Tremendous progress has been made in magnetic data storage by applying theoretical considerations to technologies accumulated empirically through a great deal of research and development. In Japan, the recording demagnetization phenomenon was eagerly analyzed by many researchers because it was a serious problem in analogue signal recording such as video tape recording using a relatively thick magnetic recording medium. Consequently, perpendicular magnetic recording was proposed as a method for extremely high-bit-density recording. This paper describes the theoretical background which has resulted in the idea of perpendicular magnetic recording. Furthermore, the possibility of magnetic recording is discussed on the basis of the results obtained theoretically by magnetic recording simulators. Magnetic storage has the potential for extremely high-bit-density recording exceeding 1 Tb/cm2. We propose the idea of 'spinic data storage' in which binary digital data could be stored into each ferromagnetic single-domain columnar particle when the perpendicular magnetizing method is used.

Recording mechanism of perpendicular recording was examined using analytical expression of shielded AMR/GMR head response. Pulse shape, roll-off performance, and noise spectra were reasonably explained by the calculated head transfer functions. Comparison with the calculation based on the formulae showed several fundamental characteristics of perpendicular recording: no large media noise at low frequencies in magnetic sense, but simply due to a reflection of a head transfer function: no severe resolution degradation: negligible noise power directly arisen from soft magnetic underlayer. This method will provide a convenient design tool for perpendicular magnetic recording.

Nonlinear phenomena in perpendicular magnetic recording employing a single-pole head and a double-layered medium were investigated. First, measurement of linear superposition in the time domain indicated than the amount of nonlinear transition shift (NLTS) was less than 10 nm. It was concluded that the nonlinearity was caused by transition shift, not by waveform distortion. By interpreting the results, we proved that the NLTS was strongly related with head field gradient and interference field from recorded magnetization. Dependence on head parameter was examined by experiments. Based on the results, a single-pole head with which transition shift can be reduced was proposed. Pseudo-random sequence analysis revealed that NLTS was several percent even at 318 kFRPI, or at a bit interval of 80 nm, which agreed with the result of measurement of linear superposition in the time domain analysis. Experiments showed that NLTS increases the shortest bit length, in contrast with the case of longitudinal recording.

The long-term bit error rate (BER) performance of partial response maximum likelihood (PRML) system using an adaptive equalizer in a perpendicular magnetic recording (PMR) channel with thermal decay is studied. A thermal decay model based on the experimental data giving the amplitude change of reproducing waveforms with the elapsed time for CoPtCr-SiO2 PMR medium is obtained. The BER performance of PR1ML channel for the 16/17(0,6/6) run-length-limited (RLL) code is evaluated by computer simulation using the model. The relationship between the ratio RJ of the jitter-like media noise power to the total noise power at the reading point and the required SNR to achieve a BER of 10-4 is also obtained and the performance is compared with that of the conventional equalization. The results show that the significant improvement in SNR by utilizing the adaptive equalization is recognized over all RJ compared with the conventional equalization.

Extremely narrow track width of deep submicron range is examined in perpendicular magnetic recording. Head field distribution of a single-pole head analyzed by 3-dimensional computer simulation results in a sharp gradient, but relatively large cross-sectional area is required to maintain head field strength. Based on this design concept, a lateral single-pole head is described and proved to attain track width of 0.4 µm. In addition, multilevel partial response appropriate to the new multitrack recording system is proposed.

In recent years, perpendicular magnetic recording have progressed rapidly. It will not be long before perpendicular magnetic recording is put into practical use. However there have been few tools contributing to the optimum design of perpendicular magnetic recording media and heads except computer simulations. The authors have introduced a simple method based on the concept of self-consistent magnetization to analytically predict a transition parameter in terms of parameters of recording media and writing heads. Moreover we have discussed the origin of media noise by using a time-domain analysis of readout voltage and Voronoi cell model analysis. In this paper, main parameters to realize high bit density recording over 100 Gbit/inch2 is discussed first through these methods, and then the current status, the future problems and the prospects in perpendicular magnetic recording technology are described.