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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Ferromagnetic Schottky junctions using half-metallic Co{sub 2}MnSi/diamond heterostructures

We demonstrate half-metallic Heusler Co{sub 2}MnSi films epitaxially grown on diamond semiconductors using the ion-beam assisted sputtering method. Lower temperature growth below ∼400 °C is key for obtaining abrupt Co{sub 2}MnSi/diamond interfaces. The Co{sub 2}MnSi films on diamond showed a negative anisotropic magnetoresistance of ∼0.2% at 10 K, suggesting the half-metallic nature of the Co{sub 2}MnSi films. Schottky junctions formed using the Co{sub 2}MnSi/diamond heterostructures at 400 °C showed clear rectification properties with a rectification ratio of ∼10{sup 3}. The Schottky barrier heights of the Co{sub 2}MnSi/diamond interfaces were estimated to be ∼0.8 eV. These results indicate that Co{sub 2}MnSi is a promising spin source for spin injection into diamond.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ferromagnetism and magneto-transport properties of Mn{sub 0.92}Ca{sub 0.08}As thin film grown on Al{sub 2}O{sub 3}(0001) substrate

The epitaxial Mn{sub 0.92}Ca{sub 0.08}As thin film was grown on Al{sub 2}O{sub 3}(0001) substrate by molecular beam epitaxy. The Curie temperature (T{sub C}) around 340 K was enhanced with the addition of Ca, compared to that of bulk MnAs (T{sub C} ∼ 318 K). The maxima magnetoresistance, ∼2.08% at 0.7 T, was observed near the critical magnetic transition temperature. Moreover, the giant magnetocaloric effect was found with the maximum magnetic entropy change, ∼200 J/kgK, around 330 K at 5 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Development and intrinsic properties of hexagonal ferromagnetic (Zr,Ti)Fe{sub 2}

Nanocrystalline Ti{sub 0.75}Zr{sub 0.25}Fe{sub 2+x} (x = 0-0.4) and Ti{sub 0.75−y}B{sub y}Zr{sub 0.25}Fe{sub 2.4} (y = 0-0.35) with high saturation magnetization have been fabricated by the melt-spinning technique. Nanocrystalline Ti{sub 0.75}Zr{sub 0.25}Fe{sub 2+x} consists of the hexagonal C14 Laves phase (Ti,Zr)Fe{sub 2}. Fe addition decreases the lattice parameter a and shrinks the cell volume. The antiferromagnetic Fe-Fe interactions may decrease with the increase of x, leading to a significant enhancement of saturation polarization (J{sub s}) and Curie temperature (T{sub c}). The magnetocrystalline anisotropy constant K also increases with increasing x. Excessive Fe addition (x > 0.25) may induce structural disorder which lowers the J{sub s} and T{sub c}. Nanocrystalline Ti{sub 0.75−y}B{sub y}Zr{sub 0.25}Fe{sub 2.4} is composed of hexagonal (Ti,Zr)Fe{sub 2} and Fe-rich amorphous phases with relatively high J{sub s}. The lattice parameters a, c and cell volume V are almost unchanged with the increase of y for y ≥ 0.16. Simultaneously, the T{sub c} of (Ti,Zr)Fe{sub 2} remains unchanged, indicating that B does not enter this lattice but takes part in forming the amorphous phase, in good agreement with the X-ray diffraction results. The volume fraction of the amorphous phase increases with the increase of B content and results in a large enhancement of J{sub s} up to 10.8 kG. Further B addition (y > 0.30) decreases J{sub s}, possibly due to the decrease of the J{sub s} of the amorphous phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Spin Josephson effect in topological superconductor-ferromagnet junction

The composite topological superconductor (TS), made of one-dimensional spin-orbit coupled nanowire with proximity-induced s-wave superconductivity, is not a pure p-wave superconductor but still has a suppressed s-wave pairing. We propose to probe the spin texture of the p-wave pairing in this composite TS by examining possible spin supercurrents in an unbiased TS/ferromagnet junction. It is found that both the exchange-coupling induced and spin-flip reflection induced spin currents exist in the setup and survive even in the topological phase. We showed that besides the nontrivial p-wave pairing state accounting for Majorana Fermions, there shall be a trivial p-wave pairing state that contributes to spin supercurrent. The trivial p-wave pairing state is diagnosed from the mixing effect between the suppressed s-wave pairing and the topologically nontrivial p-wave pairing. The d vector of the TS is proved not to be rigorously perpendicular to the spin projection of p-wave pairings. Our findings are also confirmed by the Kitaev's p-wave model with a nonzero s-wave pairing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Spin-glass behavior and anomalous magnetoresistance in ferromagnetic Ge{sub 1-x}Fe{sub x}Te epilayer

We report that the Ge{sub 1-x}Fe{sub x}Te thin film exhibits spin-glass behavior when the Fe concentration increases to 0.08. A large bifurcation between the zero-field cooling and field cooling temperature-dependent magnetization was observed. The hysteresis loops after zero-field cooling and field cooling show an exchange bias effect. A time-dependent thermoremanent magnetization follows power-law decay, which confirms the existence of spin glass. The anomalous magnetotranport properties present a further evidence for spin-glass behavior and give a freezing temperature T{sub g} ∼ 5 K in the Ge{sub 0.92}Fe{sub 0.08}Te thin film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Hierarchical cobalt-formate framework series with (4{sup 12}⋅6{sup 3})(4{sup 9}⋅6{sup 6}){sub n} (n = 1–3) topologies exhibiting slow dielectric relaxation and weak ferromagnetism

The employment of linear di-, tri-, and tetra-ammoniums has generated a hierarchy in the binodal (4{sup 12}⋅6{sup 3})(4{sup 9}⋅6{sup 6}){sub n} topologies with n = 1, 2, and 3, respectively, for the cobalt formate frameworks with increasing length of the cavities to match the ammoniums. This indicates the length-directing effect of the polyammoniums. The dynamic movements of polyammoniums between favored sites or orientations within the cavities lead to slow dielectric relaxations. All materials are spin-canted antiferromagnets in low temperatures and show reduced spontaneous magnetizations from di- and tri-, to tetra-ammoniums, because of the increased number of unique Co ions or the antiferromagnetically coupled sublattices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nanoparticles of spinel and perovskite ferromagnets and prospects for their application in medicine

In this work, nanoparticles of La{sub 0.75}Sr{sub 0.25}MnO{sub 3} compounds with perovskite structure and AFe{sub 2}O{sub 4} (A = Mn, Fe, Co, Ni, Zn) with spinel structure have been synthesized by precipitation from diethylene glycol and microemulsion using Triton X-100 surfactant. Comparative X-ray diffraction and magnetic studies of the synthesized nanoparticles have been carried out. Magnetic fluids prepared from synthesized nanopowders have been characterized by calorimetric measurements of specific loss power (SLP)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Direct observation of ferromagnetism in grain boundary phase of Nd-Fe-B sintered magnet using soft x-ray magnetic circular dichroism

We have investigated the magnetism of the grain boundary (GB) phase in a Nd{sub 14.0}Fe{sub 79.7}Cu{sub 0.1}B{sub 6.2} sintered magnet using soft x-ray magnetic circular dichroism (XMCD) at the Fe L{sub 2,3}-edges. Soft XMCD spectra were measured from the fractured surface that was confirmed to be covered with a thin GB phase by Auger electron spectroscopy. The magnetic moment of Fe in the GB phase was estimated to be m{sub GB}=1.4 μ{sub B} at 30 °C using the sum rule analysis for XMCD spectra, which is 60% of that of Fe in the Nd{sub 2}Fe{sub 14}B compound. The temperature dependence of m{sub GB} evaluated with reference to Fe in the Nd{sub 2}Fe{sub 14}B phase indicated that the Curie temperature of the GB phase is more than 50 °C lower compared to that of Nd{sub 2}Fe{sub 14}B.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Angular dependent study on ferromagnetic resonance and spin excitations by spin rectification

We report angular dependent spin rectification spectra which are applied to studying spin excitations in single permalloy stripe. Based on planar Hall effect, those spin excitations generate special resonant dc Hall voltages, which have been characterized as functions of the amplitude and direction of applied magnetic field. Through high angular resolution 2D mappings, the evolutions of different spin excitation can be directly presented, and the dynamic magnetic parameters such as the gyromagnetic ratio, effective exchange field, as well as the quantized numbers of standing spin waves can be accurately determined through fitting the angular evolution of each resonance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A comprehensive study of the magnetic, structural, and transport properties of the III-V ferromagnetic semiconductor InMnP

The manganese induced magnetic, electrical, and structural modification in InMnP epilayers, prepared by Mn ion implantation and pulsed laser annealing, are investigated in the following work. All samples exhibit clear hysteresis loops and strong spin polarization at the Fermi level. The degree of magnetization, the Curie temperature, and the spin polarization depend on the Mn concentration. The bright-field transmission electron micrographs show that InP samples become almost amorphous after Mn implantation but recrystallize after pulsed laser annealing. We did not observe an insulator-metal transition in InMnP up to a Mn concentration of 5 at. %. Instead all InMnP samples show insulating characteristics up to the lowest measured temperature. Magnetoresistance results obtained at low temperatures support the hopping conduction mechanism in InMnP. We find that the Mn impurity band remains detached from the valence band in InMnP up to 5 at. % Mn doping. Our findings indicate that the local environment of Mn ions in InP is similar to GaMnAs, GaMnP, and InMnAs; however, the electrical properties of these Mn implanted III-V compounds are different. This is one of the consequences of the different Mn binding energy in these compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Temperature evolution of electromotive force from Pt on yttrium-iron-garnet under ferromagnetic resonance

Temperature evolution of electromotive force from Pt due to the inverse spin Hall effect is studied. Pure spin current is injected from yttrium-iron-garnet by using spin pumping technique. The electromotive force from the Pt monotonically decreases with decreasing temperature, and it is showed that there is a deviation between the measured and the calculated electromotive forces.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Half-metallic ferromagnetism in chalcopyrite type compounds ZnMX{sub 2} (M=Sc, V, Mn, Fe; X = P, As)

Electronic structure and magnetic properties of ZnMX{sub 2} (M=Sc, V, Mn and Fe; X= As and P) compounds in body centred tetragonal chalcopyrite structure have been investigated using first-principles calculations based on density functional theory (DFT) within the local spin density approximation (LSDA). The spin-polarized electronic band structure and density of states of all these compounds show that the spin-up electrons have metallic and the spin-down electrons have a semiconducting gap and the magnetic moment mainly originates from the strong spin polarization of 3d states of transition metal (M=Sc, V, Mn and Fe) atoms and p-like states of anion X (P and As) atoms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Spin-current diode with a ferromagnetic semiconductor

Diode is a key device in electronics: the charge current can flow through the device under a forward bias, while almost no current flows under a reverse bias. Here, we propose a corresponding device in spintronics: the spin-current diode, in which the forward spin current is large but the reversed one is negligible. We show that the lead/ferromagnetic quantum dot/lead system and the lead/ferromagnetic semiconductor/lead junction can work as spin-current diodes. The spin-current diode, a low dissipation device, may have important applications in spintronics, as the conventional charge-current diode does in electronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Noise signatures of metastable resistivity states in ferromagnetic insulating manganite

Pronounced noise signatures enabling one to discriminate metastable resistivity states in La{sub 0.86}Ca{sub 0.14}MnO{sub 3} single crystals have been observed. The normalized noise spectra for metastable resisitivity differ both in shape and magnitude, indicating that the metastable state is associated with transition of the electronic system into another local minimum of the potential landscape. Such scenario is consistent with freezing of the electronic system into a Coulomb glass state.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Topological transformations of Hopf solitons in chiral ferromagnets and liquid crystals

Significance While arising in theories in many branches of science, from particle physics to condensed matter and cosmology, stable three-dimensional topological solitons remained experimentally elusive until very recently. We now show that such solitons can be electrically and magnetically switched between states with the same or different Hopf indices. Richness and robustness of this switching promise technological applications in the new breeds of information displays and data storage devices, as well as may provide a test ground and new inspirations for the mathematical knot theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗