Enamel covers teeth, is the hardest tissue in the vertebrate body and has a complex multiscale structure from nanometres to millimetres1. The structure comprises thin, long hydroxyapatite (Ca5(PO4)3OH) nanocrystals2, 50-70 nm wide, many micrometres long, parallel and bundled into approximately 5-µm-wide rods. The rods undulate and cross into a microscale 'decussation pattern' that toughens enamel by deflecting cracks3,4. However, the crystallographic orientation of enamel nanocrystals is poorly understood. Here we show that the misorientation angle of adjacent nanocrystals varies markedly across 12 primate teeth spanning 9 species, 17.8 million years of evolution and diverse diets. Using a method called Polarization Enabled Large Input of Crystal Angles at the Nanoscale (PELICAN)5, we compare nanocrystals in the same (pre)molar locations and show that misorientation increases with food hardness in extant and fossil non-human apes and monkeys. We compare misorientation across three major dietary shifts in human evolution: the transition to meat-eating about 2.0-1.5 million years before present6,7, to agriculture (about 12,000 years before present)8,9, and the Industrial Revolution (about 250 years before present)10. We show that over the past 1.6 million years, in the human lineage misorientation increased with time, especially when meat and stone-ground grains were introduced into human diets, but not with the Industrial Revolution. Thus, besides macro-changes, teeth adapted to dietary change at the nanoscale and crystallographically. This observation suggests that misorientation may contribute to enamel's resilience; thus, bioinspired materials may consider small misorientation angles for added resilience.

Atomically flat surfaces of van der Waals (vdW) materials pave an avenue for addressing a long-standing fundamental issue of how a compensated antiferromagnet (AFM) surface frustrates a ferromagnetic (FM) overlayer in FM/AFM heterostructures. We investigate Fe5GeTe2/NiPS3 vdW heterostructures by characterizing AFM and FM spins separately. We find that in-plane zig-zag AFM NiPS3 develops three equivalent AFM domains, which are robust against external magnetic field and magnetic coupling with Fe5GeTe2. Moreover, evidence is provided of in-plane-AFM-induced perpendicular magnetic anisotropy (PMA) in adjacent Fe5GeTe2, and an unconventional out-of-plane surface spin canting state with the Fe5GeTe2 spins spatially turn from out-of-plane direction near the interface to in-plane direction away from the interface in Fe5GeTe2/NiPS3. The out-of-plane surface spin canting is a unique property of spin frustration in vdW magnetic heterostructures.

Antiferromagnetic (AFM) spintronics offer several benefits compared to their ferromagnetic (FM) counterparts, such as high storage capacity and faster processing speed, however, difficulties in manipulating and detecting the AFM moments impede their implementation. Spin-flop coupling, the interfacial perpendicular coupling between FM and AFM moments, can be utilized to control the orientation of AFM moments with the application of moderate magnetic fields on the scale of tenths of a Tesla. In this work, epitaxial bilayers of AFM $\mathrm{L}{\mathrm{a}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Fe}{\mathrm{O}}_{3}$ (LSFO)/FM $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) with fixed LSMO thickness ($\ensuremath{\sim}85$ u.c.) and LSFO thicknesses varying from 10 to 50 u.c. were investigated to determine the effect of Sr doping and $\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Fe}{\mathrm{O}}_{3}$ magnetocrystalline anisotropy on the strength of spin-flop coupling. X-ray magnetic linear dichroism demonstrated that the spin-flop coupling strength decreased with increasing LSFO layer thickness, persisting at a thickness of 50 u.c. ($\ensuremath{\sim}20$ nm). Furthermore, photoemission electron microscopy revealed a domain-by-domain correlation between the FM and AFM domains consistent with the perpendicular orientation dictated by spin-flop coupling. These results demonstrate that LSFO/LSMO bilayers have the potential to serve as a model materials system for AFM spin transport measurements.

Applying voltage to metal-insulator transition (MIT) materials allows electrical actuation of the local electronic phase state. In MIT systems that have the electronic order coupled with the magnetic order, voltage switching of the electronic phase state can also enable the electrical manipulation of magnetic properties. In this work, we utilized x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) to investigate the control of magnetic domain configurations in ferromagnetic MIT electrical switches. For applied voltages above a threshold value, the XMCD-PEEM images show that the magnetic domains separate into two distinct regions: one with a high contrast (white/black), indicating well-defined micrometer-scale magnetic domains with a component of their magnetization aligned parallel/antiparallel to the x-ray helicity, and the other with different shades of intermediate contrast (gray). Significant changes in magnetic domain configurations upon voltage biasing were only observed in these gray regions. Furthermore, the voltage-induced magnetic domain separation was found to be bias polarity-dependent, with the gray regions expanding from the opposite sample edge when the applied voltage polarity was reversed. This polarity-dependent electrical control of magnetic domain configurations during the MIT switching opens alternative opportunities in memory applications for magnetic MIT switching materials.

Antiferromagnetic (AFM) spintronics offer several benefits compared to their ferromagnetic (FM) counterparts, such as high storage capacity and faster processing speed, however, difficulties in manipulating and detecting the AFM moments impede their implementation. Spin-flop coupling, the interfacial perpendicular coupling between FM and AFM moments, can be utilized to control the orientation of AFM moments with the application of moderate magnetic fields on the scale of tenths of a Tesla. In this work, epitaxial bilayers of AFM La0.5Sr0.5FeO3 (LSFO)/FM La0.7Sr0.3MnO3 (LSMO) with fixed LSMO thickness (similar to 85 u.c.) and LSFO thicknesses varying from 10 to 50 u.c. were investigated to determine the effect of Sr doping and La1-xSrxFeO3 magnetocrystalline anisotropy on the strength of spin-flop coupling. X-ray magnetic linear dichroism demonstrated that the spin-flop coupling strength decreased with increasing LSFO layer thickness, persisting at a thickness of 50 u.c. (similar to 20 nm). Furthermore, photoemission electron microscopy revealed a domain-by-domain correlation between the FM and AFM domains consistent with the perpendicular orientation dictated by spin-flop coupling. These results demonstrate that LSFO/LSMO bilayers have the potential to serve as a model materials system for AFM spin transport measurements.

Stabilization of topological spin textures in layered magnets has the potential to drive the development of advanced low-dimensional spintronics devices. However, achieving reliable and flexible manipulation of the topological spin textures beyond skyrmion in a two-dimensional magnet system remains challenging. Here, we demonstrate the introduction of magnetic iron atoms between the van der Waals gap of a layered magnet, Fe3GaTe2, to modify local anisotropic magnetic interactions. Consequently, we present direct observations of the order-disorder skyrmion lattices transition. In addition, non-trivial topological solitons, such as skyrmioniums and skyrmion bags, are realized at room temperature. Our work highlights the influence of random spin control of non-trivial topological spin textures. Stabilizing non-trivial magnetic spin textures at room temperature remains challenging. Here, the authors propose introducing magnetic atoms into the van der Waals gap of 2D magnets Fe3GaTe2 to stabilize the magnetic spin textures beyond skyrmion.

X-ray beams with orbital angular momentum (OAM) are a promising tool for x-ray characterization techniques. Beams with OAM have a helicity--an azimuthally varying phase--which leads to a gradient of the light field. New material properties can be probed by utilizing the helicity of an OAM beam. Here, we demonstrate a novel dichroic effect in resonant diffraction from an artificial antiferromagnet with a topological defect. We found that the scattered OAM beam has circular dichroism at the antiferromagnetic Bragg peak whose sign is coupled to its helicity, which reveals the real-space configuration of the antiferromagnetic ground state. Thermal cycling of the artificial antiferromagnet can change the ground state, as indicated by reversal of the sign of circular dichroism. This result is one of the first demonstrations of a soft x-ray spectroscopy characterization technique utilizing the OAM of x-rays. This helicity-dependent circular dichroism exemplifies the potential to utilize OAM beams to probe matter in a way that is inaccessible using currently available x-ray techniques.

Biominerals are organic–mineral composites formed by living organisms. They are the hardest and toughest tissues in those organisms, are often polycrystalline, and their mesostructure (which includes nano‐ and microscale crystallite size, shape, arrangement, and orientation) can vary dramatically. Marine biominerals may be aragonite, vaterite, or calcite, all calcium carbonate (CaCO 3 ) polymorphs, differing in crystal structure. Unexpectedly, diverse CaCO 3 biominerals such as coral skeletons and nacre share a similar characteristic: Adjacent crystals are slightly misoriented. This observation is documented quantitatively at the micro‐ and nanoscales, using polarization‐dependent imaging contrast mapping (PIC mapping), and the slight misorientations are consistently between 1° and 40°. Nanoindentation shows that both polycrystalline biominerals and abiotic synthetic spherulites are tougher than single‐crystalline geologic aragonite. Molecular dynamics (MD) simulations of bicrystals at the molecular scale reveal that aragonite, vaterite, and calcite exhibit toughness maxima when the bicrystals are misoriented by 10°, 20°, and 30°, respectively, demonstrating that slight misorientation alone can increase fracture toughness. Slight‐misorientation‐toughening can be harnessed for synthesis of bioinspired materials that only require one material, are not limited to specific top‐down architecture, and are easily achieved by self‐assembly of organic molecules (e.g., aspirin, chocolate), polymers, metals, and ceramics well beyond biominerals.

Ever since its introduction by Ludwig Boltzmann, the ergodic hypothesis became a cornerstone analytical concept of equilibrium thermodynamics and complex dynamic processes. Examples of its relevance range from modeling decision-making processes in brain science to economic predictions. In condensed matter physics, ergodicity remains a concept largely investigated via theoretical and computational models. Here, we demonstrate the direct real-space observation of ergodicity transitions in a vertex-frustrated artificial spin ice. Using synchrotron-based photoemission electron microscopy we record thermally-driven moment fluctuations as a function of temperature, allowing us to directly observe transitions between ergodicity-breaking dynamics to system freezing, standing in contrast to simple trends observed for the temperature-dependent vertex populations, all while the entropy features arise as a function of temperature. These results highlight how a geometrically frustrated system, with thermodynamics strictly adhering to local ice-rule constraints, runs back-and-forth through periods of ergodicity-breaking dynamics. Ergodicity breaking and the emergence of memory is important for emergent computation, particularly in physical reservoir computing. Our work serves as further evidence of how fundamental laws of thermodynamics can be experimentally explored via real-space imaging.

Coordinate files of every nanomagnet's position and orientation recorded at each moment in time and several temperatures.

Time-resolved momentum microscopy provides insight into the ultrafast interplay between structural and electronic dynamics. Here we extend orbital tomography into the time domain in combination with time-resolved momentum microscopy at a free-electron laser (FEL) to follow transient photoelectron momentum maps of excited states of a bilayer pentacene film on Ag(110). We use optical pump and FEL probe pulses by keeping FEL source conditions to minimize space charge effects and radiation damage. From the momentum microscopy signal, we obtain time-dependent momentum maps of the excited-state dynamics of both pentacene layers separately. In a combined experimental and theoretical study, we interpret the observed signal for the bottom layer as resulting from the charge redistribution between the molecule and the substrate induced by excitation. We identify that the dynamics of the top pentacene layer resembles excited-state molecular dynamics.

Abstract The hardest and toughest tissues formed by living organisms are organic-mineral composites termed biominerals 1,2. When they are crystalline, their mesostructure includes the nano- and micro-scale crystallite size, shape, arrangement, and orientation. Mesostructures vary enormously across marine CaCO3 biominerals (aragonite, vaterite, calcite) because they result from divergent evolution: biominerals were formed long after organisms diverged from one another 3,4. Despite such diversity, CaCO3 marine biominerals share a convergent character: adjacent crystals are similarly oriented 5-32. The reason for such convergence is unclear. Here, we show with quantitative, precise measurements at the nanoscale that the slight misorientation is consistently between 1°-40° in diverse biominerals. Can this slight misorientation confer a desirable materials property and therefore an evolutionary advantage to the forming organisms? We test and confirm this hypothesis with nanoindentation in diverse biominerals, geologic aragonite, and in abiotic, slightly misoriented, synthetic spherulites. Molecular dynamics (MD) simulations of bicrystals reveal that aragonite, vaterite, calcite, exhibit toughness peaks when they are misoriented by 10°, 20°, 30°, respectively, demonstrating that slight misorientation alone increases crack deflection and therefore fracture toughness. Slight misorientation, along with other previously known and co-existing toughening mechanisms, was selected repeatedly and convergently, during the course of evolution, to postpone fracture and thus provide organisms with competitive advantage. We anticipate slight misorientation-toughening to be a starting point for more sophisticated materials synthesis and additive manufacturing in many fields. Compared to previously known toughening mechanisms, in fact, the advantages of slight misorientation are that it can and does occur in synthetic materials, it requires one material only and no specific top-down architecture, it is easily achieved by self-assembly of organic molecules (e.g. aspirin, chocolate), polymers, metals, and ceramics 29 well beyond biominerals.

Artificial spin ices (ASI) have been widely investigated as magnetic metamaterials with exotic properties governed by their geometries. In parallel, interest in x-ray photon orbital angular momentum (OAM) has been rapidly growing. Here we show that a square ASI with a patterned topological defect, a double edge dislocation, imparts OAM to scattered x rays. Unlike single dislocations, a double dislocation does not introduce magnetic frustration, and the ASI equilibrates to its antiferromagnetic (AFM) ground state. The topological charge of the defect differs with respect to the structural and magnetic order; thus, x-ray diffraction from the ASI produces photons with even and odd OAM quantum numbers at the structural and AFM Bragg conditions, respectively. The magnetic transitions of the ASI allow the AFM OAM beams to be switched on and off by modest variations of temperature and applied magnetic field. These results demonstrate ASIs can serve as metasurfaces for reconfigurable x-ray optics that could enable selective probes of electronic and magnetic properties.

The Advanced Light Source (ALS), a U.S. Department of Energy (DOE) Office of Science user facility at Lawrence Berkeley National Laboratory (LBNL), typically hosts about 100 users per week from around the world. They use the intense light beams from ALS insertion devices and bending magnets to conduct basic, applied, and industrial research in energy science, earth and environmental science, materials science, biology, medicine, chemistry, and physics. The ALS serves a diverse national and international community of researchers who often need to travel to the ALS to use beamlines and endstations for scientific experiments. Science at the ALS came to a standstill in March 2020. The accelerating COVID-19 pandemic prompted a “shelter-in-place” declaration by six San Francisco Bay Area counties. This caused the ALS accelerator to be shut down on March 16, at which point all beamline operations stopped (Fig. 1). Short outages due to equipment malfunctions are not uncommon when operating large and complex accelerators, and the increased threat of wildfires—with the resulting power shutdowns—had caused several interruptions in user operations during the previous year. But the pandemic caused probably the largest loss of scientific productivity due to an unexpected outage since the ALS began operations, more than 25 years ago. Not only did ALS users have to leave the site quickly and with little warning, but all ALS technical, scientific, and operations staff were sent home as well to stop the exponentially growing spread of the SARS-CoV-2 virus and prevent transmission through work-related activities. Light sources are a key resource in the fight against SARS-CoV-2 because understanding the interaction of the virus with possible therapeutics and with cells in our bodies requires the bright X-rays that storage rings produce. Thus, ALS operations staff quickly began to develop a new plan for operating the facility. Normally, user operations require a fully staffed control room, a cohort of technical staff on site to respond to calls for assistance and to troubleshoot equipment, and legions of beamline staff who operate endstations and assist users in their work. The challenge was to start the accelerator and then sustain its safe operation with a minimum number of people on site, while maintaining the new social distancing requirements. After two intense weeks of planning, the new procedures were in place, and LBNL gave permission to restart facility operations on March 31 for COVID-19-related research at a few beamlines. The accelerator was initially operated by a minimum number of personnel on site, with system experts on call when needed. Most ALS staff were asked to telework, and many have continued teleworking since March 2020 (Fig. 2). As health authorities gained some level of control over the spread of the virus through increased testing, the ALS was able to bring additional staff on site to support three shifts of accelerator operators per day for 5 days per week. New safety protocols and training of

Transition metal oxide thin films and heterostructures are promising platforms to achieve full control of the antiferromagnetic (AFM) domain structure in patterned features as needed for AFM spintronic devices. In this work, soft x-ray photoemission electron microscopy was utilized to image AFM domains in micromagnets patterned into La0.7Sr0.3FeO3 (LSFO) thin films and La0.7Sr0.3MnO3 (LSMO)/LSFO superlattices. A delicate balance exists between magnetocrystalline anisotropy, shape anisotropy, and exchange interactions such that the AFM domain structure can be controlled using parameters such as LSFO and LSMO layer thickness, micromagnet shape, and temperature. In LSFO thin films, shape anisotropy gains importance only in micromagnets where at least one extended edge is aligned parallel to an AFM easy axis. In contrast, in the limit of ultrathin LSFO layers in the LSMO/LSFO superlattice, shape anisotropy effects dominate such that the AFM spin axes at micromagnet edges can be aligned along any in-plane crystallographic direction.

Among many efforts in the research of van der Waals (vdW) magnetic materials, increasing the Curie temperature above room temperature has been at the center of research in developing spintronics technology using vdW materials. Here an effective and reliable method of increasing the Curie temperature of ferromagnetic Fe3GeTe2 vdW materials by Ga implantation is reported. It is found that implanting Ga into Fe3GeTe2 by the amount of 10(-3) Ga angstrom(-3) could greatly enhance the Fe3GeTe2 Curie temperature by almost 100%. Spatially resolved microdiffraction and element-resolved X-ray absorption spectroscopy show little changes in the Fe3GeTe2 crystal structure and Fe valence state. In addition, the Ga implantation changes the Fe3GeTe2 magnetization from out-of-plane direction at low temperature to in-plane direction at high temperature. The result opens a new opportunity for tailoring the magnetic properties of vdW materials beyond room temperature.