Publication Date


Document Type


Committee Members

John Boeckl (Committee Member), Gregory Kozlowski (Committee Chair), Doug Petkie (Committee Member)

Degree Name

Master of Science (MS)


This work studies surface effects on the critical dimensions of ferromagnetic nanoparticles. Iron nanoparticles with different mean diameters from 5.9 nm to 21.4 nm used in this research were prepared by thermal decomposition of iron pentacarbonyl in the presence of oleic acid/octyl ether at Cambridge University, United Kingdom. Heating response of these ferromagnetic nanoparticles suspended in water were measured experimentally during which same amount of iron nanoparticles and di-ionized water 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. Heating rate was calculated from the initial slope of heating curve at inflection point whereby there is minimum heat loss to the surrounding. 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. The maximum value of SAR was obtained when applied frequency and current were at 175 kHz and 15 A, respectively. Equation for the critical radius for the transition from single-domain to multi-domain regime with low anisotropy was derived and numerically solved by using program written in C++ and results were analyzed to find the effect of surface parameters on the critical radius of nanoparticles. The SAR vs nanoparticles diameter shows two maxima which can be correlated to two critical dimensions. One is DC1 at 18 nm for the transition from single-domain to multi-domain configuration and second is DC2 at 10 nm for the transition from single-domain to superparamagnetic regime. Comparison of these experimental results with BOLS correlation theory has been done.

Page Count


Department or Program

Department of Physics

Year Degree Awarded


Included in

Physics Commons