We propose a model of Josephson coupling between grains to explain the millimeter-wave surface impedance of oriented, polycrystalline thin films of high Tc superconductors. An effective junction IcR product and effective grain size are calculated based on recent measurements of the surface impedance. We suggest a criterion on film quality for the observation of losses intrinsic in the superconductor. The effects of crystalline orientation on surface impedance are considered.

A series of sputtered multilayers of Ni(80)Fe(20)-Ag was prepared to examine the giant magnetoresistance effect before and after annealing. For a wide range of NiFe and Ag thicknesses, no giant magnetoresistance was observed in the unannealed films. After annealing, a large, negative magnetoresistance was observed of order 4 to 6% in applied fields of order 5 to 10 oersteds at room temperature. The appearance of giant managetoresistance is concurrent with the breakup of the NiFe layers, which is attributable to a magnetostatic interaction that favors local antiparallel alignment of the moments in adjacent layers. These structures may be of significant practical importance as sensors that require large changes in resistance at low fields, such as magnetoresistive heads used in magnetic recording systems.

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Ba-ferrite is an attractive candidate for future high-density recording media because of its large coercivity, corrosion resistance, high hardness, and durability. In contrast to most recent work on Ba-ferrite thin film media, polycrystalline films with large in-plane remanence for longitudinal recording are emphasized. Films are prepared on a variety of substrates by on-axis sputtering at low temperatures from stoichiometric targets followed by a postdeposition anneal in a rapid thermal processor at ∼850 °C to induce crystallization. Structural and chemical properties have been investigated by force microscopy, Rutherford backscattering, and other means. Stoichiometric films have large 5000 Å grains that are unsuitable for high-density recording. However, grain sizes as small as 200 Å have been produced by doping with small amounts of Cr2O3 and other additives. Compositional changes also influence crystallite orientation. Exceptional durability has been observed on disks without overcoats, presumably due to a fine-scale texturing that occurs during crystallization. Coercivities are greater than 4000 Oe even in small grain films. The effect of grain size on coercivity and signal-to-noise ratio of several Ba-ferrite disks is discussed. It is argued that the grains are magnetically decoupled based on the magnetic properties of these films.