From its inception until today, and for the foreseeable future, magnetic data storage on disks and tape has provided constantly increased storage density. This has required not only constant innovation, but also major breakthroughs in magnetic materials, both for the media and the read head. Today's disk and tape drives take advantage of novel nanoengineered composite magnetic materials and quantum mechanical processes. In this issue of MRS Bulletin, we present a number of review articles by some of the leaders in this rapidly moving field that highlight the key materials science accomplishments that have enabled the tremendous progress in hard disk drive and magnetic tape technologies. Individual articles describe the materials involved in stateof-the-art magnetic recording, advanced media for perpendicular magnetic recording, the materials challenges of achieving high performance in flexible media such as magnetic tape, the materials issues of read heads, and future avenues for magnetic storage beyond magnetic recording, such as nanowires and spintronics.

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Barium ferrite platelet-shaped particles have been prepared with a diameter of 0.1 microns, which is an order of magnitude smaller than those obtained by conventional sintering and regrinding techniques. The preparation technique used has been optimized to produce the complete ferrite with σs=68 emu/g. Due to the small particle size, extremely high intrinsic coercive forces have been obtained, (Hc=5350 Oe), in good agreement with the value calculated from the Stoner-Wohlfarth (SW) coherent rotating model for single-domain noninteracting particles when shape and crystal anisotropy are both taken into account. Furthermore, the measured hysteresis loop for an unoriented sample agrees well with the theoretical SW loop. Similar hysteretic magnetization properties have been obtained in strontium ferrite. The single-domain nature of these powders is also demonstrated by their temperature dependence of coercive force where little change is obtained over the range −200° to +150°C. An estimate of the relative interaction field magnitude for the small particles of barium ferrite has been obtained by comparing its initial anhysteretic susceptibility with that of an acicular iron oxide powder.

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The critical current density and flux-creep rate have been measured as functions of temperature and magnetic field for a ring-shaped sample of Y-Ba-Cu-0 ceramic which was specially prepared so that such measurements could be made without penetration of flux lines into the superconducting grains. The measurements were made in both the presence and the absence of a biasing magnetic field. A theoretical model is developed in which the superconducting grains are linked by junctions with a range of strengths and the model is used to describe the temperature dependence of the critical current density and low-field flux-creep rate. The results obtained from the analysis of our model are compared with those derived, less rigorously, by other workers in the case of flux creep in single crystals and epitaxial films. The application of our theory to our experimental data yields good internal consistency, and functions describing the distribution of junction strengths in our specimen with and without the bias field are obtained.