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We have investigated the microstructures of Co–Al–O granular thin films, which were prepared by the sputter-deposition technique with various oxygen partial pressures. The constituent phases, grain sizes of granular particles, and width of insulating channels have been evaluated quantitatively. The specimen with the optimum giant magnetoresistance (GMR) is composed of nanoscale Co particles, and these are completely isolated by amorphous aluminum oxide channels. The GMR behavior observed in the Co–Al–O films has a close correlation with the width of the insulating channel and the grain size of the magnetic particles, which is consistent with the spin-dependent tunneling conduction mechanism of GMR

The microstructures of Co-Al-O thin films of wide varieties of compositions are studied by transmission electron microscopy and small angle x-ray scattering ͑SAXS͒. In the superparamagnetic specimens, high resolution electron microscope images reveal that isolated spherical Co particles are surrounded by an amorphous aluminum oxide matrix. However, in the soft ferromagnetic films, the shape of the Co particles is prolate ellipsoidal. SAXS intensities from the soft magnetic specimens decrease inversely with the wave vector, q, in a low wave-vector region, while an interparticle interference peak is observed for the superparamagnetic specimens. The scattering profiles of the soft magnetic films imply that the Co particles have a cylindrical shape and are randomly oriented. The correlation between the magnetic properties and the microstructures is discussed.

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Erratum: "Structure, hyperfine interactions, and magnetic behavior of amorphous and nanocrystalline Fe 80 M 7 Structure, hyperfine interactions, and magnetic behavior of amorphous and nanocrystalline Fe 80 M 7 B 12 Cu 1 ( M=Mo , Nb, Ti) alloysThe effect of Co replacement for Fe on the microstructure and soft magnetic properties of Fe 78.8Ϫx Co x Nb 2.6 Si 9 B 9 Cu 0.6 (xϭ5 -60) nanocrystalline alloys has been studied for improving the soft magnetic properties of Fe-Si-B-Nb-Cu type alloys at a high frequency range. The magnetic anisotropy constant increases with x, but the coercivity increases when x exceeds 20, indicating that magnetic softness is degraded by replacing Fe with Co. Three-dimensional atom-probe observations have revealed that the number density of Cu-enriched clusters decreases with x, thereby decreasing the number density of the heterogeneous nucleation sites for bcc-Fe primary crystals. In addition, differential scanning calorimetry measurements show that the Cu clustering temperature shifts to a higher temperature with increasing x, suggesting that the kinetics for the Cu clustering decreases as Co content. These experimental results are discussed from the thermodynamical point of view, and the optimized Cu composition to achieve a low coercivity with 40 at % Co has been found.

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