David A Muller

Magnetic van der Waals heterostructures provide a unique platform to study magnetism and spintronics device concepts in the 2D limit. Here, studies of exchange bias from the van der Waals antiferromagnet CrSBr acting on the van der Waals ferromagnet Fe3GeTe2 (FGT) are reported. The orientation of the exchange bias is along the in‐plane easy axis of CrSBr, perpendicular to the out‐of‐plane anisotropy of the FGT, inducing a strongly tilted magnetic configuration in the FGT. Furthermore, the in‐plane exchange bias provides sufficient symmetry breaking to allow deterministic spin–orbit torque switching of the FGT in CrSBr/FGT/Pt samples at zero applied magnetic field. A minimum thickness of the CrSBr of >10 nm is needed to provide a non‐zero exchange bias at 30 K.

Perovskite nickelates have been heavily studied as a textbook example of how the interplay of structural, orbital, and charge/spin degrees of freedom drive strongly correlated phenomena in 3d transition metal oxides. The recent discovery of superconductivity in the infinite-layer nickelate thin films has provided the field another d 9 electron configuration similar to cuprates. Releasing nickelate thin films from the substrate constraint would provide a novel experimental avenue to explore the strain tunability of the metal-insulator transition in the perovskite nickelates and superconductivity in the infinite-layer nickelates. In this talk, we will discuss our progress on synthesizing freestanding perovskite nickelate membranes and bridging them to the infinite-layer nickelate phase.

T24. 00002: Spin-orbit torque in magnetic heterostructures: exchange interactions and ultrasensitive Sagnac optical interferometry*

We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow α-(AlxGa1− x) 2O3 films on (110) sapphire substrates over the 0< x< 0.95 range of aluminum content. In S-MBE, 99.98% of the gallium-containing molecular beam arrives at the substrate in a preoxidized form as gallium suboxide (Ga2O). This bypasses the rate-limiting step of conventional MBE for the growth of gallium oxide (Ga2O3) from a gallium molecular beam and allows us to grow fully epitaxial α-(AlxGa1− x) 2O3 films at growth rates exceeding 1 μm/h and relatively low substrate temperature (Tsub= 605±15○ C). The ability to grow α-(AlxGa1− x) 2O3 over the nominally full composition range is confirmed by Vegard’s law applied to the x-ray diffraction data and by optical bandgap measurements with ultraviolet–visible spectroscopy. We show that S-MBE allows straightforward composition control and bandgap selection for α-(AlxGa1− x …

Cryo-EM is a powerful tool in structural biology, providing insights through techniques like single-particle analysis (SPA) and cryogenic electron tomography (cryo-ET). In thick specimens, challenges arise as an exponentially larger fraction of the transmitted electrons lose energy from inelastic scattering and can no longer be properly focused as a result of chromatic aberrations in the post-specimen optics. Rather than filtering out the inelastic scattering at the price of reducing potential signal, as is done in energy-filtered transmission electron microscopy (EFTEM), we show how a dose-efficient and unfiltered image can be rapidly obtained using tilt-corrected bright-field scanning-TEM (tcBF-STEM) data collected on a pixelated detector. Enhanced contrast and a 3-5x improvement in collection efficiency are observed for 2D images of intact bacterial cells and large organelles using tcBF-STEM compared to EFTEM for thicknesses beyond 500 nm. As a proof of concept for the technique's performance in structural determination, we present an SPA map at a 7 angstrom nominal resolution for a highly symmetric virus-like particle (VLP) with 789 particles. These findings suggest applications for tcBF-STEM in cryo-EM of thicker cellular volumes where current approaches struggle.

2D layered materials with broken inversion symmetry are being extensively pursued as  spin source layers to realize high‐efficiency magnetic switching. Such low‐symmetry layered systems are, however, scarce. In addition, most layered magnets with perpendicular magnetic anisotropy show a low Curie temperature. Here, the experimental observation of spin–orbit torque magnetization self‐switching at room temperature in a layered polar ferromagnetic metal, Fe2.5Co2.5GeTe2 is reported. The spin–orbit torque is generated from the broken inversion symmetry along the c‐axis of the crystal. These results provide a direct pathway toward applicable 2D spintronic devices.

Electron microscopes use electrons with wavelengths of a few picometers and are potentially capable of imaging individual atoms in solids at a resolution ultimately set by the atoms themselves. Even with the development of aberration-corrector technology the best achievable resolution was more than an order magnitude worse than this, limited by both residual aberrations in the electron lenses and multiple scattering of the incident beam inside the sample. However, with recent advances in detector technology [1] to collect all scattered electrons and ptychographic algorithms to unscramble their multiple scattering, the resolution of the electron microscope is now limited only by the dose to the sample, and thermal vibrations of the atoms themselves. At high doses, these approaches have allowed us to image the detailed vibrational envelopes of individual atom columns [2]. Solving the multiple scattering problem …

Spinel oxides such as ternary cobalt manganese spinel oxides (CMOs) are promising electrocatalysts for oxygen reduction reaction (ORR) in anion exchange membrane fuel cells. Current efforts to enhance fuel cell cathode performance predominantly focus on tuning the ORR activity through the chemical and crystallographic engineering of the active material. However, the impact of ink formulation and film homogeneity on fuel cell performance remains poorly understood and under-investigated. Here we show that the deliberate retention of organic ligands can enhance the performance of a CMO/C composite by improving its film homogeneity. Surprisingly, retaining the organic ligands can optimize the catalyst–ionomer affinity and subsequent film homogeneity of this system, thus enhancing its fuel cell peak power density from 0.8 W/cm2 to 1.2 W/cm2. We demonstrate this effect by pre- and postsynthetic …