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Elizabeth Blackburn

Publications and source records attributed to Elizabeth Blackburn.

8 recordsLinked to original sources
arXiv2026

From Bloch to N\'eel: Anisotropy-dependent Domain-Wall Character in FePd Thin Films

We report an experimental investigation of the depth-dependent domain wall formation in L1$_0$-FePd thin films with high perpendicular magnetic anisotropy. Using circular dichroism X-ray resonant magnetic scattering (CD-XRMS) as a function of the incident X-ray angle, we explore the depth evolution of chiral spin textures in two samples with different strengths of magnetocrystalline anisotropy. Combined with CD-STXM, CD-ptychography, and macroscopic characterization of the structural order, magnetic properties, and surface morphology, we relate these observations to differences in the long-range order of the L1$_0$ phase of FePd. One FePd thin film with very high magnetocrystalline anisotropy, characterized by $Q_{PMA}=1.8$, exhibits an unexpectedly large N\'eel contribution. Angular-dependent CD-XRMS directly reveals a smooth transition from a hybrid Bloch-N\'eel chirality within the upper FePd layer towards a purely N\'eel-type structure at the lower FePd interface. In the second FePd sample, despite a still relatively large $Q_{PMA}=1.45$, the domain walls were found to be purely N\'eel type. These results indicate a crucial role of the long-range structural order in determining the formation of the magnetic structure.

cond-mat.mtrl-sci↗
arXiv2026

Disorder-induced chirality in superconductor-ferromagnet heterostructures revealed by neutron scattering and multiscale modeling

Chirality in superconductor-ferromagnet hybrids strongly influences phenomena such as the observable signatures of long-range triplet superconductivity, but its microscopic origin in nominally centrosymmetric ferromagnets is still unclear. Here, we combine structural characterization, polarization-analyzed grazing-incidence small-angle neutron scattering (PA-GISANS), first-principles calculations, and deep-learning-assisted multiscale modeling to study FePd and Nb/FePd heterostructures. Experimentally, we observe partial L1$_0$ order, atomic intermixing, anti-phase boundaries, and a depth-dependent defect gradient across the FePd layer, together with a finite net magnetic chirality at room temperature. The GISANS asymmetry indicates that the main chiral contribution lies in-plane, with an additional out-of-plane component associated with depth-dependent magnetic inhomogeneity. Theoretically, we show that chemical disorder in FePd, especially when combined with a compositional gradient, produces finite Dzyaloshinskii-Moriya interactions and stabilizes chiral finite-$\mathbf{q}$ magnetic modulations with mixed Bloch-N\'eel character. In the mesoscopic model, the resulting in-plane modulation length approaches the experimentally observed range. These results identify disorder and compositional gradients as intrinsic microscopic sources of net chirality in FePd-based films, showing that the observed chirality does not arise only from interface effects.

cond-mat.mtrl-sci↗
arXiv2024

3D Heisenberg universality in the Van der Waals antiferromagnet NiPS$_3$

Van der Waals (vdW) magnetic materials are comprised of layers of atomically thin sheets, making them ideal platforms for studying magnetism at the two-dimensional (2D) limit. These materials are at the center of a host of novel types of experiments, however, there are notably few pathways to directly probe their magnetic structure. We report the magnetic order within a single crystal of NiPS$_3$ and show it can be accessed with resonant elastic X-ray diffraction along the edge of the vdW planes in a carefully grown crystal by detecting structurally forbidden resonant magnetic X-ray scattering. We find the magnetic order parameter has a critical exponent of $β\sim0.36$, indicating that the magnetism of these vdW crystals is more adequately characterized by the three-dimensional (3D) Heisenberg universality class. We verify these findings with first-principle density functional theory, Monte-Carlo simulations, and density matrix renormalization group calculations.

cond-mat.str-el↗
arXiv2023

On Ultrafast X-ray Methods for Magnetism

With the introduction of x-ray free electron laser sources around the world, new scientific approaches for visualizing matter at fundamental length and time-scales have become possible. As it relates to magnetism and "magnetic-type" systems, advanced methods are being developed for studying ultrafast magnetic responses on the time-scales at which they occur. We describe three capabilities which have the potential to seed new directions in this area and present original results from each: pump-probe x-ray scattering with low energy excitation, x-ray photon fluctuation spectroscopy, and ultrafast diffuse x-ray scattering. By combining these experimental techniques with advanced modeling together with machine learning, we describe how the combination of these domains allows for a new understanding in the field of magnetism. Finally, we give an outlook for future areas of investigation and the newly developed instruments which will take us there.

cond-mat.mtrl-sci↗
arXiv2022

Symmetry protected 1D chains in mixed-valence iron oxides

During the last decade of high-pressure research a whole new series of iron oxides was discovered, like Fe$_4$O$_5$, Fe$_5$O$_6$, Fe$_7$O$_9$ etc., featuring closely related structures with arrays of one-dimensional (1D) chains of trigonal prisms embedded between slabs of octahedra. Here, we develop a unified approach to the series based on a specific crystallographic generation mechanism which predicts the structures of these oxides and naturally classifies them in terms of the slab cycle. When including magnetic interactions, we show that the 1D chains have a symmetry protection against magnetic perturbations from the iron ions in the slabs, and that the slab size determines the type of magnetic order, which is either ferromagnetic or antiferromagnetic. Dynamical mean-field theory calculations reveal the orbitally selective Mott state of the Fe ions and tendency of conductivity to low-dimensional behavior with particular enhancement along the 1D chains. Across the series, the decoupling of the chains increases, and so with the inherent charge ordering of the slabs, these structures have the potential to allow experimental realization of the model system of coupled 1D wires. We point out the possibility to stabilize these compounds in the thin-film form that, together with a wide range of possible ionic substitutions and fact that these compounds are recoverable at ambient pressure, makes them a very promising platform to engineer physical systems with interesting magnetotransport phenomena, as corroborated by the recent discovery of quantum Hall effect in ZrTe$_5$.

cond-mat.str-el↗
arXiv2020

Unconventional superconductivity in the nickel-chalcogenide superconductor, TlNi$_2$Se$_2$

We present the results of a study of the vortex lattice (VL) of the nickel chalcogenide superconductor TlNi2Se2, using small angle neutron scattering. This superconductor has the same crystal symmetry as the iron arsenide materials. Previous work points to it being a two-gap superconductor, with an unknown pairing mechanism. No structural transitions in the vortex lattice are seen in the phase diagram, arguing against d-wave gap symmetry. Empirical fits of the temperature-dependence of the form factor and penetration depth rule out a simple s-wave model, supporting the presence of nodes in the gap function. The variation of the VL opening angle with field is consistent with earlier reports of of multiple gaps.

cond-mat.supr-con↗
arXiv2011

A 17 T horizontal field cryomagnet with rapid sample change designed for beamline use

We describe a new 17 T cryomagnet for neutron, x-ray or optical experiments with rapid in-situ sample change. Sample temperatures are controllable from < 2 K to 300 K in vacuum. Alternatively a room temperature bore insert can be used for experiments in the field centre under atmospheric conditions. Some advantages of this system include very low background scattering due to the small amount of material in the beam path, rapid cooldown, and fast field ramping. Access is available in a ~10-11 degree cone around the field direction on both sides.

cond-mat.mtrl-sci↗