Tetsuya Kanbe

Experimental Study Of Thermal Decay In High Density Magnetic Recording Media

The thermal decay of written bits in CoCrPt/CrTi thin film media for high density longitudinal magnetic recording is examined using a magnetoresistive head at room temperature. A decay in signal output over time is observed for the media with a thin magnetic layer less than about 14 nm thick and the media noise increases. The thermal stability factor Ku.V/k.T of these media is estimated to be less than about 100. The signal decay and noise increase are more serious at higher linear recording densities. These results are consistent with the results of a micromagnetic simulation taking into account the thermal aftereffects. These characteristics suggest that media with a large magnetic anisotropy constant Ku will be required to realize high storage densities of over 10 Gb/in/sup 2/.

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/.

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.

Effects of underlayer grain size on the microstructure of the magnetic layer in CoCrPt media

The average grain size of the CrTi or CrTiB underlayer was reduced from 16 to 7 nm and structural changes of the CoCrPt magnetic layer deposited on them were investigated. Reduction of the underlayer grain size tends to suppress the formation of bi-crystal clusters, though the magnetic layer has a CoCrPt (11.0) crystallographic texture. The average grain size of the magnetic layer showed a minimum when that of the underlayer was 9 nm. Further reduction of the underlayer grain size to 7 nm increased the average magnetic grain size about 15%. On the other hand, when the average underlayer grain size was less than 11 nm, the normalized standard deviation of the magnetic layer remained the same upon further reduction in the normalized standard deviation of the underlayer.

Effects of boron addition to underlayer for CoCrPt media on magnetic characteristics and microstructure

Magnetic and recording characteristics of CoCrPt media with a CrTiB underlayer was investigated. Higher coercivity Hc and coercive squareness S* were obtained compared with the media that had a CrTi underlayer. The overwrite property of the media was also improved by adding boron, while the change in media noise was very small. Transmission electron microscopy analysis showed that the crystal grain-size dispersion in the magnetic layer was reduced by about 15% when boron was added to the underlayer, and the average grain size was almost the same as when the CrTi underlayer was used. The higher S* and improved overwrite property that resulted when using a CrTiB underlayer should be attributed to the reduction in the grain size dispersion, which provides a narrower switching field distribution.

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.

Effects of an intermediate layer on the magnetic and recording characteristics of CoCrPtTa media

Effects of bcc and hcp intermediate layers between a bcc–Cr80Ti20 underlayer and a hcp–CoCrPtTa magnetic layer on magnetic and recording characteristics were investigated. The medium without an intermediate layer has a low coercivity Hc of 0.27 kOe due to the perpendicular orientation of the c axis of the CoCrPtTa layer. By introducing a 5-nm-thick intermediate layer of bcc–Cr60Mo40 or hcp–Co70Cr30, the c axis of the CoCrPtTa layer can be effectively in-plane oriented, resulting in a high Hc of 2.71–2.87 kOe and a coercive squareness S* of 0.72–0.81. The medium with the Cr60Mo40 layer has lower media noise than the medium with the Co70Cr30 layer. This lower noise is considered to be caused by the small grain size of 10.4 nm. The addition of the thin Cr60Mo40 intermediate layer is therefore effective to obtain both high Hc and low noise in the CoCrPtTa media with the CrTi underlayer.

Effects of CoCrZr seed layer on noise properties and microstructure of CoCrPt media

We have developed a nonmagnetic (CoCr30)Zrx [x=7, 10, 14 at. %] seed layer for CoCrPt glass media and have compared its structural and noise properties to those of the media with a Ta/Zr dual seed layer, which have lower media noise than the media with a Cr seed layer. The media with a (CoCr30)Zr10 seed layer had lower media noise than that with the Ta/Zr dual seed layer, which is attributed to reduced grain size in the magnetic layer. However, the media noise increased drastically owing to a 78% increase of the grain size in the magnetic layer when the Zr content in the seed layer increased from 10 to 14 at. %. The transmission electron microscope analysis indicates that the (CoCr30)Zr10 seed layer has a nanocrystalline structure, while (CoCr30)Zr14 was almost amorphous. This would be the main reason of the drastic change in the grain size of the magnetic layer. The microstructure of the CoCrZr seed layer is very sensitive to the Zr content and strongly affects the microstructure of the magnetic layer an...

Study of the thermal aftereffect on longitudinal recording media by magnetic force microscopy

We investigated the thermal aftereffect of 383 K annealing of longitudinal recording media through the structural analysis of all-ones patterns observed by magnetic force microscopy (MFM). The transition width increased by 31% after annealing, and the peak height of the MFM signal decreased by 36% even at a low linear recording density of 50 kFCI. The root mean square (rms) values of the MFM signal were reduced after annealing as the recording density rose to 200 kFCI, but at 250 kFCI or higher, the rms value did not change and large magnetic clusters appeared in the tracks. The growth of nonperiodic magnetic clusters after annealing was investigated through statistical analysis. The written bits were subtracted by using a two-dimensional fast Fourier transformation (FFT) method. The number of clusters with a diameter of less than 150 nm decreased after annealing, while the number of larger clusters increased. Also, the average cluster diameter increased as the linear recording density rose. After anneali...