Field-driven magnetization dynamics of nanoparticles and nanowires
by Jie Lu
xvii, 161 p. : ill. ; 30 cm
This thesis is about micromagnetism in confined magnetic microstructures. The field-driven magnetization dynamics of nanoparticles and nanowires is systematically discussed following a clear thread of thought: from “macrospin” to “microspin”. At the same time, four topics are raised and investigated....[ Read more ]
This thesis is about micromagnetism in confined magnetic microstructures. The field-driven magnetization dynamics of nanoparticles and nanowires is systematically discussed following a clear thread of thought: from “macrospin” to “microspin”. At the same time, four topics are raised and investigated.
First, inspired by the traditional ferromagnetic resonance technique, two strategies for measuring the Gilbert damping coefficient using the magnetic circular dichroism effect are presented and discussed. The investigation is performed within a framework of the linear response of the macrospin in 2-D magnetic films to external time-dependent fields.
The object of the study then turns to Stoner particles, which are single-domain magnetic nanoparticles, that are quasi 0-D systems and still assumed to be macrospins. The field-driven magnetization reversal in multi-axial Stoner particles is investigated and the corresponding Eular equations are presented. The Eular equations provide a unified framework for research of this kind.
After that, the macrospin assumption itself is examined. The study of when and how it fails results in the famous “nucleation problem” in micromagnetism, thus the discussion then moves into the microspin category. The nucleation problem of single-domain cuboid permalloy nanowires, which are quasi 1-D systems, is investigated and a magnetization reversal mode named “domain formation and domain wall propagation” is revealed.
Field-driven magnetic domain wall propagation is an excellent example of microspin behavior, and has been a hot issue in recent spintronic research. The effects of transverse magnetic anisotropies on field-driven transverse wall propagation in narrow magnetic nanowires are systematically investigated. These results should not only deepen the understanding of the domain wall dynamics in magnetic nanowires, but also offer inspiration for further developments of ultrafast nano-devices with higher integration levels.