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Superconducting resonators with high quality factors have been fabricated from aluminum films, suggesting potential applications in quantum computing. Improvement of thin film crystal quality and removal of void and pinhole defects will improve quality factor and functional yield. Epitaxial aluminum films with superb crystallinity, high surface smoothness, and interface sharpness were successfully grown on the c-plane of sapphire using sputter beam epitaxy. This study assesses the effects of varying substrate preparation conditions and growth and prebake temperatures on crystallinity and smoothness. X-ray diffraction and reflectivity measurements yield extensive Laue oscillations and Kiessig thickness fringes for films grown at 200 °C under 15 mTorr Ar, indicating excellent crystallinity and surface smoothness; moreover, an additional substrate preparation procedure which involves (1) a modified substrate cleaning procedure and (2) prebake at 700 °C in 20 mTorr O2 is shown by atomic force microscopy to yield nearly pinhole-free film growth while maintaining epitaxy and high crystal quality. The modified cleaning procedure is environmentally friendly and eliminates the acid etch steps common to conventional sapphire preparation, suggesting potential industrial application both on standard epitaxial and patterned surface sapphire substrates.

Skyrmions hold great promise for low-energy consumption and stable high-density information storage, and stabilization of the skyrmion lattice (SkX) phase at or above room temperature is greatly desired for practical use. The topological Hall effect can be used to identify candidate systems above room temperature, a challenging regime for direct observation by Lorentz electron microscopy. Atomically ordered FeGe thin films are grown epitaxially on Ge(111) substrates with $\ensuremath{\sim}4%$ tensile strain. Magnetic characterization reveals enhancement of the Curie temperature to 350 K due to strain, well above the bulk value of 278 K. A strong topological Hall effect was observed between 10 and 330 K, with a significant increase in magnitude observed at 330 K. The increase in magnitude occurs just below the Curie temperature, similar to the onset of the SkX phase in bulk FeGe. The results suggest that strained FeGe films may host a SkX phase above room temperature when significant tensile strain is applied.

Magnetic damping impacts essential dynamics for spintronic device applications, but its fundamental mechanisms in various materials – including simple ferromagnetic metals – have yet to be understood. Here, we experimentally correlate damping with structural and transport properties of epitaxial thin films of Fe. At room temperature, the effective Gilbert damping parameter is independent of whether these films are coherently strained or partially relaxed. However, at low temperature, we find that coherently strained Fe films with higher crystalline quality and conductivity exhibit higher damping. The enhancement of low-temperature damping is greater than that from classical eddy current loss. Our observation of such conductivity-like damping, possibly governed by the intraband scattering mechanism [1], provides fundamental insight into the role of crystallinity in damping in ferromagnetic metals. [1] K. Gilmore, Y. U. Idzerda, M. D. Stiles, Phys. Rev. Lett. 99, 027204 (2007); M. A. W. Schoen et al. Nat. Phys. 12, 839 (2016).

Confirming the origin of Gilbert damping by experiment has remained a challenge for many decades, even for simple ferromagnetic metals. In this Letter, we experimentally identify Gilbert damping that increases with decreasing electronic scattering in epitaxial thin films of pure Fe. This observation of conductivity-like damping, which cannot be accounted for by classical eddy current loss, is in excellent quantitative agreement with theoretical predictions of Gilbert damping due to intraband scattering. Our results resolve the longstanding question about a fundamental damping mechanism and offer hints for engineering low-loss magnetic metals for cryogenic spintronics and quantum devices.

Fabrication of voltage tunable high-frequency devices using magnetostrictive ferromagnet-piezoelectric hybrid structures requires materials with low damping and narrow linewidth to achieve low microwave loss. Galfenol exhibits superior magnetostriction, stability over a wide range of temperatures, and is free of rare earth elements, making it an economical and promising candidate, if the microwave losses can be minimized. We report the fabrication, structural and magnetic characterization, and study of dynamic properties of epitaxial FeGa thin films exhibiting an ultra-low residual linewidth, Δ H 0 = 13 ± 1 Oe – a requirement for low microwave loss and effective damping parameter, α eff , as low as 0.0065 - 0.0001 + 0.0005 for the 16 nm thick film. Similarly, we found α eff = 0.0039 - 0.0007 + 0.0028 and Δ H 0 = 71 ± 1 Oe for the 24 nm thick film, demonstrating its potential for applications in magnetic memory and high frequency devices.

Vertical heterojunction p-CuI/n-Ga2O3 diodes were fabricated on commercial β-Ga2O3 substrates using the reaction of epitaxially-sputtered Cu with natural I2 vapor at room temperature followed by either a high temperature I2 gas reaction or an I2 solution treatment to remove iodine vacancies. Results show that using an epitaxially-oriented over a polycrystalline Cu layer produces larger and more strongly bonded CuI crystals. Hall and current–voltage measurements support rectifying behavior consistent with p-CuI/n-Ga2O3 heterojunction characteristics including 8 orders of magnitude I on/I off ratio and an ideality factor of 1.37 measured on the sample with the lowest concentration of iodine vacancies.