Micromagnetic modelling and magnetic force microscopy of supermagnetism in patterned nanomagnetic arrays
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Advanced magnetic materials have played an important role in, and continue to pavethe way for, innovative technological advancements. Modern day computers, sensors,and biomedicine would not be possible without the use of such materials. Assembliesof magnetic metamaterials, comprised of a complex microscopic structure, presents anew and promising opportunity to specifically tailor nearly all magnetic properties of amaterial. This thesis presents an in-depth, multipronged attempt at understanding andcreating specific instances of such magnetic materials with emergent ensemble properties. Micromagnetic modeling of stable (and ground) states of such structures have beencarried out. The simulation results are used to predict and verify the observation ofphysical instances of corresponding structures. Emergent superferromagnetic and super-antiferromagnetic behavior was found for structures of different lattice geometries, intwo-dimensional, patterned permalloy thin film. Of note is the long-range order of thesuperferromagnetic states and the indication that certain structures can be coerced intoboth superferromagnetic and superantiferromagnetic metastable states. Physical structures of ordered nanomagnets were designed and later fabricated atNTNU NanoLab s cleanroom facilities. The samples were inspected through the use ofmagnetic force microscopy at cryogenic temperatures and subjected to varying appliedmagnetic fields in order to classify the structures behavior. A stable, physical, super-ferromagnetic state was clearly observed and classified for triangular lattice geometries.Similar states were found for square lattice geometries, in addition to indication of thepresence of a switchable superantiferromagnetic state. Additionally, several auxiliaryresults were obtained and auspicious suggestions for further work is provided.