Yotsuo Yahisa

Magnetic properties and read/write characteristics of Co‐Cr‐(Pt,Ta)/ (Cr‐Ti,Cr) thin film media

A Cr‐Ti underlayer is found to enhance the in‐plane coercive forces of Co‐Cr‐Pt and Co‐Cr‐Ta films; the maximum coercive force was 3.5 kOe for (CoCr0.15)0.84Pt0.16/CrTi0.2. The crystallites of Cr‐Ti grow in a more highly oriented and uniform manner than ones of Cr, and their lattice spacings are closer to those of Co alloys than Cr, improving the epitaxial growth of Co‐alloy crystallites with c‐axis in‐plane oriented components on the Cr‐Ti underlayer. The crystalline anisotropy constant of Co‐Cr‐Pt with a high Pt concentration is found by torque measurement to be larger than that of Co‐Cr‐Ta. These can produce extremely high coercive forces in Co‐Cr‐Pt/Cr‐Ti. The C/Co‐Cr‐Pt/Cr‐Ti thin film media with high coercive forces show excellent read/write characteristics; the linear densities at 50% signal drop are very high, 175 and 101 kFCI, for the C/Co‐Cr‐Pt/Cr‐Ti media at head‐to‐magnetic layer spacings of 0.01 and 0.07 μm.

Electron spectroscopic imaging analysis of compositional inhomogeneity in CoCrTa longitudinal thin film media

The topographical nature of the compositional inhomogeneity in Co-17at.%Cr-5at.%Ta/Cr longitudinal thin film media deposited at different substrate temperature Ts, was analyzed using electron spectroscopic imaging. In the CoCrTa film deposited at high Ts, Cr segregates to the grain boundaries and intragrains, resulting in a two-dimensional network. The compositional variation grew as Ts became high. The concentration of the Cr enriched region was in the range 20-30 at.%, and that of the Cr depleted region was in the range 5-10 at.% for the sample Ts=270/spl deg/C. A strain-free CoCrTa(11.

Magnetic and recording characteristics of Cr, Ta, W and Zr pre-coated glass disks

Magnetic and recording characteristics of CoCrPt/CrTi media which are deposited on Cr, Ta, W and Zr pre-coated glass disks, are examined. High S* was obtained on Ta and Zr. The largest output signal and the lowest DC-erase and recording noise were obtained on Ta. The recording noise on Zr pre-coated disk was second lowest. When the pre-coating thickness is increased, H/sub c/ on Ta increased by 700 Oe but the H/sub c/ increase on Zr was small. On the other hand, the DC-erase noise stayed constant and the recording noise decreased on Ta and both DC-erase noise and recording noise slightly increased on Zr. The /spl delta/M measurement revealed that the increase of Ta thickness caused the reduction of magnetic interaction between CoCrPt crystals. Strong Co(110)/Cr(100) orientation was observed on Ta and no major difference in crystal grain size was observed between Ta, Zr pre-coated media. The low DC-erase noise characteristics on Ta pre-coating would be attributed mainly to strong in-plane c-axis orientation.

Reduction of Co–Cr–Pt media noise by addition of Ti to Cr underlayer

Effects of Ti addition to a Cr underlayer on the magnetic and crystallographic properties of Co–Cr–Pt media were investigated. C/Co–Cr20–Pt (Pt: 8 and 12 at. %)/Cr–Ti (Ti: 0–30 at. %) films were deposited on textured Ni–P/Al–Mg substrates by dc magnetron sputtering. In‐plane Hc and S* increased as Ti was added to the Cr underlayer. The media noise at 167 kFCI decreased with an increase of the Ti content from 0 to 20 at. %. The normalized media noise of Co72Cr20Pt8/Cr75Ti25 media was 20% lower than that of Co68Cr20Pt12/Cr90Ti10 media where their coercivity and S* were almost the same. Further increase of the Ti caused the increase of the media noise. Transmission electron microscopy studies showed that average grain size of Cr–Ti films decreased from 30 to 20 nm with the increase of the Ti content from 0 to 20 at. %. The activation volume of Co68Cr20Pt12 films measured from the time dependences of remanence coercivity decreased by 30% as the Ti content increased from 0 to 20 at. %. The reduction of media n...

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.

Observation of Compositional Separation in CoCrTa Thin Film Using Transmission Electron Microscope with Imaging Filter

The elemental mapping of a CoCrTa thin film deposited at 270° C has been performed using a transmission electron microscope equipped with an imaging filter. A compositional separation, which consists of Co-enriched areas and a Cr-enriched phase around them, is quantitatively observed. The Co-enriched areas are about 20 nm in diameter and the Cr-enriched phase extends with a two-dimensional network, which corresponds to grain boundaries. Intragrain Cr-enriched areas, which are less enriched than at the grain boundaries, are also observed.

Read and write characteristics of Co-Ni-Zr-M/Cr thin films for longitudinal recording

The magnetic and crystallographic properties and read and write characteristics of sputtered C/Co-Ni-Zr/Cr and C/Co-Ni-Zr-M/Cr (M=V, Nb, Ta, Cr, Mo, W, Cu, Si, Al, Ru and Pt) thin films are investigated. The saturation magnetic flux density B/sub s/ of all C/Co-Ni-Zr-M/Cr films decreases as the amount of additive element increases. The coercivity of C/Co-Ni-Zr-Cr/Cr and C/Co-Ni-Zr-Pt/Cr is higher than that of C/Co-Ni-Zr/Cr films with comparable B/sub s/. The larger the perpendicular anisotropy K/sub p/ and the smaller the anisotropy constant K/sub n/, the lower the media noise N and the higher the S/N ratio. The reduction of K/sub n/ and N are strongly connected to grain separation and grain size reduction. The larger the B/sub s/.tmag, the higher E/sub II/ and N and the lower D/sub 50/ and the S/N ratio. All films except those with Si, Ru, and Pt additives have large K/sub p/, a small K/sub n/, and a high S/N ratio. In particular, C/Co-Ni-Zr-M/Cr (M=Cr, Mo, W, and Al) disks have a better S/N ratio and D/sub 50/ than C/Co-Ni-Zr/Cr disks. >

Grain size effect on noise properties in CoCrTa thin film media

Grain growth of Cr and CoCrTa thin film was examined using high resolution transmission electron microscopy (HRTEM) and high resolution scanning microscopy (HRSEM). The effect of crystallography on media noise was studied. The grain size of the CoCrTa thin film increases with thickness and retains a bi-crystal structure over a range of Cr grain size. Media noise at a high recording density seems to increase with the grain size of Cr underlayer surface. This suggests that the micromagnetization process can be influenced by a bi-crystal structure of Co alloy films at their initial layers.

Low noise antiferromagnetically coupled media with CrTiB underlayer

In order to reduce the grain size, 1.5–3 at. % B was added to the CrTi underlayer of the antiferromagnetically coupled media that has CoCrPtB/Ru/CoCrPt dual magnetic layers. The average grain size of the CrTi20 underlayer was reduced from 16.1 to 11.9 nm by 3 at. % B addition, which resulted in 12% grain size reduction of the magnetic layer deposited on it. Owing to the grain size reduction, the media noise was reduced 15%, while PW50 was almost identical. By using a thicker CrTi20B3 underlayer, signal-to-noise ratio was improved about 1 dB without decreasing the thermal stability factor.

Noise reduction by surface oxidization of a CoCrZr seed layer on glass substrates for CoCrPt/CrTi thin film media

A method of surface oxidization of a CoCrZr seed layer has been developed. This method can control the microstructure of a CoCrPt/CrTi thin film medium on the glass substrate. By exposing the surface of the CoCrZr seed layer to just a little oxygen (in the order of 10-5 Torr), the crystal orientation of the CrTi underlayer deposited on the seed layer is changed from (110) to (200). The crystal grain size of the underlayer is also affected, and smaller grains can be obtained by the surface oxidization of the seed layer. These changes in microstructure of the CrTi underlayer result in magnetic crystal grains with small grain size and in-plane c-axis orientation. Both these properties improve the read/write performance considerably.