permalloy films of the composition ranging from 70- to 90-percent Ni. The anisotropy of films deposited at room temperature comes from six different origins, whose activation energies are E_{1} eV (0.17-0.2 eV), E_{2} \simeq E_{3} \simeq 0.5 eV, E_{4} \simeq E_{5} \simeq 1.1 eV, and E_{6} = 2.0 eV, respectively. The compositional dependence of contributions from each origin can be used in order to elucidate the whole mechanism of the anisotropy in detail. The component of activation energy from 0.2 to 0.5 eV is closely related to the magnetoelastic anisotropy, while that of 1.1 eV is almost independent of the film composition. The component with the activation energy of 2.0 eV proved to be the same as that found in bulk Permalloy. Furthermore, the effects of the preparation condition of films on the anisotropy are also discussed.

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.

Origin of the Periodic Component of Anisotropy Dispersion in Ni-Fe Films II

The periodic component of the angular dispersion α90 was measured on Ni-Fe films of various compositions deposited onto glass substrates kept at different temperatures. When the substrate temperature ts is about 300°C, the films are almost free from the stress and thus the angular dispersion α90 comes mainly from the magneto-crystalline anisotropy K1 of the crystallites. However, if ts is far below 300°C, then α90 comes not only from K1 but also from the magneto-elastic anisotropy Kσ, α90∝(K12+Kσ2)1/2/Ku, where Ku is the uniaxial anisotropy constant of the film. The anisotropic part of the stress σa estimated from α90 depends on the substrate temperature as σa~(300-ts)×107(dyn/cm2).

Crystallographic Structure and Magnetic Properties of Co Fine Particles Encaged in Carbon Nanocapsules

Cobalt crystallites wrapped in multilayered graphitic cages (nano-capsules) were produced by an arc discharge method. Structural characterization by X-ray diffraction and transmission electron microscopy revealed that the wrapped cobalt particles were in an fcc phase, with a trace amount of hcp Co. The particles were nominally spherical in shape, and typically 10-100 nm in diameter. The core Co metal was protected against oxidation and coalescence. Temperature dependence of the saturation magnetization (M s) and the coercive force (H c) was measured between -200° C and 800° C for powder samples, which revealed that the measured M s was consistent with that for fcc Co over that temperature range. Magnetic tapes prepared from the present powder exhibited H c of 250 Oe and 30% remanent magnetization of the M s at room temperature.

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.