Gregory Kozlowski (Advisor), Sarah Tebbens (Committee Member), Zafer Turgut (Committee Member)
Master of Science (MS)
The influence of surface effects on a hysteresis loop for single domain, ferromagnetic nanoparticles was examined. Theoretical equations were derived to describe the magnetic behavior of the domains and a MATLAB program was used to solve them. M-H curves were calculated for the case when a magnetic field is applied in the favorable magnetization direction (easy axis). In contrast, the calculations show there were no hysteresis loops when the magnetic field was applied perpendicular to the easy axis. Our studies showed how parameters of the surface such as a associated with saturation magnetization near the surface of nanoparticles and Ks related to anisotropy had an impact on the hysteresis loop. The hysteresis loops were calculated for single-domain nanoparticles of MnBi, CoPt, and FePt. These materials have a wide range of values of radius R between the critical radius Rc10 for transition to the superparamagnetic phase and the critical radius Rc20 for transition to a multi-domain structure and also for high and low values of the volume anisotropy K0 which were used for analysis. The results showed that coercivity increased with increasing values of a, which is related to a decreasing interaction between magnetic moments, and thus saturation magnetization at the surface. They also showed that the coercivity increased with increasing values of Ks, which is related to the anisotropy. In contrast, the remanence decreased with increasing values of a and remained constant with increasing values of Ks. In addition, the coercivity and remanence increased with increasing values of the radius R of the single domain region. Furthermore, theoretical results showed that the area enclosed by each hysteresis loop have almost the same value of energy density for different values of a whereas, the area enclosed by each hysteresis loop has an increased value of energy density for increasing values of Ks.
Department or Program
Department of Physics
Year Degree Awarded
Copyright 2018, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.