Monte Carlo simulation of magnetic domain structure and magnetic properties near the morphotropic phase boundary
The magnetization properties changing with the anisotropy energy barrier (a) and temperature (b) under a constant field.
Chemistry↗
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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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High-temperature magnetic blocking and magneto-structural correlations in a series of dysprosium( iii ) metallocenium single-molecule magnets
Subtle changes in ligand substitution result in substantial changes in molecular structure and magnetic properties in a series of dysprosium( iii ) metallocenium salts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Exploring room-temperature transport of single-molecule magnet-based molecular spintronics devices using the magnetic tunnel junction as a device platform
A device architecture utilizing a single-molecule magnet (SMM) as a device element between two ferromagnetic electrodes may open vast opportunities to create novel molecular spintronics devices.
42 ENGINEERING↗
Electron transfer induced magnetic ordering of metal-cyanide magnets
Solution synthesis of molecular cyanide magnets via FeSe template is promoted by thermal activation, where TCNE molecules substitute Se atoms in two-dimensional FeSe framework.
36 MATERIALS SCIENCE↗
Relaxation dynamics in see-saw shaped Dy( iii ) single-molecule magnets
Unusual see-saw shaped Dy( iii ) single-molecule magnets, [K(DME) n ][L Ar Dy(X) 2 ] (L Ar = {C 6 H 4 [(2,6- i PrC 6 H 3 )NC 6 H 4 ] 2 } 2− ), X = Cl ( 1 ) and X = I ( 2 ) were synthesized and display high effective energy barriers ( U eff = 1278–1334 K) in zero field.
Harriman, Katie L. M.↗
Clean measurements of the nucleon axial-vector and free-neutron magnetic form factors
We discuss the feasibility of a weak charged current experiment using a low energy electron beam. A first goal is to measure the Q{sup 2} dependence of the axial-vector form factor g{sub a}(Q{sup 2}). It can be measured model-independently and as robustly as for electromagnetic form factors from typical electron scattering experiments, in contrast to the methods used so far to measure g{sub a}(Q{sup 2}). If g{sub a}(Q{sup 2}) follows a dipole form, the axial mass can be extracted with a better accuracy than the world data altogether. The most important detection equipment would be a segmented neutron detector with good momentum and angular resolution that is symmetric about the beam direction, and covers a moderate angular range. A high intensity beam (100 uA) is necessary. Beam polarization is highly desirable as it provides a clean measurement of the backgrounds. Beam energies between 70 and 110 MeV are ideal. This range would provide a Q{sup 2} mapping of g{sub a} between 0.01 <Q{sup 2}< 0.04 GeV{sup 2}. 60 days of beam can yield 14 data points with a subpercent statistical and point to point uncorrelated uncertainties on each point. Such an experiment may also allow to measure the free-neutron magnetic form factor G{sub M}{sup n}. The experiment employs the usual techniques of electron-nucleon scattering and presents no special difficulty. Higher energy extensions are possible. They could yield measurements of g{sub a}(Q{sup 2}) up to Q{sup 2}=3 GeV{sup 2} and the possibility to access other form factors, such as the almost unknown pseudoscalar form factor g{sub P}. However, the experiments become much more challenging as soon as beam energies pass the pion production threshold.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Resolving the controversy of a possible relationship between perpendicular magnetic anisotropy and the magnetic damping parameter
We use broadband ferromagnetic resonance spectroscopy to systematically measure the Landau-Lifshitz damping parameter, perpendicular anisotropy, and the orbital moment asymmetry in Co{sub 90}Fe{sub 10}/Ni multilayers. No relationship is found between perpendicular magnetic anisotropy and the damping parameter in this material. However, inadequate accounting for inhomogeneous linewidth broadening, spin-pumping, and two-magnon scattering could give rise to an apparent relationship between anisotropy and damping. In contrast, the orbital-moment asymmetry and the perpendicular anisotropy are linearly proportional to each other. These results demonstrate a fundamental mechanism by which perpendicular anisotropy can be varied independently of the damping parameter.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Layer resolved magnetic domain imaging of epitaxial heterostructures in large applied magnetic fields
In this work, we use X-ray Excited Luminescence Microscopy to investigate the elemental and layer resolved magnetic reversal in an interlayer exchange coupled (IEC) epitaxial Fe/Cr wedge/Co heterostructure. The transition from strongly coupled parallel Co-Fe reversal for Cr thickness t(Cr) < 0.34 nm to weakly coupled layer independent reversal for t(Cr) > 1.5 nm is punctuated at 0.34 < t(Cr) < 1.5 nm by a combination of IEC guided domain wall motion and stationary zig zag domain walls. Domain walls nucleated at switching field minima are guided by IEC spatial gradients and collapse at switching field maxima.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions
Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, which is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Tuning the magnetoresistance symmetry of Pt on magnetic insulators with temperature and magnetic doping
We present a comparison study of the temperature dependence of the intriguing magnetoresistance (MR) in Pt/YIG (yttrium iron garnet), Pt/YIG BB (the YIG substrate has been bombarded with Ar + ), and Pt/SiO 2 (with different Fe doping levels). With decreasing temperature, the MRs in Pt/YIG and Pt/YIG BB change symmetry from R z = R x > R y at room temperature to R x > R z > R y at low temperature. A similar behavior in both Pt/YIG and Pt/YIG BB implies that the underlying physics is due to magnetic scattering, instead of the pure spin current across the interface. By changing the Fe doping level in the SiO 2 substrate, we can further systematically modulate the symmetry of MR in Pt/SiO 2 (Fe doped). The doping level dependent symmetry can also qualitatively explain the controversy over the MRs of Pt/YIG and similar structures at low temperature.
36 MATERIALS SCIENCE↗
Axial magnetic field injection in magnetized liner inertial fusion
MagLIF is a fusion concept using a Z-pinch implosion to reach thermonuclear fusion. In current experiments, the implosion is driven by the Z-machine using 19 MA of electrical current with a rise time of 100 ns. MagLIF requires an initial axial magnetic field of 30 T to reduce heat losses to the liner wall during compression and to confine alpha particles during fusion burn. This field is generated well before the current ramp starts and needs to penetrate the transmission lines of the pulsed-power generator, as well as the liner itself. Consequently, the axial field rise time must exceed hundreds of microseconds. Any coil capable of being submitted to such a field for that length of time is inevitably bulky. The space required to fit the coil near the liner, increases the inductance of the load. In turn, the total current delivered to the load decreases since the voltage is limited by driver design. Yet, the large amount of current provided by the Z-machine can be used to produce the required 30 T field by tilting the return current posts surrounding the liner, eliminating the need for a separate coil. However, the problem now is the field penetration time, across the liner wall. This paper discusses why skin effect arguments do not hold in the presence of resistivity gradients. Numerical simulations show that fields larger than 30 T can diffuse across the liner wall in less than 60 ns, demonstrating that external coils can be replaced by return current posts with optimal helicity.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Evaluation of magnetic field error in ExtendedEBIS
The upgrade of the EBIS, called ExtendedEBIS, is now in progress in Brookhaven National Laboratory. Two 5T-superconducting solenoids have been placed in series with 200 mm distance from each other for higher trap capacity and production of polarized 3He ions. Since the two superconducting solenoids are used, the field error is expected to be larger. In this research, the field error is estimated based on simulation. It was found that the magnetic field line can be 17 mm off from the center axis at the entrance of the collector, and this offset can be adjusted by three types of correction coils. Additionally, mismatch of the spin direction of polarized 3He due to the misalignment was estimated to be small.
Ikeda, Shunsuke (ORCID:0000000339800577)↗
Axial magnetic flux amplification in Hall-magnetohydrodynamic simulations of externally magnetized z-pinches
It is shown that externally magnetized gas-puff z-pinches under compression can exhibit robust axial flux amplification under suitable axial boundary conditions. This effect relies upon the Hall term in the generalized Ohm's law to generate azimuthal currents in the presence of a driving axial electric field. Under dynamic compression, the total current tends to flow in a mostly force-free boundary layer, separating the predominately azimuthal field outside the layer and the predominately axial field inside the layer. The effect only appears to occur if the axial boundaries allow for outflow or absorption of electromagnetic energy. The effect is mitigated by imposing either periodic or conducting axial boundary conditions. A semi-analytic equilibrium analysis agrees with steady-state solutions of the time-dependent electron-magnetohydrodynamic equations and provides an estimate of the scaling of the boundary layer as well as suggesting a scenario for the formation of the boundary layer. When operative, the effect can significantly impede plasma compression due to the increase in axial flux that diffuses into the pre-compressed plasma or through the presence of conductors that inhibit movement of the generated axial flux. Several facilities have noted unusual implosion behavior in z-pinch experiments with applied axial fields that does not appear to be explainable within the standard magnetohydrodynamic model. In conclusion, it is suggested that these experiments can be explained by the axial flux amplification and concentration effect
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Anisotropic upper critical field of pristine and proton-irradiated single crystals of the magnetically ordered superconductor RbEuFe{sub 4}As{sub 4
We present a study of the upper critical field H-c2 of pristine and proton-irradiated RbEuFe4As4 crystals in pulsed magnetic fields of up to 65 T. The data for H-c2 reveal pronounced downwards curvature, particularly for the in-plane field orientation, and a superconducting anisotropy that decreases with decreasing temperature. These features are indicative of Pauli paramagnetic limiting. For the interpretation of these data, we use a model of a clean single-band superconductor with an open Fermi surface in the shape of a warped cylinder, which takes into account Zeeman spin splitting. Fits to the data reveal that the in-plane upper critical field is Pauli paramagnetic limited, while the out-of-plane upper critical field is orbitally limited and that the orbital and paramagnetic fields have opposite anisotropies. A consequence of this particular combination is the unusual inversion of the anisotropy H-c2(ab) < H-c2(c) of the irradiated sample at temperatures below 10 K. The fits also yield an in-plane Maki parameter alpha(110)(M) approximate to 2.6 exceeding the critical value for the formation of the Fulde-Ferrell-Larkin-Ovchinnikov state. Nevertheless, the current measurements did not reveal direct evidence for the occurrence of this state.
Smylie, M. P.↗
Flat-band magnetism and helical magnetic order in Ni-doped SrCo 2 As 2
A series of Sr(Co 1-$x$ Ni $x$ ) 2 As 2 single crystals was synthesized, allowing a comprehensive phase diagram with respect to field, temperature, and chemical substitution to be established. Our neutron diffraction experiments revealed a helimagnetic order with magnetic moments ferromagnetically aligned in the ab plane and a helimagnetic wave vector of $q$= (0,0,0.56) for $x$= 0.1 . Finally, the combination of neutron diffraction and angle-resolved photoemission spectroscopy measurements shows that the tuning of a flat band with $d_{x^2-y^2}$ orbital character drives the helimagnetism and indicates the possibility of a quantum order-by-disorder mechanism.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Tuning Edge Localized Spin Waves in Magnetic Microstripes by Proximate Magnetic Structures.
The propagation of edge localized spin waves (E-SWs) in yttrium iron garnet (YIG; Y3Fe5O12) microstripes with and without magnetic microstructures in close proximity is investigated by micromagnetic simulations. A splitting of the dispersion curve with the presence of permalloy (Py; Ni81Fe19) stripe is observed. The results show that E-SWs on the two edges of YIG stripe have different wavelengths, group velocities, and decay lengths at the same frequencies. The role of the Py stripe was found to be the source of the inhomogeneous static dipolar field without dynamic coupling with YIG. This work opens new perspectives for the design of innovative spin wave interference-based logic devices.
Zhang, Zhizhi↗