JILA Science Seminar

Title: Coherent X-ray Interactions with Artificial Spin Ices

Speaker: J. Todd Hastings, Professor of Electrical Engineering and Associate Dean for Research and Graduate Studies at the University of Kentucky

Event: Artificial spin ices (ASI) are arrays of nanomagnets that serve as model systems for collective magnetic behavior as well as platforms for unconventional computing and control of X-ray beams. Here we show how coherent X-ray scattering can probe the magnetic order and dynamics of ASIs and how ASIs can serve as optical metamaterials in the soft X-ray region. An example is the Ni0.8Fe0.2 square ASI whose geometry can be tuned to place a magnetic phase transition near room temperature. This system orders into an antiferromagnetic ground state and exhibits spontaneous nucleation and annihilation of super-domain walls. We show that this dynamic process can be imaged using Bragg coherent diffraction imaging (BCDI) with coherent, resonant soft X-ray illumination[1]. The square ASI can also manipulate the X-ray beam, and the addition of an even-charge topological defect is known to produce X-ray orbital angular momentum at the magnetic Bragg condition. Here we show that magnetic scattering from square ASIs with odd-charge topological defects produces fractional X-ray OAM beams that rotate based on the thermal motion of a super-domain wall[2].

[1] X. M. Chen et al., “Visualization of Single Spin-chain Propagation using Bragg Coherent Diffraction Imaging,” arXiV Oct. 22, 2026, doi: 10.48550/arXiv.2610.31919.
[2] P. D. Montgomery et al., “X-ray Fractional Orbital Angular Momentum from Coherent Magnetic Scattering,” arXiv Jun. 02, 2026, doi: 10.48550/arXiv.2606.03625.