Kazuetsu Yoshida

Microstructure and magnetic properties of CoCr thin films formed on Ge layer

To improve the c-axis oriented columnar growth, the nucleation of CoCr crystals on various underlayers which are formed on substrates prior to CoCr alloy deposition is studied. Microstructures of vacuum deposited CoCr alloy films are examined by transmission electron microscopy (TEM). It is found that an amorphous-like Ge is a suitable underlayer material to prepare highly oriented CoCr films. Cross-sectional TEM study indicates that the CoCr film formed on Ge layer consists of pillarlike crystals grown vertically throughout the film thickness. The CoCr film formed on Ge layer has a large perpendicular magnetic anisotropy. The read-write (R/W) characteristics have been markedly improved using the highly oriented CoCr film and a very high recording density of D 50 =230 kFCI is achieved, The role of the Ge layer on nucleation of CoCr crystal is discussed.

Observation of recorded magnetization pattern by electron holography

Electron holography was employed for experiments involving a high‐density magnetic recording, in which it was possible to directly observe streams of magnetic flux. The magnetic flux distribution in recorded films, and the maximum packing density in high‐coercivity evaporated cobalt film were investigated. With magnetic longitudinal recording the resultant highest density was 170 000 bits per inch. This experiment has proven that electron holography is useful for the study of magnetic recording.

Study of Co‐Cr films for perpendicular magnetic recording using nuclear magnetic resonance

A 59Co nuclear magnetic resonance measurement and a transmission electron microscope observation are utilized to investigate the compositional distribution of Co‐Cr films with and without heat treatment. The spin‐echo spectra of evaporated films are found to be entirely different from those of Co‐Cr alloy powders. The spectra of films comprise a very complicated hyperfine field distribution and the resonant frequencies are much higher than those of powder samples, implying the existence of various kinds of segregation regions typical of a film. Chrysanthemumlike patterns, which disappear with heat treatment, are also observed for chemically etched films. This disappearance is accompanied by the disappearance of the highest‐frequency resonant line.

Observation of recorded magnetization patterns by electron holography

Magnetization patterns recorded on Co thin films prepared by oblique incidence vacuum deposition were directly observed by electron holography. Complicated ellipse-like interference fringes were observed along the sawtooth-like walls in the transition regions. Stray magnetic flux was observed in empty space beyond the edge of the film. The following results were obtained from analysis of these interference images. The smaller the product of the remanence and the film thickness, and the higher the coercivity, the narrower is the transition length that determines the limit of the recording density of a medium. It was confirmed that longitudinal magnetic recording of a density of up to 170 kBPI is attainable using Co film 30 nm thick and with coercivity of 112 kA/m. It was quantitatively proven that the intensity of the recorded magnetization in a medium is equal to its remanence when the magnetized area is distinguishable from the transition region.

A method of measuring anisotropy field of polycrystalline thin-film media

Ferromagnetic resonance (FMR) is used to measure the magnetic anisotropy field Hk and its dispersion of poly-crystalline recording media. This method does not use any single crystal substrate. A high-intensity field is applied vertically to a sample surface to completely saturate the magnetization and a high-frequency (over 50 GHz) magnetic field is applied in the surface. An FMR simulator based on the Landau–Lifshitz–Gilbert equation confirms that the magnetic (exchange and/or magnetostatic) interactions have very little effect on the resonant frequency in the configuration used. The linewidth of the FMR spectrum is affected by the Hk dispersion and damping constant. Methods using a torque or magnetization curve include magnetic interactions, resulting in a systematic error to the value of Hk. This FMR method is applied to CoCrPt-alloy thin-film media with a Cr-alloy underlayer grown on a glass substrate. A conventional torque method is also used for comparison. The axis of hexagonal-close-packed Co magn...

Thermal aftereffects in thin film magnetic recording media

Thermal aftereffects in written bits in CoCrPt thin film magnetic recording media are examined using a magnetoresistive (MR) head and a magnetic force microscope (MFM). Decays in signal output over time at room temperature in media with very thin magnetic layers of about 14-nm thickness or less were observed by using an MR head. The decay in signal output was accompanied by an increase in medium noise. Even with a precise examination of cross-track profile using an MFM, no change in track width caused by thermal aftereffects can be detected. Thermal decay of the signal output in a 14-nm thick magnetic layer with small remanence thickness product M/sub r/t/sub mag/ of about 40 G-/spl mu/m was successfully reduced by increasing the platinum content in the CoCrPt magnetic layer or by adding boron to the CrTi underlayer without increasing the medium noise. The reduction of thermal decay is considered to be caused by the increase of magneto crystalline anisotropy and increase in magnetic-crystal-grain size. These results suggest that it is possible to reduce the medium noise without reducing the crystal grain size and without much degradation of thermal stability even for media with small M/sub r/t/sub mag/ which is needed to achieve a recording density of 10 Gb/in/sup 2/.

Bicrystal cluster structure and magnetic properties of CoCrTa/Cr thin film media

Structures of bicrystal clusters of CoCrTa thin film media are examined using high resolution transmission electron microscopy (HRTEM), and the effects of the bicrystal clusters on magnetic hysteresis were studied using micromagnetic simulation. The bicrystal cluster of CoCrTa consists of two crystallographic variants grown on a single Cr underlayer grain with their c-axes normally-aligned in the film plane. The typical number of grains in each cluster is 2 to 3. With the bicrystal structure, coercivity decreases significantly as grain size decreases when intergranular exchange coupling is strong, and high hysteresis squareness can be obtained. Coercivity in the small grain size region can be increased by reducing the exchange coupling.

Sensitivity‐enhanced electron holography and its application to magnetic recording investigations

The sensitivity for electron‐phase measurement in electron holography has been improved to better than 2π/100 by the application of digital interferometry at the optical reconstruction stage. This enables quantitative measurement of magnetic flux as small as (1/100)(h/e)(=4.1×10−17 Wb), hitherto undetectable, with high spatial resolution. With this technique, we have observed the distribution of leakage magnetic field from a thin cross section of a perpendicularly magnetized recording film (cobalt‐chromium) with a recording density as high as 300 kFCI (85 nm bit length), the highest density ever directly observed.

Measurement of intensity of recorded magnetization on Co-Cr film by electron holography

Electron holography has excellent features that permit the direct observation of magnetic flux in micro regions and the quantitative measurement of the flux intensity. Using this method, the intensity of recorded magnetization on a Co-cr single layer medium is measured. As a result, it is revealed that the demagnetization factor, which is determined by the aspect ratio of the recorded bit cell, dominates the magnetization recorded in contact with a head. It is also learned that the spacing loss in the recording process is -160d/λ[dB).

Wear-resistant properties of protective layers applied to thin film metallic media

Wear resistant properties of inorganic protective layers applied to thin film metalic media are determined for several combinations of protective layer and sliding head materials. When a fluid lubricant is applied, medium durability tends to improve with increasing hardness of the protective layer material. Durability also depends on the slider material.