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Co-Ag granular films having various Co grain sizes are prepared by rf sputtering under various sputtering conditions. The Co grain sizes are derived from the magnetization curves by dividing them into ferromagnetic and superparamagnetic components. As the Co content decreases, the radii of the superparamagnetic Co grains, r g , decrease and the distances between the Co grains, t g , increase. The magnetoresistance is proportional to the volume density of superparamagnetic grains or related to kr g 3 exp(Ϫt g /l) with kϭ3.8ϫ10 2 ⍀/cm 2 and lϭ20 Å, implying that the giant magnetoresistance is caused by the spin-dependent scattering in the inner part of the superparamagnetic Co grains as well as at the grain surfaces. Furthermore, it is found that the extraordinary Hall effect arises mainly from the side jump mechanism, and that significant perpendicular magnetic anisotropy appears in the Co composition range between 40 and 70 at %.

Co/Au multilayers have been prepared on glass substrates by electron-beam evaporation techniques. The perpendicular anisotropy is induced when the Co layer thickness is less than 12 Å and its origin is discussed phenomenologically. In the perpendicular magnetic multilayers, large giant magnetoresistance appears and it consists of hysteretic and nonhysteretic components. The occurrence mechanism of these components has been discussed and it is suggested that the former arises from antiparallel spin alignment between adjacent Co layers due to the random wall position layer by layer, and the later is related to the granular-type giant magnetoresistance.

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400 0 e and SOOoe.With annealing, the saturation magnetization Ms and the saturation Kerr rotation angle increase and approach the values of alloyed films. On the other hand, the perpendicular anisotropy energy decreases monotonically owing to both the reduction of the interfacial anisotropy energy and the increase of the demagnetizing energy 2nMs2,These changes in the magnetic properties are explained by the alloying at the layer boundaries due to annealing. The diffusion process is analyzed by means of X-ray diffraction method and is suggested to be connected with the "grain boundary diffusion", The change in the composition profiles in the double layered films of 1000j\Co/1OOOj\Pt has been examined by Rutherford Backscattering Spectroscopy. The RBS data also indicate that Co and Pt atoms migrate through the grain boundaries and the column boundaries.