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All sources NASA NTRS DOE OSTI

DOE OSTI2022

Structures and Magnetic Properties of K 2 Pd 4 U 6 S 17 , K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 Synthesized Using the Boron–Chalcogen Mixture Method

A series of A 2 M 4 U 6 S 17 (A = Alkali metal, M = Pd or Pt) compounds, specifically K 2 Pd 4 U 6 S 17 , K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 , were synthesized using the combined Boron-Chalcogen Mixture (BCM) and molten flux crystal growth methods. The formation of the Rb- and Cs- containing analogues resulted from the in-situ alkali polysulfide flux formation formed from the alkali carbonates. The successful synthesis of single crystals of the title compounds allowed for their structural characterization by single crystal X-ray diffraction. The structure determination revealed disorder of the alkali cations in Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 , while the potassium cations in K 2 Pd 4 U 6 S 17 and K 2 Pt 4 U 6 S 17 were fully ordered. Here, magnetic measurements were performed on samples of K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 that contained small amounts of paramagnetic β-US 2 and diamagnetic PtS. Antiferromagnetic order is observed at T N = 9.1 K for K 2 Pt 4 U 6 S 17 . No long-range magnetic order was observed for Rb 2 Pt 4 U 6 S 17 and Cs 2 Pt 4 U 6 S 17 . Uranium moments of 2.5, 2.6, and 2.6 μB were measured for K 2 Pt 4 U 6 S 17 , Rb 2 Pt 4 U 6 S 17 , and Cs 2 Pt 4 U 6 S 17 , respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1979

A matrix solution for the simulation of magnetic fields with ideal current loops

A matrix formulation is presented for describing axisymmetric magnetic field data with ideal current loops. A computer program written in APL is used to invert the matrix and hence to solve for the coil strengths which are used to represent the field data. Examples are given of the coil representation for (1) measured magnetic data, (2) refocusing fields, and (3) PPM focusing fields.

Stankiewicz, N.↗

DOE OSTI2025

Altermagnetism in the layered intercalated transition metal dichalcogenide CoNb 4 Se 8

Altermagnets (AMs) are a new class of magnetic materials that combine the beneficial spintronics properties of ferromagnets and antiferromagnets, garnering significant attention recently. Here, we have identified altermagnetism in a layered intercalated transition metal diselenide, CoNb 4 Se 8 , which crystallizes with an ordered sublattice of intercalated Co atoms between NbSe 2 layers. Single crystals are synthesized, and the structural characterizations are performed using single crystal diffraction and scanning tunneling microscopy. Magnetic measurements reveal easy-axis antiferromagnetism below 168 K. Density functional theory (DFT) calculations indicate that A-type antiferromagnetic ordering with easy-axis spin direction is the ground state, which is verified through single crystal neutron diffraction experiments. Electronic band structure calculations in this magnetic state display spin-split bands, confirming altermagnetism in this compound. The layered structure of CoNb 4 Se 8 presents a promising platform for testing various predicted properties associated with altermagnetism.

36 MATERIALS SCIENCE↗

DOE OSTI2020

A-type antiferromagnetic order in MnBi 4 Te 7 and MnBi 6 Te 10 single crystals

MnBi 4 Te 7 and MnBi 6 Te 10 are two members with n = 2 and 3 in the family of MnBi 2 n Te 3 n + 1 where the n = 1 member, MnBi 2 Te 4 , has been intensively investigated as the first intrinsic antiferromagnetic topological insulator. In this work, we report the A-type antiferromagnetic order in these two compounds by measuring magnetic properties, electrical and thermal transport, specific heat, and single-crystal neutron diffraction. Both compounds order into an A-type antiferromagnetic structure as does MnBi 2 Te 4 with ferromagnetic planes coupled antiferromagnetically along the crystallographic c axis. While no evidence for any in-plane ordered moment is found for MnBi 2 Te 4 or MnBi 6 Te 10 , weak reflections at half- L positions along the [0 0 L ] direction are observed for MnBi 4 Te 7 suggesting an in-plane ordered moment around 0.15 μ B / Mn . The ordering temperature, T N , is 13 K for MnBi 4 Te 7 and 11 K for MnBi 6 Te 10 . The magnetic order is also manifested in the anisotropic magnetic properties. Furthermore, for both compounds, the interlayer coupling is weak and a spin-flip transition occurs when a magnetic field of around 1.6 kOe is applied along the c axis at 2 K. As observed in MnBi 2 Te 4 , when cooling across T N , no anomaly was observed in the temperature dependence of thermopower. On the other hand, critical scattering effects are observed in thermal conductivity although the effect is less pronounced than that in MnBi 2 Te 4 .

36 MATERIALS SCIENCE↗

DOE OSTI2020

Parallel high-frequency magnetic sensing with an array of flux transformers and multi-channel optically pumped magnetometer for hand MRI application

Here, we investigate an approach for parallel high-frequency magnetic sensing based on a multi-channel radio frequency (RF) optically pumped magnetometer (OPM) coupled to multiple flux transformers (FTs) with a focus on hand magnetic resonance imaging (MRI) application at ultra-low field (ULF). Multiple RF OPM sensing channels are realized by using a single large-area alkali-metal vapor cell and two laser beams for pumping and probing, shared for all the channels. This design leads to significant cost reduction when multi-channel sensing is desirable, as in the case of ULF MRI. The FT, composed of two connected coils, serves as a transmitter of a target magnetic field to the OPM, while decoupling the OPM from untargeted magnetic fields in the sensing area that can limit the OPM performance. For hand MRI application, theoretical and numerical analysis is performed to determine an optimal geometry for the FT array that could improve signal-to-noise ratio (SNR) and sufficiently reduce crosstalk between FTs. We estimate that the optimized multi-channel FT-OPM sensor can achieve a magnetic field sensitivity of the order of 1 fT / Hz 1 / 2 above 100 kHz, which would be sufficient for 1 mm resolution MRI. In general, the multi-channel capability enables simultaneous magnetic measurements, thus reducing the sensing time and improving the SNR, and we anticipate many applications of the multi-channel FT-OPM sensor beyond the targeted here hand MRI: anatomical parallel ULF MRI of the human brain and other parts of the body, airport security screening, magnetic material imaging, and many others.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Strangely attractive: Collaboration and feedback in the field of molecular magnetism

The fluid synergy between experimentalists and theoreticians has, for decades, led to a deeper understanding of the processes that govern single-molecule magnets. This approach has allowed for the establishment of proven design criteria for the control of magnetic properties through molecular architecture and the development of new magnetic measurement techniques and innovative computational methodologies. Here, we give an account of the experimental and theoretical joint endeavor carried out as part of the synthesis group led by David Mills and the computational/theoretical team led by Nicholas Chilton, together with colleagues in synthetic f-element chemistry and magnetism at the University of Manchester. In addition, we provide a personal perspective on collaborative work in molecular magnetism and how such collaborations are essential for advancing the field further.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1972

Iron-titanium-chromite, a possible new carrier of remanent magnetization in lunar rocks.

Magnetic measurements of synthetic titanchromites reveal a characteristic transition at low temperature, making it possible to identify the presence of titanchromites in lunar rocks 12063, 14321 (dark clasts), and 14310. It is shown that titanchromites with a high chromium content could be the carriers of intermediate stability natural remanent magnetization observed in lunar rocks. Such natural remanent magnetization is acquired by transition thermoremanent magnetization at low temperature and cannot be duplicated by laboratory thermoremanent magnetization imparted above room temperature. The latter process will not yield the correct lunar paleointensity.

Banerjee, S. K.↗

NASA NTRS1979

Magnetometer bias determination and attitude determination for near-earth spacecraft

A simple linear-regression algorithm is used to determine simultaneously magnetometer biases, misalignments, and scale factor corrections, as well as the dependence of the measured magnetic field on magnetic control systems. This algorithm has been applied to data from the Seasat-1 and the Atmosphere Explorer Mission-1/Heat Capacity Mapping Mission (AEM-1/HCMM) spacecraft. Results show that complete inflight calibration as described here can improve significantly the accuracy of attitude solutions obtained from magnetometer measurements. This report discusses the difficulties involved in obtaining attitude information from three-axis magnetometers, briefly derives the calibration algorithm, and presents numerical results for the Seasat-1 and AEM-1/HCMM spacecraft.

Lerner, G. M.↗

DOE OSTI2023

Tetragonal Kondo Insulator EuCd 2 Sb 2 Discovered via High Pressure High Temperature Synthesis

Abstract Magnetic and electronic properties of quantum materials heavily rely on the crystal structure even in the same chemical compositions. In this study, it is demonstrated that a layered tetragonal EuCd 2 Sb 2 structure can be obtained by treating bulk trigonal EuCd 2 Sb 2 under high pressure (6 GPa) and high temperature (600 °C). Magnetization measurements of the newly formed layered tetragonal EuCd 2 Sb 2 confirm an antiferromagnetic ordering with Neel temperature ( T N ) around 16 K, which is significantly higher than that ( T N ≈ 7 K) of trigonal EuCd 2 Sb 2 , consistent with heat capacity measurements. Moreover, bad metal behavior is observed in the temperature dependence of the electrical resistivity and the resistivity shows a dramatic increase around the Neel temperature. Electronic structure calculations with local density approximation dynamic mean–field theory (LDA+DMFT) show that this material is strongly correlated with well‐formed large magnetic moments, due to Hund's coupling, which is known to dramatically suppress the Kondo scale.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1985

Rapid Solidification of Magnetic Oxides

The enhanced control over microstructural evolution inherent in rapid solidification processing techniques are exploited to create novel ceramic magnetic materials. The great sensitivity of magnetic properties to local structure provides a powerful probe both for the study of structure and of microscopic solidification mechanisms. The first system studied is the SrO-Fe2O3 binary, which contains the commercially important hard magnetic compound strontium hexaferrite. The products were analyzed by transmission electron microscopy, Mossbauer spectroscopy, magnetic measurements, and differential thermal analysis. As-quenched ribbons contain high concentrations of super-paramagnetic particles, 80 to 250 Angstroms in diameter, in a glassy matrix. This suggests the possibility of crystallizing monodomain strontium hexaferrite during subsequent heat treatment, with a resulting increase in coercivity over conventionally processed ferrite magnets. That magnetic properties can be controlled in solidification processing by varying the quench rate is demonstrated.

Kalonji, G.↗

DOE OSTI2022

Electronic excitations of α - Fe 2 O 3 heteroepitaxial films measured by resonant inelastic x-ray scattering at the Fe L edge

Resonant inelastic x-ray scattering (RIXS) spectra of hematite (α-Fe 2 O 3 ) were measured at the Fe L 3 edge for heteroepitaxial thin films which were undoped and doped with 1% Ti, Sn, or Zn, in the energy-loss range in excess of 1 eV to study electronic transitions. The spectra were measured for several momentum transfers q, conducted at both low temperature (T=14 K) and room temperature. While we cannot rule out dispersive features possibly owing to propagating excitations, the coarse envelopes of the general spectra did not appreciably change shape with q, implying that the bulk of the observed L-edge RIXS intensity originates from (mostly) nondispersive ligand field excitations. Summing the RIXS spectra over q and comparing the results at T=14 K to those at T=300 K revealed pronounced temperature effects, including an intensity change and energy shift of the ≈1.4 eV peak, a broadband intensity increase of the 3-4 eV range, and higher energy features. The q-summed spectra and their temperature dependencies are virtually identical for nearly all of the samples with different dopants, save for the temperature dependence of the Ti-doped sample's spectrum, which we attribute to being affected by a large number of free charge carriers. Comparing with magnetization measurements for different temperatures and dopings likewise did not show a clear correlation between the RIXS spectra and the magnetic ordering states. To clarify the excited states, we performed spin multiplet calculations which were in excellent agreement with the RIXS spectra over a wide energy range and provide detailed electronic descriptions of the excited states. Furthermore, the implications of these findings to the photoconversion efficiency of hematite photoanodes is discussed.

36 MATERIALS SCIENCE↗

NASA NTRS1982

Sources of lunar magnetic anomalies and their bulk directions of magnetization - Additional evidence from Apollo orbital data

A relatively high-amplitude magnetic anomaly directly detected with the Apollo 15 subsatellite magnetometer and centered near the crater Gerasimovich on the southeastern lunar far side is found to correlate with the location of a conspicuous Reiner Gamma-type swirl marking visible on a Zond 8 photograph. Examinations of available direct and indirect orbital magnetics measurements demonstrate that most strong anomalies occur in areas where morphologically similar markings are concentrated. Even though photogeologic studies indicate an impact-related origin for the swirls, both the swirls and their associated strong anomalies tend to exist preferentially in or near areas that have been seismically modified. Modeling of improved vector magnetic anomaly maps is used to infer 28 independent bulk directions of magnetization for relatively strong and isolated lunar magnetic anomaly sources.

Hood, L. L.↗

NASA NTRSDate not supplied

Scalar Atomic Defect-Based Solid-State Self-calibrating Magnetometer (3SM) for Space Plasma Analysis

The Earth’s magnetosphere is a system of multiple, co-located particle populations interacting via plasma waves. Things to understand are driving processes, radiation belt and ring current issues, auroral physics, internal plasma processes, and magnetosphere-ionosphere mapping issues. These plasma-physics processes enable the Earth’s magnetosphere to evolve in response to temporal changes in the solar wind and they underlie the phenomena of space weather, which impacts spacecraft systems, astronauts, radio communications, and ground based electric-power grids. The objective of 3SM is to measure magnetic field strength and to calibrate the Vector Magnetometer (VM) device to maintain absolute accuracy during a mission. The 3SM features make the instrument preferably suited not only for the traditional role of scalar magnetometers as absolute references for the calibration of the on-board vector instruments, but also for extended operational capacities, such as higher frequency scalar measurements (of potential interest for magnetosphere studies for the low frequency part of the spectrum) or autonomous scalar / vector operations. Diamond has been the solid-state platform of choice for quantum device technologies for some time, however, it suffers from difficulties such as scalability, integration, and cost. While the diamond platform is very useful for quantum technologies, further development is needed to make it viable. The material platform of choice for NASA Glenn’s Quantum Sensing And Spin Physics (Q-SASP) is silicon carbide (SiC). This is due to the much higher industry development of the SiC material platform for high-power and high-temperature electronics. It leverages both the decades-long SiC development expertise and infrastructure at NASA Glenn and its growing capabilities in quantum metrology. To make SiC devices usable for quantum technologies such as quantum sources, a much deeper understanding of defects is needed. Q-SASP is developing quantum metrology capabilities to evaluate the energy structure, defect formation energy, band structure augmentation, generation/recombination rates, and limits of dipole-dipole coupling in non-metal implanted SiC devices. This can be achieved by analysis of zero-field splitting, low-field resonance, and singlet-triplet mixing through various forms of Electrically Detectable Magnetic Resonance (EDMR) and Near-Zero Field Magnetic Resonance (NZFMR) spectroscopy. This work will discuss recent system developments, device developments, computational modeling, and spectroscopy results and analysis of defects created by non-metal implantations in SiC devices. The defect formation energies of V Si ,V C , V C V Si , N C V Si , N Si , N C in 4H-SiC are previously reported values in other research [2]-[3]. The defect formation energies of PSi and PC were calculated in GPAW [fig 1A]. The basic underlying mechanism of the zero-field phenomenon is the mixing of singlet and triplet states [4]-[5]. In most spin-dependent transport, two electron spins are involved, and thus one must consider each of their interactions with the field. We investigated the electronic and magnetic properties of 4H-SiC and 6H-SiC. The defect formation energy helps us determine what types of defects we are observing in the SiC EDMR experiment. They have very low formation energy (it is negative). The phosphorus substitution in 4H-SiC is a very stable defect. The band diagrams provide us with vital information about how the electronic properties of SiC (such as band gap) change as we add non-metal defects. The zero-field splitting parameters allow us to study the inflection point in the NZFMR [fig 1B]. We clearly observed zero-field splitting. We also noted that the zero-field splitting remained constant with changing bias. We aspect it zero-field splitting to remain constant while the hyperfine and exchange interaction perturbations shift under the influence of an external magnetic field. This is the essence of quantum magnetometry and self-calibration.

space plasma↗

DOE OSTI2020

Insensitivity of Magnetic Coupling to Ligand Substitution in a Series of Tetraoxolene Radical-Bridged Fe 2 Complexes

The elucidation of magnetostructural correlations between bridging ligand substitution and strength of magnetic coupling is essential to the development of high-temperature molecule-based magnetic materials. Toward this end, we report the series of tetraoxolene-bridged Fe II 2 complexes [(Me 3 TPyA) 2 Fe 2 ( R L)] n + (Me 3 TPyA = tris(6-methyl-2-pyridylmethyl)amine; n = 2: OMe LH 2 = 3,6-dimethoxy-2,5-dihydroxo-1,4-benzoquinone, Cl LH 2 = 3,6-dichloro-2,5-dihydroxo-1,4-benzoquinone, Na 2 [ NO 2 L] = sodium 3,6-dinitro-2,5-dihydroxo-1,4-benzoquinone; n = 4: SMe 2 L = 3,6-bis(dimethylsulfonium)-2,5-dihydroxo-1,4-benzoquinone diylide) and their one-electron-reduced analogues. Furthermore, variable-temperature dc magnetic susceptibility data reveal the presence of weak ferromagnetic superexchange between Fe II centers in the oxidized species, with exchange constants of J = +1.2(2) (R = OMe, Cl) and +0.3(1) (R = NO 2 , SMe 2 ) cm –1 . In contrast, X-ray diffraction, cyclic voltammetry, and Mössbauer spectroscopy establish a ligand-centered radical in the reduced complexes. Magnetic measurements for the radical-bridged species reveal the presence of strong antiferromagnetic metal–radical coupling, with J = -57(10), -60(7), -58(6), and -65(8) cm –1 for R = OMe, Cl, NO 2 , and SMe 2 , respectively. The minimal effects of substituents in the 3- and 6-positions of R L x –• on the magnetic coupling strength is understood through electronic structure calculations, which show negligible spin density on the substituents and associated C atoms of the ring. Finally, the radical-bridged complexes are single-molecule magnets, with relaxation barriers of U eff = 50(1), 41(1), 38(1), and 33(1) cm –1 for R = OMe, Cl, NO 2 , and SMe 2 , respectively. Taken together, these results provide the first examination of how bridging ligand substitution influences magnetic coupling in semiquinoid-bridged compounds, and they establish design criteria for the synthesis of semiquinoid-based molecules and materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Alignment of the Alpha Magnetic Spectrometer (AMS) in space

Abstract The Alpha Magnetic Spectrometer (AMS) is a precision particle physics detector operating at an altitude of $$\sim 410$$ ∼ 410 km aboard the International Space Station. The AMS silicon tracker, together with the permanent magnet, measures the rigidity (momentum/charge) of cosmic rays in the range from $$\sim 0.5$$ ∼ 0.5 GV to several TV. In order to have accurate rigidity measurements, the positions of more than 2000 tracker modules have to be determined at the micron level by an alignment procedure. The tracker was first aligned using the 400 GeV/c proton test beam at CERN and then re-aligned using cosmic-ray events after being launched into space. A unique method to align the permanent magnetic spectrometer for a space experiment is presented. The developed underlying mathematical algorithm is discussed in detail.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Magnetocaloric effect in the vicinity of the magnetic phase transition in NdCo 2–x Fe x compounds

In the present paper, the magnetocaloric effect (MCE) of NdCo 2-x Fe x (x = 0, 0.2, 0.4, 0.6) compounds was investigated by magnetization measurements. Here, the temperature-dependent high-resolution synchrotron x-ray diffraction study shows a magnetostructural transition from the paramagnetic cubic phase to the ferromagnetic tetragonal phase below their Curie temperatures. Differential scanning calorimetry analysis shows the absence of thermal hysteresis, indicating the second-order nature of the magnetostructural phase transition in these compounds. The maximum values of magnetic entropy change (ΔS M ) and wide operating temperature (OT) are obtained under a field change of 5 T, which are 7.33 Jkg -1 K -1 , 6.45 Jkg -1 K -1 , 5.71 Jkg -1 K -1 , 4.70 Jkg -1 K -1 and 78 K, 82 K, 85 K, 92 K for x = 0, 0.2, 0.4, and 0.6, respectively. The corresponding values of relative cooling power (RCP) are 529.96 Jkg -1 , 497.25 Jkg -1 , 470.55 Jkg -1 , and 428.31 Jkg -1 . The observed wide OT range and large RCP values are comparable with Gd, Gd 5 Ge 2 Si 2 , and some rare-earth-based giant magnetocaloric materials, making this series of compounds suitable for magnetic refrigeration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Unusual magnetic and transport properties in HoMn 6 Sn 6 kagome magnet

Here, with intricate lattice structures, kagome materials are an excellent platform to study various fascinating topological quantum states. In particular, kagome materials, revealing large responses to external stimuli such as pressure or magnetic field, are subject to special investigation. Here we study the kagome-net HoMn 6 Sn 6 magnet that undergoes paramagnetic to ferrimagnetic transition (below 376 K) and reveals spin-reorientation transition below 200 K. In this compound, we observe the topological Hall effect and substantial contribution of anomalous Hall effect above 100 K. We unveil the pressure effects on magnetic ordering at a low magnetic field from the pressure tunable magnetization measurement. By utilizing high-resolution angle-resolved photoemission spectroscopy, Dirac-like dispersion at the high-symmetry point K is revealed in the vicinity of the Fermi level, which is well supported by the first-principles calculations. Our investigation will pave the way to understanding the magnetotransport and electronic properties of various rare-earth-based kagome magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Fluid Mixing during Phase Separation in Crystallizing White Dwarfs

Abstract Accurate models of cooling white dwarfs must treat the energy released as their cores crystallize. This phase transition slows the cooling by releasing latent heat and also gravitational energy, which results from phase separation: liquid C is released from the solid C/O core, driving an outward carbon flux. The Gaia color–magnitude diagram provides striking confirmation of this theory by revealing a mass-dependent overdensity of white dwarfs, indicating slowed cooling at the expected location. However, the observed overdensity is enhanced relative to the models. Additionally, it is associated with increased magnetism, suggesting a link between crystallization and magnetic field generation. Recent works aimed at explaining an enhanced cooling delay and magnetic field generation employ a uniform mixing prescription that assumes large-scale turbulent motions; we show here that these calculations are not self-consistent. We also show that thermohaline mixing is most likely efficient enough to provide the required chemical redistribution during C/O phase separation, and that the resulting velocities and mixing lengths are much smaller than previous estimates. These reduced fluid motions cannot generate measurable magnetic fields, suggesting any link with crystallization needs to invoke a separate mechanism. Finally, this mixing alters the chemical profiles, which in turn affects the frequencies of the pulsation modes.

79 ASTRONOMY AND ASTROPHYSICS↗