Study On The Influence Of The Surface Anisotropy And Shape On The Magnetic Properties Of Nanoparticles

Nano-magnetic material is a new-style material which appeared in 1980s. Now nano-magnetic material has great importance in information and technique field, especially in information storage. In this paper, a modified Monte Carlo method was adopted to investigate the thermodynamic properties and magnetization behavior of ferromagnetic(FM) and antiferromagnetic (AFM) nanoparticles with egg-shape and perpendicular surface anisotropy. The main jobs and conclusions are as follows.1. Simulation of the FM egg-shaped nanoparticle to investigate the relation between surface exchange interaction, surface and body exchange interaction and surface anisotropy and the thermodynamic properties. It is found that the transition temperature of system does not change, while the max-magnetic susceptibility and the max-magnetic specific heat increase when the surface and body exchange interaction increase. The max-magnetic susceptibility decreases and max-magnetic specific heat increases when the surface anisotropy and surface and body exchange interaction increase.2. Simulation of the AFM egg-shaped nanoparticle to investigate the relation between surface exchange interaction, surface and body exchange interaction and surface anisotropy and the thermodynamic properties. It is found that the max-magnetic susceptibility of system decreases and the max-magnetic specific heat increases when the body and surface exchange interaction, surface exchange interaction and surface anisotropy increase.3. Simulation of the FM egg-shaped nanoparticle in an external magnetic field along the symmetry axis to investigate the relation between surface exchange interaction, surface and body exchange interaction and surface anisotropy and the hysteresis loops, exchange bias and coercivity. It is found that the hysteresis loops of system becomes narrow, exchange bias increases at first and then becomes invariable and the coercivity decreases at first and then becomes invariable when the surface anisotropy increases. The hysteresis loops of system become narrow, exchange bias increases, and the coercivity decreases when the body and surface exchange interaction increases. In an magnetic field along the asymmetry axis, as the surface anisotropy increases, the hysteresis loops become narrow, the exchange bias increases at first and then decreases, and finally becomes invariable, the coercivity decreases at first and then becomes invariable. As the exchange interaction between spins in core and surface, the hysteresis loop gradually becomes wider, and the coercivity increases.4. Simulation of the AFM egg-shaped nanoparticle in an external magnetic field along the symmetry axis. It is found that the hysteresis loops change little as the exchange interaction between spins on surface or some on surface and the other in the core and the surface anisotropy increase. In an external magnetic field along the asymmetry axis, the hysteresis loops become longer as the surface anisotropy increases. The hysteresis loops move down when the surface exchange interaction and the core-surface exchange interaction increase.