Osamu Kitakami

Noise from underlayer of perpendicular magnetic recording medium

Noise from the underlayer is observed with a Mn‐Zn ferrite head and a Co‐Mo‐Zr low coercivity amorphous underlayer. Three kinds of noise are observed, spike noise (s), medium noise (m), and low noise (l). s noise is generated through the domain walls of an underlayer. m noise originates from the interaction between an underlayer and the reproducing head’s residual magnetization. Three effective methods are tested for reducing the noise: (1) increase of coercivity of an underlayer, (2) use of an ac‐erased head, and (3) use of a thin‐film head.

Observations on Perpendicular Magnetic Recordings of High Recording Densities on Co-Cr Films by the Colloid-SEM Method

Perpendicular magnetic recordings of 5 to 100 kBPI densities on evaporated Co-24 wt%Cr films of 2200 A in thickness have been observed by the colloid-SEM method and by the conventional magnetic powder pattern technique. The latter technique, using an optical microscope, gives satisfactory results for recording densities of 5 and 10 kBPI. For high recording densities of 50 and 100 kBPI, clear recorded patterns have been successfully obtained by the colloid-SEM method where dried powder patterns are made under external magnetic fields of 200 to 300 Oe applied vertically to the film planes. It is shown that a better recording can be determined from the obtained patterns, even in high-density recordings. Some discussions are given regarding the relation between the single-domain behaviour of columnar grains in the films and obtained recorded patterns.

The effect of Ti underlayer on magnetic properties of Co-Cr thin films

The effect of a Ti underlayer on Co-Cr thin film was investigated from the crystallographic and morphological points of view. The Co-Cr film on a Ti underlayer has a larger perpendicular magnetic anisotropy and coercive force than that deposited directly on a polyimide film substrate. It is found that the improvement of perpendicular magnetic properties by the insertion of a Ti underlayer is not due to the improvement of the crystallographic c-axis orientation, but is due to the formation of a uniform columnar structure.

Influence of initial growth layer and Ti underlayer on magnetic properties and recording characteristics of very thin films of evaporated Co-Cr media

A Co-Cr film deposited directly on a substrate has an initial growth layer with low coercivity. However, the existence of a Ti underlayer prevents the formation of such a layer. As a result, Co-Cr film deposited on a Ti underlayer has high perpendicular anisotropy and coercivity even in cases of extremely thin film thickness (200 AA). As for the read-write characteristics of Co-Cr thin-film media, the existence of such an initial growth layer greatly improves the reproduced output level. The cause for this is considered to be that the free charges which appear on the back surface of the perpendicular recording layer are reduced and the demagnetization field acting on the recorded magnetization subsequently decreases due to the existence of the initial growth layer. >

Magnetic and crystallographic study of Co electrodeposited alumite films

Magnetic properties and crystallographic structures of alumite films of which pores were filled with Co were investigated. The perpendicular magnetic anisotropy energy of the films was smaller than their shape anisotropy energy, which is due to the magnetocrystalline anisotropy of hcp‐Co particles in the pores. The c‐axis orientation of hcp‐Co particles was found to be influenced by the pH near the cathode and the ac frequency used in the deposition. The c axis rose from the in‐plane direction of the film to the normal one when the Co was electrodeposited into the pores at high pH value and low ac frequency, and the perpendicular magnetic anisotropy of the films increased. The deposition of Co at high pH value and low ac frequency was supposed to decrease the current density in the reduction process of Co2+ ions, which caused the preferred c‐axis orientation to the normal direction of the film.

Study on the surface oxidation of Co-Cr films

The tribological properties of a Co-Cr thin film were greatly improved by surface oxidation. According to surface analyses, a Cr-rich oxidized region in which Cr is oxidized to Cr/sub 2/O/sub 3/ was formed near the surface of the film. This region plays an important role in improving the mechanical durability of the film. However, when the oxidation is carried out for a long time, a thick Co-rich oxidized region grows on the Cr-rich oxidized one. As a result, the durability deteriorates. >

Improvement of the reproduced output of Co-Cr thin film media by insertion of very thin soft magnetic underlayer

In order to improve the reproduced output of a Co-Cr perpendicular magnetic recording medium, a very thin ( approximately 10 nm) soft magnetic underlayer such as a Permalloy film was inserted between the recording layer and the substrate. An evaluation using a ring-type head showed that the reproduced output of the Co-Cr medium was greatly increased by the underlayer without any deterioration in its high-density recording characteristics. The increase is attributed to the decrease of the demagnetizing field acting on the recorded magnetization, which is caused by the establishment of horseshoe magnetization modes in the vicinity of recording transition regions. >

The effect of initial growth layer on magnetic properties of Co-Cr films

The effect of a Ti underlayer, which increases the perpendicular coercive force of Co-Cr films, was investigated. To clarify the cause of this phenomenon, the film-thickness dependence of the magnetic properties was examined. It was found that the coercive force of a Co-Cr film deposited directly on a polymide substrate decreases drastically when it becomes thinner than 50 nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when the film becomes as thin as 20 nm. The film with the underlayer has a distinct uniform columnar structure, whereas the film without it has a 50-nm-thick initial growth layer with no clear structure. Measurements of the temperature dependence of magnetic properties and observations of segregated microstructures indicate that the improvement of magnetic properties by the insertion of the Ti underlayer is mainly due to the improvement of shape anisotropy resulting from the formation of a distinctly segregated microstructure. >

An Experiment for Estimating Inclination of Recorded Magnetization in an Obliquely Metal-Evaporated Tape by Using the Bitter Pattern Technique

Inclination of recorded magnetization in an obliquely metal-evaporated (ME) tape is estimated by the Bitter pattern technique. Although the contrast of the Bitter pattern evolved in a magnetic field of various directions to the film plane is generally asymmetric with respect to recording transitions, it becomes symmetric only when that magnetic field is applied in a direction determined by the recorded magnetization. For the Co-Ni-O film recorded at 1.5 kFCl, the inclination of magnetization is estimated to be about 40°. It is also shown that this value of the inclination agrees well with the theory.

Brillouin scattering in Fe-polyethylene co-evaporated films

Abstract Spin waves in soft ferromagnetic Fe-polyethylene co-evaporated films have been studied in Brillouin scattering. Scattering from the standing spin waves and the Damon-Eshbach surface wave has been observed. The magnetic constants of the films are discussed.