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29 Si nuclear magnetic resonance study of URu 2 Si 2 under pressure
Wereport 29Si nuclearmagneticresonancemeasurementsofsinglecrystalsandalignedpowdersof URu2Si2 under pressureinthehiddenorderandparamagneticphases.We find thattheKnightshift decreases withappliedpressure,consistentwithpreviousmeasurementsofthestaticmagneticsus- ceptibility.Previousmeasurementsofthespinlatticerelaxationtimerevealedapartialsuppressionof the densityofstatesbelow30K.Thissuppressionpersistsunderpressure,andtheonsettemperatureis mildly enhanced.
YCrWO 6 : Polar and Magnetic Oxide with CaTa 2 O 6 -Related Structure
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Spin-Selective Oxygen Evolution Reaction in Chiral Iron Oxide Nanoparticles: Synergistic Impact of Inherent Magnetic Moment and Chirality
Electron spin polarization is identified as a promising avenue for enhancing the oxygen evolution reaction (OER), which is the bottleneck that limits the energy efficiency of water-splitting. Here, in this work, we report that both ferrimagnetic (f-Fe 3 O 4 ) and superparamagnetic iron oxide (s-Fe 3 O 4 ) catalysts can exhibit external magnetic field (Hext)-induced OER enhancement, and the activity is proportional to their intrinsic magnetic moment. Additionally, the chirality-induced spin selectivity (CISS) effect was utilized in synergy with Hext to get a maximum enhancement of up to 89% improvement in current density (at 1.8 V vs RHE) with a low onset potential of 270 mV in s-Fe 3 O 4 catalysts. Spin polarization and the resultant spin selectivity suppress the production of H 2 O 2 and promote the formation of ground state triplet O 2 during the OER. Furthermore, the design of chiral s-Fe 3 O 4 with synergistic spin potential effect demonstrates a high spin polarization of ∼42%, as measured using conductive atomic force microscopy (c-AFM).
Interaction of Hydrocarbons with Clays under Reservoir Conditions: In Situ Infrared and Nuclear Magnetic Resonance Spectroscopy and X-ray Diffraction for Expandable Clays with Variably Wet Supercritical Methane
The results from novel in situ high-pressure nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, and X-ray diffraction (XRD) investigation of the interaction of the smectite hectorite with variably wet supercritical methane (scCH4) at 90 bar and 323 K (hydrostatic conditions equivalent to ~1 km depth) show that CH4 occurs in the clay interlayers, in pores external to the individual clay particles, and as bulk fluid. The occupancy of each environment depends on the relative humidity (RH) of the CH4-rich fluid and the hydration energy and size of the charge-balancing cation. As RH increases, the fraction of interlayer and interparticle CH4 decreases, although with Cs+, addition of a small amount of H2O initially increases CH4 uptake. Maximum interlayer CH4 adsorption occurs when the mean basal spacing just permits methane intercalation (~11.5 Å) and never below this basal spacing. It is also higher with divalent cations than with monovalent cations. The data show that CH4 adsorption occurs predominantly via a weak dispersion interaction with the clay and that its intercalation occurs via a passive space-filling hydrophobic mechanism. The results suggest that, under reservoir conditions, smectite interlayers may provide a reservoir for CH4 under low-water conditions.
High-Field One-Dimensional and Two-Dimensional 27Al Magic-Angle Spinning Nuclear Magnetic Resonance Study of ?-, d-, and ?-Al2O3 Dominated Aluminum Oxides: Toward Understanding the Al Sites in ?-Al2O3
Herein, a detailed analysis was carried out using high-field (19.9 T) 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) on three specially prepared aluminum oxide samples where the ?-, d-, and ?-Al2O3 phases are dominantly expressed through careful control of the synthesis conditions. Specifically, two-dimensional (2D) multiquantum (MQ) MAS 27Al was used to obtain high spectral resolution, which provided a guide for analyzing quantitative 1D 27Al NMR spectra. Six aluminum sites were resolved in the 2D MQ MAS NMR spectra, and seven aluminum sites were required to fit the 1D spectra. A set of octahedral and tetrahedral peaks with well-defined quadrupolar line shapes was observed in the ?-phase dominant sample and was unambiguously assigned to the ?-Al2O3 phase. The distinct line shapes related to the ?-Al2O3 phase provided an opportunity for effectively deconvoluting the more complex spectrum obtained from the d-Al2O3 dominant sample, allowing the peaks/quadrupolar parameters related to the d-Al2O3 phase to be extracted. The results show that the d-Al2O3 phase contains three distinct AlO sites and three distinct AlT sites. This detailed Al site structural information offers a powerful way of analyzing the most complex ?-Al2O3 spectrum. It is found that the ?-Al2O3 phase consists of Al sites with local structures similar to those found in the d-Al2O3 and ?-Al2O3 phases albeit with less ordering. Spin–lattice relaxation time measurement further confirms the disordering of the lattice. Collectively, this study uniquely assigns 27Al features in transition aluminas, offering a simplified method to quantify complex mixtures of aluminum sites in transition alumina samples.
Structural and Magnetic Evolution of Bimetallic MnAu Clusters Driven by Asymmetric Atomic Migration
The nanoscale structural, compositional, and magnetic properties are examined for annealed MnAu nanoclusters. The MnAu clusters order into the L10 structure, and monotonic size-dependences develop for the composition and lattice parameters, which are well reproduced by our density functional theory calculations. Simultaneously, Mn diffusion forms 5 Å nanoshells on larger clusters inducing significant magnetization in an otherwise antiferromagnetic system. The differing atomic mobilities yield new cluster nanostructures that can be employed generally to create novel physical properties.
Ordering of room-temperature magnetic skyrmions in a polar van der Waals magnet
Abstract Control and understanding of ensembles of skyrmions is important for realization of future technologies. In particular, the order-disorder transition associated with the 2D lattice of magnetic skyrmions can have significant implications for transport and other dynamic functionalities. To date, skyrmion ensembles have been primarily studied in bulk crystals, or as isolated skyrmions in thin film devices. Here, we investigate the condensation of the skyrmion phase at room temperature and zero field in a polar, van der Waals magnet. We demonstrate that we can engineer an ordered skyrmion crystal through structural confinement on the μ m scale, showing control over this order-disorder transition on scales relevant for device applications.
Bifunctional nanoparticles for SERS monitoring and magnetic intervention of assembly and enzyme cutting of DNAs
The ability to detect and intervene in DNA assembly, disassembly, and enzyme cutting processes in a solution phase requires effective signal transduction and stimulus response. This report demonstrates a novel bifunctional strategy for the creation of this ability using gold- and silver-coated MnZn ferrite nanoparticles (MZF@Au or MZF@Ag) that impart magnetic and surfaceenhanced Raman scattering (SERS) functionalities to these processes. The double-stranded DNA linkage of labeled gold nanoparticles with MZF@Au (or MZF@Ag) produces interparticle "hot-spots" for real-time SERS monitoring of the DNA assembly, disassembly, or enzyme cutting processes, during which the magnetic component provides an effective means for intervention in the solution. The unique combination of the nanoprobes functionalities serves a new paradigm for the design of functional nanoprobes in biomolecular recognition and intervention.
Structural changes correlated with magnetic spin state isomorphism in the S 2 state of the Mn 4 CaO 5 cluster in the oxygen-evolving complex of photosystem II
The Mn 4 CaO 5 cluster in photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (S i , i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in the S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. As a result, such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis.
Enforcing Ising-like magnetic anisotropy via trigonal distortion in the design of a W( v )–Co( ii ) cyanide single-chain magnet
A new octacyanotungstate( v ) singe chain magnet with an effective energy barrier of 39.7(3) cm −1 is achieved by enforcing Ising-like magnetic anisotropy via introduction of trigonal distortion with a fac -tridentate capping ligand.
Slow magnetic dynamics in a family of mononuclear lanthanide complexes exhibiting the rare cubic coordination geometry
Synthesis, magnetic, and theoretical studies of a new family of mononuclear lanthanide complexes exhibiting the very rare cubic coordination geometry.
Low temperature structures and magnetic interactions in the organic-based ferromagnetic and metamagnetic polymorphs of decamethylferrocenium 7,7,8,8-tetracyano- p -quinodimethanide, [FeCp* 2 ]˙ + [TCNQ]˙ −
To identify the genesis of the differing magnetic behaviors for the ferro- (FO) and metamagnetic (MM) polymorphs of [FeCp* 2 ][TCNQ] the low temperature structures of each polymorph were determined from high-resolution synchrotron powder diffraction data.
Tuning the optical and magnetic properties of lanthanide single-ion magnets using nitro-functionalized trispyrazolylborate ligands
We report the synthesis, crystal structures, photophysical and magnetic properties of 11 novel lanthanide complexes with the asymmetrically functionalized trispyrazolylborate ligand 4-nitrotrispyrazolylborate, 4-NO 2 Tp–: [Ln(4-NO 2 Tp) 3 ] (Ln = La–Dy, except Pm). In-depth photophysical characterization of the ligands via luminescence, reflectance and absorption spectroscopic techniques, decay lifetimes, quantum yields supported by time-dependent density functional theory (TD-DFT) and natural bond order (NBO) analysis reveal that n-NO 2 Tp– ligands are dominated by intra-ligand charge transfer (ILCT) transitions and that second-sphere interactions are critical to the stabilization of the T 1 state of n-NO 2 Tp– ligands and hence their ability to sensitize Ln 3+ emission. The luminescence properties of the complexes indicate that 4-NO 2 Tp– is a poor sensitizer of Ln 3+ emission, unlike 3-NO 2 Tp–. Moreover, [Nd(4-NO 2 Tp) 3 ] (crystallized as a hexane solvate) displays single-molecule magnet (SMM) properties, with longer relaxation times and larger barrier than the non-functionalized [NdTp 3 ], attributed to the addition of the NO 2 -group and subsequent rigidification of the molecular structure.
Packing bimodal magnetic particles to fabricate highly dense anisotropic rare earth bonded permanent magnets
Bimodal particles of NdFeB and SmFeB yielded high-density bonded magnets. The energy product of 20 MGOe with 81 vol% magnet loading was demonstrated.
The magnetic recoil spectrometer for measurements of the absolute neutron spectrum at OMEGA and the NIF
The neutron spectrum produced by deuterium-tritium (DT) inertial confinement fusion implosions contains a wealth of information about implosion performance including the DT yield, iontemperature, and areal-density. The Magnetic Recoil Spectrometer (MRS) has been used at both the OMEGA laser facility and the National Ignition Facility (NIF) to measure the absolute neutron spectrum from 3 to 30 MeV at OMEGA and 3 to 36 MeV at the NIF. These measurements have been used to diagnose the performance of cryogenic target implosions to unprecedented accuracy. Interpretation of MRS data requires a detailed understanding of the MRS response and background. This paper describes ab initio characterization of the system involving Monte Carlo simulations of the MRS response in addition to the commission experiments for in situ calibration of the systems on OMEGA and the NIF.
Effect of Cr substitution on the magnetic and magnetic-transport properties of Fe{sub 2}Mn{sub 1-x}Cr{sub x}Si alloys
Fe{sub 2}Mn{sub 1-x}Cr{sub x}Si (x = 0, 0.1, and 0.2) alloys were investigated for their magnetic and transport properties in view of the expected half metallicity. It is found that Cr substitution suppresses the antiferromagnetic phase present in parent Fe{sub 2}MnSi, which completely disappears for x = 0.2. Curie temperature of the alloys increases from 230 K to 299 K as x is increased from 0 to 0.2. The value of the Rhodes-Wohlfarth ratio indicates that the system shows iterant magnetism. Resistivity measurements also show absence of antiferromagnetic phase for x = 0.2. Resistivity data have been fitted by considering the electron-phonon and electron-magnon scattering contributions, which indicates the presence of half metallicity in these compounds. Temperature dependence of resistivity data shows magnetoresistance of −3% and −2.5% at Curie temperature with applied field of 50 kOe for x = 0.1 and 0.2, respectively.
Electromagnetic momentum and the energy–momentum tensor in a linear medium with magnetic and dielectric properties
In a continuum setting, the energy–momentum tensor embodies the relations between conservation of energy, conservation of linear momentum, and conservation of angular momentum. The well-defined total energy and the well-defined total momentum in a thermodynamically closed system with complete equations of motion are used to construct the total energy–momentum tensor for a stationary simple linear material with both magnetic and dielectric properties illuminated by a quasimonochromatic pulse of light through a gradient-index antireflection coating. The perplexing issues surrounding the Abraham and Minkowski momentums are bypassed by working entirely with conservation principles, the total energy, and the total momentum. We derive electromagnetic continuity equations and equations of motion for the macroscopic fields based on the material four-divergence of the traceless, symmetric total energy–momentum tensor. We identify contradictions between the macroscopic Maxwell equations and the continuum form of the conservation principles. We resolve the contradictions, which are the actual fundamental issues underlying the Abraham–Minkowski controversy, by constructing a unified version of continuum electrodynamics that is based on establishing consistency between the three-dimensional Maxwell equations for macroscopic fields, the electromagnetic continuity equations, the four-divergence of the total energy–momentum tensor, and a four-dimensional tensor formulation of electrodynamics for macroscopic fields in a simple linear medium.