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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.

Chemical and biological agents continue to pose a threat to U.S. national security. The development of next generation of devices to sense, detect, filter, and remove these threats remains a priority of the U.S. Department of Defense. Zr(OH)4 is currently being developed as a decontaminant and is being engineered into suitable forms capable of removing chemical warfare agents. As such, having a detailed understanding of the local structure of amorphous Zr(OH)4 and heat treated ZrO2 analogs is a crucial step in developing these compounds as suitable countermeasures against chemical threats. In this study, zirconium hydroxide powders were calcined at various temperatures to study the effects of porosity, surface area, structure, and electronic properties as a function of temperature. Different characterization techniques were used to demonstrate that the surface area and porosity decreased as the material changed from an amorphous phase to a monoclinic crystal structure. Analysis of X-ray pair distribution function data provided a detailed representation of the local structure of amorphous Zr(OH)4 and its thermal decomposition into ZrO2. Impedance analysis showed both the dielectric constants and capacitance decreased by two orders of magnitude as crystallinity increased, correlating to a lowered concentration of defects, such as surface hydroxyl groups that contribute to leakage current.

We report a resonant elastic x-ray scattering study of a thin-film sample of ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$, which has one of the highest ferrimagnetic transition temperatures among ordered double perovskites. We found resonantly enhanced magnetic Bragg peaks at $\mathbf{Q}=$ (odd, odd, odd) at both the rhenium ${L}_{2}$ and ${L}_{3}$ edges, which coincide with the structural Bragg peaks of ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$. By analyzing the widths of these Bragg peaks, we extracted very different structural and magnetic correlation lengths. The former is about 15 nm, while the latter is constrained by the instrumental resolution to be at least 90 nm. We argue that a finite structural correlation length is consistent with the existence of antiphase nanodomains in our sample. On the other hand, a much larger magnetic correlation length indicates that the magnetic correlation extends far beyond the boundaries of individual domains and is consistent with strong antiferromagnetic coupling between different antiphase domains. Last, from the azimuthal dependence of the magnetic intensity, we show that the magnetic moments lie perpendicular to the $c$ axis, which explains the earlier bulk magnetization data.

Volatile organic compounds (VOCs) pose an occupational exposure risk due to their commonplace usage across industrial and vocational sectors. With millions of workers annually exposed, monitoring personal VOC exposures becomes an important task. As such, there is a need to improve current monitoring techniques by increasing sensitivity and reducing analysis costs. Recently, our lab developed a novel, preanalytical technique known as photothermal desorption (PTD). PTD uses pulses of high-energy, visible light to thermally desorb analytes from carbonaceous sorbents, with single-walled carbon nanotube buckypapers (BPs) having the best overall performance. To apply this new technology most effectively for chemical analysis, a better understanding of the theoretical framework of the thermal phenomena behind PTD must be gained. The objectives of the present work were 3-fold: measure the thermal response of BPs during irradiation with light; determine the best method for conducting such measurements; and determine the thermal conductivity of BPs. BPs were exposed to four energy densities, produced by light pulses, ranging from 0.28 to 1.33 J/cm2, produced by a xenon flash lamp. The resulting temperature measurements were obtained via fast response thermocouple (T/C) mounted to BPs by three techniques (pressing, adhering, and embedding). Temperature increase measured by T/C using the adhering and pressing techniques resulted in similar values, 29.2 ± 0.8 to 56 ± 3 °C and 29.1 ± 0.9 to 50 ± 5 °C, respectively, while temperature increase measured by embedding the T/C into the BP showed statistically larger increases ranging from 35.2 ± 0.9 to 76 ± 4 °C. Peak BP temperatures for each mounting technique were also compared with the temperatures generated by the light source, which resulted in embedded BPs demonstrating the most temperature conversion among the techniques (74-86%). Based on these results, embedding T/Cs into the BP was concluded to be the best way to measure BP thermal response during PTD. Additionally, the present work modeled BP thermal conductivity using a steady-state comparative technique and found the material's conductivity to be 10.6 ± 0.6 W/m2. The present work's findings will help pave the way for future developments of the PTD method by allowing calculation of the energy density necessary to attain a desired sorbent temperature and providing a means for comparing BP fabrication techniques and evaluating BP suitability for PTD before conducting PTD trials with analytes of interest. Sorbents with greater thermal conductivity are expected to desorb more evenly and withstand higher energy density exposures.

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.

Zirconium hydroxide has been investigated as a candidate nitrogen dioxide dielectric sensor using impedance spectroscopy analysis. Significant changes in electronic and physical properties down to our dosage minimum of 2 ppm h have been observed. Using disc-shaped pressed pellets of Zr(OH)4 in parallel plate geometry, we observe a maximum signal shift of 35% at 2 ppm h dosage, which increases six orders of magnitude as the dosage reaches 1000 ppm h. Changes in impedance correlate with nitrogen and oxygen atomic ratio increases observed via X-ray photoelectron spectroscopy (XPS) at higher NO2 dosages. In contrast to the sharp frequency-dependent features and net impedance decreases during NO2 exposures, Zr(OH)4 exhibits a large and broad impedance increase after exposure to humid air (water vapor). The results indicate that Zr(OH)4 could be used as a selective low-cost impedance-based NO2 detector by applying frequency-dependent impedance fingerprinting.

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.

Zirconium hydroxide powders were calcined at 100, 250, 500, and 1000 °C to study the effects of porosity, surface area, structure, and electronic properties as a function of temperature. Characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), ultraviolet–visible (UV–vis) spectroscopy, and transmission electron microscopy (TEM) demonstrated that the powder surface area and porosity decreased as the material changed from an amorphous phase to a monoclinic crystal structure. Impedance analysis showed both the dielectric constants and capacitance decreased by 2 orders of magnitude as crystallinity increased, correlating to a lowered concentration of defects, such as surface hydroxyl groups that contribute to leakage current.

The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. As reported previously Sr2CrOsO6 crystallizes with R 3 ¯ symmetry due to a−a−a− octahedral tilting. A decrease in the tolerance factor leads to a−a−b+ octahedral tilting and P21/n space group symmetry for Ca2CrOsO6. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 μB. Sr2CrOsO6 orders at 660 K while Ca2CrOsO6 orders at 490 K. Variable temperature magnetization measurements suggest that the magnetization of the Cr3+ and Os3+ sublattices have different temperature dependences in Sr2CrOsO6. This leads to a non-monotonic temperature evolution of the magnetic moment. Similar behavior is not seen in Ca2CrOsO6. Both compounds have similar levels of Os/Cr antisite disorder, with order parameters of η=80.2(4)% for Sr2CrOsO6 and η=76.2(5)% for Ca2CrOsO6, where η=2θ−1 and θ is the occupancy of the osmium ion on the osmium-rich Wyckoff site.

Electrical impedance spectroscopy, in conjunction with the metal–organic framework (MOF) UiO-66-NH2, is used to detect trace levels of the explosive simulant 2,6-dinitrotoluene. The combination of porosity and functionality of the MOF provides an effective dielectric structure, resulting in changes of impedance magnitude and phase angle. The promising data indicate that MOFs may be used in low-cost, robust explosive detection 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.

Zirconium hydroxide has been investigated as a candidate nitrogen dioxide dielectric sensor using impedance spectroscopy analysis. Significant changes in electronic and physical properties down to our dosage minimum of 2 ppm h have been observed. Using disc-shaped pressed pellets of Zr(OH)

We report the superconducting transition temperature T c versus thickness d F of Ferromagnet/Superconductor (F/S) bilayers, where F is a strong 3d ferromagnet (Ni, Ni 0.81 Fe 0.19 (Permalloy), Co 0.5Fe 0.5) and S = Nb, taken from superfluid density measurements rather than resistivity. By regrouping the many physical parameters that appear in theory, we show that the effective exchange energy is determined from the F film thickness d F where T c versus d F begins to flatten out. Using this rearranged theory, we conclude 1) the effective exchange energy, E e x , is about 15 times smaller than measured by ARPES and five times smaller than deduced in previous studies similar to ours; 2) the dirty-limit coherence length, ξ F , for Cooper pairs in F is larger than the electron mean free path, l F ; and 3) the 3d-F/Nb interface is enough of a barrier that Cooper pairs typically must hit it several times before getting through. The Py/Nb and CoFe/Nb interfaces are more transparent than the Ni/Nb interface.

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.

Innovation is driven by the materials mankind has mastered to advance society. Our information age traces back to wartime invention of methods to fabricate silicon and germanium crystals with defects lower than 1 part in 100, a threshold at which the intrinsic properties could then be applied. Today, complex materials (>2 elements with atomic ordering) are at a similar inflection point. Unfortunately, improvement beyond 1 defect in 4 has proven challenging: energetic defects abound and many elements are not compatible with current low-defect growth techniques. Despite significant external funding for the materials themselves, a lack of funding for new synthetic technologies has left us with methods unable to reach the inflection point. Our goal is to transform materials discovery by developing a complex material thin film system that can attain 99% atomic ordering in today’s “too-complex” materials. This talk will highlight our progress in thin film growth via Sputter Beam Epitaxy, an approach combining the fabrication strengths of off-axis magnetron sputtering and molecular beam epitaxy.

Using aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), we investigate ordering phenomena in epitaxial thin films of the double perovskite Sr_{2}CrReO_{6}. Experimental and simulated imaging and diffraction are used to identify antiphase domains in the films. Image simulation provides insight into the effects of atomic-scale ordering along the beam direction on HAADF-STEM intensity. We show that probe channeling results in ±20% variation in intensity for a given composition, allowing 3D ordering information to be probed using quantitative STEM.

The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. As reported previously Sr2CrOsO6 crystallizes with R 3 ¯ symmetry due to a−a−a− octahedral tilting. A decrease in the tolerance factor leads to a−a−b+ octahedral tilting and P21/n space group symmetry for Ca2CrOsO6. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 μB. Sr2CrOsO6 orders at 660 K while Ca2CrOsO6 orders at 490 K. Variable temperature magnetization measurements suggest that the magnetization of the Cr3+ and Os3+ sublattices have different temperature dependences in Sr2CrOsO6. This leads to a non-monotonic temperature evolution of the magnetic moment. Similar behavior is not seen in Ca2CrOsO6. Both compounds have similar levels of Os/Cr antisite disorder, with order parameters of η=80.2(4)% for Sr2CrOsO6 and η=76.2(5)% for Ca2CrOsO6, where η=2θ−1 and θ is the occupancy of the osmium ion on the osmium-rich Wyckoff site.

Bulk NdNiO3 exhibits a metal-to-insulator transition (MIT) as the temperature is lowered that is also seen in tensile strained films. In contrast, films that are under a large compressive strain typically remain metallic at all temperatures. To clarify the microscopic origins of this behavior, we use position averaged convergent beam electron diffraction in scanning transmission electron microscopy to characterize strained NdNiO3 films both above and below the MIT temperature. We show that a symmetry lowering structural change takes place in case of the tensile strained film, which undergoes an MIT, but is absent in the compressively strained film. Using space group symmetry arguments, we show that these results support the bond length disproportionation model of the MIT in the rare-earth nickelates. Furthermore, the results provide insights into the non-Fermi liquid phase that is observed in films for which the MIT is absent., Comment: Accepted for publication in Scientific Reports

Diffusion of iron and nickel in an Fe 64 Ni 36 alloy was measured via the use of focused-ion-beam (FIB) milling and energy dispersive x-ray spectroscopy (EDX) to 65 GPa and ∼2200 K. The experiments were performed using a combination of micro-fabricated samples in the laser-heated diamond-anvil cell (DAC), increasing the pressure range for experimentally determined interdiffusion coefficients in FeNi alloys by >40 GPa. Diffusivity in the iron–nickel system follows a homologous temperature relationship D = D 0 exp(−19.3(2.7) T m / T ) where D 0 is 4.6(7)×10 −4 m 2 s −1 , with zero-pressure activation energy, 301(40) kJ mol −1 , consistent with measurements at lower pressures. At inner core conditions, this predicts an inner core solid-state diffusivity of 1×10 −14 m 2 s −1 ( T m / T =0.95), with an inner core viscosity of 10 20 –10 22 Pa s assuming power-law creep ( n =3) with a deviatoric stress of 10 3 –10 4 Pa.

The authors have used a combination of monochromatized x-ray photoemission spectroscopy and Rutherford backscattering spectrometry to develop a protocol for determining bulk film stoichiometry and charge state of Sr2FeMoO6 epitaxial films These studies identify an optimum ion sputtering process for removing surface contaminants while avoiding preferential sputtering of film constituents or alteration of their characteristic valence states. For Sr2FeMoO6, low energy (500 eV), glancing incidence Ar+ sputtering for short (tens of seconds) periods is successful in achieving stoichiometric compositions and characteristic charge states of the film constituents. The evolution of composition and valence state with sputtering provides a guide to measure stoichiometry and charge state of complex oxide thin films in general.

The discovery of new phenomena in layered and nanostructured magnetic devices is driving rapid growth in nanomagnetics research. Resulting applications such as giant magnetoresistive field sensors and spin torque devices are fuelling advances in information and communications technology, magnetoelectronic sensing and biomedicine. There is an urgent need for high-resolution magnetic-imaging tools capable of characterizing these complex, often buried, nanoscale structures. Conventional ferromagnetic resonance (FMR) provides quantitative information about ferromagnetic materials and interacting multicomponent magnetic structures with spectroscopic precision and can distinguish components of complex bulk samples through their distinctive spectroscopic features. However, it lacks the sensitivity to probe nanoscale volumes and has no imaging capabilities. Here we demonstrate FMR imaging through spin-wave localization. Although the strong interactions in a ferromagnet favour the excitation of extended collective modes, we show that the intense, spatially confined magnetic field of the micromagnetic probe tip used in FMR force microscopy can be used to localize the FMR mode immediately beneath the probe. We demonstrate FMR modes localized within volumes having 200 nm lateral dimensions, and improvements of the approach may allow these dimensions to be decreased to tens of nanometres. Our study shows that this approach is capable of providing the microscopic detail required for the characterization of ferromagnets used in fields ranging from spintronics to biomagnetism. This method is applicable to buried and surface magnets, and, being a resonance technique, measures local internal fields and other magnetic properties with spectroscopic precision.

The authors report the growth of iron nitride on zinc-blende gallium nitride using molecular beam epitaxy. First, zinc-blende GaN is grown on a magnesium oxide substrate having (001) orientation; second, an ultrathin layer of FeN is grown on top of the GaN layer. In situ reflection high-energy electron diffraction is used to monitor the surface during growth, and a well-defined epitaxial relationship is observed. Cross-sectional transmission electron microscopy is used to reveal the epitaxial continuity at the gallium nitride-iron nitride interface. Surface morphology of the iron nitride, similar to yet different from that of the GaN substrate, can be described as plateau valley. The FeN chemical stoichiometry is probed using both bulk and surface sensitive methods, and the magnetic properties of the sample are revealed.

Ferromagnetic δ -phase manganese gallium layers with Mn / ( Mn + Ga ) = 60 % have been successfully grown on ScN(0 0 1) by molecular beam epitaxy, expanding possibilities for ferromagnetic layers on nitride semiconductors. The in-plane epitaxial relationship of manganese gallium with respect to scandium nitride is determined to be [ 1 0 0 ] MnGa / / [ 1 1 0 ] ScN and [ 1 1 0 ] MnGa / / [ 1 0 0 ] ScN . Vibrating sample magnetometry measurements indicate out-of-plane magnetization of the film, suggesting strong magnetic anisotropy along the manganese gallium c -axis.

A newly substituted series of perovskites, Bi x La 2− x Mn M O 6 with M = Ni, Co and x = 0.25, 0.50, were synthesized using a citrate sol–gel technique. The crystal structure, established from neutron diffraction, is a distorted double perovskite with partial transition metal B -site ordering. These perovskites crystallize in the centrosymmetric space group, P 2 1 / n , with structures that are similar to the x = 0 end members. All samples are prone to non-stoichiometry involving substitution of Mn onto the Ni/Co sites, in addition to varying degrees of antisite disorder. The neutron powder diffraction and magnetization measurements reveal ferromagnetism in all samples with ordering temperatures between 220 K and 280 K. The M = Co samples have lower Curie temperatures, but higher coercivities. There is a clear link between the degree of transition metal site disorder and the saturation magnetization values. Electrical measurements demonstrate the presence of mixed ionic and electronic conductivity.

Resistances that exceed the Mott-Ioffe-Regel limit, known as bad metal behavior, and non-Fermi liquid behavior are ubiquitous features of the normal state of many strongly correlated materials. Here we establish the conditions that lead to bad metal and non-Fermi liquid phases in NdNiO3, which exhibits a prototype, bandwidth-controlled metal-insulator transition. We show that resistance saturation is determined by the magnitude of the Ni eg orbital splitting, which can be tuned by strain in epitaxial films, causing the appearance of bad metal behavior under certain conditions. The results shed light on the nature of a crossover to non-Fermi liquid metal phase and provide a predictive criterion for strong localization. They elucidate a seemingly complex phase behavior as a function of film strain and confinement and provide guidelines for orbital engineering and novel devices., Comment: Manuscript text, 5 figures and supplement

Resistive switching effects in transition metal oxide-based devices offer new opportunities for information storage and computing technologies. Although it is known that resistive switching is a defect-driven phenomenon, the precise mechanisms are still poorly understood owing to the difficulty of systematically controlling specific point defects. As a result, obtaining reliable and reproducible devices remains a major challenge for this technology. Here, we demonstrate control of resistive switching based on intentional manipulation of native point defects. Oxide molecular beam epitaxy is used to systematically investigate the effect of Ti/Sr stoichiometry on resistive switching in high-quality Pt/SrTiO3 junctions. We demonstrate resistive switching with improved state retention through the introduction of Ti- and Sr-excess into the near-interface region. More broadly, the results demonstrate the utility of high quality metal/oxide interfaces and explicit control over structural defects to improve control, uniformity and reproducibility of resistive switching processes. Unintentional interfacial contamination layers, which are present if Schottky contacts are processed at low temperature, can easily dominate the resistive switching characteristics and complicate the interpretation if nonstoichiometry is also present.

Structural relaxation in a ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$ epitaxial film, which exhibits strong spin-orbit coupling, leads to depth-dependent magnetism. We combine two depth-resolved synchrotron x-ray techniques---two-dimensional reciprocal space mapping and x-ray magnetic circular dichroism---to quantitatively determine this effect. An 800-nm-thick film of ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$, grown with tensile epitaxial strain on ${\mathrm{SrCr}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_{3}(225\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/{\text{(LaAlO}}_{3}{)}_{0.3}({\text{Sr}}_{2}{\mathrm{AlTaO}}_{6}{)}_{0.7}$, relaxes away from the ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}{\text{/SrCr}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_{3}$ interface to its bulk lattice parameters, with much of the film being fully relaxed. Grazing incidence x-ray diffraction of the film elucidates the in-plane strain relaxation near the film-substrate interface, while depth-resolved x-ray magnetic circular dichroism at the Re L edge reveals the magnetic contributions of the Re site. The smooth relaxation of the film near the interface correlates with changes in the magnetic anisotropy. This provides a systematic and powerful way to probe the depth-varying structural and magnetic properties of a complex oxide with synchrotron-source x-ray techniques.

We report the discovery of extraordinarily large anisotropy fields and strain-tunable magnetocrystalline anisotropy in ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$ epitaxial films. We determine the strain-induced tetragonal distortions and octahedral rotations in ${\mathrm{Sr}}_{2}{\mathrm{CrReO}}_{6}$ epitaxial films grown on (${\mathrm{LaAlO}}_{3}$)${}_{0.3}$(${\mathrm{Sr}}_{2}{\mathrm{AlTaO}}_{6}$)${}_{0.7}$ (LSAT), ${\mathrm{SrTiO}}_{3}$ (STO), and ${\mathrm{SrCr}}_{0.5}{\mathrm{Nb}}_{0.5}{\mathrm{O}}_{3}$/LSAT substrates using x-ray diffraction and density functional theory. The structural distortions drive dramatic changes in magnetocrystalline anisotropy. We use magnetometry measurements and first principles calculations to determine the atomic origins of the large anisotropy observed. These techniques elucidate the interplay between structural deformations and magnetic behavior and lay the groundwork for the study of other strongly correlated systems in this class of ferromagnetic oxides.

We have analyzed the magnetic configuration for highly ordered ${\mathrm{Sr}}_{2}$${\mathrm{CrReO}}_{6}$ films as a function of epitaxial strain using magnetometry and x-ray magnetic circular dichroism (XMCD) measurements of Cr, Re, and O sites. The in-plane magnetic moments change significantly when tensile strain is applied. O $K$-edge XMCD indicates that O sites carry at least a portion of the bulk magnetization. Spin moment values measured for Cr match calculations incorporating spin-orbit effects, while both spin and orbital moments measured for Re sites are slightly higher than previously predicted. Finally, we discuss large changes in the x-ray absorption near-edge structure that are observed at the Cr and Re $L$ edges due to epitaxial strain.

We demonstrate tuning of magnetocrystalline anisotropy in high-quality ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ epitaxial films over a range of several thousand Gauss using strain induced by epitaxial growth on substrates of varying lattice constants. Spectroscopic measurements reveal a striking, linear dependence of the out-of-plane anisotropy on the strain-induced tetragonal distortion of the ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ lattice. This anisotropy can be tuned from $+2000$ to $\ensuremath{-}3300\text{ }\text{ }\mathrm{Oe}$, a range sufficient to rotate the easy axis from in plane to out of plane. Combined with its half-metallicity and high Curie temperature, this result implies a broad range of scientific and technological applications for this novel spintronic material.

We demonstrate tuning of magnetocrystalline anisotropy in high-quality Sr(2)FeMoO(6) epitaxial films over a range of several thousand Gauss using strain induced by epitaxial growth on substrates of varying lattice constants. Spectroscopic measurements reveal a striking, linear dependence of the out-of-plane anisotropy on the strain-induced tetragonal distortion of the Sr(2)FeMoO(6) lattice. This anisotropy can be tuned from +2000 to -3300 Oe, a range sufficient to rotate the easy axis from in plane to out of plane. Combined with its half-metallicity and high Curie temperature, this result implies a broad range of scientific and technological applications for this novel spintronic material.

Polarons are critical to our understanding of many condensed matter systems, but are difficult to observe and characterize. By combining cathodoluminescence spectroscopy measurements with insights from first-principles calculations, we have identified transitions involving two distinct and simultaneous polaronic states in relaxed BaxSr1−xTiO3 films grown by molecular beam epitaxy. These polaronic optical transitions arise from two discrete Ti-O-Ti bonding configurations simultaneously present in the system, one with a 180° bond angle and the other with buckled geometry due to octahedral tilting. By compositional modulation, we show that we can semi-quantitatively probe the population of each bonding configuration.

We report growth of Sr${}_{2}$CrReO${}_{6}$ epitaxial films with 99$%$ Cr/Re ordering and crystalline perfection comparable to those of high-quality semiconductor films. The Sr${}_{2}$CrReO${}_{6}$ films show a Curie temperature of 508 K and a saturation magnetization of 1.29 ${\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit, which confirms the presence of strong spin-orbit coupling. Unexpectedly, electrical transport and optical absorption measurements indicate that Sr${}_{2}$CrReO${}_{6}$ is a semiconductor with a band gap of 0.21 eV. The unique combination of high temperature ferrimagnetism and semiconductivity is both scientifically interesting and highly attractive for applications.

A major challenge to achieving positional control of fluid borne submicron sized objects is regulating their Brownian fluctuations. We present a magnetic-field-based trap that regulates the thermal fluctuations of superparamagnetic beads in suspension. Local domain-wall fields originating from patterned magnetic wires, whose strength and profile are tuned by weak external fields, enable the bead trajectories within the trap to be managed and easily varied between strong confinements and delocalized spatial excursions that are described remarkably well by simulations.

Phase-pure, fully epitaxial ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ films with a high degree of Fe/Mo ordering have been fabricated using ultrahigh vacuum sputtering and verified by a variety of techniques. Through identifying and controlling critical factors, such as stoichiometry, phase purity, and double-perovskite ordering, that complicate the growth of ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ films, we demonstrate characteristics of high-quality ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ films that have not been shown before. Our results include the first report of distinct magnetic shape anisotropy and via scanning transmission electron microscopy, the first direct observation of clear Fe/Mo ordering within the double perovskite framework.

We have characterized a new Magnetic Force Microscopy (MFM) probe based on an iron filled carbon nanotube (FeCNT) using MFM imaging on permalloy (Py) disks saturated in a high magnetic field perpendicular to the disk plane. The experimental data are accurately modeled by describing the FeCNT probe as having a single magnetic monopole at its tip whose effective magnetic charge is determined by the diameter of the iron wire enclosed in the carbon nanotube and its saturation magnetization 4 \pi M_s ~ 2.2 x 10^4 G. A magnetic monopole probe enables quantitative measurements of the magnetic field gradient close to the sample surface. The lateral resolution is defined by the diameter of the iron wire ~15 nm and the probe-sample separation. As a demonstration, the magnetic field gradients close to the surface of a Py dot in domain and vortex states were imaged., Comment: 6 pages, 7 figures

We present a multiplex method, based on microscopic programmable magnetic traps in zigzag wires patterned on a platform, to simultaneously apply directed forces on multiple fluid-borne cells or biologically inert magnetic microparticles or nanoparticles. The gentle tunable forces do not produce damage and retain cell viability. The technique is demonstrated with T-lymphocyte cells remotely manipulated (by a joystick) along desired trajectories on a silicon surface with average speeds up to $20\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{s}$.

We report the first measurements of the effective superfluid density n_S(T) \propto \lambda^{-2}(T) of Superconductor-Ferromagnet (SC/FM) bilayers, where \lambda is the effective magnetic field penetration depth. Thin Nb/Ni bilayers were sputtered in ultrahigh vacuum in quick succession onto oxidized Si substrates. Nb layers are 102 A thick for all samples, while Ni thicknesses vary from 0 to 100 A. T_C determined from \lambda^{-2}(T) decreases rapidly as Ni thickness d_Ni increases from zero to 15 A, then it has a shallow minimum at d_Ni \approx 25 A. \lambda^{-2}(0) behaves similarly, but has a minimum several times deeper. In fact, \lambda^{-2}(0) continues to increase with increasing Ni thickness long after T_C has stopped changing. We argue that this indicates a substantial superfluid density inside the ferromagnetic Ni films., Comment: 13 pages, 2 figures, MMM 2007 proceedings