Search NASA⌕ Search

SEARCH · Search NASA

Results for “MAGNETIC INSULATION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Study on the Properties of Novel Soft Magnetic Composites of FeSiAl

In this paper, we compounded the FeSiAl powder with a novel amorphous inorganic insulation agent (AIIA). Silicone resin (3 wt.%) was used as organic insulating agent, and the inorganic insulating agent was Fe{sub 83.5}Si{sub 7.5}B{sub 5}Cr{sub 4} amorphous powder (0, 1, 2, 3, and 4 wt.%). Amorphous powder was prepared by passivation pretreatment before compounding. The results showed that the addition of amorphous inorganic insulating agent will significantly affect the soft magnetic properties of FeSiAl powders. Compared with the pure FeSiAl powder having only silicone resin the saturation magnetization of composite powders slightly increased (by 0.1–4.9%). When AIIA content was 2 wt.%, the sample had the highest initial permeability, which increased by 14.6%. At the same time, the core loss was also reduced by 15.7% (B{sub m} = 5 mT, f = 1000 kHz) when AIIA content was also 2 wt.%.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Proximity enhanced magnetism at NiFe 2 O 4 /Graphene interface

Here, we explore the change in effective magnetic anisotropy of the ferrimagnetic (FM) insulator nickel ferrite (NFO) thin film due to the inclusion of monolayer graphene (MLG) grown on top of the NFO layer. This was done by performing radio frequency (RF) transverse susceptibility (TS) measurements on bare NFO and NFO/MLG bilayer samples for both in-plane (IP) and out-of-plane (OOP) configurations utilizing a tunnel diode oscillator technique. Our magnetometry measurements indicated an enhancement in the overall saturation magnetization of the NFO/MLG bilayer with respect to the bare NFO film. The TS measurements reveal that the inclusion of MLG reduces the effective magnetic anisotropy for both IP and OOP configurations drastically, by up to a factor of 2 over the temperature range 40 K ≤ T ≤ 280 K. Since NFO is a magnetic substrate, it is possible that NFO could induce magnetic ordering in MLG at the NFO/MLG interface via the magnetic proximity effect. Furthermore, since NFO is insulating and MLG is a semimetal, there likely exists a large conductivity difference at the interface, making charge transfer plausible. These two effects could modify the interfacial magnetism leading to a change in the effective magnetic anisotropy. These results highlight the importance of understanding the interfacial magnetism of FM/MLG heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Interface-induced phenomena in magnetism

Our article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. We provide an overview for the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. Our article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Axion optical induction of antiferromagnetic order

Using circularly polarized light to control quantum matter is a highly intriguing topic in physics, chemistry and biology. Previous studies have demonstrated helicity-dependent optical control of chirality and magnetization, with important implications in asymmetric synthesis in chemistry; homochirality in biomolecules; and ferromagnetic spintronics. We report the surprising observation of helicity-dependent optical control of fully compensated antiferromagnetic order in two-dimensional even-layered MnBi 2 Te 4 , a topological axion insulator with neither chirality nor magnetization. Furthermore, to understand this control, we study an antiferromagnetic circular dichroism, which appears only in reflection but is absent in transmission. We show that the optical control and circular dichroism both arise from the optical axion electrodynamics. Our axion induction provides the possibility to optically control a family of PT-symmetric antiferromagnets (P, inversion; T, time-reversal) such as Cr 2 O 3 , even-layered CrI3 and possibly the pseudo-gap state in cuprates. In MnBi 2 Te 4 , this further opens the door for optical writing of a dissipationless circuit formed by topological edge states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Superconductor to weak-insulator transitions in disordered tantalum nitride films

Here, we study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents zν ≈ 1.3, with a corresponding critical field H c << H c2 , the upper critical field. The Hall effect exhibits a crossing point near H c , but with a nonuniversal critical value ρ c xy comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Phonon modes and Raman signatures of MnBi 2n Te 3n+1 (n=1,2,3,4) magnetic topological heterostructures

An intrinsic antiferromagnetic topological insulator MnBi 2 Te 4 arises when intercalating a Mn-Te bilayer chain in a topological insulator, Bi 2 Te 3 . We present observations on the inter- and intralayer phonon modes of the generalized MnBi 2n Te 3n+1 (n=1,2,3,4) family using cryogenic low-frequency Raman spectroscopy with various polarization configurations. Two peaks at 66 and 112 cm –1 show abnormal perturbation in Raman linewidths below magnetic transition temperature due to spin-phonon coupling. In MnBi 4 Te 7 , B i2 Te 3 layers induce Davydov splitting of the A1g mode around 137 cm –1 at 5 K. The out-of-plane interlayer force constant estimated using the linear chain model was (3.98±0.14)×10 19 N/m 3 , three times weaker than that of Bi 2 Te 3 . Adding more Bi 2 Te 3 layers, such as MnBi 6 Te 10 and MnBi 8 Te 13 , makes Bi 2 Te 3 properties more dominant than magnetic properties. Our work experimentally and theoretically discovers the dynamics of phonon modes of MnBi 2n Te 3n+ 1 family, facilitating utilization of magnetic topological heterostructures.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Giant electron–phonon coupling of the breathing plane oxygen phonons in the dynamic stripe phase of $\hbox {La}_{1.67}\hbox {Sr}_{0.33}\hbox {NiO}_4$

Doped antiferromagnets host a vast array of physical properties and learning how to control them is one of the biggest challenges of condensed matter physics. La 1.67 Sr 0.33 NiO 4 (LSNO) is a classic example of such a material. At low temperatures holes introduced via substitution of La by Sr segregate into lines to form boundaries between magnetically ordered domains in the form of stripes. The stripes become dynamic at high temperatures, but LSNO remains insulating presumably because an interplay between magnetic correlations and electron–phonon coupling localizes charge carriers. Magnetic degrees of freedom have been extensively investigated in this system, but phonons are almost completely unexplored. We searched for electron–phonon anomalies in LSNO by inelastic neutron scattering. Giant renormalization of plane Ni–O bond-stretching modes that modulate the volume around Ni appears on entering the dynamic charge stripe phase. Other phonons are a lot less sensitive to stripe melting. Dramatic overdamping of the breathing modes indicates that dynamic stripe phase may host small polarons. We argue that this feature sets electron–phonon coupling in nickelates apart from that in cuprates where breathing phonons are not overdamped and point out remarkable similarities with the colossal magnetoresistance manganites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature

We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usual ${\rm si}{{{\rm n}}^{2}}\theta $ relation well established in the collinear magnet yttrium iron garnet, with $\theta $ the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex angular dependence with four maxima are observed within one sweep cycle. The number of maxima as well as the relative strength of different maxima depend strongly on temperature and field strength. Lastly, our results evidence a complex SMR behavior in the non-collinear magnetic regime that goes beyond the conventional formalism developed for collinear magnetic structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Measurements of the Magnetic-Field-Tuned Conductivity of Disordered Two-Dimensional Mo 43 ⁢Ge 57 and InO 𝑥 Superconducting Films: Evidence for a Universal Minimum Superfluid Response

Our measurements of the low frequency ac conductivity in strongly disordered two-dimensional films near the magnetic-field-tuned superconductor-to-insulator transition show a sudden drop in the phase stiffness of superconducting order with either increased temperature or magnetic field. Surprisingly, for two different material systems, the abrupt drop in the superfluid density in a magnetic field has the same universal value as that expected for a Berezinskii-Kosterlitz-Thouless transition in a zero magnetic field. As a result, the characteristic temperature at which phase stiffness is suddenly lost can be tuned to zero at a critical magnetic field, following a power-law behavior with a critical exponent consistent with that obtained in previous dc transport studies on the dissipative side of the transition.

Misra, S.↗
DOE OSTI2014

Spin counting in electrically detected magnetic resonance via low-field defect state mixing

The work herein describes a method that allows one to measure paramagnetic defect densities in semiconductor and insulator based devices with electrically detected magnetic resonance (EDMR). The method is based upon the mixing of defect states which results from the dipolar coupling of paramagnetic sites at low magnetic fields. We demonstrate the measurement method with spin dependent tunneling in thin film dielectrics; however, the method should be equally applicable to paramagnetic defect density measurements in semiconductors via the more commonly utilized EDMR technique called spin dependent recombination.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Near net shape bulk laminated silicon iron electric steel for improved electrical resistance and low high frequency loss

The invention involves producing discontinuous, flake-shaped particles of a soft magnetic material, coating the flake-shaped particles with an electrically insulating coating, and consolidating the coated flaked-shaped particles to form a soft magnetic bulk shape. The consolidated bulk shape can comprise a layer or a simple or complex 3D magnet part shape, which has a consolidated layered microstructure that includes laminated soft magnetic regions that are substantially encapsulated by an electrical insulating layer to increase the resistivity of soft magnetic material, especially when used in silicon iron magnet parts.

Cui, Jun↗
DOE OSTI2015

Self-duality and a Hall-insulator phase near the superconductor-to-insulator transition in indium-oxide films

We combine measurements of the longitudinal ( ρ x x ) and Hall ( ρ x y ) resistivities of disordered 2D amorphous indium-oxide films to study the magnetic-field tuned superconductor-to-insulator transition (H-SIT) in the T → 0 limit. At the critical field, H c , the full resistivity tensor is T independent with ρ x x ( H c ) = h / 4 e 2 and ρ x y ( H c ) = 0 within experimental uncertainty in all films (i.e., these appear to be “universal” values); this is strongly suggestive that there is a particle–vortex self-duality at H = H c . The transition separates the (presumably) superconducting state at H < H c from a “Hall-insulator” phase in which ρ x x → ∞ as T → 0 whereas ρ x y approaches a nonzero value smaller than its “classical value” H / n e c ; i.e., 0 < ρ x y < H / n e c . A still higher characteristic magnetic field, H c * > H c , at which the Hall resistance is T independent and roughly equal to its classical value, ρ x y ≈ H / n e c , marks an additional crossover to a high-field regime (probably to a Fermi insulator) in which ρ x y > H / n e c and possibly diverges as T → 0 . We also highlight a profound analogy between the H-SIT and quantum-Hall liquid-to-insulator transitions (QHIT).

14 SOLAR ENERGY↗
DOE OSTI2022

Experimental study of electromagnetic wave scattering from a gyrotropic gaseous plasma column

We experimentally demonstrate the controlled scattering of incident transverse-electric electromagnetic waves from a gyrotropic magnetized plasma cylindrical discharge. Scattered electromagnetic waves can bend left and right by changing the external magnetic field of a plasma rod. Measured scattered wavefronts are in good agreement with electromagnetic simulations. A gyrotropic response is observed for incident wave frequencies ranging from 3.5 to 5.6 GHz for conditions corresponding to a ratio of cyclotron frequency to plasma frequency, ω ce /ω p ≈ 0.16. In conclusion, the observation of a gyrotropic response from cylindrical plasma discharges paves the way for their use as building blocks for future devices such as magnetized plasma photonic crystals, topological insulators, plasma metamaterials, non-reciprocal waveguide structures, and other devices, which require a tunable gyrotropic response from centimeter to meter-scale materials with application-specific geometry.

42 ENGINEERING↗
DOE OSTI2024

Edge magnetoplasmon dispersion and time-resolved plasmon transport in a quantum anomalous Hall insulator

A quantum anomalous Hall (QAH) insulator breaks reciprocity by combining magnetic polarization and spin-orbit coupling to generate a unidirectional transmission of signals in the absence of an external magnetic field. Such behavior makes QAH materials a good platform for the innovation of circulator technologies. However, it remains elusive as to how the wavelength of the chiral edge plasmon relates to its frequency and how the plasmon wave packet is excited in the time domain in a QAH insulator. Here, we investigate the edge magnetoplasmon (EMP) resonances in Cr-(Bi,Sb) 2 Te 3 by frequency and time domain measurements. From disk shaped samples with various dimensions, we obtain the dispersion relation of EMPs and extract the drift velocity of the chiral edge state. From the time-resolved transport measurements, we identify the velocity of the plasmon wave packet and observe a transition from the edge to bulk transport at an elevated temperature. We show that the frequency and time domain measurements are well modeled by loss from the microwave induced dissipative channels in the bulk area. Our results demonstrate that the EMP decay rate can be significantly reduced by applying a low microwave power and fabricating devices of larger diameter ≥ 100 µ m . In a R = 125 µ m sample, a nonreciprocity of 20 dB has been realized at 1.3 GHz, shining light on using QAH insulators to develop on-chip nonreciprocal devices. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Implosion of auto-magnetizing helical liners on the Z facility

In the first auto-magnetizing liner implosion experiments on the Z Facility, precompressed internal axial fields near 150 T were measured and 7.2-keV radiography indicated a high level of cylindrical uniformity of the imploding liner's inner surface. An auto-magnetizing (AutoMag) liner is made of discrete metallic helical conductors encapsulated in insulating material. Here, the liner generates internal axial magnetic field as a 1–2 MA, 100–200 ns current prepulse flows through the helical conductors. After the prepulse, the fast-rising main current pulse causes the insulating material between the metallic helices to break down ceasing axial field production. After breakdown, the helical liner, nonuniform in both density and electrical conductivity, implodes in 100 ns. In-flight radiography data demonstrate that while the inner wall maintains cylindrical uniformity, multiple new helically oriented structures are self-generated within the outer liner material layers during the implosion; this was not predicted by simulations. Furthermore, liner stagnation was delayed compared to simulation predictions. An analytical implosion model is compared with experimental data and preshot simulations to explore how changes in the premagnetization field strength and drive current affect the liner implosion trajectory. Both the measurement of >100 T internal axial field production and the demonstration of cylindrical uniformity of the imploding liner's inner wall are encouraging for promoting the use of AutoMag liners in future MagLIF experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Unconventional thermal metallic state of charge-neutral fermions in an insulator

Quantum oscillations in transport and thermodynamic parameters at high magnetic fields are an unambiguous signature of the Fermi surface, the defining characteristic of a metal. Recent observations of quantum oscillations in insulating SmB 6 and YbB 12 , therefore, have been a big surprise—despite the large charge gap inferred from the insulating behaviour of the resistivity, these compounds seemingly host a Fermi surface at high magnetic fields. However, the nature of the ground state in zero field has been little explored. Here, we report the use of low-temperature heat-transport measurements to discover gapless, itinerant, charge-neutral excitations in the ground state of YbB 12 . At zero field, sizeable linear temperature-dependent terms in the heat capacity and thermal conductivity are clearly resolved in the zero-temperature limit, indicating the presence of gapless fermionic excitations with an itinerant character. Remarkably, linear temperature-dependent thermal conductivity leads to a spectacular violation of the Wiedemann–Franz law: the Lorenz ratio is 10 4 –10 5 times larger than that expected in conventional metals, indicating that YbB 12 is a charge insulator and a thermal metal. Furthermore, we find that these fermions couple to magnetic fields, despite their charge neutrality. Our findings expose novel quasiparticles in this unconventional quantum state.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Dielectric screening and electric field control of ferromagnetism at the CaMnO 3 /CaRuO 3 interface

Control of magnetism by an applied electric field is a desirable technique for the functionalization of magnetic materials. Motivated by recent experiments, we study the electric field control of the interfacial magnetism of CaRuO 3 /CaMnO 3 (CRO/CMO) (001), a prototype interface between a non-magnetic metal and an antiferromagnetic insulator. Even without the electric field, the interfacial CMO layer acquires a ferromagnetic moment due to a spin-canted state, caused by the Anderson-Hasegawa double exchange (DEX) between the Mn moments and the leaked electrons from the CRO side. An electric field would alter the carrier density at the interface, leading to the possibility of controlling the magnetism, since DEX is sensitive to the carrier density. We study this effect quantitatively using density-functional calculations in the slab geometry. We find a text-book like dielectric screening of the electric field, which introduces polarization charges at the interfaces and the surfaces. The extra charge at the interface enhances the ferromagnetism via the DEX interaction, while away from the interface the original AFM state of the Mn layers remains unchanged. The effect could have potential application in spintronics devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Transverse barrier formation by electrical triggering of a metal-to-insulator transition

Application of an electric stimulus to a material with a metal-insulator transition can trigger a large resistance change. Resistive switching from an insulating into a metallic phase, which typically occurs by the formation of a conducting filament parallel to the current flow, is a highly active research topic. Using the magneto-optical Kerr imaging, we found that the opposite type of resistive switching, from a metal into an insulator, occurs in a reciprocal characteristic spatial pattern: the formation of an insulating barrier perpendicular to the driving current. This barrier formation leads to an unusual N-type negative differential resistance in the current-voltage characteristics. We further demonstrate that electrically inducing a transverse barrier enables a unique approach to voltage-controlled magnetism. By triggering the metal-to-insulator resistive switching in a magnetic material, local on/off control of ferromagnetism is achieved using a global voltage bias applied to the whole device.

36 MATERIALS SCIENCE↗