抄録
A remarkable reduction in coercivity Hc was found in sputtered (Fe70Co30)99(Al2O3)1 films on Ni-Fe and Cu underlayers. A decrease in Hc from 80 to 4∼6 Oe was observed for Ni-Fe and Cu underlayers as thin as 2 nm, but the decrease was less for Ta. No significant difference in soft magnetic properties was observed with the thickness of a Ni-Fe layer in the range 0.5∼10 nm, that with of a Cu layer in the range 0.2∼10 nm, or with that of an Fe-Co-Al-O layer in the range 50∼480 nm. The optimized film has a saturation magnetization of 23.5 kG; the real part of the permeability shows frequencies up to 1.3 GHz of 1200∼2520, and the imaginary permeability peaks at beyond 2 GHz, corresponding to the ferromagnetic resonance frequency. All underlayers induced a bcc-(110) preferred grain orientation in Fe-Co, and this orientation was strongest with Ta. Transmission electron microscopy of cross-sections showed that clear columnar grains were visible with all underlayers, with an average grain size of around 50 nm with Ta, dropping to 7-10 nm for Ni-Fe and Cu. This allows us to explain qualitatively the reduction in Hc using Hoffmann’s ripple theory.
