Amorphous Ultrafine Metallic Particles

A review on the preparation method of amorphous ultrafine metallic particles and their magnetic properties is given; sputter-etching an appropriate polymer substrate produces a densely-packed array of needle-1ike projections on the polymer surface. RF sputter deposition of an adequate alloy onto this surface produces an array of elongated finger-like projections of amorphous magnetic materials, with diameter well under 1μm and aspect ratios of 5 or more. These finger-like projections meet the definition of ultrafine particles(UFP). Planar samples prepared in this way have a magnetic easy axis perpendicular to the sample surface with K_u/2πM_s^2=0.1～0.2, and have coercive field up to 700 Oe. A maximum coercive field of almost 1200 Oe is obtained for annealed samples at about 500℃. The anisotropy varied linearly with M_s^2, suggesting that its origin is largely the shape anisotropy of the particles. Furthermore, the coercive field varied linearly with K_u/M_s, as predicted by a Stoner-Wohlfarth single domain model. An attempt is made to these particles film as a perpendicular recording media