Surface Effects on Critical Dimensions of Ferromagnetic Nanoparticles

The present work studies surface effects on the critical dimensions of ferromagnetic nanoparticles. Iron nanoparticles with different mean diameters were irradiated by an alternating magnetic field and the increase in temperature of these samples was measured. Heating performance of nanoparticles was described in terms of Specific Absorption Rate (SAR) which depends on the heating rate. Experimental results were analyzed to find the critical diameters for the transition from single-domain to superparamagnetic regime and from single-domain to multi-domain regime. Also, frequency and current dependence of SAR was studied. Equation for the critical radius for the transition from single-domain to multi-domain regime with low anisotropy was derived and solved numerically. The results were analyzed to find the effect of surface parameters on the critical radius of nanoparticles. Comparison of these experimental results with BOLS correlation theory has been done.