Nano-granular metal/insulator multilayer for reader shielding materials

We have developed materials with high resistivity and permeability. It consists of multilayered magnetic metal/insulator films such as CoFe/Al/sub 2/O/sub 3/, NiFe/Al/sub 2/O/sub 3/ and NiFe/SiO/sub 2/. The thickness of each layer is around 1 nm. This film consists of metal granules around nm size covered with insulator as evidenced by using transmission electron microscopy (TEM). The multilayer film CoFe/Al/sub 2/O/sub 3/, showed a resistivity of more than 10 m/spl Omega/cm and a coercivity of the hard axis was between 80 and 240 A/m, and saturation magnetization was higher than 0.9 T. The permeability of this film was around 250 up to GHz level. In this study, the film structure offering the highest resistivity and permeability was 20 to 40 layers of CoFe(1.3-1.5 nm)/Al/sub 2/O/sub 3/(1.0-1.2 nm) bilayer. Nano-granular high-resistivity materials are therefore appropriate for using as head shielding material.