Study of ultrathin Pt/Co/Pt trilayers modified by nanosecond XUV pulses from laser-driven plasma source

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 Pt1-xCox 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 Pt1-xCox 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

Microstructural magnetic phases in superconducting FeTe0.65Se0.35

In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogenities in the iron chalcogenide system FeTe1-xSex and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe0.65Se0.35 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 a presence of nanometre scale hexagonal regions coexisting with tetragonal host lattice, a chemical disorder demonstrating non homogeneous distribution of host atoms in the crystal lattice, as well as hundreds-of-nanometres-long iron-deficient bands. From magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry nanometre scale regions with structure of Fe7Se8 type. Our results suggest that nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe-Te-Se chalcogenides and we find a surprising correlation indicating that faster grown crystal of inferior crystallographic properties is a better superconductor.Comment: 16 pages, 8 figures, 2 table

Structural pathways for ultrafast melting of optically excited thin polycrystalline Palladium films

Due to its extremely short timescale, the non-equilibrium melting of metals is exceptionally difficult to probe experimentally. The knowledge of melting mechanisms is thus based mainly on the results of theoretical predictions. This work reports on the investigation of ultrafast melting of thin polycrystalline Pd films studied by optical laser pump - X-ray free-electron laser probe experiments and molecular-dynamics simulations. By acquiring X-ray diffraction snapshots with sub-picosecond resolution, we capture the sample's atomic structure during its transition from the crystalline to the liquid state. Bridging the timescales of experiments and simulations allows us to formulate a realistic microscopic picture of melting. We demonstrate that the existing models of strongly non-equilibrium melting, developed for systems with relatively weak electron-phonon coupling, remain valid even for ultrafast heating rates achieved in femtosecond laser-excited Pd. Furthermore, we highlight the role of pre-existing and transiently generated crystal defects in the transition to the liquid state.Comment: main manuscript 33 pages, 9 figures; supplemental material 19 pages, 13 figures - all in one fil

Wpływ modyfikacji skrobi ziemniaczanej na obraz jej ziarn badanych przy użyciu mikroskopu elektronowego

An electron microscope was used to study the granules of native and modified patata starch. Acid modification caused lesions in the granules and revealed their internal structure. Granules modified by the phosphate method exhibited small modules on their surface, underwent aggregation and tended to stretch.Badano naturalną skrobię ziemniaczaną oraz po jej modyfikacji metodą kwasową wg Nowickiego [2] i fosforanową wg Świderskiego [7] pod mikroskopem elektronowym skaningowym przy powiększeniu od 400 do 20000 razy. Ziarna naturalnej skrobi miały wielkość od ok. 5 do 100 μm, duże miały kształt jajowaty, a małe kulisty (fot. 1-a). Na powierzchni ziarn występowały linie dzielące je na owalne pola o zbliżonej powierzchni (fot. 1-b), a przy powiększeniu 20000 razy widoczna była delikatna chropowatość powierzchni (fot. 1-c). Ziarna skrobi modyfikowanej metodą kwasową charakteryzowały się zróżnicowanymi ubytkami i budową warstwową (fot. 2). W niektórych ziarnach widać warstwy biegnące radialnie od środka ziarna do jego powierzchni (fot. 3-a, 3-b) oraz ich podział dichotoniczny na coraz delikatniejsze i cieńsze elementy (fot. 4-a, 4-b). Ziarna skrobi modyfikowanej metodą fosforanową nie wykazały ubytków (fot. 5-a), natomiast na ich powierzchni obserwowanej w powiększeniu 10000 razy widoczne były drobne guzki (fot. 6-a). Ziarna wykazały tendencję do zlepiania się (fot. 6-b) i tworzenia rozciągniętych pasm (fot. 5-a). Wśród ziarn małych wystąpiły ziarna z regularnymi wgłębieniami (fot. 5-b)

Magnetism and Superconductivity in Nd0.81\text{}_{0.81}Sr0.19\text{}_{0.19}MnO3\text{}_{3}/YBa2\text{}_{2}Cu3\text{}_{3}O7\text{}_{7} Superlattices

We report on the growth, structural and magnetic characterization of Nd$\text{}_{0.81}$Sr$\text{}_{0.19}$MnO$\text{}_{3}$/YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ (NSMO/YBCO) superlattices. The NSMO system for the doping level of x=0.19 is a ferromagnetic insulator. Multilayers with a fixed NSMO thickness of 13 unit cells and a varying YBCO layer thickness from 2 unit cells to 6 unit cells were sputtered on LaAlO$\text{}_{3}$ substrates. An onset of superconducting transition is seen starting from the multilayer with 3 unit cells of YBCO layer thickness. Hysteresis loops recorded above and below the superconducting transition show a signature of interlayer exchange coupling

Structural Properties of Co and CoFe Electrodes Forming a Magnetic Tunnel Junction

The M$\text{}_{1}$/MgO/M$\text{}_{2}$ trilayer tunnel magnetoresistance systems are studied by means of X-ray diffraction, NMR, and transmission electron microscopy techniques. As M$\text{}_{1}$ and M$\text{}_{2}$ electrodes we used Co, Fe, and CoFe layers. The growth mechanism and structural quality of both electrodes and of the epitaxial MgO barrier forming the magnetic tunnel junctions are experimentally examined. It is shown that the crystallographic coherence of magnetic tunnel junctions across the MgO barrier is significantly disturbed by imperfect crystal structure of magnetic electrodes. The NMR results indicate a difference in short-range order between bottom and top electrodes

Structural Properties of Co and CoFe Electrodes Forming a Magnetic Tunnel Junction

The M$\text{}_{1}$/MgO/M$\text{}_{2}$ trilayer tunnel magnetoresistance systems are studied by means of X-ray diffraction, NMR, and transmission electron microscopy techniques. As M$\text{}_{1}$ and M$\text{}_{2}$ electrodes we used Co, Fe, and CoFe layers. The growth mechanism and structural quality of both electrodes and of the epitaxial MgO barrier forming the magnetic tunnel junctions are experimentally examined. It is shown that the crystallographic coherence of magnetic tunnel junctions across the MgO barrier is significantly disturbed by imperfect crystal structure of magnetic electrodes. The NMR results indicate a difference in short-range order between bottom and top electrodes

The Influence of Technological PVD Process Parameters on the Topography, Crystal and Molecular Structure of Nanocomposite Films Containing Palladium Nanograins

The paper describes the preparation and characteristics of films composed of Pd nanograins placed in carbonaceous matrix. Films were obtained in PVD (Physical Vapor Deposition) process from two sources containing: the first one – fullerene powder and the second one – palladium acetate. The topographical, morphological and structural changes due to different parameters of PVD process were studied with the use of Atomic Force Microscopy and Scanning Electron Microscopy, whereas the structure was studied with the application of the Transmission Electron Microscopy and Fourier Transform Infrared Spectroscopy methods. It was shown that topographical changes are connected with the decomposition ratio of Pd acetate as well as the form of carbonaceous matrix formed due to this decomposition. Palladium nanograins found in all films exhibit the fcc structure type and their diameter changes from 2 nm to 40 nm depending on the PVD process parameters

Superconductivity and Magnetism in Nd0.5\text{}_{0.5}Sr0.5\text{}_{0.5}MnO3\text{}_{3}/YBa2\text{}_{2}Cu3\text{}_{3}O7\text{}_{7} Superlattices

We report the synthesis and characterization of Nd$\text{}_{0.5}$Sr$\text{}_{0.5}$MnO$\text{}_{3}$/YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ superlattices. X-ray diffraction studies show that the superlattices are [001] oriented. We observe that the magnetic ground state of Nd$\text{}_{0.5}$Sr$\text{}_{0.5}$MnO$\text{}_{3}$ system in a multilayered structure is strongly dependent on the substrate