Ian L. Sanders

A magnetic evaluation of interaction and noise characteristics of CoNiCr thin films

The nature of media recording noise in metallic, quasiparticulate thin films is principally related to the grain size, crystallographic orientation, and intergranular exchange and magnetostatic coupling in the films. In this study the results of a magnetic evaluation of magnetostatic interactions in CoNiCr thin films of varying Cr underlayer thickness are reported. The evaluation is undertaken through the measurement and comparison of remanence curves. The results presented here indicate enhanced cooperative switching as Cr underlayer thickness is reduced from 2000 to 100 A, with a strong correlation between signal‐to‐noise measurements. In addition, the transition from principally exchange‐coupled to quasiparticulate thin films, as Cr underlayer thickness increases, has been established.

Reduction of media noise in thin film metal media by lamination

The properties of laminated films of longitudinal Co-alloy media have been investigated. Significant reductions in the media noise are observed compared with single-layer films of the same total thickness, while the signal amplitude is unaffected. There are at least two reasons for this improved performance. Thin media layers exhibit inherently better signal-to-media-noise ratios, which are retained when several thin films are separated by nonmagnetic interlayers. A laminated media structure also offers a media-noise advantage since noise sources in the individual magnetic layers can be independent of one another. It is concluded that lamination can be used to improve the noise performance of metal-film media by simply repeating known process steps. >

Beyond discrete tracks : other aspects of patterned media

The surface of a thin‐film disk can be patterned using standard lithographic techniques to form discrete tracks as narrow as 0.5 μm. These studies have been extended to patterns formed when an etched track is broken into discrete segments by etching away some portions of a discrete track. Abrupt changes in the magnetization can be obtained by dc erasing the medium, giving readback signals with ∼50% of the amplitude of conventional transitions when the gap of the readback head is aligned with the edge of the media pattern. The implications of these results for servo and read‐only applications are discussed.

Recording characteristics of submicron discrete magnetic tracks

Discrete magnetic tracks with widths as narrow as 0.5 μm have been formed by etching the surface of Co-alloy film disks. Transitions can be written and read back from widely spaced discrete tracks using conventional heads. A linear variation of pulse area with track width is observed for isolated pulses. Noise measurements for tracks that are either dc erased or written with transition densities up to 3000 flux reversals/mm show a linear variation of media noise with (track width)1/2, in agreement with the behavior expected for media noise uncorrelated across the width of the track.

Influence of coercivity squareness on media noise in thin-film recording media

Signal and media noise measurements have been made for a wide variety of Co‐alloy longitudinal magnetic recording media. A strong correlation between media noise and the coercivity squareness, S*, is observed at high transition density. The optimum ratio of isolated pulse amplitude to media noise is found for S*≂0.75. This behavior arises from reduced ferromagnetic exchange coupling between neighboring grains of the film which influence both the coercivity squareness and also the uniformity of the domain boundary at the recorded transitions. The low‐noise characteristics of sputtered γ‐Fe2O3 also appear to correlate with low values of coercivity squareness. This work confirms that for systems in which media noise is a limiting factor, optimum performance may require considerably lower values of coercivity squareness than commonly used, determined by the relative contribution of media noise to the overall system noise.

Separation of magnetic and topographic effects in force microscopy

Several techniques are presented which allow magnetic force microscopy to be performed while simultaneously mapping the surface topographic features of a magnetic sample. The separation of magnetic and topographic features measured simultaneously with a scanning force microscope is made possible by an instrument based on a differential interferometer that can detect cantilever deflections of 0.005 nm at a frequency as low as 1 Hz. Two different applications are presented.

Magnetic characterisation of thin film recording media

The basic magnetic characterization techniques for thin recording media are critically examined in relation to the requirements for modern high-storage-density materials. The applicability and usefulness of remanence curves for the characterization of thin-film media are discussed together with the recently developed Delta I(H) technique. The origins of the relation between these measurements and cooperative reversal are presented, together with the improved data showing the correlation between Delta I(H) and noise. This discussion is extended to include the time-dependent phenomena and in particular the activation volume, including the effects of intergranular coupling. Data are presented to show these effects in both single-layer alloy films and laminated systems, and the implications for ultimate recording density are discussed. >

Magnetic and recording characteristics of very thin metal-film media

The recording performance of very thin sputtered Co-alloy longitudinal film media has been examined. Measurements made using magnetic layers as thin as 50 AA show that the thinner films exhibit improved signal-to-noise characteristics. Similar trends have been observed in both CoNiCr and CoPtCr alloys on Cr and CrV underlayers. Improvement in signal-to-noise ratio is accompanied by a reduction in coercivity squareness as the film thickness is reduced. Large variations of coercivity with film thickness are also observed in the range 50-300 AA. It is suggested that changes in grain size and grain boundary separation during the early stages of film growth play a role in these effects. >

Interaction effects in multi-layer thin film media

The authors report on the magnetic properties of CoPtCr multilayer thin film media. Measurements of delta (H) were made for a range of CoPtCr films with differing numbers of layers, but with a constant overall total magnetic layer thickness. The results indicate that the multilayer films show two types of switching behavior due to the difference in the Cr underlayer and interlayer thicknesses. It is concluded that interactions within the film are reduced when the magnetic single layer is laminated with chromium. Thus the recording performance is expected to be improved as the number of the layers increases, due to the reduction in intergranular coupling between and possibly within the layers. >

Influence of Au and Ag at the interface of sputtered giant magnetoresistance Fe/Cr multilayers

Multilayer films consisting of 20-AA Fe and 15-AA Cr with amounts of Au and Ag varying from 0 to 4 AA deposited at alternate Fe/Cr interfaces have been RF-diode-sputtered, and their magnetic and magnetotransport properties have been measured. When no noble metal is included, the films exhibit strong antiparallel coupling between adjacent Fe layers, with saturation fields as large as 7 kOe, and giant magnetoresistance (GMR) of 6% at 300 K, similar to that of MBE (molecular beam epitaxy)-grown films reported by others. The interruption of intimate contact between Fe and Cr at the interface resulting from noble-metal deposition gives rise to a substantial decrease in the magnitude of the GMR and the interfacial coupling. This suggests that the mechanism of GMR is associated with Fe and Cr in contact, as is required by models invoking spin-dependent impurity scattering. The results also suggest that the antiparallel coupling arises from direct exchange. >