Tokuho Takagaki

Investigation of 2 Gb/in/sup 2/ magnetic recording at a track density of 17 kTPI

Developments of magnetic head, recording medium, positioning, and signal processing technologies made it possible to perform magnetic recording at an areal density of 2 Gb/in/sup 2/ on a prototype 3.5-in diameter hard disk drive. A track density of 17 kTPI, which is comparable to or even greater than that used in optical storage systems, is used to minimize the reduction in the physical clearance between the medium and the head. The authors outline the system and its component technologies. The read/write characteristics of the 3.5-in prototype disk system are also reported. >

Morphological structures and magnetic properties of sputtered thin film media

Morphological structures and magnetic properties of sputtered Co-Ni-Zr/Cr films are investigated in order to clarify the origin of an undesirable magnetic anisotropy induced by inline sputter deposition during disk transfer. The film deposition onto nontextured substrates at lower Ar pressure makes this anisotropy larger. Co-Ni-Zr/Cr films deposited at 1.3 Pa are observed to have bow-like columnar structures of Cr films and a preferential Cr and Co orientation inclined about 20 degrees from the direction normal to the film surface toward the transfer direction. As a result, the tendency of the magnetocrystalline anisotropy axis to face toward the transfer direction causes the magnetic anisotropy. This can be understood to be the origin of the undesirable anisotropy. On the other hand, the films deposited at 4.0 Pa have straight columnar structures of Cr films and a preferential Cr orientation normal to the film surface. It is concluded that the morphological and crystallographic structures of Cr films strongly affect the magnetic properties of Co-alloy/Cr films. >

H/sub c/ measurement of microscopic regions on thin film magnetic disc using longitudinal Kerr effect

A longitudinal Kerr magnetooptical microscope system with a read/write testing unit and a positioning unit was developed for nondestructive measurement of the coercive force (Hc) in thin-film magnetic disks. This system measures the magnetooptical hysteresis loop from an area 2-30 mu m in diameter on a disk with a C/CoNi/Cr layer. The magnetic field strength at the disk surface was estimated from the coil current in a Weiss-type magnet. The absolute value of the field strength was calibrated by a Hall sensor. The actual H/sub c/ values were measured and compared with the result obtained by a vibrating sample magnetometer in order to determine the accuracy, which was found to be within 2%. It took 36 min. to complete the H/sub c/ measurement at 144 points over a 5.25 in. disk for a mean spot size of 30 mu m. >

In-Plane Crystalline Orientation and Magnetic Anisotropy of Co-Ni-Zr Media

The in-plane crystalline orientation of a longitudinal thin film medium was investigated to clarify the relation between the crystalline orientation and the magnetic anisotropy. As is well known, the anisotropy is induced by deposition onto a moving disk substrate (transport deposition) and is changed by substrate texturing. It has heretofore been difficult to determine the crystalline orientation by X-ray diffraction because of the very intense background reflection. We have developed a precise background correction method enabling measurement of the pole figure of the longitudinal medium. It is clear that the c-axis of a medium on a mirror-polished substrate is essentially oriented in the direction of substrate motion, and that the axis of a medium on a textured substrate tends to be oriented in the texturing direction.

The micro-structure of γ-Fe 2 O 3 film with Ar-O 2 -H 2 O process

The micro-structure of the γ-Fe 2 O 3 film with reactive sputtering process in Ar-O 2 -H 2 O was studied using X-ray diffraction and a cross-sectional High-Resolution TEM. The results are as follows: the film has a columnar structure and the diameter of each column is 100-300 A; both oriented columns and micro-crystallite columns coexist in the film; the crystallinity in the micro-crystallite columns was found to contribute to the magnetic properties.