[en] This work reports structural properties of room temperature ferromagnetic Fe doped ZnO nanofibers (NFs). The NFs were obtained by electrospinning and calcination in air. The input atomic ratio of Fe to Zn ions was about 0.1. The structural characterization was performed by X-ray (XRD) examination, using the synchrotron radiation, and Energy-Filtered Transmission Electron Microscopy (EFTEM) analysis. Incorporating Fe ions into ZnO does not affect the crystal structure of the wurtzite host. No clear evidence of the second phase (Fe, FeO, Fe₂O₃ or ZnFe₂O₄) was detected. Diameters of crystals responsible for the magnetic properties ranged from 3 to 10 nm. We did not observe any precipitates of the different phase with diameters equal or larger than 1.5 nm. It implies that the magnetic signal comes from Fe ions built-in ZnO crystals. No other crystals (besides ZnO crystals) were observed in this range of sizes. We propose that the low activation energy for the nanocrystals growth in NFs allows a large amount of doped ions to be built-in the ZnO crystals. - Highlights: • The structural studies of Fe doped ZnO nanofibers (ferromagnetic at room temperature) were reported. • Incorporating at. 10% Fe ions into ZnO did not modify the wurtzite structure of the nanofibers. • The structural analysis (resolution about 1.5 nm) did not reveal any evidence of a second phase. • The ferromagnetic signal came from Fe ions built-in ZnO crystals. • The low activation energy for ZnO crystal growth was responsible for higher level of doping

[en] Highlights: • ns XUV irradiation of Pt/Co/Pt layers induces magnetic reorientation to out-of-plane. • Irradiation induced atomic diffusion leads to Pt_1-xCo_x alloys formation. • Two layers composed of Pt_1-xCo_x alloys with different Co concentrations are formed. • Magnetic properties Pt/Co/Pt layers depend on composition of alloys. • Other parameters - lateral strain and alloy thickness – do not vary between samples. We have studied the structural mechanisms responsible for the magnetic reorientation between in-plane and out-of-plane magnetization in the (25 nm Pt)/(3 and 10 nm Co)/(3 nm Pt) trilayer systems irradiated with nanosecond XUV pulses generated with laser-driven gas-puff target plasma source of a narrow continuous spectrum peaked at wavelength of 11 nm. The thickness of individual layers, their density, chemical composition and irradiation-induced lateral strain were deduced from symmetric and asymmetric X-ray diffraction (XRD) patterns, grazing-incidence X-ray reflectometry (GIXR), grazing incidence X-ray fluorescence (GIXRF), extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) measurements. In the as grown samples we found, that the Pt buffer layers are relaxed and that the layer interfaces are sharp. As a result of a quasi-uniform irradiation of the samples, the XRD, EXAFS, GIXR and GIXRF data reveal the formation of two distinct layers composed of Pt_1-xCo_x alloys with different Co concentrations, dependent on the thickness of the as grown magnetic Co film but with similar ∼1% lateral tensile residual strain. For smaller exposure dose (lower number of accumulated pulses) only partial interdiffusion at the interfaces takes place with the formation of a tri-layer composed of Co-Pt alloy sandwiched between thinned Pt layers, as revealed by TEM. The structural modifications are accompanied by magnetization changes, evidenced by means of magneto-optical microscopy. The difference in magnetic properties of the irradiated samples can be related to their modification in Pt_1-xCo_x alloy composition, as the other parameters (lateral strain and alloy thickness) remain almost unchanged. The out-of-plane magnetization observed for the sample with initially 3 nm Co layer can be due to a significant reduction of demagnetization factor resulting from a lower Co concentration.

[en] Elastic model of continuum material is often used to simulate the relaxation of crystalline heterostructures. There are many reports on the successful application of the theory of elasticity to nano-sized crystalline heterostructures, even if the continuum condition for them is hardly fulfilled. On the other hand, progress in epitaxial growth allows for the preparation of stable ultra-thin layers with thickness of few monolayers. For such ultra-thin layers, results provided by continuum model and molecular statics/dynamics calculations become diverging. The key problem seems to be located at the modelling of the interface between layers, which is problematic in the continuum approach. By applying a step-wise substitutive compositional interfacial function, it is possible to obtain good agreement with molecular dynamics calculations, even for a single monolayer heterostructure. We propose another approach that uses composition as an extra parameter during finite element calculations, along with classical nodal displacements. Such an approach creates a chemo-elastic coupling that allows to interpolate the composition much like in the case of atomistic calculations. (paper)

[en] C-Pd films were obtained by Physical Vapor Deposition (PVD) or by annealing of these initial PVD films at 650°C in different time (5, 10 and 30 minutes) in argon flow. These C-Pd films were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and FTIR spectroscopy. The sensing properties of the films were studied in a specially prepared chamber allowing for measurements of the changes in resistivity as a function of gas composition changes. It was found that annealing changes the films morphology, topography and structure, and consequently their sensing properties

[en] In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogeneities in the iron chalcogenide system FeTe_1−xSe_x and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe_0.65Se_0.35 studied with transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy and their magnetic and superconducting properties characterized with magnetization, specific heat and magnetic resonance spectroscopy. Our data demonstrate the presence of nanoscale hexagonal regions coexisting with a tetragonal host lattice, a chemical disorder demonstrating a nonhomogeneous distribution of host atoms in the crystal lattice, as well as iron-deficient bands hundreds of nanometres in length. From the magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe–Te–Se to Fe₃O₄ inclusions and to hexagonal symmetry nanoscale regions with a structure of the Fe₇Se₈ type. Our results suggest that a nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe–Te–Se chalcogenides and we find a surprising correlation indicating that a faster grown crystal of inferior crystallographic properties is a better superconductor. (paper)

[en] Despite many efforts, the origin of a ferromagnetic (FM) response in ZnMnO and ZnCoO is still not clear. Magnetic investigations of our samples, not discussed here, show that the room temperature FM response is observed only in alloys with a non-uniform Mn or Co distribution. Thus, the control of their distribution is crucial for the explanation of contradicted magnetic properties of ZnCoO and ZnMnO reported till now. In this paper, we discuss advantages of the atomic layer deposition (ALD) growth method, which enables us to control the uniformity of ZnMnO and ZnCoO alloys. Properties of ZnO, ZnMnO and ZnCoO films grown by the ALD are discussed. (paper)

[en] The magnetic anisotropy of La_0.7Sr_0.3MnO₃ nanopowders was measured as a function of temperature by the modified singular point detection technique. In this method singularities indicating the anisotropy field were determined analyzing ac susceptibility data. The observed relationship between temperature dependence of anisotropy constant and temperature dependence of magnetization was used to deduce the origin of magnetic anisotropy in the nanopowders. It was shown that magnetic anisotropy of La_0.7Sr_0.3MnO₃ nanopowder is determined by the two-ion (dipolar or pseudodipolar) and single-ion mechanisms. Highlights: ► TEM observations did not reveal core-shell particles. ► Magnetic anisotropy of nanoparticles was measured using a singular point detection technique. ► Magnetic measurement indicated on core-shell magnetic structure particles

[en] Three series of core–shell maghemite nanoparticles were prepared by a template synthesis using surface active oligoperoxides and further surface initiated grafting functional polymers, forming shell suitable for biomedical applications. Because the polymer shells prevent exchange coupling between maghemite particles, the overall magnetic properties of the samples studied are dominated by dipolar interparticle interactions. Only the sample with the highest polymer fraction displays superparamagnetic relaxation phenomena close to the room temperature. On cooling, the magnetostatic interactions lead to a disordered collective magnetic state that should be described in terms of a spin-glass phenomenology. This collective freezing cannot however be considered as a generic spin-glass phase transition at a well-defined temperature but rather as freezing to a metastable glass-like state of locally correlated structural domains (clusters) without a long-range order. A quasi static spin ordering is only achieved at temperatures much below the freezing temperature. - Highlights: • Core–shell γ-Fe_2O_3/polymer particles were prepared using new surface active oligoperoxides. • Grafting of particle shells with functional polymers, suitable for biomedical applications. • Magnetic properties of nanocomposites are dominated by dipolar interactions. • On cooling magnetostatic interactions lead to a spin-glass-like state. • The most diluted maghemite particles display superparamagnetism at 300 K

[en] X-ray Free Electron Lasers (XFELs) have the potential to contribute to many fields of science and to enable many new avenues of research, in large part due to their orders of magnitude higher peak brilliance than existing and future synchrotrons. To best exploit this peak brilliance, these XFEL beams need to be focused to appropriate spot sizes. However, the survivability of X-ray optical components in these intense, femtosecond radiation conditions is not guaranteed. As mirror optics are routinely used at XFEL facilities, a physical understanding of the interaction between intense X-ray pulses and grazing incidence X-ray optics is desirable. We conducted single shot damage threshold fluence measurements on grazing incidence X-ray optics, with coatings of ruthenium and boron carbide, at the SPring-8 Angstrom compact free electron laser facility using 7 and 12 keV photon energies. The damage threshold dose limits were found to be orders of magnitude higher than would naively be expected. The incorporation of energy transport and dissipation via keV level energetic photoelectrons accounts for the observed damage threshold