Y.W. Tahk

Transition noise characteristics of PMR media with the synthetic antiferromagnetic coupled soft underlayer

Previously, we have shown that the transition position shift in a perpendicular recording medium with a recording layer and a soft underlayer (SUL) is one of the major noise sources in high-density recording when abrupt single pole head field is applied. In this paper, we have considered a head rise time calculated from micromagnetic calculation for three different damping constants of pole tip. Also, in order to reduce the transition position shift, a modified medium with a synthetic antiferromagnetically coupled (SAFC) SUL was investigated. The SAFC-SUL was assumed to the 20-nm-thick top SUL with Ms of 800 emu/cc and the 80-nm-thick bottom-SUL with magnetization saturation (Ms) of 1200 emu/cc separated by a 0.6 nm Ru layer. The media with SAFC-SUL showed lower noise and higher signal-to-noise ration than the media with conventional SUL. The lower noise in the SAFC-SUL seems to be associated with suppressed vortex formation in the SUL by synthetic antiferromagnetic coupling in the SUL.

Effects of magnetic damping constant of the soft underlayer on SNR in double layered perpendicular magnetic recording media

The magnetic dynamics of a total recording system composed of a single pole head and a perpendicular recording medium with a soft underlayer was performed by a three-dimensional micromagnetic model. In this paper, the effect of the magnetic damping constant of the soft underlayer (SUL) on the signal-to-noise ration (SNR) was systematically studied for the case of abrupt change in head field. For this purpose, the different damping constants (/spl alpha/) of 1.0, 0.1, 0.03, and 0.01 were studied in a conventional SUL. In all cases, SNR rapidly decreased with decreasing /spl alpha/ of SUL. The longer range magnetic fluctuation in the SUL for smaller damping constant affects the shift of the transition region of the bits more. For comparison, we have shown SNR for the same media with a head field rise time was considered.

Spin tilting phenomenon in the strongly coupled AFC media

It has been reported that a new layered structure of antiferromagnetically coupled (AFC) media with high antiferromagnetic exchange constant J of 0.9 erg/cm/sup 2/ can be achieved by insertion of Co layers. In such AFC media with high J value, a spin-tilting (or spin-flopping) phenomenon similar to that of the synthetic antiferromagnetic structure (SyAF) of the MR sensor can occur. The purpose of this work is to find relationships between the degree of spin-tilting and the recording characteristics such as SNR and thermal decay. Micromagnetic simulations have been performed for various thicknesses (t/sub 2/) and magnetic properties of the bottom layer, since the spin-tilting can be directly related to them.

Effects of CrMo spacer layer on thermal stability and magnetic properties in an antiferromagnetically coupled medium

In this work, magnetic properties and thermal stability of antiferromagnetically coupled AFC medium with a CrMo spacer layer instead of the conventional Ru spacer layer were studied. It was found that a reduction of Mr/Ms could also be obtained in the AFC medium with a CrMo spacer layer due to the antiferromagnetic coupling, similar to the conventional AFC medium with a Ru spacer layer. Thermal stability ratio, KUV/kBT for the proposed medium was slightly smaller than that of the conventional AFC medium with a Ru spacer layer, but larger than that of a single magnetic layer medium. By a comparison of the switching field distribution and ΔM of the AFC medium with those of the conventional AFC medium, it is conjectured that the intergranular exchange coupling decreases when a CrMo is used as a spacer layer.

Effect of grain size distribution on thermal decay in perpendicular recording with double layered media and single pole head by micromagnetic modeling

In this work, micromagnetic simulations of the read/write process for perpendicular systems have been performed. In higher recording densities, grain size distribution is more important due to the dependency of thermal decay and SNR on grain size distribution. Therefore the magnetic layer was simulated by a Voronoi cell with different standard deviation of grain sizes. The effect of a soft under layer (SUL) on read/write was calculated by using a cubic cell. For a realistic writing head field, we used the single pole head field calculated by micromagnetics. Width and thickness of the write pole was 60 nm and 160 nm, respectively. Head sweep velocity during the writing process was taken to be 40 m/s. SNR and thermal decay at a linear density of 1058 kfci were calculated as a function of the different standard deviations of grain sizes. Thermal decay over a long time scale was investigated by the Langevin equation and the time-temperature scaling method. SNR is calculated by the reciprocity principle in a shielded magnetoresistive head.

Enhancement of grain isolation by interlayer diffusion in AFC media with CrMo spacer layer

It was found that a reduction in M/sub r/t can be obtained in the new antiferromagnetically coupled (AFC) medium with a CrMo spacer layer due to antiferromagnetic (AF) coupling, which is similar to the conventional AFC medium with a Ru spacer layer. From the results of /spl Delta/M and magnetic force microscopy (MFM), it was found that the intergranular exchange coupling decreases when CrMo is used as a spacer layer. Micromagnetic simulations of /spl Delta/M and MFM analyses gave consistent results with experiment, i.e., 1) AFC media with higher intergranular exchange coupling constant have larger magnetic cluster and higher /spl Delta/M peak and 2) the media with higher AF coupling constant have smaller magnetic cluster and smaller /spl Delta/M. In this paper, we propose that the media noise of the AFC media with a CrMo spacer layer may be improved by a reduction in the magnetic cluster size, due to the decrease of the intergranular exchange coupling between magnetic grains.

Micromagnetic Modeling of Spin-valve MR Head with Synthetic Antiferromagnet (SyAF)

MR transfer behaviors of the permanent magnet biased spin valve MR sensors with SyAF (synthetic antiferromagnet) layers were studied by micromagnetics modeling. For narrow track MR heads, various height to width ratios were considered together with strength of permanent magnets which stabilizes the free layer. As the MR sensor width is reduced to 0.12 ㎛, sensor height less than 0.09 ㎛ is needed to show good linearity and the Mr-t of permanent magnets smaller than 0.2 memu/㎠ is sufficient for the domain stabilization. The conditions for single domain behavior of the free layer were also investigated through optimizing the biasing strength of permanent magnet, the shield gap and the aspect ratio of MR sensor.