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Annealing effects in plated-wire memory elements. I - Interdiffusion of copper and Permalloy.
Results of investigations using X-ray diffraction and electron-beam microprobe techniques have shown that copper and Permalloy platings interdiffuse at low temperatures when plated-wire memory elements are annealed for times as short as 50 hr. Measurable interdiffusion between Permalloy platings and gold substrates does not occur in similar conditions. Both magnetic and compositional changes during aging are found to occur by a thermally activated process with activation energies around 38 kcal/mol. It is shown, however, that copper-diffusion and magnetic-dispersion changes during aging are merely concurrent processes, neither being the other's cause.
Single-integral form of the dispersion relation for waves in a magnetized plasma
Wave dispersion relations in uniform magnetized plasma represented in single integral form, discussing model loss-cone and temperature anisotropy distributions
Magnetic structure and dispersion relation of the S = 1 2 quasi-one-dimensional Ising-like antiferromagnet BaCo 2 V 2 O 8 in a transverse magnetic field
Here, BaCo 2 V 2 O 8 consists of Co chains in which a Co 2+ ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo 2 V 2 O 8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis. We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 XXZ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.
Dynamic coupling and spin-wave dispersions in a magnetic hybrid system made of an artificial spin-ice structure and an extended NiFe underlayer
We present a combined experimental and numerical study of the spin-wave dispersion in a NiFe artificial spin-ice (ASI) system consisting of an array of stadium-shaped nanoislands deposited on the top of a continuous NiFe film with non-magnetic spacer layers of varying thickness. The spin-wave dispersion, measured by wavevector resolved Brillouin light scattering spectroscopy in the Damon–Eshbach configuration, consists of a rich number of modes, with either stationary or propagating character. We find that the lowest frequency mode displays a bandwidth of ~0.5 GHz, which is independent of the presence of the film underneath. On the contrary, the Brillouin light scattering intensity of some of the detected modes strongly depends on the presence of the extended thin-film underlayer. Micromagnetic simulations unveil the details of the dynamic coupling between the ASI lattice and film underlayer. Interestingly, the ASI lattice facilitates dynamics of the film either specific wavelengths or intensity modulation peculiar to the modes of the ASI elements imprinted in the film. Our results demonstrate that propagating spin waves can be modulated at the nanometer length scale by harnessing the dynamic mode coupling in the vertical, i.e., the out-of-plane direction of suitably designed magnonic structures.
Solar Wind Magnetic Field Line Dispersal: Multispacecraft Analysis and Comparison with Theoretical Results
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Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: Role of dispersion, nonlinearity, and damping
Nonlocal compensation of magnetic damping by spin injection has been theoretically shown to display dynamic, noncollinear magnetization states that carry spin currents over micrometer distances. Such states can be generically referred to as dissipative exchange flows (DEFs) because spatially diffusing spin currents are established by the mutual exchange torque exerted by neighboring spins. Analytical studies to date have been limited to the weak spin injection assumption whereby the equation of motion for the magnetization is mapped to hydrodynamic equations describing spin flow and then linearized. In this work, we analytically and numerically study easy-plane ferromagnetic channels subject to spin injection of arbitrary strength at one extremum under a unified hydrodynamic framework. We propose that DEFs generally exhibit a nonlinear profile along the channel accompanied by a nonlinear frequency tunability. At large injection strengths, we fully characterize a magnetization state we call a contact-soliton DEF (CS-DEF) composed of a stationary soliton at the injection site, which smoothly transitions into a DEF and exhibits a negative frequency tunability. The transition between a DEF and a CS-DEF occurs at the maximum precessional frequency and coincides with the Landau criterion: a subsonic to supersonic flow transition. Leveraging the hydraulic-electrical analogy, the current-voltage characteristics of a nonlinear DEF circuit are presented. Micromagnetic simulations of nanowires that include magnetocrystalline anisotropy and nonlocal dipole fields are in qualitative agreement with the analytical results. The magnetization states found here along with their characteristic profile and spectral features provide quantitative guidelines to pursue an experimental demonstration of DEFs in ferromagnetic materials and establish a unified description for long-distance spin transport.
MAVEN Observations of Energy-Time Dispersed Electron Signatures in Martian Crustal Magnetic Fields
Energy-time dispersed electron signatures are observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission in the vicinity of strong Martian crustal magnetic fields. Analysis of pitch angle distributions indicates that these dispersed electrons are typically trapped on closed field lines formed above strong crustal magnetic sources. Most of the dispersed electron signatures are characterized by peak energies decreasing with time rather than increasing peak energies. These properties can be explained by impulsive and local injection of hot electrons into closed field lines and subsequent dispersion by magnetic drift of the trapped electrons. In addition, the dispersed flux enhancements are often bursty and sometimes exhibit clear periodicity, suggesting that the injection and trapping processes are intrinsically time dependent and dynamic. These MAVEN observations demonstrate that common physical processes can operate in both global intrinsic magnetospheres and local crustal magnetic fields.
Magnetic properties of stable dispersions of subdomain magnetite particles
Stable colloidal dispersions of subdomain magnetite particles correlated for magnetic properties in terms of size distribution and volumetric concentration by superparamagnetic theory
Aqueous Superparamagnetic Magnetite Dispersions with Ultrahigh Initial Magnetic Susceptibilities
Superparamagnetic nanoparticles with a high initial magneti susceptibility χo are of great interest in a wide variety of chemical, biomedical, electronic, and subsurface energy applications. In order to achieve the theoretically predicted increase in χ o with the cube of the magnetic diameter, new synthetic techniques are needed to control the crystal structure, particularly for magnetite nanoparticles larger than 10 nm. Aqueous magnetite dispersions (Fe 3 O 4 ) with a χ o of 3.3 (dimensionless SI units) at 1.9 vol %, over 3- to 5-fold greater than those reported previously, were produced in a one-pot synthesis at 210 °C and ambient pressure via thermal decomposition of Fe(II) acetate in triethylene glycol (TEG). The rapid nucleation and focused growth with an unusually high precursor-to-solvent molar ratio of 1:12 led to primary particles with a volume average diameter of 16 nm and low polydispersity according to TEM. The morphology was a mixture of stoichiometric and substoichiometric magnetite according to X-ray diffraction (XRD) and Mössbauer spectroscopy. Finally, the increase in χ o with the cube of magnetic diameter as well as a saturation magnetization approaching the theoretical limit may be attributed to the highly crystalline structure and very small nonmagnetic layer (~1 nm) with disordered spin orientation on the surface.
New dispersion relation for a strongly magnetized degenerate electron plasma with anisotropic pressure.
A new dispersion relation for an unbounded degenerate electron plasma imbedded in a superstrong magnetic field is derived on the basis of the Canuto-Chiu equation of state. The properties of the various types of waves are discussed for two density regimes of astrophysical interest. Propagation parallel and perpendicular to the magnetic field are examined in detail.
Unravelling Magnetic Nanochain Formation in Dispersion for In Vivo Applications
Self-assembly of iron oxide nanoparticles (IONPs) into 1D chains is appealing, because of their biocompatibility and higher mobility compared to 2D/3D assemblies while traversing the circulatory passages and blood vessels for in vivo biomedical applications. In this work, parameters such as size, concentration, composition, and magnetic field, responsible for chain formation of IONPs in a dispersion as opposed to spatially confining substrates, are examined. In particular, the monodisperse 27 nm IONPs synthesized by an extended LaMer mechanism are shown to form chains at 4 mT, which are lengthened with applied field reaching 270 nm at 2.2 T. The chain lengths are completely reversible in field. Using a combination of scattering methods and reverse Monte Carlo simulations the formation of chains is directly visualized. The visualization of real-space IONPs assemblies formed in dispersions presents a novel tool for biomedical researchers. This allows for rapid exploration of the behavior of IONPs in solution in a broad parameter space and unambiguous extraction of the parameters of the equilibrium structures. Additionally, it can be extended to study novel assemblies formed by more complex geometries of IONPs.
Hourglass Dispersion and Resonance of Magnetic Excitations in the Superconducting State of the Single-Layer Cuprate HgBa 2 CuO 4 + δ Near Optimal Doping
Here, we use neutron scattering to study magnetic excitations near the antiferromagnetic wave vector in the underdoped single-layer cuprate HgBa 2 CuO 4 + δ (superconducting transition temperature T c ≈ 88 K , pseudogap temperature T* ≈ 220 K ). The response is distinctly enhanced below T* and exhibits a Y -shaped dispersion in the pseudogap state, whereas the superconducting state features an X -shaped (hourglass) dispersion and a further resonancelike enhancement. We also observe a large spin gap of about 40 meV in both states. This phenomenology is reminiscent of that exhibited by bilayer cuprates. The resonance spectral weight, irrespective of doping and compound, scales linearly with the putative binding energy of a spin exciton described by an itinerant-spin formalism.
Dispersion Characteristics and Phase Index of One-Dimensional Magnetized Ferrite Photonic Crystals in Transverse Magnetization Configuration for TE Modes
The dispersion characteristics and phase index of magnetized one-dimensional ferrite photonic crystals in transverse magnetization for transverse electric modes are investigated. The dispersion relation and expression for phase index are derived by using transfer matrix method. The effects of structural parameters such as external magnetic fields, filling factor, and β on dispersion properties and phase index are investigated. The dielectric nature of the considered magnetized ferrite photonic crystal structure is demonstrated. Also, the band structure for ω < 1.5 × 10{sup 10} rad s{sup − 1} is strongly affected by external magnetic fields. It is observed that phase index occurs in the form of lobes and is found to be controlled by external magnetic field, β, and filling factor.
Nuclear Magnetic Resonance Dynamics of LiTFSI–Pyrazole Eutectic Solvents
Deep Eutectic Solvents (DESs) have emerged as promising candidates to replace conventional organic solvents in various technological applications due to their low vapor pressure, non-flammability, and ease of preparation at low costs. In particular, Type IV DESs, which are composed of metal salts and hydrogen bond donors, are possible replacements for lithium-ion battery electrolytes. In this study, we investigate the molecular dynamics of solvents of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and pyrazole (PYR) at varying LiTFSI:PYR molar ratios (1:2, 1:3, 1:4, 1:5) using Nuclear Magnetic Resonance Dispersion (NMRD) and Pulsed Field Gradient (PFG) Nuclear Magnetic Resonance (NMR). PFG NMR reveals composition-dependent diffusion trends, while NMRD provides molecular-level insights into the longitudinal relaxation rate (R 1 = 1/T 1 ). Notably, the LiTFSI:PYR (1:2) sample shows distinct behavior across both techniques, exhibiting enhanced relaxation rates and lower self-diffusion for 1 H compared to the other nuclei ( 19 F and 7 Li), suggestive of stronger and more efficient Li + –pyrazole interactions, as confirmed by the modeling of the relaxation profiles. Our study advances understanding of ion dynamics in azole-based eutectic solvents, supporting their potential use in safer battery electrolytes.
High fidelity simulations of contaminant dispersion in an urban environment with comparison to magnetic resonance imaging measurements
The dispersion of a contaminant in an urban environment has the potential to impact a large population of people. In this work, a complex urban canopy flow based on the Oklahoma City downtown business district circa 2003 is studied using Magnetic Resonance Imaging (MRI) and high-fidelity Large Eddy Simulations (LES). MRI is a novel experimental technique that can provide high-resolution measurements in four dimensions (three spatial and temporal) for lab scale models. The experiments and simulations use the same geometry and boundary conditions providing a one-to-one comparison of the two methods. Results are presented on the time-averaged velocity and concentration fields, the temporal dynamics of the concentration plumes for a transient release, and a novel Cloud Identification Algorithm that can separate plumes produced by periodic contaminant releases used for ensemble averaging over many releases. The MRI and LES datasets both include millions of measurement voxels and the comparisons highlight the complex 3D nature of the flow including strong vertical velocities in spanwise street canyons and flow acceleration in streamwise street canyons. The concentration fields are qualitatively similar albeit the LES shows larger dispersion. A quantitative analysis with performance measures compares the datasets pointwise and demonstrates that the two 3D datasets are similar with respect to many measures including a fractional bias of 0.02 (ideal=0.0), correlation coefficient of 0.87 (ideal = 1.0), and the fraction points within a factor of 2 is 0.98 (ideal = 1.0). Plume analysis compares the arrival and residence time of contaminant and is found to vary significantly with location within the urban environment with arrival times between 0 and 1.25 and differences within the contaminant cloud less than 10% at most locations.
Kinematics of Magnetic Bright Features in the Solar Photosphere
Convective flows are known as the prime means of transporting magnetic fields on the solar surface. Thus, small magnetic structures are good tracers of turbulent flows. We study the migration and dispersal of magnetic bright features (MBFs) in intergranular areas observed at high spatial resolution with Sunrise/IMaX. We describe the flux dispersal of individual MBFs as a diffusion process whose parameters are computed for various areas in the quiet-Sun and the vicinity of active regions from seeing-free data. We find that magnetic concentrations are best described as random walkers close to network areas (diffusion index, γ=1.0), travelers with constant speeds over a supergranule (γ=1.9--2.0), and decelerating movers in the vicinity of flux emergence and/or within active regions (γ=1.4--1.5). The three types of regions host MBFs with mean diffusion coefficients of 130 km{sup 2} s{sup −1}, 80–90 km{sup 2} s{sup −1}, and 25–70 km{sup 2} s{sup −1}, respectively. The MBFs in these three types of regions are found to display a distinct kinematic behavior at a confidence level in excess of 95%.
Calibration of proton dispersion for the NIF electron positron proton spectrometer (NEPPS) for short-pulse laser experiments on the NIF ARC
Experiments using the Advanced Radiographic Capability (ARC) laser at the National Ignition Facility (NIF) aim to characterize short-pulse-driven proton beams for use as both probes and drivers for high-energy-density physics experiments. Measurements of ARC-driven proton beam characteristics, such as energy spectrum and conversion efficiency, rely on the NIF Electron Positron Proton Spectrometer (NEPPS). The NEPPS diagnostic is a version of an existing particle spectrometer which is used for detecting MeV electron and positron spectra via permanent magnetic field dispersion. These spectrometers have not yet been calibrated for protons and instead use an analytical calculation to estimate the dispersion. Small variations in the field uniformity can affect the proton dispersion due to the relatively small resolving power (E/dE) for this diagnostic. A broadband energy, laser-accelerated proton source was produced at the Titan laser to experimentally calibrate the proton dispersion. These experimental data were used to test the theoretical dispersion. Numerical simulations using measurements of the magnetic field variation within the diagnostic were used to obtain a realistic proton dispersion curve for the new NEPPS units. In conclusion, this procedure for obtaining each independent dispersion is applicable to all EPPS and NEPPS diagnostics, given the axial magnetic field profile.