The magnetoresistive (MR) switching behavior of small permalloy/silicon monoxide/permalloy sandwich elements is investigated. A comparison with single layer elements shows that the best MR-switching results are found for the sandwich structures with the smallest dimensions (10×100 μm). A theoretical calculation based on the magnetostatic coupling between the two permalloy layers of the sandwich and on inhomogeneous demagnetizing fields shows good agreement with the experimental results. The formation of magnetic domain configurations other than those found in small single layer elements is illustrated using a ferrofluid observation technique.

We have studied the I-V characteristics, the dc resistance at the origin R(T), and the critical current It(T) of arrays consisting of n • n (n = 10, 20, 30, and 40) In squares separated by Au/In regions. The superconducting squares have side ds(In) from 7.5 to 15 tzm and dN(Au/In) from 2.5 to 11 ~m. These devices show two transition temperatures in their R(T) curve; one at Tcc near Tc(In) and another one at T* above Tc(Au/In). The I-V curves for each temperature region resemble recent published results on NbN granular films. These arrays follow a formalism proposed by Wolf, Gubser, and Imry to describe the transition to a resistanceless state at T*. The measured values of I~(T) are larger than expected from n noninteracting Bardeen-Johnson functions in parallel, although the exponential behavior in temperature is followed. They are compatible with the idea of bands in the quasiparticle spectrum in the Au/In regions. Deviations in I~(T) from an exponential behavior in T near T* have been analyzed by applying to SNS arrays ideas developed for phase transitions in SIS arrays. Evidence that at T* we may be observing a phase transition at Tcj due to the Josephson coupling between In squares exists but it needs the development of theoretical work to be put on more solid grounds.

Fabrication techniques for devices having dimensions of about a micrometer are presented. A versatile low-cost photolithographic microscope projection technique and chemical etching are used as part of the fabrication process. The whole procedure is proposed as an alternative to razor blade or diamond scratching techniques in laboratory research at low temperatures. A detailed description of the equipment and methods is given. Specific examples of one material devices and two material devices are described in connection with physical problems of recent interest. The broad field of application of the techniques shown make them appropriate for creating structures that might have defined and reproducible forms from millimeter dimensions down to 0.5 microm.

We have studied devices consisting of 20 x 20 two dimensional arrays of proximity effect junctions of Au/In. The DC resistance at the origin as a function of temperature shows a transition at Tc (In) and another one at T*c, below Tc (In) but above Tc (Au/In). At T*c the devices go into a resistanceless state even though they are composed of SNS junctions. Different shapes of the current-voltage curves characterize each temperature region

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