Particle size effects and surface anisotropy in Fe-based granular films

Abstract

Structure and magnetic properties of Fe/SiO 2 and Fe/Al 2 O 3 granular films were studied in the particle size (d) range of 1–50 nm. The coercivity (H c ) shows a maximum around 600 Oe at the particle size d m ≈18 nm , and then decreases in the larger particle size range for both Fe/SiO 2 and Fe/Al 2 O 3 systems at room temperature. A relation of coercivity, particle size, and temperature was built by using the Néel–Brown theory and the Stoner–Wohlfarth model basically. The experimental results were successfully fitted by assuming that the α-Fe particles possess uniaxial surfaceanisotropy K s ≈0.4 erg/cm 2 .