Satoshi Matsunuma

Influence of underlayers on the soft properties of high magnetization FeCo films

A remarkable reduction in coercivity Hc was found in sputtered Fe65Co35(=FeCo) films on Cu, NiFe, Ru, Ta/Cu, Ta/NiFe, or Cu/IrMn underlayers. A decrease in Hc from 120 to 7–12 Oe was observed for Cu, NiFe, and Ru underlayers as thin as 2.5 nm but less for Ta. A Cu underlayer significantly reduced the maximum anisotropy fields from 2 kOe to 40 Oe, resulting in a well-defined in-plane average uniaxial anisotropy field Hk∼30 Oe. The saturation magnetostriction with Cu was (47±4)×10−6, independent of Cu and FeCo thicknesses. In-plane tensile film stress decreased with underlayer thickness tUL from 2 to 0.2 GPa but much less rapidly than the reduction in Hc. All underlayers induced a (110) texture in FeCo, which was strongest with Ta. Transmission electron microscopy of cross-sections showed an unusually long range coherence with low angle grain boundaries in the FeCo without an underlayer. Clear columnar grains were visible with all underlayers with an average grain size of ∼50 nm with Ta dropping to 9–10 nm ...

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/.

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...

Microstructure and magnetic properties of a Co/Pd multilayer on a controlled Pd/Si seed layer for double-layered perpendicular magnetic recording media

A 10 nm Pd/Si dual thin film was developed as a seed layer for a Co/Pd multilayer in double-layered perpendicular magnetic recording media. The Pd/Si seed layer, sputter deposited under Ar sputtering gas containing N2 and postannealed at 400 °C, markedly reduced intergranular exchange coupling of the Co/Pd multilayered film, resulting in a decrease in both the slope parameter, defined as 4π(dM/dH)H=Hc, and the magnetic cluster size. Consequently, medium noise was essentially reduced, thereby improving the signal-to-noise ratio of the Co/Pd recording media on a CoZrNb soft magnetic underlayer. The addition of N2 gas effectively decreased the grain size of Pd in the seed layer. A Pd/Si seed layer prepared with both processes exhibited a granular structure of fine Pd-rich grains surrounded by a Si-rich amorphous region, which provided nucleation sites for the growth of well-separated Co/Pd multilayered grains.

Amplitude Dependence of the Lateral-Vibration Wear Test for Perpendicular Recording Magnetic Disks Treated by Heat Curing

The tribological characteristics of perfluoropolyether (PFPE) and heat-treated PFPE lubricant films deposited on magnetic thin diamond-like carbon (DLC) film-coated disks by dip coating were studied using lateral modulation frictional force microscopy (LM-FFM). The topography and microstructural properties of the DLC film disk before PFPE lubricant dip coating were investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM) in the dynamic force modulation (DFM) and frictional force modulation (FFM) modes. The TEM and AFM images show valleys and fine spaces formed between grain boundaries. It is possible that free lubricants reserved in these valleys and spaces during dip coating replenished the surface as a result of tip sliding. In wear tests, the friction properties of the PFPE-DLC disk without heat curing were improved due to the supply of lubricant.

Strong uniaxial magnetic anisotropy in CoFe films on obliquely sputtered Ru underlayer

Co90Fe10 films with an in-plane uniaxial magnetic anisotropy have been grown on an obliquely sputtered thin Ru underlayer. The anisotropy field can be increased up to 200 Oe. The hysteresis curves show a very high squareness in the easy axis direction and almost no hysteresis in the hard axis direction, suggesting that the induced uniaxial anisotropy is uniform throughout the films. The switching characteristics of the nanoelements fabricated from the films by e-beam lithography are also investigated. There is no degradation of the magnetic anisotropy after the annealing and lithographical process.

Comparison of Playback Performance of Facing Targets Sputtered Perpendicular and Longitudinal Tape Media

Playback performances of sputtered perpendicular recording tape media were investigated in comparison with longitudinal media. Perpendicular (Media P, out-of-plane coercivity of 318.3 kA/m) and longitudinal (Media L, inplane coercivity of 279.3 kA/m) recording tape media were deposited by facing targets sputtering from the same target of Co74Pt16Cr10-SiO2 for the recording layer at room temperature. For Media P, a soft magnetic FeCoB(50 nm) layer and a Ru(5 nm) seed layer were formed between the recording layer and an Aramid substrate. On the playback test by a drum tester with a ring writer/GMR reader, the waveform of all-ones signal at 5 kfci indicates that Media P has a dipulse response and the shorter PW50 value than Media L. Measured values of D50 were 233 kfci for Media P and 216 kfci for Media L, respectively. Saturation curves show that Media P has good writability. The signal-to-noise ratio (SNR) value of Media P is higher by 2.4 dB at 337 kfci than Media L. These high-resolution and high SNR properties indicate that sputtered perpendicular tape media are suitable for extremely high-density recording.

Theoretical simulation of resonance Raman bands of amorphous carbon

Abstract Simulations of resonance Raman spectra of chromophore models for amorphous carbon were carried out in consideration of resonance enhancement by using the Albrecht A term. Relative resonance Raman intensity of each vibrational mode was calculated with the electronic transition analysis by a Complete Neglect of Differential Overlaps (CNDO/S) method including configuration interaction and the vibrational analysis by a Parametric Method 3 (PM3) method. Condensed aromatic cluster containing four to six benzene rings gave similar spectra as reported experimental spectra excited with the incident photon energy of 2.41 or 2.54 eV. A slight high-frequency shift of the main peak of Raman spectrum was simulated on sp 2 clusters of smaller size which have higher resonance energies compared to the above condensed aromatic clusters. These simulated results were consistent with reported dependence of incident photon energies for the band shape of Raman spectra and suggested that a complex of many sizes of sp 2 clusters which have six or less benzenes is the origin of resonance Raman spectra of amorphous carbon. Attached sp 3 carbon round sp 2 carbon chromophore showed little effect on the band shape of calculated resonance Raman spectra. It was postulated that information on sp 3 network structure hardly appears in resonance Raman spectra compared to sp 2 cluster when a visible light is used for the excitation.

Time and temperature dependences of the magnetization reversal in a Co/Pd multilayer film

The time and temperature dependences of the magnetization reversal have been measured in a high-coercivity Co∕Pd multilayer film characterized by nucleation and domain wall motion. The time and field dependences of magnetic relaxation curves at room temperature were interpreted in terms of an energy barrier that depends linearly on reverse field, suggesting a Sharrock-type [M. P. Sharrock and J. T. McKinney, IEEE Trans. Magn. 17, 3020 (1981)] equation for the time and temperature dependences of coercivity with unity exponent. The sweep rate and temperature dependence of the coercivity were analyzed using the Sharrock equation to obtain the temperature dependence of the intrinsic, short-time coercivity H0 and the zero-field energy barrier E0. A single power law behavior was found for H0 versus the saturation magnetization Ms.

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.