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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Spin injection by spin–charge coupling in proximity induced magnetic graphene

Abstract Within the field of spintronics major efforts are directed towards developing applications for spin-based transport devices made fully out of two-dimensional materials. In this work we present an experimental realization of a spin-valve device where the generation of the spin signal is exclusively attributed to the spin-dependent conductivity of the magnetic graphene resulting from the proximity of an interlayer antiferromagnet, chromium sulfide bromide (CrSBr). We clearly demonstrate that the usage of the conventional air-sensitive 3D magnetic contacts can be fully avoided when graphene/CrSBr heterostructures are employed. Moreover, apart from providing exceptionally long spin relaxation length, the usage of graphene for both generation and transport of the spin allows to automatically avoid the conductivity mismatch between the source and the channel circuits that has to be considered when using conventional low-resistive contacts. Our results address a necessary step in the engineering of spintronic circuitry out of layered materials and precede further developments in the area of complex spin-logic devices. Moreover, we introduce a fabrication procedure where we designed and implemented a recipe for the preparation of electrodes via a damage-free technique that offers an immediate advantage in the fields of air-sensitive and delicate organic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Engineering diamond interfaces free of dark spins

Nitrogen-vacancy (NV) centers in diamond are utilized extensively as quantum sensors for imaging fields at the nanoscale. The ultrahigh sensitivity of NV magnetometers has enabled the detection and spectroscopy of individual electron spins, with potentially far-reaching applications in condensed matter physics, spintronics, and molecular biology. However, the surfaces of these diamond sensors naturally contain electron spins, which create a background signal that can be hard to differentiate from the signal of the target spins. In this study, we develop a surface modification approach that eliminates the unwanted signal of these so-called dark electron spins. Our surface passivation technique, based on coating diamond surfaces with a thin titanium oxide (Ti⁢O 2 ) layer, reduces the dark spin density. The observed reduction in dark spin density aligns with our findings on the electronic structure of the diamond-Ti⁢O 2 interface. The reduction, from a typical value of 2000 μm −2 to a value below that set by the detection limit of our NV sensors (200 μm −2 ), results in a twofold increase in Hahn-echo coherence time of near surface NV centers. Furthermore, we derive a comprehensive spin model that connects dark spin relaxation with NV coherence, providing additional insights into the mechanisms behind the observed spin dynamics. Our findings are directly transferable to other quantum platforms, including nanoscale solid-state qubits and superconducting qubits.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Optical Detection of Long Electron Spin Transport Lengths in a Monolayer Semiconductor

Using a spatially resolved optical pump-probe experiment, we measure the lateral transport of spin-valley polarized electrons over very long distances (tens of micrometers) in a single WSe 2 monolayer. By locally pumping the Fermi sea of 2D electrons to a high degree of spin-valley polarization (up to 75%) using circularly polarized light, the lateral diffusion of the electron polarization can be mapped out via the photoluminescence induced by a spatially separated and linearly polarized probe laser. In this work, up to 25% spin-valley polarization is observed at pump-probe separations up to 20 μm. Characteristic spin-valley diffusion lengths of 18 ± 3 μm are revealed at low temperatures. The dependence on temperature, pump helicity, pump intensity, and electron density highlight the key roles played by spin relaxation time and pumping efficiency on polarized electron transport in monolayer semiconductors possessing spin-valley locking.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Detecting rare earth elements via optically detected magnetic resonance (ODMR) and spin-relaxometry using nitrogen vacancy centers in nanodiamonds

Nanodiamonds embedded with nitrogen-vacancy (NV) centers are emerging as powerful tools in quantum sensing due to their remarkable sensitivity to local variations in electromagnetic fields, temperature, and pressure. These point defects in the diamond lattice can be probed using optically detected magnetic resonance (ODMR) and spin relaxometry techniques, allowing for the detection and characterization of magnetic nanoparticles and ions. The sensing mechanism relies on laser-induced excitation of the NV center's non-degenerate triplet ground state, which promotes electrons to an excited state. Subsequent photoluminescence (PL) emission, which is spin-state dependent, is then measured. These spin states are highly responsive to magnetic perturbations in the surrounding environment. By analyzing changes in the ODMR spectra and spin relaxation times, we can effectively monitor how magnetic species influence the NV center's spin dynamics, thus enabling sensitive and selective characterization of nanoscale magnetic materials. These techniques have been applied for the characterization of transition metals and rare earth elements which shows natural ferromagnetic properties.

magnetic nanopartgicles and ions↗
DOE OSTI2025

Determining hexavalent chromium transport properties in alkaline nuclear waste using nuclear magnetic resonance spectroscopy

This study focuses on the transport properties of hexavalent chromium, specifically the chromate anion, to improve predictive models and environmental remediation strategies for Cr(VI) migration. Using 53 Cr Nuclear Magnetic Resonance (NMR) spectroscopy, the research quantifies chromate in multicomponent electrolytes replicating nuclear waste conditions at the Hanford Site in Washington State. The consistency of the 53 Cr NMR signal integral with chromate concentration, despite varying matrix compositions, establishes it as a reliable concentration indicator. The transport properties of chromate in an alkaline solution were assessed using relaxation-based measurements via saturation recovery and Carr-Purcell-Meiboom-Gill experiments, determining spin-lattice and spin-spin relaxation times. These measurements, combined with the Bloembergen-Purcell-Pound equation, helped estimate the rotational correlation time and the 53 Cr self-diffusion coefficient using Stokes-Einstein-Debye and Stokes-Einstein equations. Direct measurements were obtained through pulsed field gradient stimulated echo 53 Cr NMR spectroscopy. Monte Carlo simulations further estimated uncertainty propagation. The results enhance comprehension of chromate transport and highlight prospects for identifying transport properties of NMR-active nuclei, traditionally considered unreachable.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Giant spin-selective bandgap renormalization in CsPbBr 3 colloidal nanocrystals

The spin-dependence of the strongly correlated phenomena and many-body interactions play an important role in quantum information science. In particular, it is quite interesting but unclear how the spin degree of freedom ramifies the bandgap renormalization, one of the fundamental many-body phenomena. We report the first room-temperature observation of giant spin-selective bandgap renormalization (SS-BGR) in CsPbBr 3 colloidal nanocrystals using time-resolved circularly polarized femtosecond pump-probe spectroscopy. The SS-BGR results from many-body interactions among carriers with the same spin that renormalize their joint density of states by 57+/- 1 meV, visualized here as photoinduced absorption (PIA) below band-edge transition energy when the pump and probe are co-polarized. The hallmark result of spectrally resolved SS-BGR is in stark contrast to the usually submerged signal in II-VI and III-V semiconductors and is 3 orders of magnitude larger than that observed in Ge/SiGe quantum wells, highlighting the unique and beneficial band structure of the metal-halide semiconductors. We propose that the PIA, due to SS-BGR, can be used to describe the spin-polarization and spin-relaxation dynamics. The experimental and theoretical findings open up new possibilities for optical manipulation of spin degrees of freedom and their many-body interactions in metal-halide perovskite nanocrystals for potential room-temperature applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Charge-spin interconversion in epitaxial Pt probed by spin-orbit torques in a magnetic insulator

We measure spin-orbit torques (SOTs) in a model system of all-epitaxial ferrite/Pt bilayers to gain insights into charge-spin interconversion in Pt. With negligible electronic conduction in the insulating ferrite, the crystalline Pt film acts as the sole source of charge-to-spin conversion. A small fieldlike SOT independent of Pt thickness suggests a weak Rashba-Edelstein effect at the ferrite/Pt interface. By contrast, we observe a sizable dampinglike SOT that depends on the Pt thickness, from which we deduce the dominance of an extrinsic spin-Hall effect (skew scattering) and Dyakonov-Perel spin relaxation in the crystalline Pt film. Furthermore, our results point to a large internal spin-Hall ratio of ≈ 0.8 in epitaxial Pt. Furthermore, our experimental work takes an essential step towards understanding the mechanisms of charge-spin interconversion and SOTs in Pt-based heterostructures, which are crucial for power-efficient spintronic devices.

36 MATERIALS SCIENCE↗
NASA NTRS2014

Spin Qubits in Germanium Structures with Phononic Gap

We propose qubits based on shallow donor electron spins in germanium structures with phononic gap. We consider a phononic crystal formed by periodic holes in Ge plate or a rigid cover / Ge layer / rigid substrate structure with gaps approximately a few GHz. The spin relaxation is suppressed dramatically, if the Zeeman frequency omegaZ is in the phononic gap, but an effective coupling between the spins of remote donors via exchange of virtual phonons remains essential. If omegaZ approaches to a gap edge in these structures, a long-range (limited by detuning of omegaZ) resonant exchange interaction takes place. We estimate that ratio of the exchange integral to the longitudinal relaxation rate exceeds 10(exp 5) and lateral scale of resonant exchange 0.1 mm. The exchange contribution can be verified under microwave pumping through oscillations of spin echo signal or through the differential absorption measurements. Efficient manipulation of spins due to the Rabi oscillations opens a new way for quantum information applications.

Qubit↗
DOE OSTI2024

Inverse chirality-induced spin selectivity effect in chiral assemblies of π -conjugated polymers

Coupling of spin and charge currents to structural chirality in non-magnetic materials, known as chirality-induced spin selectivity, is promising for application in spintronic devices at room temperature. Although the chirality-induced spin selectivity effect has been identified in various chiral materials, its Onsager reciprocal process, the inverse chirality-induced spin selectivity effect, remains unexplored. Here we report the observation of the inverse chirality-induced spin selectivity effect in chiral assemblies of π-conjugated polymers. Using spin-pumping techniques, the inverse chirality-induced spin selectivity effect enables quantification of the magnitude of the longitudinal spin-to-charge conversion driven by chirality-induced spin selectivity in different chiral polymers. By widely tuning conductivities and supramolecular chiral structures via a printing method, we found a very long spin relaxation time of up to several nanoseconds parallel to the chiral axis. Furthermore, our demonstration of the inverse chirality-induced spin selectivity effect suggests possibilities for elucidating the puzzling interplay between spin and chirality, and opens a route for spintronic applications using printable chiral assemblies.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Cryogenic masers

Various factors affecting the frequency stability of hydrogen masers are described and related to maser design parameters. The long-term frequency stability of a hydrogen maser is limited by the mechanical stability of the cavity, and the magnitudes of the wall relaxation, spin exchange, and recombination rates which affect the Q of the line. Magnetic resonance studies of hydrogen atoms at temperatures below 1 K and in containers coated with liquid helium films demonstrated that cryogenic masers may allow substantial improvements in all of these parameters. In particular the thermal expansion coefficients of most materials are negligible at 1 K. Spin exchange broadening is three orders of magnitude smaller at 1 K than at room temperature, and the recombination and wall relaxation rates are negligible at 0.52 K where the frequency shift due to the 4 He-coated walls of the container has a broad minimum as a function of temperature. Other advantages of the helium-cooled maser result from the high purity, homogeneity, and resilence of helium-film-coated walls and the natural compatibility of the apparatus with helium-cooled amplifiers.

Berlinsky, A. J.↗
DOE OSTI2025

Localized triplons and site stuffing in the quantum dimer magnet BiYbGeO5

Thermodynamic and muon spin relaxation measurements have recently highlighted BiYbGeO5 as a new example of a rare-earth-based quantum dimer magnet with isolated Yb3+ spin-1/2 dimers. However, direct spectroscopic evidence of the triplet excitations and measurements of the structural disorder are lacking. In this work, polycrystalline BiYbGeO5 was synthesized using conventional high-temperature solid-state methods and investigated via high-resolution neutron powder diffraction and inelastic neutron scattering. Diffraction measurements down to 58 mK reveal no signatures of magnetic order and indicate that nearly 20% of Yb3+ sites are replaced by nonmagnetic Bi3+, introducing significant structural disorder. Inelastic neutron scattering shows dispersionless triplon excitations, consistent with localized, noninteracting spin dimers. Fits to the triplet excitation spectrum with an XXZ-type anisotropic exchange give 𝐽XX=0.100⁢(1)⁢meV and 𝐽Z=0.202⁢(1)⁢meV. These findings establish BiYbGeO5 as a structurally disordered but magnetically well-isolated quantum dimer system, providing a model platform for studying the resilience of entangled spin states to site dilution.

Kapoor, Rachit [Brock University, Canada]↗
DOE OSTI2023

Giant interfacial spin Hall angle from Rashba-Edelstein effect revealed by the spin Hall Hanle process

The Rashba-Edelstein effect (REE), which generates interfacial spin polarization and subsequent spin current, is a compelling spin-charge conversion mechanism for spintronic applications, since it’s not limited by the elemental spin-orbit couplings. In this work we demonstrate REE at Pt/ferroelectric interfaces by showing a positive correlation between polarization and effective spin Hall angle in the recently elucidated spin Hall Hanle effects (SHHE), in which a Larmor precession of spin polarization in a diffusion process from the interface manifest as magnetoresistance and Hall effect. We show that REE leads to a large enhancement of the effective spin Hall angle of ferroelectric interface Pt/h-LuFeO 3 compared with that of Pt/Al 2 O 3 , without obvious differences in the spin relaxation time. Modeling using SHHEs involving REE as an additional source of interfacial polarization suggests that REE can lead to an interfacial spin Hall angle (0.4 ± 0.1) in Pt/h-LuFeO 3 that is one order of magnitude larger than the bulk value of Pt. Our results demonstrate that a ferroelectric interface can produce large spin-charge conversion and that SHHEs are a sensitive tool for characterizing interfacial spin-transport properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Monte Carlo modeling of spin-polarized photoemission from p -doped bulk GaAs

Here, the anticorrelation between quantum efficiency (QE) and electron spin polarization (ESP) from a ρ-doped GaAs activated to negative electron affinity is studied in detail using an ensemble Monte Carlo approach. The photoabsorption, momentum and spin relaxation during transport, and tunneling of electrons through the surface potential barrier are modeled to identify fundamental mechanisms, which limit the efficiency of GaAs spin-polarized electron sources. In particular, we study the response of QE and ESP to various parameters, such as the photoexcitation energy, doping density, and electron affinity level. Our modeling results for various transport and emission characteristics are in good agreement with available experimental data. Our findings show that the behavior of both QE and ESP at room temperature can be fully explained by the bulk relaxation mechanisms and the time that electrons spend in the material before being emitted.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Short-range spin freezing in the double trillium lattice spin-liquid candidate KSrFe 2 ⁢(PO 4 ) 3 revealed via 31 P NMR

A comprehensive 31 P nuclear magnetic resonance (NMR) study, combined with thermodynamic measurements and first-principles band-structure calculations, has been conducted to explore the ground state of the 𝑆=5/2 double trillium lattice antiferromagnet KSrFe 2 ⁢(PO 4 ) 3 . Our experimental results indicate that the magnetic ground state is neither a conventional three-dimensional (3D) long-range order (LRO) nor a pure gapless spin-liquid state, as conjectured previously [Boya et al., APL Mater. 10, 101103 (2022)]. Specifically, the observation of a nearly field-independent NMR linewidth below 𝑇* = (3.5 ± 0.4)⁢ K, and a significant enhancement of spin-spin relaxation rate 1/𝑇 2 below 2⁢𝑇* (where 𝑇* is the characteristic temperature identified from the magnetic susceptibility), indicate a complex magnetic ground state where spin freezing coexists with persistent dynamics. Furthermore, we argue that the lack of magnetic LRO and the persistence of strong magnetic fluctuations in KSrFe 2 ⁢(PO 4 ) 3 are unlikely to originate from intersite K/Sr disorder, rather they arise due to intrinsic magnetic frustration. In conclusion, our findings position KSrFe 2 ⁢(PO 4 ) 3 into a broader family of geometrically frustrated magnets characterized by coexisting spin freezing and pronounced antiferromagnetic fluctuations, marking it as a promising platform for investigating exotic phenomena in 3D frustrated magnets.

Exotic phases of matter↗
DOE OSTI2023

Indistinguishable telecom band photons from a single Er ion in the solid state

Atomic defects in the solid state are a key component of quantum repeater networks for long-distance quantum communication1. Recently, there has been significant interest in rare earth ions, in particular Er 3+ for its telecom band optical transition that allows long-distance transmission in optical fibres. However, the development of repeater nodes based on rare earth ions has been hampered by optical spectral diffusion, precluding indistinguishable single-photon generation. Here, we implant Er 3+ into CaWO 4 , a material that combines a non-polar site symmetry, low decoherence from nuclear spins and is free of background rare earth ions, to realize significantly reduced optical spectral diffusion. For shallow implanted ions coupled to nanophotonic cavities with large Purcell factor, we observe single-scan optical linewidths of 150 kHz and long-term spectral diffusion of 63 kHz, both close to the Purcell-enhanced radiative linewidth of 21 kHz. This enables the observation of Hong–Ou–Mandel interference between successively emitted photons with a visibility of V = 80(4)%, measured after a 36 km delay line. We also observe spin relaxation times T 1,s = 3.7 s and T 2,s > 200 μs, with the latter limited by paramagnetic impurities in the crystal instead of nuclear spins. Furthermore, this represents a notable step towards the construction of telecom band quantum repeater networks with single Er 3+ ions.

42 ENGINEERING↗
DOE OSTI2021

Predicting 1 H NMR relaxation in Gd 3+ -aqua using molecular dynamics simulations

Atomistic molecular dynamics simulations are used to predict 1 H NMR T 1 relaxation of water from paramagnetic Gd 3+ ions in solution at 25 °C. Simulations of the T 1 relaxivity dispersion function r 1 computed from the Gd 3+ – 1 H dipole–dipole autocorrelation function agree within ≃8% of measurements in the range f 0 ≃ 5 ↔ 500 MHz, without any adjustable parameters in the interpretation of the simulations, and without any relaxation models. Here the simulation results are discussed in the context of the Solomon-Bloembergen-Morgan inner-sphere relaxation model, and the Hwang-Freed outer-sphere relaxation model. Below f 0 ≲ 5 MHz, the simulation overestimates r 1 compared to measurements, which is used to estimate the zero-field electron-spin relaxation time. The simulations show potential for predicting r 1 at high frequencies in chelated Gd 3+ contrast-agents used for clinical MRI.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗