Takanobu Takayama

Time dependence of remanence coercivity and medium noise in obliquely evaporated Co films

Abstract The fluctuation fields of magnetic viscosity and read and write characteristics are measured to investigate the origin of medium noise in obliquely evaporated cobalt films. Medium noise increases with increasing product of activation volume and saturation magnetization per unit volume. Therefore, medium noise is believed to depend on the size of the minimum unit of magnetic moment in reversal.

Co/Pd multilayer media with Pd inorganic granular seed layer for perpendicular recording

We have investigated the Co/Pd multilayer media with a Pd–SiN granular seed layer as perpendicular recording media. The Pd–SiN granular seed layer and the Co(0.2 nm)/Pd(0.8 nm) multilayer were formed by dc and rf sputtering at room temperature on a FeTaC soft magnetic underlayer. The Pd–SiN granular seed layer of 3 nm was very effective to get good magnetic properties with coercivity of 3.9 kOe, a nucleation field of −2.1 kOe, and a M–H slope parameter 4π(dM/dH)H=Hc of 1.4. In addition, it was found that growth of multilayer grains is sensitive to surface conditions of the soft magnetic underlayer. The average column diameter of 13.7 nm with a dispersion of 21.7% was evaluated from the plan-view transmission electron microscope image of well-separated Co/Pd columns with a boundary, which was grown on the Pd–SiN seed layer and the soft magnetic underlayer with Ar plasma etching. Atomic force microscope measurements showed that mean roughness (Ra) of the FeTaC surface decreased from 0.46 to 0.39 nm by the p...

Perpendicular magnetic recording media based on Co-Pd multilayer with granular seed layer

We have investigated Co-Pd multilayers deposited on a Pd-SiN granular seed layer and a FeTaC soft magnetic underlayer (SUL) for perpendicular magnetic recording. The Pd-SiN granular seed layer of 3 nm was found to be very effective for good magnetic properties with coercivity of 3.9 kOe, a negative nucleation field of -2.1 kOe, and a M-H loop slope parameter 4/spl pi/ (dM/dH)/sub H=Hc/ of 1.3. The average column diameter of 13.7 nm with a dispersion of 21.7% was evaluated from the transmission electron microscopy image of well-separated columns with a clear boundary. This Co-Pd medium gave better playback performances by a merged ring giant magnetoresistive head compared to the medium with a Pd seed layer. The effect of Ar plasma etching on the SUL was also investigated to improve playback performance.

Origin of perpendicular magnetic anisotropy of Co-CoO evaporated film

Abstract The magnetic properties and microstructure of Co-CoO evaporated film, which is one of the most promising candidates for perpendicular magnetic recording media, are examined. Large perpendicular anisotropy and coercivity are caused by introducing oxygen into a Co film. The examined films consist of a mixture of metallic hexagonal closed packing Co crystallites and Co mono-oxide crystallites of a columnar structure 10 nm wide. The c -axis of the Co crystallites has a tendency to orient perpendicularly to the film plane. To investigate the origin of the perpendicular anisotropy, the magnetic anisotropy due to the columnar structure is calculated and compared with experimental results. As a result, it is found that the dependence of the perpendicular anisotropy on saturation magnetization can be explained by taking into account both the magnetocrystalline and shape anisotropy.

Observation of domains in obliquely evaporated Co–CoO films by spin-polarized scanning electron microscopy

Magnetic domains in the remanent magnetization state of obliquely evaporated recording media Co–CoO films were studied by spin-polarized scanning electron microscopy. Inverse domains densely distributed in the media were found to have a closure-domainlike structure at the surface to reduce the magnetostatic energy. The size of the inverse domains depends on the direction of the external magnetic fields that were applied when the remanent states were formed. Using these results, the relationship between the inverse domains and the carrier-to-noise ratio for this kind of recording media is discussed.

Nuclear magnetic resonance study of Co‐CoO films for perpendicular magnetic recording (abstract)

Co‐CoO films, which are evaporated in the atmosphere of a small amount of O2, have large perpendicular magnetic anisotropy and show excellent read‐write (R‐W) characteristics. With heat treatment, the microstructure of a film changed and the R‐W characteristics were further improved.1,2 This result indicates that the microstructure of a film changed and the R‐W characteristics were further improved.1,2 This result indicates that the microstructure of a film closely relates with the R‐W characteristics as it does so for Co‐Cr films. We measured the spin‐echo spectra of a film having various magnetizations to investigate the relationships between R‐W characteristics and film microstructure, because NMR is very sensitive to the slight changes of film microstructure.1 A strong absorption was observed at 223 MHz which is for α‐Co. The intensity decreased drastically as the amount of oxygen in the films increased and very broad satellites appeared around 250 MHz, implying that Co atoms having a larger magnetic ...

The improvement of the C/Nm characteristics by using the tail-off recording in the obliquely evaporated Co-CoO tape

TAIL-OFF RECORDING METHOD A new recording method to improve the U N characteristics of the obliquely evaporated CO-COO tape was proposed. In this tail-off method, the recording current was cut for a certain period before applying the reverse current as shown in figure 1. CiN CHARACTERISTICS Fig. 2 shows the carrier signal output (C), the media noise (N) and the carrier-to-noise ratio (C/Nm) characteristics measured at h= 0.46 pm. Using the tail-off method, C increased by 2 dB and Nm decreased by 1 dB then C/Nm increased by 3 dB compared to the conventional method in this case under the M.M.F. (Magneto Motive Force) condition for maximum C output. Datasigns 0 1 0 1 0 0 0 1 1

Improvement of C/Nm characteristics by using tail-off recording method in obliquely evaporated Co-CoO tape

A new recording method to improve the R/W characteristics of Co-CoO obliquely evaporated tape is proposed. Using a tail-off method in which the recording current is cut for a certain period before applying the reverse field, the carrier-to-noise ratio increased by 2 to 3 dB compared to in the conventional method using a rectangular wave current. The above improvement was found to be due to an increase of carrier output and a decrease of media noise. The increase of carrier output can be explained as a suppression of demagnetization caused by the trailing edge field. On the other hand, the decrease of media noise is explained as an increase of the trailing edge field applied in the hard axis of the media which narrows the width of the domain.