Co-γFe₂O₃ longitudinal magnetic recording media obtained by annealing CoO-Fe₃O₄ were prepared on NiO underlayer. The coercivity H_c was varied with the Co content, namely, the atomic ratio of Co/Fe in Co-γFe₂O₃, and the oxygen partial pressure in deposition of CoO-Fe₃O₄. The H_c of the media with Co/Fe = 4 at% was 2000-3500 Oe, 1.3-3.6 times higher than that of Co-γFe₂O₃ media without NiO underlayer. The grain size of Co-γFe₂O₃ became smaller with decreasing the thickness. The read/write characteristics of the media with no overcoat were evaluated in contact recording. Co-γFe₂O₃ media on NiO had higher D₅₀ and lower medium noise than those of the media without NiO underlayer.

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This paper describes the operation characteristics of an orthogonal-core type push-pull parametric transformer with an inductive load. We analyzed the characteristics on the basis of the circuit equation of the transformer, derived under simple assumptions. From the analytical results, it is obvious that the output power and maximum load in the transformer with an inductive load are smaller than those in the transformer with a resistive load. Some useful information for practical application of the transformer were obtained.

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The authors describe a new type of micromagnetic device, which has a transmission-line structure composed of magnetic/dielectric multilayers with top and bottom parallel conductor lines. Both the electromagnetic field and the distributed constant circuit are analyzed. On the assumption that the electromagnetic mode is TEM, the results of field analysis show that the electromagnetic energy propagates mainly through the dielectric layer when conductive magnetic/insulative dielectric multilayers are used. The transmission parameters, however, depends not only on the dielectric layer, but also on the conductive magnetic layer. The transmission-line micromagnetic devices will be used in many kinds of equipment, such as λ/4 transformers, short termination inductors and magnetic field sensors.

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