Synthesis of Co/sub 100-x/Pt/sub x/ alloy fine particles with high coercivity

In the present study, we have prepared and investigated Co/sub 100-x/Pt/sub x/ (0/spl les//spl times//spl les/40) fine particles with the average diameter of D=3/spl sim/40 nm. At a fixed D/spl sim/10 nm, the room temperature coercivity H/sub c/ increases with the Pt content x and takes a maximum value of 1000 Oe at x/spl sim/25 at.% for 3D random assemblies of the particles. Such remarkable enhancement of the coercivity due to Pt is attributed to very strong magnetic anisotropy, as evaluated by the law of approach to saturation. At x/spl sim/25 at.%, H/sub c/ increases with D due to suppression of thermal agitation and takes a maximum of 4000 Oe around at D/spl sim/15 nm. Micromagnetic calculations taking into account dipolar interactions between particles have verified that the magnetic behaviors of Co/sub 75/Pt/sub 25/ fine particles can be explained by the coherent rotation model.