C. H. Hee

Approaches to tilted magnetic recording for extremely high areal density

In this paper, we systematically present our fundamental understanding of the advantages of tilted magnetic recording. We investigate the various configurations of tilted magnetic recording including tilted longitudinal recording, tilted perpendicular recording with tilted media and normal single pole head, and tilted perpendicular recording with perpendicular media and tilted writing head. Tilted media with easy axis along the down-track and cross-track directions and tilted media with varied in-plane orientation ratios have been investigated and compared in detail. One important finding is that slightly oriented (in-plane) tilted media show a tremendous improvement in recording performance, which may release the pressure on the fabrication of perfect tilted hard disk magnetic media. Various fabrication methods for tilted media have also been discussed.

Tilted media by micromagnetic simulation: A possibility for the extension of longitudinal magnetic recording?

In this article, we have studied the potential of tilted media to extend the longitudinal recording density via micromagnetic simulation. The magnetization reversal mechanism is systematically analyzed to determine the angular dependence of coercivity of this media. Such a characteristic determines the recording performance for different recording directions. A sharp transition is observed for the good recording direction. In contrast, large transition noise is observed for the bad recording direction. Tilted media have the advantage similar to the perpendicular media for extreme high recording density, resulting from the use of high Ku and low demagnetization field at the transition. Most importantly, the magnetization in the tilted configuration can be reversed effectively with a longitudinal ring head.

Role of thermal energy on the magnetic properties of laminated antiferromagnetically coupled recording media

The effect of thermal energy (kBT), which has been found to play some important roles in the magnetic properties of recently developed antiferromagnetically coupled media, is described. It was observed that the thermal energy helps to obtain an antiparallel configuration of moments at remanence. Therefore, a reduction in the remnant moment–thickness product (Mrδ) is observed, even for smaller values of J (interface coupling constant) than those used in simulations that do not consider thermal energy. The magnetic viscosity measurement helps to distinguish the magnetization decay behavior of the top and bottom layers. The magnetic moments of top and bottom layers show maximum decay at different fields and the decay rates approximately scale with their thickness. Viscosity results also point out that the magnetization reversal of the bottom layer should occur in the first quadrant, in order to obtain a low noise and thermally stable media. Micromagnetic simulation was performed by including thermal effects....

Effect of magnetic anisotropy distribution in longitudinal thin film media

The effects of anisotropy axes distribution on the properties of longitudinal recording media are simulated using the micromagnetic modeling. The angle between the anisotropy axis and the preferred direction is assumed to follow the Gaussian distribution. Hysteresis loops are simulated with the field applied in the preferred direction and perpendicular to it. Orientation ratios (OR) are calculated for different anisotropy distribution. OR (coercivity) increased from 1.4 to 79.2 when standard deviation of anisotropy distribution σ decreased from 0.7 to 0.05. The effect of the anisotropy distribution on the recording performance is evaluated, too. The results show that narrowing the anisotropy distribution will increase the OR and decrease the transition noise power and transition length. It was found that a critical point occurred at σ=0.15, below which the OR can be maintained at a sufficiently high value and yet the integrated noise power can be kept low.

Effect of competing energies on the transition noise of oriented magnetic media

There has been some disagreement in observation of the effect of oriented media on the recording performance from earlier and recent studies. In this letter, we have identified the reasons behind these disagreements by studying the effect of the energy ratio of local anisotropy (Ku) and long range magnetostatic interaction energies (Kd) (Q=Ku/Kd). The magnetization reversal mechanism is observed to be different in the recorded bit transition of different magnetic properties (Q) of the media. The results on the effect of Q and the linear density of various oriented media are presented and discussed in detail. It is observed that the transition for high Q media does not follow arctan transition form. Oriented high Q media show better recording performance than isotropic media, even at higher linear density.

Effect of orientation ratio on recording performance for longitudinal thin film media

The effects of orientation ratio (OR) on longitudinal thin film media recording performance are studied via micromagnetic modeling. The OR of the media is controlled by the anisotropy axes distribution. Along the preferred anisotropy direction, the coercivity and the remanence increases with decreasing standard deviation of anisotropy distribution /spl sigma/ and gives rise to an OR as high as 90. Highly oriented media show an ultra low transition noise and high effective track width. However, it is observed that highly oriented media exhibits a large track edge bending which increases the track edge noise. Effect of saturation magnetization (M/sub s/) on the recording pattern for highly oriented media (OR=22.5) is investigated. Low magnetization is found to induce even lower transition noise and slightly higher effective track width. Edge percolation is observed when M/sub s/ increases up to 800 emu/cm/sup 3/. However, the noise magnitude at this edge does not change much when M/sub s/, is decreased to 200 emu/cm/sup 3/.

Dynamic orientation ratio in longitudinal recording media

The origin of orientation ratio (OR) in longitudinal recording media has been controversial in the literature. In the past, the observation of a higher OR for thinner magnetic films has been attributed to stress or thermal effects. Our measurements, carried out over a larger range of time scales, confirm that the thermal effects play a major role in the observation of a higher OR for thinner magnetic films. We point out that the OR is dynamic and follows a ln(t) behavior at larger time scales (5–1000 s). Our studies indicate that a larger OR and a more dynamic behavior of OR will be observed when KuV/kBT values are smaller. We also propose that the slope of dynamic OR can be used to compare the recording performance of media indirectly.

Performance analysis of recording system with tilted head field and perpendicular media

In this article, we systematically studied the performance of recording system with tilted head field and perpendicular media without soft underlayer. The dependence of recording performance on different exchange couplings are also discussed.

Effects of stabilizing layer and layer configuration on recording performance of laminated antiferromagnetically coupled media

The recording performance of laminated antiferromagnetically coupled (LAC) media was characterized to study the effect of stabilizing layer thickness and layer configuration. A smaller pulse width, PW50, was achieved at thicker stabilizing layer from experimental and micromagnetic simulation results. Increasing the stabilizing layer thickness did not cause significant overwrite degradation for LAC media but the nonlinear transition shift was found to be worse. Experimental results showed that the recording performance of a new three-layer media with middle layer functions as the main layer gave higher SNR, lower noise properties, and better thermal stability although the overwrite properties may not be so good as compared to conventional single layer media and two layer LAC media. The signal decay rate of the three-layer LAC media has been reduced by 16% as compared to conventional two layer LAC media.

Origin of thermal stability in laminated antiferromagnetically coupled media

Summary form only given. Recently, laminated antiferromagnetically coupled (LAC) media were introduced to overcome the thermal stability issues of longitudinal recording. It is proven that this media shows a better thermal stability at lower M/sub r//spl delta/ values. However, there has been some controversy in the origin of thermal stability. Lohau et al. (Appl. Phys. Lett. vol.78, p.2748 (2001)) has reported that the thermal stability of LAC media is independent of bottom layer thickness. Theories based on single-grain also indicate the thermal stability is determined by the top layer properties and the antiferromagnetic coupling constant, J. On the other hand, there are some experimental studies, which indicate that the bottom layer parameters contribute very much to thermal stability. At present, there is no clear understanding on the origin of improved thermal stability in LAC media. In order to extend the life of longitudinal recording, it is essential to understand the origin of improved thermal stability in LAC media. Therefore, in this study, we carry out experiments to understand the thermal stability in LAC media.