arXiv subjects

M. E. Henderson

Publications and source records attributed to M. E. Henderson.

7 recordsLinked to original sources

arXiv2024

Quantum Advancements in Neutron Scattering Reshape Spintronic Devices

Topological magnetism has sparked an unprecedented age in quantum technologies. Marked by twisted spin structures with exotic dynamical modes, topological magnets have motivated a new generation of spintronic devices which transcend the limits of conventional semiconductor-based electronics. While existing material probes have biased studies and device conceptualizations for thin samples in two dimensions, advancements in three-dimensional probing techniques using beams of neutrons, are transforming our understanding of topological and emergent physics to reimagine spintronic devices. Here, we review recent neutron scattering breakthroughs which harness quantum degrees of freedom to enable three-dimensional topological investigations of quantum materials. We discuss applications of structured and tomographic neutron scattering techniques to topological magnets, with particular emphasis on magnetic skyrmion systems and their inspired three-dimensional logic device infrastructures through novel multi-bit encoding and control schemes. SANS-based dynamic visualizations and coherent manipulations of three-dimensional topological qubits are proposed using electric field controls of depth-dependant helicities and spin-orbit tuning of the neutron beam. Together, these investigations uncover a new world of three-dimensional topological physics which enhances spintronic devices through a novel set of structures, dynamics, and controls, unique to three-dimensional systems.

cond-mat.mtrl-sci↗

arXiv2023

Phase and contrast moiré signatures in two-dimensional cone beam interferometry

Neutron interferometry has played a distinctive role in fundamental science and characterization of materials. Moiré neutron interferometers are candidate next-generation instruments: they offer microscopy-like magnification of the signal, enabling direct camera recording of interference patterns across the full neutron wavelength spectrum. Here we demonstrate the extension of phase-grating moiré interferometry to two-dimensional geometries. Our fork-dislocation phase gratings reveal phase singularities in the moiré pattern, and we explore orthogonal moiré patterns with two-dimensional phase-gratings. Our measurements of phase topologies and gravitationally induced phase shifts are in good agreement with theory. These techniques can be implemented in existing neutron instruments to advance interferometric analyses of emerging materials and precision measurements of fundamental constants.

physics.app-ph↗

arXiv2023

Cone beam neutron interferometry: from modeling to applications

Phase-grating moire interferometers (PGMIs) have emerged as promising candidates for the next generation of neutron interferometry, enabling the use of a polychromatic beam and manifesting interference patterns that can be directly imaged by existing neutron cameras. However, the modeling of the various PGMI configurations is limited to cumbersome numerical calculations and backward propagation models which often do not enable one to explore the setup parameters. Here we generalize the Fresnel scaling theorem to introduce a k-space model for PGMI setups illuminated by a cone beam, thus enabling an intuitive forward propagation model for a wide range of parameters. The interference manifested by a PGMI is shown to be a special case of the Talbot effect, and the optimal fringe visibility is shown to occur at the moire location of the Talbot distances. We derive analytical expressions for the contrast and the propagating intensity profiles in various conditions, and analyze the behaviour of the dark-field imaging signal when considering sample characterization. The model's predictions are compared to experimental measurements and good agreement is found between them. Lastly, we propose and experimentally verify a method to recover contrast at typically inaccessible PGMI autocorrelation lengths. The presented work provides a toolbox for analyzing and understanding existing PGMI setups and their future applications, for example extensions to two-dimensional PGMIs and characterization of samples with non-trivial structures.

physics.app-ph↗

arXiv2022

Skyrmion Alignment and Pinning Effects in a Disordered Multi-Phase Skyrmion Material Co8Zn8Mn4

Underlying disorder in skyrmion materials may both inhibit and facilitate skyrmion reorientations and changes in topology. The identification of these disorder-induced topologically active regimes is critical to realizing robust skyrmion spintronic implementations, yet few studies exist for disordered bulk samples. Here, we employ small-angle neutron scattering (SANS) and micromagnetic simulations to examine the influence of skyrmion order on skyrmion lattice formation, transition, and reorientation dynamics across the phase space of a disordered polycrystalline Co$_{8}$Zn$_{8}$Mn$_{4}$ bulk sample. Our measurements reveal a new disordered-to-ordered skyrmion square lattice transition pathway characterized by the novel promotion of four-fold order in SANS and accompanied by a change in topology of the system, reinforced through micromagnetic simulations. Pinning responses are observed to dominate skyrmion dynamics in the metastable triangular lattice phase, enhancing skyrmion stabilization through a remarkable and previously undetected skyrmion memory effect which reproduces previous ordering processes and persists in zero field. These results uncover the cooperative interplay of anisotropy and disorder in skyrmion formation and restructuring dynamics, establishing new tunable pathways for skyrmion manipulation.

cond-mat.mtrl-sci↗

arXiv2022

Three-Dimensional Neutron Far-Field Tomography of a Bulk Skyrmion Lattice

Skyrmions are topologically-protected spin textures thought to nucleate and annihilate on points of vanishing magnetization, called Bloch points. However, owing to a lack of bulk techniques, experimental visualizations of skyrmion lattices and their stabilization through defects in three-dimensions remain elusive. Here, we present a tomographic algorithm applied to a Co$_8$Zn$_8$Mn$_4$ skyrmion lattice host, processing multi-projection small angle neutron scattering measurements to generate mean scattering feature reconstructions (MSFR) of the bulk spin textures. Digital phantoms validated the algorithm; reconstructions of the sample show a disordered skyrmion lattice with a topological saturation of 63~\%, exhibiting three-dimensional topological transitions through two different emergent (anti)monopole defect pathways with densities of 147~$μ$m$^{-3}$ and 21~$μ\mathrm{m}^{-3}$ for branching and segmentation events, respectively. Our techniques produce experimentally-informed visualizations of bulk skyrmion lattice structures and defects, enabling future bulk studies over a wide variety of sample shapes and chemistries, magnetic phases, and external parameters.

cond-mat.mtrl-sci↗

arXiv2022

Experimental Realization of Neutron Helical Waves

Methods of preparation and analysis of structured waves of light, electrons, and atoms have been advancing rapidly. Despite the proven power of neutrons for material characterization and studies of fundamental physics, neutron science has not been able to fully integrate such techniques due to small transverse coherence lengths, the relatively poor resolution of spatial detectors, and low fluence rates. Here, we demonstrate methods that are practical with the existing technologies, and show the experimental achievement of neutron helical wavefronts that carry well-defined orbital angular momentum (OAM) values. We discuss possible applications and extensions to spin-orbit correlations and material characterization techniques.

physics.app-ph↗

arXiv2020

Characterization of a Disordered Above Room Temperature Skyrmion Material Co8Zn8Mn4

Topologically non trivial spin textures host great promise for future spintronic applications. Skyrmions in particular are of burgeoning interest owing to their nanometric size, topological protection, and high mobility via ultra-low current densities. It has been previously reported through magnetic susceptibility, microscopy, and scattering techniques that Co$_{8}$Zn$_{8}$Mn$_{4}$ forms an above room temperature triangular skyrmion lattice. Here we report the synthesis procedure and characterization of a polycrystalline Co$_{8}$Zn$_{8}$Mn$_{4}$ bulk sample. We employ powder x-ray diffraction, backscatter Laue diffraction, and neutron diffraction as characterization tools of the crystallinity of the samples, while magnetic susceptibility and Small Angle Neutron Scattering (SANS) measurements are performed to study the skyrmion phase. Magnetic susceptibility measurements show a dip anomaly in the magnetization curves which persists over a range of approximately 305 K- 315 K. SANS measurements reveal a rotationally disordered polydomain skymrion lattice. Applying a recently developed symmetry-breaking magnetic field sequence, we were able to orient and order the previously jammed state to yield the prototypical hexagonal diffraction patterns, with secondary diffraction rings.

cond-mat.mtrl-sci↗