Yumiko Haga

Thermal stability and hardness of metastable Co–C composite alloy films

Abstract Co–C alloy films containing metastable cobalt carbides have been prepared by a new type of co-sputtering deposition technique and their thermal stability was examined and discussed in terms of the concept of the formation enthalpy. Dynamic hardness and magnetic properties, such as saturation magnetization, were also evaluated for the Co–C alloy films. Both hardness and magnetization of the films were found to decrease almost linearly with increasing fraction of carbon content in the film, suggesting that the measurement of hardness can serve as a monitor of film qualities. It is also shown that the hardness of metastable cobalt carbides is greater than that of the Co–C alloy film.

Observation of magnetic structures in Fe granular films by differential phase contrast scanning transmission electron microscopy

Differential phase contrast (DPC) scanning transmission electron microscopy was applied to investigate the magnetic structures of Fe granular films. The DPC images showed a cluster-like contrast of 200 nm in the lateral size, which could not be observed by Lorentz transmission electron microscopy in the Fresnel mode. The magnetization vector map reproduced from the DPC images indicated that a magnetization loop generally intersects several isolated particles of 20–40 nm in diameter. The films composed of densely dispersed magnetic particles showed larger magnetization loops, while more separately dispersed films tended to have smaller loops, or magnetization closures in one particle. The loop size is associated with the strength of magnetic interaction between magnetic particles.

Structures and Magnetic Properties of Fe/Co Multilayer Films Prepared by DC Sputtering

We have synthesized Fe/Co multilayer films with various layer thickness ratios by a two-facing-target-type dc sputtering method. The film texture and microstructure of as-deposited films were characterized by X-ray diffraction and by cross-sectional transmission electron microscopy. The films are constructed with alternately stacking Fe(110) and Co(0001) planes. A good orientation relationship between constituent Fe and Co layers is realized over several layers. When the thickness of each layer is equal, the saturation magnetization (4πMs) is a constant of about 2 T (20 kGauss) regardless of layer period. No remarkable layer period dependence of the coercivity is seen.

Self-alignment of metallic nanowires in CaF2-based composite films grown on stepped NaCl substrates

Abstract Self-aligned metallic nanowires have been formed in CaF 2 -based composite films grown on stepped NaCl (101) substrates. The nanowires were columns standing perpendicular to the {100} facets of the substrates, and have in-plane anisotropic microstructure with respect to the films.

Magnetic properties of Fe-based amorphous/nanocrystalline alloy bilayer ribbons

Abstract An Fe-based amorphous/nanocrystalline bilayer ribbon was prepared by a combination of rapid quenching and subsequent annealing. The B  H loop exhibits low coercivity and a reversible change in magnetic induction which is quite different from the two-step B  H loop of lap-wound monolayer ribbons. This result for a bilayer ribbon arises from interlayer stresses induced by nanocrystallization of one layer with lower crystallization temperature.

Hysteresis Loops and Microstructures of Fe/Ag Multilayer Films

The relationship between magnetic properties and microstructures in the Fe/Ag system has been investigate. Fe/Ag multilayer films with a thickness ratio of 1/10=Fe/Ag were prepared by a double-facing-target-type dc sputtering apparatus. The M-H loops measured using a vibrating sample magnetometer showed that they had some uniaxial anisotropies in the film plane, and some steps were observed on the loops measured for the average easy axis, especially when the Fe layer thickness was larger than 6.5 nm. It was found that the number of steps was equal to that of inserted Fe layers. Microstructures of the films were investigated by X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. The films were composed of alternate stacking of Fe{110} and Ag{111} planes and constructed with many columns growing along the stacking direction. The origin of steps on the M-H loops is discussed on the basis of experimental results.

Preparation and Magnetooptical Properties of AlN–Fe Granular Film

AlN films including Fe nanoparticles have been prepared from sputtered films with Al–N–Fe composition by annealing in a vacuum furnace. Faraday rotation angles and M–H loops of AlN–Fe granular films have been measured. The maximum value of Faraday rotation angle is estimated to be 1.1°/µm at a wavelength of about 500 nm. The microstructures of the films are characterized by transmission electron microscopy and X-ray diffractometry. The structural features are related to the magnetic properties.

Microstructure and preferred orientation in pure titanium films deposited by two-facing-target-type DC sputtering

Pure Ti films were produced by two-facing-target-type DC sputtering under various preparation conditions such as sputtering gas pressure, substrate temperature and film thickness, and their microstructures were investigated by both X-ray diffractometry and scanning electron microscopy. The microstructures were explained well in terms of structure zone, based on the Thorntons model concerning the morphology in sputtered films. It is also shown that a one-to-one correspondence does not always exist between columnar structure and preferred orientation.

Magnetic and structural properties of Fe/Ag and Fe/Ta multilayer films prepared by dc sputtering

Abstract We investigated Fe/Ag and Fe/Ta multilayer films by X-ray diffraction and transmission electron microscopy. The individual Fe layers in multilayer films used in this study have various structural and magnetic features. We also characterized the structural features on the basis of the magnetic properties, especially the coercive forces of individual Fe layers.

Columnar structures in Fe-based metallic multilayers prepared with the facing-target-type DC sputtering method

Structural features of Fe films and Fe-based multilayers with Ag, Cu, Cr and Mo sublayers were investigated; we focused on structural features such as the asymmetric shape and the alignment of the columns in the film plane. As a result, common structural features were found to be related to factors such as the substrate temperatures, the melting points of the elements concerned with surface diffusion, and the incident directions of the sputtered particles to the substrate originating from the arrangement of the targets. In the case of multilayers, such structural features were found to vary depending on combinations of the metal elements and the thickness ratios of the constituent sublayers.