Fundamental Magnetic Interactions in Patterned Nanostructures: Simulation, Fabrication and High-Resolution Microscopy
Through the use of complimentary
multi-technique experimental approaches, investigations of fundamental magnetic interactions, such as
magnetostatic, direct exchange, and indirect exchange, in nanomagnetic
structures perturbed by static and high frequency excitation, are presented.
Suggestions of using
dipolar coupled single domain patterned nanomagnets for applications such as
logic, has demonstrated the potential for low-power room temperature operation.
The fundamental evolution of reaching desired states can be described as an
energy minimization process, where elements exhibit preferential magnetization axes due to engineered shape anisotropies, and local energy minima are reached
utilizing external stimuli and strong magnetostatic interactions. Magnetic
Force Microscopy (MFM) was implemented in conjunction with NIST’s micromagnetic
framework OOMMF, in order to detail the energies associated with different
local ground states of coupled nanomangets. The kink energy and magnetic
frustrations in ferromagnetic and anti-ferromagnetic ordered elements in
various directional applied fields will also be discussed.
Dipolar interactions produce
long range force fields but stronger yet are the quantum mechanical short range
exchange interactions of neighboring spins. The competing energies of exchange
interactions in domain walls and magnetic flux due to surface
charges at boundaries can lead to interesting topological charges in room
temperature nanomagnetic systems. In a properly engineered nanodisk, magnetic
vortices appear, with two degrees of freedom (chirality and polarity), four
degenerate states, and exhibit radial symmetry at equilibrium. Utilizing
ferromagnetic resonance, transmission electron microscopy, and x-ray
transmission microscopy, details of competing direct exchange, demagnetization,
indirect exchange energies in magnetic vortex systems are investigated through
the observation of core deformation in static fields. The use of high frequency
field excitations applied in-situ in TEM to dual vortex core indirect exchange
coupled nanodisk heterostructues and the frequency response probed through the time
averaged orbital amplitude are also presented.
