M. R. Madison

10 Gbit/in.2 longitudinal media on a glass substrate (invited)

This article reports on the properties of the media prepared on glass substrates which were used in IBM’s 10 Gbit/in.2 demonstration. In order to support a linear density of 315 kbpi and a track density of 33 ktpi, the remanant coercivity Hcr and remanant moment thickness product Mrt of the magnetic layer were 3450 Oe and 0.37 memu/cm2, respectively. The media used a NiAl seed layer, a CrV underlayer, a Co alloy magnetic layer, and a carbon overcoat protection layer. The magnetic film had a grain size of 12 nm as observed by transmission electron microscopy. The preferred orientation (PO) of the magnetic layer was (1010). This PO enables one to sustain high coercivities at low values of Mrt. It is observed that the c-axis in-plane texture of the magnetic layer is critical to achieve a low noise medium. Using a focused-ion-beam (FIB) trimmed giant magnetoresistance head and conventional partial response maximum likelihood channel, the on-track-error rates were measured at the 10−10 level.

Temperature distributions produced in an N‐layer film structure by static or scanning laser or electron beam with application to magneto‐optical media

The classic problem of heat flow in multilayer film structures has been revisited from the perspective of engineering applications for fields such as optical storage media design, laser annealing of semiconductor materials, electron beam lithography, and ion implantation. A compact recursive structure N‐layer Green’s function is developed from the coupled partial differential equations of thermal conduction. Temperature profiles are calculated for the absorption of normally incident continuous and pulsed‐Gaussian‐beam irradiation, on both static and moving media, with variable absorption across the source layer. General beam, amplitude‐time dependencies can be calculated with this formalism; however, only simple rectangular pulses are treated in the text. General N‐layer solutions are developed, and compact, recursive‐integral formulas, whose evaluation is enhanced with modern computer languages such as c and apl, are derived. In addition, we offer a clear physical interpretation of the results expressed ...

Demonstration of 35 Gbits/in/sup 2/ in media on glass substrates

A recording density of 35 Gbits/in/sup 2/ was achieved in longitudinal recording media with high-sensitivity GMR heads. The media displayed excellent thermal stability as a result of a CoPtCrB alloy with high magnetocrystalline anisotropy and relatively narrow grain size distribution. The degree of Co easy-axis orientation in the plane of the /spl mu/m was greatly improved and the grain size was reduced in the media on glass substrates. Estimates of the switching volume from dynamic coercivity and signal-to-noise measurements are larger than the physical grain size, suggesting that intergranular interactions improve stability. A potential path to further increases in recording density above 35 Gbits/in/sup 2/ is to use antiferromagnetically coupled magnetic layers in the media.

Beyond 10 Gb/in/sup 2/: Using a merged notched head (FIB-defined writer and GMR reader) on advanced low noise media

We demonstrated recording performance at greater than 10 Gb/in/sup 2/ with data rates up to 25 MB/s, using a single combined write and read head (Merge Notched head).

Erase band and transition charge-model and MFM

The three-dimensional magnetic vector field for a magnetic recording head with unequal pole width is used as an input to a two dimensional extension of the Williams Comstock model to calculate transition charge, erase band widths, and to simulate magnetic force microscope images. Modeling results are compared to MFM images.

Advanced write heads for high density and high data rate recording

Advanced write head designs improve write efficiency by reducing yoke length to less than 15 /spl mu/m, adapting a sunken coil/P1 pedestal structure with stitched pole, and utilizing high moment poles with greater than 2 T moment. Sufficient bit-error rate was achieved up to 680 kBPI using heads with 50-60 GB/in/sup 2/ dimensions. For wider track width heads, spin-stand testing showed good writing parametrics and soft error rate up to 1.0-1.1 Gb/s channel data rate, with product electronics and channels. The feasibility of high-speed recording up to 1.5 Gb/s is demonstrated using experimental write drivers.

Design tradeoffs for beyond 20 Gb/in.2: Using a merged notched head on advanced low noise media (invited)

Design considerations for areal densities beyond 20 Gb/in.2 are discussed, and in particular a demonstration at 24.8 Gb/in.2 is shown. The demonstrations used a single combined write and read head (Merge, Notched head). In this article we will discuss the tradeoffs in kilobytes per inch (KBPI) and tracks-per-inch in obtaining areal densities at 25 Gb/in.2 densities. The KBPI is limited by both the total signal-to-noise ratio and the nonlinear-transition shift. Simple estimates of the increase in channel performance from class IV partial response (PR4), extended partial response 4 (EPR4), and modified EEPR4, as well as the addition of codes which eliminate bit shift and tribit errors are discussed as large contributors to the increase in the areal density.

Thermal mark characterization on static magneto-optical media

The authors explore the thermal behavior of multilayer magnetooptic (MO) storage media in thermomagnetic recording. An attempt has been made to develop a variety of useful models for heat transfer in these disks that can be readily interpreted for ongoing media design activity. Experimental techniques have been devised that can probe the spatial and temporal distribution of the thermal field in the MO storage film. An important feature of these experimental methods is that they use conventional recording hardware for testing recording performance. The experimental work focuses on static, zero-velocity recording experiments in order to clarify the methodology of using thermomagnetic recording process as a high-speed, high-resolution thermometer for the MO film. It is found that each of the models (finite element and method of images) provides an accurate description of experimental measurements of the thermal field in typical MO disk structures. >

Mixed magnetization states for field modulation writing of MO media

Direct overwrite of thermomagnetically written domains in rare‐earth transition‐metal thin films using magnetic field modulation has previously been reported. The written magnetization during the low field portion of the field modulation is unsaturated. A new technique for directly measuring the amount of mixed magnetization produced during continuous power laser writing was developed. The field dependence of both the measured amount of mixed magnetization and the measured integrated noise demonstrates a continuously varying mixture of microdomains, plus it yields a direct measure of the saturation field. A comparison to theory using a thermomagnetic write and read simulation was performed. Patterns corresponding to those written experimentally (long, continuous strips) were modeled and characterized. Measures of the mixed states were extracted from the simulation results as a function of applied bias field. From the simulations we computed the average signal, as well as an estimate of the integrated nois...

A model of write noise in magneto-optical media

Analytic models for calculating the contribution to noise power from the writing of periodic patterns of marks in magneto‐optical recording are presented. The write noise power distributions are calculated assuming three different models of stochastic variation of the mark edge placement. The standard deviations of the edge placements are estimated from experimental power spectrum.