Magnetic Anisotropic Energy Gap and Strain Effect in Au Nanoparticles

Po-Hsun Shih,Shengyun Wu

doi:10.1007/s11671-009-9438-z

Abstract

We report on the observation of the size effect of thermal magnetization in Au nanoparticles. The thermal deviation of the saturation magnetization departs substantially from that predicted by the Bloch T3/2-law, indicating the existence of magnetic anisotropic energy. The results may be understood using the uniaxial anisotropy Heisenberg model, in which the surface atoms give rise to polarized moments while the magnetic anisotropic energy decreases as the size of the Au nanoparticles is reduced. There is a significant maximum magnetic anisotropic energy found for the 6 nm Au nanoparticles, which is associated with the deviation of the lattice constant due to magnetocrystalline anisotropy.

Highlights

We report on the observation of the size effect of thermal magnetization in Au nanoparticles
The most frequent effects of the small size are lattice rearrangement, crystalline imperfections, a higher degree of localization, and narrowed valence band width. It has been reported in previous studies [2, 4] that individual Pd and Au nanoparticles may reach their ferromagnetic moment at low temperatures, and that, theoretically, there may be a slight
We discuss the effects of surface polarization and weak magnetic anisotropy in Au nanoparticles, which indicate the appearance of ferromagnetic spin polarization and magnetic anisotropic energy at low temperatures

Summary

Introduction

We report on the observation of the size effect of thermal magnetization in Au nanoparticles. The origin of the ferromagnetism observed in filled 4d or 5d electron nanoparticle systems can be explained as due to giant magnetic anisotropy [8] and Fermi-hole effects [9] that influence the evolution from the surface polarization spins to the diamagnetic bulk state.

Results

Conclusion