Magnetic anisotropy and behaviors of Fe nanoparticles

We have studied the magnetic properties of bcc-Fe fine particles with a diameter D of 3 similar to 40 mn prepared by a vapor condensation process. The particles exhibit uniaxial anisotropy of 2.0 similar to 3.0 x 10(6) erg/cc which is much larger than that of bulk Fe (0.5 x 10(6) erg/cc). Numerical calculations taking into account dipolar interaction and thermal agitation reproduce the particle size dependence of coercivity very well. According to the present work, magnetization reversal of Fe particles proceeds via coherent rotation for D < 15 similar to 20 mn and via incoherent rotation for D > 15 similar to 20 run. It is, however, still uncertain why the magnetic anisotropy of Fe fine particles is uniaxial and so large.