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Mesoscale self organization of polydisperse magnetic nanoparticles at the water surface
Get PDFIn this study, we investigated the self ordering process in Langmuir films of polydisperse iron oxide nanoparticles on a water surface, employing in situ x ray scattering, surface pressure area isotherm analysis, and Brewster angle microscopy. X ray reflectometry confirmed the formation of a monolayer, while grazing incidence small angle x ray scattering revealed short range lateral correlations with a characteristic length equal to the mean particle size. Remarkably, our findings indicated that at zero surface pressure, the particles organized into submicrometer clusters, merging upon compression to form a homogeneous layer. These layers were subsequently transferred to a solid substrate using the Langmuir Schaefer technique and further characterized via scanning electron microscopy and polarized neutron reflectometry. Notably, our measurements revealed a second characteristic length in the lateral correlations, orders of magnitude longer than the mean particle diameter, with polydisperse particles forming circular clusters densely packed in a hexagonal lattice. Furthermore, our evidence suggests that the lattice constant of this mesocrystal depends on the characteristics of the particle size distribution, specifically the mean particle size and the width of the size distribution. In addition, we observed internal size separation within these clusters, where larger particles were positioned closer to the center of the cluster. Finally, polarized neutron reflectometry measurements provided valuable insights into the magnetization profile across the laye
Transient grating spectroscopy on a DyCo5 thin film with femtosecond extreme ultraviolet pulses
No full textSurface acoustic waves SAWs are excited by femtosecond extreme ultraviolet EUV transient gratings TGs in a room temperature ferrimagnetic DyCo5 alloy. TGs are generated by crossing a pair of EUV pulses from a free electron laser with the wavelength of 20.8 amp; 8201;nm matching the Co M edge, resulting in a SAW wavelength of amp; 923; amp; 8201; amp; 8201;44 amp; 8201;nm. Using the pump probe transient grating scheme in reflection geometry, the excited SAWs could be followed in the time range of amp; 8722;10 to 100 ps in the thin film. Coherent generation of TGs by ultrafast EUV pulses allows to excite SAW in any material and to investigate their couplings to other dynamics, such as spin waves and orbital dynamics. In contrast, we encountered challenges in detecting electronic and magnetic signals, potentially due to the dominance of the larger SAW signal and the weakened reflection signal from underlying layers. A potential solution for the latter challenge involves employing soft x ray probes, albeit introducing additional complexities associated with the required grazing incidence geometr
Fabrication of nanocrystalline high entropy oxide CoNiFeCrMnOx thin film electrodes by dip coating for oxygen evolution electrocatalysis
No full textThe variation of calcination conditions allows for adjusting the oxidation states and coordination sites of near surface elements in sol gel derived high entropy oxides. Optimized synthesis conditions resulted in fabrication of nanocrystalline CoNiFeCrMnOx thin films with 1 2 nm pores, showing low OER overpotentials of 258 mV VS. RHE at 10 mA cm amp; 8722;
Field induced bound state condensation and spin nematic phase in SrCu2 BO3 2 revealed by neutron scattering up to 25.9 T
Get PDFIn quantum magnetic materials, ordered phases induced by an applied magnetic field can be described as the Bose Einstein condensation BEC of magnon excitations. In the strongly frustrated system SrCu2 BO3 2, no clear magnon BEC could be observed, pointing to an alternative mechanism, but the high fields required to probe this physics have remained a barrier to detailed investigation. Here we exploit the first purpose built high field neutron scattering facility to measure the spin excitations of SrCu2 BO3 2 up to 25.9 T and use cylinder matrix product states MPS calculations to reproduce the experimental spectra with high accuracy. Multiple unconventional features point to a condensation of S amp; 8201; amp; 8201;2 bound states into a spin nematic phase, including the gradients of the one magnon branches and the persistence of a one magnon spin gap. This gap reflects a direct analogy with superconductivity, suggesting that the spin nematic phase in SrCu2 BO3 2 is best understood as a condensate of bosonic Cooper pair
Size Dependence and High Temperature Stability of Radial Vortex Magnetic Textures Imprinted by Superconductor Stray Fields
Get PDFSwirling spin textures, including topologically nontrivial states, such as skyrmions, chiral domain walls, and magnetic vortices, have garnered significant attention within the scientific community due to their appeal from both fundamental and applied points of view. However, their creation, controlled manipulation, and stability are typically constrained to certain systems with specific crystallographic symmetries, bulk or interface interactions, and or a precise stacking sequence of materials. Recently, a new approach has shown potential for the imprint of magnetic radial vortices in soft ferromagnetic compounds making use of the stray field of YBa2Cu3O7 amp; 948; superconducting microstructures in ferromagnet superconductor FM SC hybrids at temperatures below the superconducting transition temperature TC . Here, we explore the lower size limit for the imprint of magnetic radial vortices in square and disc shaped structures as well as the persistence of these spin textures above TC, with magnetic domains retaining partial memory. Structures with circular geometry and with FM patterned to smaller radius than the superconductor island facilitate the imprinting of magnetic radial vortices and improve their stability above TC, in contrast to square structures where the presence of magnetic domains increases the dipolar energy. Micromagnetic modeling coupled with a SC field model reveals that the stabilization mechanism above TC is mediated by microstructural defects. Superconducting control of swirling spin textures, and their stabilization above the superconducting transition temperature by means of defect engineering holds promising prospects for shaping superconducting spintronics based on magnetic texture
Long range superconducting proximity effect in YBa2Cu3O7 La0.7Ca0.3MnO3 weak link arrays
Get PDFThe interplay between ferromagnetism and superconductivity has attracted substantial interest due to its potential for exotic quantum phenomena and advanced electronic devices. Although ferromagnetism and superconductivity are antagonistic phenomena, ferromagnets F can host spin triplet superconductivity induced via proximity with superconductors S . To date, most of the experimental effort has been focused on single S F S junctions. Here, we have found the fingerprints of long range superconducting proximity effect in micrometric weak link arrays, formed by embedding YBa2Cu3O7 superconducting islands in a half metallic ferromagnet La0.7Ca0.3MnO3 film. These arrays show magnetoresistance oscillations that appear at temperatures below the critical temperature of YBa2Cu3O7 for currents below a threshold, indicating their superconducting origin. This realization paves the way for device architectures displaying macroscopic quantum interference effects, which are of interest for field sensing applications, among other
Optical absorption spectra in the far infrared range and phonons of CdSe1 xTex thin films
Get PDFOptical reflection spectra of CdSe1 xTex thin films deposited on quartz substrates are measured using the synchrotron radiation in the spectral range of 20 500 cm amp; 8722;1. The absorption bands of CdSe, CdTe, CdSe0.75Te0.25, CdSe0.5Te0.5, and CdSe0.25Te0.75 films are localized in the range of 20 220 cm amp; 8722;1. The imaginary parts of the dielectric function amp; 949;2 amp; 955; amp; 8722;1 of CdTe1 xSex crystals calculated in the framework of the density functional theory are in good agreement with the experimental reflection spectra of CdTe1 xSex films. The eigenvectors of the dynamical matrix CdTe1 xSex crystals are analyzed for several phonon modes to understand the difference between the frequency dependences of the calculated vibration density of states and the imaginary part of dielectric function amp; 949;2 amp; 955; amp; 8722;1 . Small features of the experimental reflective spectra of CdSe1 xTex films in the ranges 50 70 cm amp; 8722;1 and 80 120 cm amp; 8722;1 are explained using the analysis of results of the molecular dynamics. During comparative molecular dynamics calculations, it was found that the vibration density of states of a thin CdTe slab with a surface to volume number of atoms relation of NS NV 0.2, experienced a redshift of approximately 30 cm amp; 8722;1. This shift was observed in comparison with the CdTe single crysta
A Blyholder mechanism in the chemisorption of N2O on Ni 111 studied with Auger photoelectron coincidence spectroscopy
Get PDFIn heterogeneous catalysis the surface adsorbate bond strength is critical for the function of the system. Here we study a series consisting of multilayer, bilayer and monolayer N2O on Ni 111 and employ Auger photoelectron coincidence spectroscopy APECS to study the interaction between the molecule and the substrate directly. We observe intensity in the nitrogen Auger spectra that arise from the interaction between molecule and surface not observed in free molecules whereas the oxygen spectra are thickness independent. Since the two nitrogen atoms of N2O are chemically inequivalent we can assign the intensity present in the bilayer and monolayer cases to orbitals centered on the terminal nitrogen which is closest to the Ni 111 surface. Using ab initio, molecular dynamics and solid state density functional theory calculations we infer a Blyholder model of the surface bond as consisting of donation from the terminal nitrogen lone pair valence orbital with back donation from the metal into the unoccupied orbitals on that nitrogen. This coincidence technique can readily be used to study substrate?adsorbate interactions directly with chemical and orbital specificity this opens up prospects to study fundamental steps of molecular adsorption and heterogeneous catalysis with unprecedented detai
Unveiling the nanomorphology of hfn thin films by ultrafast reciprocal space mapping
Get PDFHafnium Nitride HfN is a promising and very robust alternative to gold for applications of nanoscale metals. Details of the nanomorphology related to variations in strain states and optical properties can be crucial for applications in nanophotonics and plasmon assisted chemistry. Ultrafast reciprocal space mapping URSM with hard X rays is used to unveil the nanomorphology of thin HfN films. Static high resolution X ray diffraction reveals a twofold composition of the thin films being separated into regions with identical lattice constant and similar out of plane but hugely different in plane coherence lengths. URSM upon femtosecond laser excitation reveals different transient strain dynamics for the two respective Bragg peak components. This unambiguously locates the longer in plane coherence length in the first 15 nm of the thin film adjacent to the substrate. The transient shift of the broad diffraction peak displays the strain dynamics of the entire film, implying that the near substrate region hosts nanocrystallites with small and large coherence length, whereas the upper part of the film grows in small columnar grains. The results illustrate that URSM is a suitable technique for non destructive and depth resolved investigations of the morphology of nanostructure
Influence of nanohydration on the structure and radiation induced fragmentation of gas phase biomolecules
No full textIn the biological medium, water conditions the structure and function of biomolecules, with the first solvation shell playing a fundamental role in these properties. To understand this particular role of water, a bottom up approach can be utilized, such as investigating the stepwise hydration of biomolecules in the gas phase. In her thesis, Juliette Leroux presents an experimental and theoretical study on the influence of nanohydration on the structure and physical processes of gas phase biomolecules by irradiation with soft X ray photon