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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Modulation of the magnetic domain size induced by an electric field

The electric field (EF) effect on the magnetic domain structure of a Pt/Co system was studied, where an EF was applied to the top surface of the Co layer. The width of the maze domain was significantly modified by the application of the EF at a temperature slightly below the Curie temperature. After a detailed analysis, a change in the microscopic exchange stiffness induced by the EF application was suggested to dominate the modulation of the domain width observed in the experiment. The accumulation of electrons at the surface of the Co layer resulted in an increase in the microscopic exchange stiffness and the Curie temperature. The result was consistent with the recent theoretical prediction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

The role of weak interlayer coupling in the spin-reorientation of perpendicular ultrathin Co-Fe-B/MgO-based heterostructures

Ultrathin magnetic tunneling structures implicate fundamental interlayer exchange coupling between magnetic layers. Here, we describe its important role in the spin-reorientation transition of weakly coupled perpendicular ultrathin Ta/Co-Fe-B/MgO/Co-Fe-B/Ta heterostructures. Near the spin-reorientation, the domain structure is quite sensitive to weak interlayer exchange coupling. Antiferromagnetic coupling stabilizes homogeneous perpendicular magnetization at the remanence, whereas ferromagnetic coupling favors in-/out-of-plane stripe domains. Close to the spin-reorientation transition, even the subtle changes of interlayer exchange coupling can lead to reversible switching between stable in- and out-of-plane states. Our results suggest that this multi-stability caused by the interplay of perpendicular anisotropy and weak interlayer coupling can be utilized in perpendicular spin torque devices operating under reduced spin currents.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Kinetics of magnetization reversal in a heterophase nanomagnet with spatially modulated anisotropy

Magnetization reversal modes in a thin-film NiFeCuMo ferromagnet (FM) with periodically varying in-plane anisotropy are studied by the magneto-optical indicator film (MOIF) technique. The uni-directional anisotropy in FM regions exchange-coupled to a FeMn antiferromagnet (AFM) film in the form of square mesh stripes is alternated by the uniaxial anisotropy in the FM regions inside this mesh. It is shown that the boundaries formed along the edges of these stripes, which separate FM regions with different anisotropy, crucially influence the kinetics of domain-structure transformation in both types of FM regions. It is established that the lateral exchange anisotropy in the ferromagnet, which is determined by the stabilization of the spin distribution in the FM layer along the FM-(FM/AFM) interface, leads to the asymmetry of the magnetization reversal in FM regions bordered with an FM/AFM structure. Anisotropy of the mobility of 180-degree “charged” and “uncharged” domain walls situated, respectively, perpendicular and parallel to the unidirectional anisotropy axis is revealed. The difference observed between the mobilities of charged and uncharged domain walls is attributed to the difference in the spin distribution in these walls with respect to the unidirectional anisotropy axis and is a key factor for the difference between the magnetization reversal kinetics in horizontal and vertical exchange-biased FM stripes. Drastic differences are revealed in the asymmetry of magnetization reversal processes in mutually perpendicular narrow stripes of FM/AFM structures. Possible mechanisms of magnetization reversal in low-dimensional FM-(FM/AFM) heterostructures are discussed with regard to the effect of domain walls localized on the edges of AFM layers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Magnetic stripe domains of [Pt/Co/Cu]{sub 10} multilayer near spin reorientation transition

The dependence of magnetic anisotropy, magnetic domain patterns and magnetization reversal processes in [Pt/Co(t{sub Co})/Cu]{sub 10} film stack epitaxied on Cu (111) substrate have been studied as a function of the Co layer thickness t{sub Co}, by magneto-optic polar Kerr magnetometry and microscopy. We find the film undergoes spin reorientation transition from out-of-plane to in-plane as t{sub Co} increases. The SRT thickness is verified by Rotating-field Magneto-Optic Kerr effect method. The film exhibits the stripe domain structures at remanence with the width decreasing while t{sub Co} approaches SRT. As demonstrated by the first order reversal curve measurement, the magnetization reversal process encompasses irreversible domain nucleation, domain annihilation at large field and reversible domain switching near remanence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Relaxation of the magnetic state of a ferromagnetic–superconducting layered structure

We have proposed a real-time method of neutron reflectometry. The magnetic state of the Ta/V/FM/Nb/Si ferromagnetic–superconducting system has been analyzed. Relaxation of the inhomogeneous magnetic state with a characteristic time of several hours, which depends on the magnetic field magnitude and temperature, has been observed. The relaxation of the domain structure has changed upon a transition of the V and Nb layers to the superconducting state. It has been concluded that real-time reflectometry data for polarized neutrons are important for determining the origin of magnetism in ferromagnetic–superconducting layered structures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Ferroelectric domain building blocks for photonic and nonlinear optical microstructures in LiNbO{sub 3}

The ability to manipulate the size and depth of poling inhibited domains, which are produced by UV laser irradiation of the +z face of lithium niobate crystals followed by electric field poling, is demonstrated. It is shown that complex domain structures, much wider than the irradiating laser spot, can be obtained by partially overlapping the subsequent UV laser irradiated tracks. The result of this stitching process is one uniform domain without any remaining trace of its constituent components thus increasing dramatically the utility of this method for the fabrication of surface microstructures as well as periodic and aperiodic domain lattices for nonlinear optical and surface acoustic wave applications. Finally, the impact of multi exposure on the domain characteristics is also investigated indicating that some control over the domain depth can be attained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Enhanced magnetic hysteresis in Ni-Mn-Ga single crystal and its influence on magnetic shape memory effect

Enhanced magnetic hysteresis due to boron doping in combination with magnetic shape memory effect in Ni-Mn-Ga single crystal results in new interesting functionality of magnetic shape memory (MSM) alloys such as mechanical demagnetization. In Ni{sub 50.0}Mn{sub 28.5}Ga{sub 21.5} single crystal, the boron doping increased magnetic coercivity from few Oe to 270 Oe while not affecting the transformation behavior and 10 M martensite structure. However, the magnetic field needed for MSM effect also increased in doped sample. The magnetic behavior is compared to undoped single crystal of similar composition. The evidence from the X-ray diffraction, magnetic domain structure, magnetization loops, and temperature evolution of the magnetic coercivity points out that the enhanced hysteresis is caused by stress-induced anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Periodic domain patterning by electron beam of proton exchanged waveguides in lithium niobate

Formation of domain structure by electron beam irradiation in congruent lithium niobate covered by surface dielectric layer with planar and channel waveguides produced by Soft Proton Exchange (SPE) process has been studied. Formation of domains with arbitrary shapes as a result of discrete switching has been revealed. The fact was attributed to ineffective screening of depolarization field in the crystals with a surface layer modified by SPE process. The dependences of the domain sizes on the dose and the distance between irradiated areas have been revealed. Finally, we have demonstrated that electron beam irradiation of lithium niobate crystals with surface resist layer can produce high quality periodical domain patterns after channel waveguide fabrication. Second harmonic generation with normalized nonlinear conversion efficiency up to 48%/(W cm{sup 2}) has been achieved in such waveguides.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Enhancement of the magnetocapacitance effect in an external electric field in La{sub x}Bi{sub 1-x}FeO{sub 3} films

The goal of the study is to determine the value of magnetocapacitance under the substitution of lanthanum for bismuth in thin La{sub x}Bi{sub 1-x}FeO{sub 3} films and to find out the effect of an external bias electric field on the magnetocapacitance effect. To solve this task, the dielectric permittivity, the magnetic permeability, and the loss tangent are measured in La{sub x}Bi{sub 1-x}FeO{sub 3} films in magnetic fields of up to 8 kOe in the range of temperatures 100 K < T < 1000 K. Maxima of the permittivity and permeability at low temperatures and the dependence of the permeability on the prehistory of a sample are found. An increase in the magnetocapacitance due to the substitution of lanthanum for bismuth is observed. A giant enhancement of magnetocapacitance in an external electric bias field is revealed. These phenomena are attributed to the rearrangement of the domain structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Quaternary structure independent folding of voltage-gated ion channel pore domain subunits

Every voltage-gated ion channel (VGIC) has a pore domain (PD) made from four subunits, each comprising an antiparallel transmembrane helix pair bridged by a loop. The extent to which PD subunit structure requires quaternary interactions is unclear. In this report we present crystal structures of a set of bacterial voltage-gated sodium channel (BacNa V ) 'pore only' proteins that reveal a surprising collection of non-canonical quaternary arrangements in which the PD tertiary structure is maintained. This context-independent structural robustness, supported by molecular dynamics simulations, indicates that VGIC-PD tertiary structure is independent of quaternary interactions. This fold occurs throughout the VGIC superfamily and in diverse transmembrane and soluble proteins. Strikingly, characterization of PD subunit-binding Fabs indicates that non-canonical quaternary PD conformations can occur in full-length VGICs. Together, our data demonstrate that the VGIC-PD is an autonomously folded unit. This property has implications for VGIC biogenesis, understanding functional states, de novo channel design, and VGIC structural origins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Magnetic phases in Pt/Co/Pt films induced by single and multiple femtosecond laser pulses

Ultrathin Pt/Co/Pt trilayers with initial in-plane magnetization were irradiated with femtosecond laser pulses. In this way, an irreversible structural modification was introduced, which resulted in the creation of numerous pulse fluence-dependent magnetic phases. This was particularly true with the out-of-plane magnetization state, which exhibited a submicrometer domain structure. This effect was studied in a broad range of pulse fluences up to the point of ablation of the metallic films. In addition to this single-pulse experiment, multiple exposure spots were also investigated, which exhibited an extended area of out-of-plane magnetization phases and a decreased damage threshold. Using a double exposure with partially overlapped spots, a two-dimensional diagram of the magnetic phases as a function of the two energy densities was built, which showed a strong inequality between the first and second incoming pulses.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Domain imaging on multiferroic BiFeO{sub 3}(001) by linear and circular dichroism in threshold photoemission

We demonstrate ferroelectric domain imaging at BiFeO{sub 3}(001) single crystal surfaces with laser-based threshold photoemission electron microscopy (PEEM). Work function differences and linear dichroism allow for the identification of the eight independent ferroelectric domain configurations in the PEEM images. There, the determined domain structure is consistent with piezoresponse force microscopy of the sample surface and can also be related to the circular dichroic PEEM images. Our results provide a method for efficient mapping of complex ferroelectric domains with laser-excited PEEM and may allow lab-based time-resolved studies of the domain dynamics in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Symmetry breaking during low-temperature domain formation in micron-sized magnetite crystals

We report the results of synchrotron Bragg Coherent x-ray Diffraction Imaging (BCDI) experiments to investigate domain formation in a micron-sized magnetite crystal undergoing the Verwey transition at low temperature. A strong splitting of the measured 311 Bragg reflection was observed in the low-temperature phase, indicating the formation of domains. BCDI revealed pronounced strain distributions, characterized by a clear layered stripe domain structure in real-space. Stripes were seen only along the [001] crystallographic direction, normal to the substrate surface direction, breaking the symmetry of the cubic high-temperature phase. It is argued that other domain directions were suppressed by the sample mounting orientation. More surprisingly, only a single domain orientation was observed, suggesting an additional symmetry-breaking influence originating from the shape of the crystal. Gaining insight into how thermal effects induce the formation of layered or striped phases offers a valuable framework for understanding the development of mesoscopic domains and strain patterns in functional materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Irreversible magnetization switching at the onset of superconductivity in a superconductor ferromagnet hybrid

We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well as magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Impact of pulse poling on static and dynamic ferroelastic-domain contributions in tetragonal Pb(Ti, Zr)O{sub 3} films determined by in-situ x–ray diffraction analysis

The effects of bipolar pulse poling on the ferroelastic domain structure and their contribution to the electrical and piezoelectric properties of Pb(Ti{sub 0.7}Zr{sub 0.3})O{sub 3} films are investigated. Micro x-ray diffraction measurements clearly show that the volume fraction of the c-domain increases irreversibly as the poling field is increased, leading to changes in the remanent polarization, dielectric constant, and piezoelectric coefficient. Theoretical estimations well explain the changes of remanent polarization and dielectric constant, but the increase in piezoelectric coefficient is much larger than the theoretical estimation. In-situ x-ray diffraction analysis under an electric field reveals that this disagreement is due to the unexpected activation of the ferroelastic domain wall motion. Our results provide new insight into the poling effect on the electric and piezoelectric properties of ferroelectric films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Structural and electronic properties of V{sub 2}O{sub 3} ultrathin film on Ag(001): LEED and photoemission study

V{sub 2}O{sub 3} ultrathin films were grown on Ag(001) substrate by reactive evaporation of vanadium (V) metal in presence of oxygen and their structural and electronic properties were studied by Low Energy Electron Diffraction (LEED), X-ray Photo Electron Spectroscopy (XPS) and Angle Resolved Photoemission Spectroscopic (ARPES) techniques, respectively. On top of square symmetry substrate Ag(001), hexagonal surface of V{sub 2}O{sub 3} (0001) is stabilized in the form of two domain structure, rotated by 30°(or 90°)to each other, has been observed by LEED. Rather than epitaxial flat monolayer, formation of well-ordered V{sub 2}O{sub 3} (0001) island has been confirmed from the LEED and the Photoemission Spectroscopic (PES) study. Stoichiometry of the grown film was confirmed by the XPS study. Evolution of valance band electronic structure of V{sub 2}O{sub 3} (0001) surface has been studied as a function of film thickness by ARPES.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structural and evolutionary relationships of “AT-less” type I polyketide synthase ketosynthases

Acyltransferase (AT)-less type I polyketide synthases (PKSs) break the type I PKS paradigm. They lack the integrated AT domains within their modules and instead use a discrete AT that acts in trans, whereas a type I PKS module minimally contains AT, acyl carrier protein (ACP), and ketosynthase (KS) domains. Structures of canonical type I PKS KS-AT didomains reveal structured linkers that connect the two domains. AT-less type I PKS KSs have remnants of these linkers, which have been hypothesized to be AT docking domains. Natural products produced by AT-less type I PKSs are very complex because of an increased representation of unique modifying domains. AT-less type I PKS KSs possess substrate specificity and fall into phylogenetic clades that correlate with their substrates, whereas canonical type I PKS KSs are monophyletic. We have solved crystal structures of seven AT-less type I PKS KS domains that represent various sequence clusters, revealing insight into the large structural and subtle amino acid residue differences that lead to unique active site topologies and substrate specificities. Here, one set of structures represents a larger group of KS domains from both canonical and AT-less type I PKSs that accept amino acid-containing substrates. One structure has a partial AT-domain, revealing the structural consequences of a type I PKS KS evolving into an AT-less type I PKS KS. These structures highlight the structural diversity within the AT-less type I PKS KS family, and most important, provide a unique opportunity to study the molecular evolution of substrate specificity within the type I PKSs.

59 BASIC BIOLOGICAL SCIENCES↗