Synthesis of Co100-xPtx alloy fine particles with high coercivity

In the present study, we have prepared and investigated Co100-xPtx (0 less than or equal to x less than or equal to 40) fine particles with the averag e diameter of D = 3 similar to 40 nm. At a fixed D similar to 10 nm, the ro om temperature coercivity H-c increases with the Pt content x and takes a m aximum value of 1000 Oe at x similar to 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 a pproach to saturation. At x similar to 25 at.%, Hc increases with D due to suppression of thermal agitation and takes a maximum of 4000 Oe around at D similar to 15 nm. Micromagnetic calculations taking into account dipolar i nteractions between particles have verified that the magnetic behaviors Of Co75Pt25 fine particles can be explained by the coherent rotation model.