Chiaki Okuyama

Magnetic relaxation in thin film media as a function of orientation ratio

Abstract We investigated the thermal relaxation of isotropic and oriented media having the same K u V/kT via a method combining micromagnetic and Monte Carlo simulations and experiments. Through simulations and experiments, we ascertained that the thermal stability of remanent magnetization increases with increased circumferential orientation. We also confirmed via simulations that written dibit and continuous bits are thermally stabilized by circumferential orientation media.

Study of in-plane magnetic anisotropy in Co-based thin-film media

The relationship among macroscopic in-plane magnetic anisotropy, the crystal structure of both the Co-based magnetic layer and the Cr under-layer, and the surface morphology of the textured substrate was studied. In the highly oriented media, the preferred orientation of the c-axis of Co to the circumferential direction and the distortion of the Cr crystal lattice were observed. In-plane magnetic anisotropy is induced when the grain of the under-layer is smaller than the texture grooves.

Reproduced output reduction in thin film media by thermal fluctuations

Abstract Demagnetizing fields in recorded bits accelerate thermal decay of data output in magnetic recording media. The spread of the transition area also promotes the reduction of obtained data output. By comparing the time dependencies of data output at several recording densities from spin stand data with the time dependencies of the remanent magnetization in various reverse fields, the demagnetizing fields in the recorded bits for different recording densities were estimated. The difference observed between the time dependence of data output and that of remanent magnetization was experimentally clarified to be due to the increase in the transition length. We describe a method to account for both magnetization decay and transition broadening in the thermal degradation of the output signal.

Track Edge Noise Characteristics Of Co-Cr-Pt-Ta Media

Introduction As aerial density of recording media increases and tracks become narrower to achieve the high track density, track edge noise becomes an important factor that cannot be neglected. Our previous study found that CoCrPtTa media had good potential for 5 Gb/inz recording because of high Hc and low noise character [ 11. In this paper, we discuss the track edge noise profiles and side erasure by comparing CoCrF’tTa and CoCrTa media. Experiment Co,Cr,,P&Ta, /Cr,,,Mo,, (CCPT) and Co,,Cr,,Ta, /Cr (CCT) were deposited on a textured NiP/AI substrate by DC magnetron sputtering. A head with wrlhng and M R element assembled In a single device was used to evaluate RIW performance. High Bs material of 1.5 T was lammated on the trailing pole. The core width of writing and MR element is 2.8 and 1.5 pm, respectively. Results and Discussion The Magnetic properties of CCPT and CCT are shown in Table 1. Recording density dependence of medium noise is shown in Fig.1, and maximum DC demagnetized noise (Nd) [2] are also plotted. Medium noise of CCPT is well suppressed at high density region in comparison with C a . Figure 2 shows the cross-track profiles of medium noise on both media. CCI‘ has a distinct increasing of noise around track edge, otherwise track edge noise of CCPT medium is well suppressed. Track edge noise coursed by mainly disorder of magnetization at edge. That magnetic confusion is caused by same mechanism of E€ demagnetizing [3, 4, 51. It is reasonable that the track edge noise is prominent in CCT because its medium has large Nd value. The reason of low noise character in CCW is due to reduce the exchange coupling between grains [ 6 ] . Figure 3 (a) and (b) shows the MFM image of overlapped tracks. The overwritten patterns were synthesized that recording track of 150 kFCI was written on the isolated 120 kFCI. We observed that transition pattern of the CCPT medium was quite clear, and that the sides erase band was narrower. Furthermore, output agamst off track distance was measured by spectrumanalyzer. We can evaluate the width of side erasure to perform this measurement because outputs signals of different frequency are simultaneously detected [7]. We were not able to observe any side erasure in the CCPT medium, but we did observe a 0.21 pm side erasure in the CCI‘ medium, as shown in Fig.3 (c). CCPT medium mentioned above has a high Hc value and restraint exchange interactions by adding Pt and quantities of Cr. This is the reason that CCPT medium is hard to occur the side erasure. Conclusion If we presume that 20,000 TPI is required for 5 Gbiin’ recording, side erasure bands should be narrower than 0.13 pm that is one tenth of track pitch (1.3pm). In CCPT media, since track edge noise and side erasure are not remarkable, the off-track characteristics of CCPT media are well suited for over 20,000 TPI recording.