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DTSTART;TZID=America/Toronto:20231026T140000
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URL:https://uwaterloo.ca/institute-for-quantum-computing/events/melissa-hen
 derson-phd-thesis-defence
LOCATION:PHY - Physics 352 200 University Avenue West Waterloo ON N2L 3G1 C
 anada
SUMMARY:Melissa Henderson PhD Thesis Defence
CLASS:PUBLIC
DESCRIPTION:NEUTRON SCATTERING INVESTIGATIONS OF THREE-DIMENSIONAL TOPOLOGI
 CAL\nSTATES\n\nPhysics\, 200 University Ave West\, Room PHY 352\nWaterloo\
 , ON\, CA N2L 3G1\n\nMagnetic skyrmions represent a unique class of topolo
 gical magnet\ncharacterized by nanometric swirling spin-textures which pos
 sess a\nnon-trivial Berry curvature. The combination of their topological\
 nstability\, unique transport properties\, and emergent dynamics has made\
 nskyrmions the forerunner for novel spintronic high-density memory and\nul
 tra-low power logic device applications. In this thesis\, we explore\nthe 
 development and application of various neutron scattering\ntomography and 
 structured neutron beam techniques for\nthree-dimensional investigations o
 f bulk magnetic topological\nmaterials and their defect-mediated dynamical
  phenomena.\nCharacterization of the disordered multi-phase bulk skyrmion 
 material\,\nCo8Zn8Mn4\, was performed through detailed SANS measurements o
 ver the\nentire temperature-magnetic field phase diagram of the material a
 s a\nfunction of a dynamic skyrmion ordering sequence. 2D SANS images in\n
 combination with micromagnetic simulations reveal a novel\ndisordered-to-o
 rdered skyrmion square lattice transition pathway which\nrepresents a new 
 type of non-charge conserving topological transition.\nIn the metastable s
 kyrmion triangular lattice phase\, dynamical\nfield-dependent skyrmion res
 ponses showed an exotic memory phase in\nspite of hysteresis protocols inv
 olving field-induced saturation into\nthe ferromagnetic phase. Three-dimen
 sional examinations of skyrmion\nstabilization mechanisms and their dynami
 cal defect pathways were\nexplored using a novel SANS tomography technique
  which processes\nmulti-projection neutron scattering images as its input.
  Application\nof the technique to the ordered thermal equilibrium skyrmion
 \ntriangular lattice phase yielded the first three-dimensional\nvisualizat
 ions of a bulk skyrmion lattice. The reconstructions\nunveiled a host of e
 xotic skyrmion features\, such as branching\,\nsegmented\, twisting\, and 
 filament structures\, mediated by\nthree-dimensional topological transitio
 ns through two different\nemergent monopole (MP)-antimonopole (AMP) defect
  pathways. Finally\,\nthe direct identification and determination of topol
 ogical features\nand defects in bulk micromagnetic materials\, without a p
 riori\nknowledge of the sample\, was explored using holographic approaches
  for\nthe generation of neutron helical waves. Linear neutron waves in a\n
 conventional SANS setup were input on microfabricated gratings which\ncons
 ist of arrays of various q-fold fork-dislocation phase-gratings\nwith nano
 metric spatial dimensions. Far-field scattering images\nexhibited doughnut
  intensity profiles centered on the first\ndiffraction orders\, thereby de
 monstrating the tunable generation of\ntopological neutron states for phas
 e- and topology-matched studies of\nquantum materials. The amalgamation of
  these works demonstrates the\ndevelopment and application of novel tools 
 for direct investigations\nof bulk topological magnetic materials\, while 
 uncovering a diverse\ncollection of skyrmion energetics\, disorder-depende
 nt dynamics\, and\nthree-dimensional topological transition defect pathway
 s. These\nmethods and results open the door to a new generation of neutron
 \nscattering techniques for the probing of exotic topological\ninteraction
 s and the complete standalone characterization of quantum\nmaterials and t
 heir topological phenomena.
DTSTAMP:20260420T051026Z
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