Magnetic properties of amorphous FeCo base ultrafine particles

RF sputter deposition of (FeCo)80B20onto a sputter-etched polyimide substrate produces a dense array of elongated finger-like projections of amorphous ferromagnetic material, with diameters less than 1000 Å and aspect ratio about 4. These particles, which we call ultrafine amorphous particles, have a magnetic easy axis perpendicular to the substrate. The coercive field and magnetic anisotropy depend strongly on the Fe/Co ratio and also on the annealing conditions. A maximum coercive field of almost 1200 Oe is obtained for (Fe0.4Co0.6)80B20particles annealed at about 500°C. After this treatment the particles are crystalline.