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Despite the importance of rhodium complexes in catalysis, and the favorable 100% natural abundance of the spin-1/2 103Rh nucleus, there are few reports of 103Rh nuclear magnetic resonance (NMR) parameters in the literature. In part, this is the consequence of the very low gyromagnetic ratio of 103Rh and its dismal NMR sensitivity. In a previous paper [Harbor-Collins et al., J. Chem. Phys. 159, 104 307 (2023)], we demonstrated an NMR methodology for 1H-enhanced 103Rh NMR and demonstrated an application to the 103Rh NMR of the dirhodium formate paddlewheel complex. In this paper, we employ selective 18O labeling to break the magnetic equivalence of the 103Rh spin pair of dirhodium formate. This allows the estimation of the 103Rh–103Rh spin–spin coupling and provides access to the 103Rh singlet state. We present the first measurement of a 18O-induced 103Rh secondary isotope shift as well as the first instance of singlet order generated in a 103Rh spin pair. The field-dependence of 103Rh singlet relaxation is measured by field-cycling NMR experiments. [ABSTRACT FROM AUTHOR]

The nuclear magnetic resonance (NMR) spectroscopy of spin-1/2 nuclei with low gyromagnetic ratio is challenging due to the low NMR signal strength. Methodology for the rapid acquisition of 103Rh NMR parameters is demonstrated for the case of the rhodium formate "paddlewheel" complex R h 2 (H C O 2 ) 4 . A scheme is described for enhancing the 103Rh signal strength by polarization transfer from 1H nuclei, which also greatly reduces the interference from ringing artifacts, a common hurdle for the direct observation of low-γ nuclei. The 103Rh relaxation time constants T1 and T2 are measured within 20 min by using 1H-detected experiments. The field dependence of the 103Rh T1 is measured. The high-field relaxation is dominated by the chemical shift anisotropy mechanism. The 103Rh shielding anisotropy is found to be very large: |Δσ| = 9900 ± 540 ppm. This estimate is compared with density functional theory calculations. [ABSTRACT FROM AUTHOR]

In vivo phosphorus-31 (31P) magnetic resonance spectroscopy (MRS) imaging (MRSI) is an important non-invasive imaging tool for studying cerebral energy metabolism, intracellular nicotinamide adenine dinucleotide (NAD) and redox ratio, and mitochondrial function. However, it is challenging to achieve high signal-to-noise ratio (SNR) 31P MRS/MRSI results owing to low phosphorus metabolites concentration and low phosphorous gyromagnetic ratio ( γ ). Many works have demonstrated that ultrahigh field (UHF) could significantly improve the 31P-MRS SNR. However, there is a lack of studies of the 31P MRSI SNR in the 10.5 Tesla (T) human scanner. In this study, we designed and constructed a novel 31P-1H dual-frequency loop-dipole probe that can operate at both 7T and 10.5T for a quantitative comparison of 31P MRSI SNR between the two magnetic fields, taking into account the RF coil B1 fields (RF coil receive and transmit fields) and relaxation times. We found that the SNR of the 31P MRS signal is 1.5 times higher at 10.5T as compared to 7T, and the power dependence of SNR on magnetic field strength (B0) is 1.9. [ABSTRACT FROM AUTHOR]

Magnetic resonance (MR) with sodium (23Na) is a noninvasive tool providing quantitative biochemical information regarding physiology, cellular metabolism, and viability, with the potential to extend MR beyond anatomical proton imaging. However, when using clinical scanners, the low detectable 23Na signal and the low 23Na gyromagnetic ratio require the design of dedicated radiofrequency (RF) coils tuned to the 23Na Larmor frequency and sequences, as well as the development of dedicated phantoms for testing the image quality, and an MR scanner with multinuclear spectroscopy (MNS) capabilities. In this work, we propose a hardware and software setup for evaluating the potential of 23Na magnetic resonance imaging (MRI) with a clinical scanner. In particular, the reliability of the proposed setup and the reproducibility of the measurements were verified by multiple acquisitions from a 3T MR scanner using a homebuilt RF volume coil and a dedicated sequence for the imaging of a phantom specifically designed for evaluating the accuracy of the technique. The final goal of this study is to propose a setup for standardizing clinical and research 23Na MRI protocols. [ABSTRACT FROM AUTHOR]

Quantum magnetic sensors based on nitrogen vacancy (NV) centers are expected to be used for various biological and medical applications. Continuously excited (CE) Ramsey magnetometry is one of the most sensitive measurement protocols and has the potential to improve the sensitivity of sensors using additional quantum manipulations to extend the spin dephasing time. In a typical ensemble NV measurement, the spin dephasing time is limited by inhomogeneous coupling. To overcome this limitation, a magnetometry that extends the CE Ramsey protocol with a double‐quantum (DQ) Ramsey sequence and spin bath driving is developed. It is demonstrated that the electric noise due to the spatial inhomogeneity of the crystal strain is cancelled out by the DQ Ramsey, and the magnetic noise due to the P1 centers was suppressed by spin bath driving. Compared to the conventional CE Ramsey, the CE‐DQ Ramsey with spin bath driving effectively doubles the gyromagnetic ratio and yields a twofold extension of T2*, corresponding to a fourfold enhancement of the photon‐shot‐noise limited sensitivity. [ABSTRACT FROM AUTHOR]

Broadband ferromagnetic resonance (BFMR) spectroscopy analysis can be achieved with different setups involving the frequency-sweep and field-sweep setups. To evaluate and compare the two former regimes, a frequency-sweep and a field-sweep shortcut BFMR regimes were conducted on Co–Ni ferrite nanoparticles that were synthesized by the co-precipitation method of metal chlorides. The nanoparticles were structurally and magnetically characterized, with an average particle size of around 23 nm and a spinel structure. The saturation magnetization was about 59 emu/g, and the coercivity was about 30 Oe. The BFMR analyses were achieved through a frequency range of (2–26) GHz and a field range of (0-104 )Oe. The two regimes, frequency sweep and field sweep, showed linear behavior between the resonance field and resonance frequency. The frequency–sweep regime displayed more complicated curves involving small multi-peaks within the multi-FMR absorption band that were not found in the field sweep regime. The intercepts of the linear dispersion relationship between the two regimes are nearly equivalent to each other. The field-sweep g-factor was higher and more reasonable than the frequency-sweep one, whereas its damping factor was lower. The fluctuation in the frequency linewidth vs. resonance field in the frequency-sweep method is higher than that for the field-sweep. [ABSTRACT FROM AUTHOR]

Polarization transfers are crucial building blocks in magnetic resonance experiments, i.e., they can be used to polarize insensitive nuclei and correlate nuclear spins in multidimensional nuclear magnetic resonance (NMR) spectroscopy. The polarization can be transferred either across different nuclear spin species or from electron spins to the relatively low-polarized nuclear spins. The former route occurring in solid-state NMR can be performed via cross polarization (CP), while the latter route is known as dynamic nuclear polarization (DNP). Despite having different operating conditions, we opinionate that both mechanisms are theoretically similar processes in ideal conditions, i.e., the electron is merely another spin-1/2 particle with a much higher gyromagnetic ratio. Here, we show that the CP and DNP processes can be described using a unified theory based on average Hamiltonian theory combined with fictitious operators. The intuitive and unified approach has allowed new insights into the cross-effect DNP mechanism, leading to better design of DNP polarizing agents and extending the applications beyond just hyperpolarization. We explore the possibility of exploiting theoretically predicted DNP transients for electron–nucleus distance measurements—such as routine dipolar-recoupling experiments in solid-state NMR. [ABSTRACT FROM AUTHOR]

The measured ground- and isomeric-state magnetic moments of 175,177Yb have been theoretically investigated for the first time using the method based on the Quasiparticle Phonon Nuclear Model (QPNM). In this method, spin-polarization is produced through interaction between the magnetic dipole (M1) excitations of the core and the odd particle. It provides a quenched spin gyromagnetic factor whose magnitude depends on the density of 1+ levels in the core. gR factors, one of the essential inputs of the magnetic moment calculations, have been computed with a newly developed approach. The predictions of theory for the magnetic moments are in excellent agreement with experimental data. [ABSTRACT FROM AUTHOR]

High-field nuclear magnetic resonance (NMR) spectroscopy is an indispensable technique for identification and characterization of chemicals and biomolecular structures. In the vast majority of NMR experiments, nuclear spin polarization arises from thermalization in multi-Tesla magnetic fields produced by superconducting magnets. In contrast, NMR instruments operating at low magnetic fields are emerging as a compact, inexpensive, and highly accessible alternative but suffer from low thermal polarization at a low field strength and consequently a low signal. However, certain hyperpolarization techniques create high polarization levels on target molecules independent of magnetic fields, giving low-field NMR a significant sensitivity boost. In this study, SABRE (Signal Amplification By Reversible Exchange) was combined with high homogeneity electromagnets operating at mT fields, enabling high resolution 1H, 13C, 15N, and 19F spectra to be detected with a single scan at magnetic fields between 1 mT and 10 mT. Chemical specificity is attained at mT magnetic fields with complex, highly resolved spectra. Most spectra are in the strong coupling regime where J-couplings are on the order of chemical shift differences. The spectra and the hyperpolarization spin dynamics are simulated with SPINACH. The simulations start from the parahydrogen singlet in the bound complex and include both chemical exchange and spin evolution at these mT fields. The simulations qualitatively match the experimental spectra and are used to identify the spin order terms formed during mT SABRE. The combination of low field NMR instruments with SABRE polarization results in sensitive measurements, even for rare spins with low gyromagnetic ratios at low magnetic fields. [ABSTRACT FROM AUTHOR]

The direct matrix elements of the energy operator for the spin–other-orbit interaction of the npn'h and np5n'h configurations are determined. The direct matrix elements together with exchange elements are intended for further numerical calculation of fine-structure parameters and other characteristics of atoms such as gyromagnetic ratios. The coefficients for radial integrals are calculated in the single-configuration approximation, in the formalism of irreducible tensor operators, and in two representations, i.e., LSJM and uncoupled angular momentum. A formula has been derived for calculating the direct matrix elements of the considered configuration in the uncoupled angular momentum representation and has been tested on small rank matrices with M = ±7 (1 rank) and M = ±6 (4 rank). All other direct matrix elements have been calculated for a matrix with M = 0 (12 rank). The obtained values have been transformed into the LSJM representation using the matrix of Clebsch–Gordan coefficients and compared with an independent calculation in the LSJM representation. The complete agreement of the direct matrix elements of the interaction considered in two different calculation schemes indicates that the obtained results are reliable. [ABSTRACT FROM AUTHOR]

Measurements are presented of the frequency and field dependent, complex magnetic permeability, μ(f, H) = μ′(f, H)-i μ″(f, H), of a kerosene-based ferrofluid sample with magnetite particles, over the frequency range, f, of 0.4–6 GHz, and polarizing field, H, range of 0–102 kA/m. In this frequency range, both the ferromagnetic resonance at a frequency, fres, and the corresponding maximum absorption at a frequency, fmax, were determined. From the H dependence of both fres and the ratio of fmax/fres, we determined the anisotropy field, HA, the anisotropy constant Keff, the gyromagnetic ratio, γ , the damping parameter, α , the spectroscopic splitting factor, g, and the internal magnetic viscosity, η m . Also, the theoretical Néel relaxation time, τ N , was evaluated. Furthermore, the measurements of, μ(f), enabled one to study the effect of, H, on the the specific absorption rate, SAR, and the time dependence of the variation in temperature, ΔT, of the investigated ferrofluid sample. The SAR was calculated, using a new equation for the calculation of the SAR of ferrofluids. This equation offers a more precise computation of the SAR in that it takes into account the density of the ferrofluid ρF, as opposed to using just the density of the dispersed solid particles, ρS. These results illustrate how control of the SAR and the variation in ΔT, of the ferrofluid sample, through the variation of H, and has applications in the treatment of cancer by magnetic hyperthermia, for modeling bio-heat transfer phenomena, microwave heating or the possibility of use of the ferrofluid as a shield material against microwave electromagnetic radiation. Also, knowledge of the magnetic parameters of ferrofluids, is useful in the design and manufacture of some microwave devices. [ABSTRACT FROM AUTHOR]

17O and 14N are attractive targets for in vivo NMR spectroscopy and imaging, but low gyromagnetic ratios γ and fast spin relaxation complicate observations. This work explores indirect ways of detecting some of these sites with the help of proton‐detected double resonance techniques. As standard coherence transfer methods are of limited use for such indirect detection, alternative routes for probing the quadrupolar spectra on 1H were tested. These centered on modulating the broadening effects imparted onto protons adjacent to the low‐γ species through J couplings through either continuous wave or spin‐echo double‐resonance decoupling/recoupling sequences. As in all cases, the changes imparted by these double‐resonance strategies were small due to the fast relaxation undergone by the quadrupoles, the sensitivity of these approaches was amplified by transferring their effects onto the abundant water 1H signal. These amplifications were mediated by the spontaneous exchanges that the labile 1Hs bound to 17O or 14N undergo with the water protons. In experiments designed on the basis of double‐resonance spin echoes, these enhancements were imparted by looping the transverse encodings together with multiple longitudinal storage periods, leading to decoupling‐recoupling with exchange (D‐REX) sequences. In experiments designed on the basis of continuous on/off quadrupolar decoupling, these solvent exchanges were incorporated into chemical‐exchange saturation transfer schemes, leading to decoupling‐recoupling with saturation transfer (D‐REST) sequences. Both of these variants harnessed sizable proportions of the easily detectable water signals, in order to characterize the NMR spectra and/or to image with atomic‐site specificity the 17O and 14N species. [ABSTRACT FROM AUTHOR]

With the development of heteronuclear fluorine, sodium, phosphorus, and other probes and imaging technologies as well as the optimization of magnetic resonance imaging (MRI) equipment and sequences, multi-nuclear magnetic resonance (multi-NMR) has enabled localize molecular activities in vivo that are central to a variety of diseases, including cardiovascular disease, neurodegenerative pathologies, metabolic diseases, kidney, and tumor, to shift from the traditional morphological imaging to the molecular imaging, precision diagnosis, and treatment mode. However, due to the low natural abundance and low gyromagnetic ratios, the clinical application of multi-NMR has been hampered. Several techniques have been developed to amplify the NMR sensitivity such as the dynamic nuclear polarization, spin-exchange optical pumping, and brute-force polarization. Meanwhile, a wide range of nuclei can be hyperpolarized, such as 2H, 3He, 13C, 15 N, 31P, and 129Xe. The signal can be increased and allows real-time observation of biological perfusion, metabolite transport, and metabolic reactions in vivo, overcoming the disadvantages of conventional magnetic resonance of low sensitivity. HP-NMR imaging of different nuclear substrates provides a unique opportunity and invention to map the metabolic changes in various organs without invasive procedures. This review aims to focus on the recent applications of multi-NMR technology not only in a range of preliminary animal experiments but also in various disease spectrum in human. Furthermore, we will discuss the future challenges and opportunities of this multi-NMR from a clinical perspective, in the hope of truly bridging the gap between cutting-edge molecular biology and clinical applications. [ABSTRACT FROM AUTHOR]

Energy levels of pentacoordinate d5 to d9 complexes were evaluated according to the generalized crystal field theory at three levels of sophistication for two limiting cases of pentacoordination: trigonal bipyramid and tetragonal pyramid. The electronic crystal field terms involve the interelectron repulsion and the crystal field potential; crystal field multiplets account for the spin–orbit interaction; and magnetic energy levels involve the orbital– and spin–Zeeman interactions with the magnetic field. The crystal field terms are labelled according to the irreducible representations of point groups D3h and C4v using Mulliken notation. The crystal field multiplets are labelled with the Bethe notations for the respective double groups D'3 and C'4. The magnetic functions, such as the temperature dependence of the effective magnetic moment and the field dependence of the magnetization, are evaluated by employing the apparatus of statistical thermodynamics as derivatives of the field-dependent partition function. When appropriate, the formalism of the spin Hamiltonian is applied, giving rise to a set of magnetic parameters, such as the zero-field splitting D and E, magnetogyric ratio tensor, and temperature-independent paramagnetism. The data calculated using GCFT were compared with the ab initio calculations at the CASSCF+NEVPT2 level and those involving the spin–orbit interaction. [ABSTRACT FROM AUTHOR]

Recently, the 'Muon g-2' experiment at Fermilab announced a new measurement of the muon's anomalous magnetic moment with better than one-in-a-million accuracy. While confirming the earlier measurement at the Brookhaven National Lab, it has also strengthened the discrepancy with the theoretical calculations, which have also been performed with the same level of accuracy. We shall discuss the physics behind the anomalous magnetic moment of the muon and some theoretical and experimental aspects of its determination. We shall also touch upon what this discrepancy, if confirmed, would mean for our knowledge of particle physics. [ABSTRACT FROM AUTHOR]

Monitoring the tissue sodium content (TSC) in the intervertebral disk geometry noninvasively by MRI is a sensitive measure to estimate changes in the proteoglycan content of the intervertebral disk, which is a biomarker of degenerative disk disease (DDD) and of lumbar back pain (LBP). However, application of quantitative sodium concentration measurements in 23Na‐MRI is highly challenging due to the lower in vivo concentrations and smaller gyromagnetic ratio, ultimately yielding much smaller signal relative to 1H‐MRI. Moreover, imaging the intervertebral disk geometry imposes higher demands, mainly because the necessary RF volume coils produce highly inhomogeneous transmit field patterns. For an accurate absolute quantification of TSC in the intervertebral disks, the B1 field variations have to be mitigated. In this study, we report for the first time quantitative sodium concentration in the intervertebral disks at clinical field strengths (3 T) by deploying 23Na‐MRI in healthy human subjects. The sodium B1 maps were calculated by using the double‐angle method and a double‐tuned (1H/23Na) transceive chest coil, and the individual effects of the variation in the B1 field patterns in tissue sodium quantification were calculated. Phantom measurements were conducted to evaluate the quality of the Na‐weighted images and B1 mapping. Depending on the disk position, the sodium concentration was calculated as 161.6 mmol/L–347 mmol/L, and the mean sodium concentration of the intervertebral disks varies between 254.6 ± 54 mmol/L and 290.1 ± 39 mmol/L. A smoothing effect of the B1 correction on the sodium concentration maps was observed, such that the standard deviation of the mean sodium concentration was significantly reduced with B1 mitigation. The results of this work provide an improved integration of quantitative 23Na‐MRI into clinical studies in intervertebral disks such as degenerative disk disease and establish alternative scoring schemes to existing morphological scoring such as the Pfirrmann score. [ABSTRACT FROM AUTHOR]

Dynamic nuclear polarization (DNP) is theoretically able to enhance the signal in nuclear magnetic resonance (NMR) experiments by a factor γe/γn, where γ's are the gyromagnetic ratios of an electron and a nuclear spin. However, DNP enhancements currently achieved in high-field, high-resolution biomolecular magic-angle spinning NMR are well below this limit because the continuous-wave DNP mechanisms employed in these experiments scale as ω0-n where n ~ 1-2. In pulsed DNP methods, such as nuclear orientation via electron spin-locking (NOVEL), the DNP efficiency is independent of the strength of the main magnetic field. Hence, these methods represent a viable alternative approach for enhancing nuclear signals. At 0.35 T, the NOVEL scheme was demonstrated to be efficient in samples doped with stable radicals, generating ¹H NMR enhancements of ~430. However, an impediment in the implementation of NOVEL at high fields is the requirement of sufficient microwave power to fulfill the on-resonance matching condition, ω0I = ω1S, where ω0I and ω1S are the nuclear Larmor and electron Rabi frequencies, respectively. Here, we exploit a generalized matching condition, which states that the effective Rabi frequency, ωeff1S, matches ω0I. By using this generalized off-resonance matching condition, we generate ¹H NMR signal enhancement factors of 266 (~70% of the on-resonance NOVEL enhancement) with ω1S/2π = 5 MHz. We investigate experimentally the conditions for optimal transfer of polarization from electrons to ¹H both for the NOVEL mechanism and the solid-effect mechanism and provide a unified theoretical description for these two historically distinct forms of DNP. [ABSTRACT FROM AUTHOR]

[Display omitted] • Established feasibility of 39K PFGSTE NMR in concentrated potassium nitrite solutions despite unfavorable NMR properties • Identified viable spin-lattice and spin-spin relaxation coefficients permissive for 39K NMR diffusometry • Found links between alkali cation self-diffusion, water activation energy, and hydration enthalpy in concentrated alkali nitrite solutions While pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has found widespread use in the quantification of self-diffusivity for many NMR-active nuclei, extending this technique to uncommon nuclei with unfavorable NMR properties remains an active area of research. Potassium-39 (39K) is an archetypical NMR nucleus exhibiting an unfavorable gyromagnetic ratio combined with a very low Larmor frequency. Despite these unfavorable properties, this work demonstrates that 39K PFGSTE NMR experiments are possible in aqueous solutions of concentrated potassium nitrite. Analysis of the results indicates that 39K NMR diffusometry is feasible when the nuclei exhibit spin–lattice and spin–spin relaxation coefficients on the order of 60–100 ms and 50–100 ms, respectively. The diffusivity of 39K followed Arrhenius behavior, and comparative 23Na, 7Li, and 1H PFGSTE NMR studies of equimolal sodium nitrite and lithium nitrite solutions led to correlations between the enthalpy of hydration with the activation energy governing self-diffusion of the cations and also of water. Realizing the feasibility of 39K PFGSTE NMR spectroscopy has a widespread impact across energy sciences because potassium is a common alkali element in energy storage materials and other applications. [ABSTRACT FROM AUTHOR]

The gyromagnetic ratio Îł is a key quantity that determines spin and magnetic properties. In this study, Îł is investigated via the electric detection of ferromagnetic resonance and first-principles calculations for c -axis oriented hcp-Co1âˆ' x Ir x ( 0.00 â©˝ x â©˝ 0.23 ) soft magnetic films with easy-plane magnetocrystalline anisotropy. Îł increases linearly from 19.13 GHz kOeâˆ'1 for pure Co film to 19.32 GHz kOeâˆ'1 at x = 0.23, which is in agreement with the calculated result. The calculations reveal that the primary reason for the variation of Îł is the different trends in the spin and orbital magnetic moments of the neighboring Co atoms of Ir, especially the linear increase of the latter. An investigation into the electronic structure indicates that the increase in these orbital magnetic moments is due to the appearance of 3 d unoccupied minority states moving towards the Fermi level, which is induced by the local lattice distortion centered at Ir. Our findings provide the important Îł data for the applications of CoIr soft magnetic films in high-frequency electromagnetic and spintronic devices, and will provide guidance in the understanding of the dynamic magnetic properties in disordered binary magnetic alloys. [ABSTRACT FROM AUTHOR]

Realizing atomically flat interfaces between the ultrathin perovskite oxides is a challenging task, which usually possess different chemical environments, depending on the terminating lattice planes. Hence, tuning the interfaces across the heterostructures for desired electrical and magnetic properties is a powerful approach in oxide electronics. Focusing on these aspects, in the present work we employ a novel strategy of engineering the interfaces through the layer stacking sequence and degree of strain to probe the changes occurring in the local atomic environment at the interfaces, magnetic behaviour, and electronic properties of ferromagnetic bilayers La0.7Sr0.3MnO3 (LSMO)/LaCoO3 (LCO) grown by the pulsed laser deposition technique. The biaxial tensile strain experienced by these layers drives the ferromagnetic (FM) ordering temperatures to lower values as compared to their bulk counterparts. Interestingly, the bilayer sequence LCO (15 nm)/LSMO (5 nm) (BL2) exhibits large magnetocrystalline anisotropy (Ku ≈ 4.7 × 104 erg/cc) and weak anti-FM coupling across the interface of the two FM constituents, resulting in a partial compensation in the magnetic moment of the system within a specific temperature window (ΔT = 184 − 82 K). However, for T ≤ 82 K, the FM superexchange interaction between the trivalent Co high-spin and low-spin states dominates the overall magnetic ordering in BL2. The magnetodynamic features probed by the frequency dependent FM resonance (FMR) on this system yield the gyromagnetic ratio (γ/2π ∼ 29.22 GHz/T), demagnetization fields (4πMeff ∼ 3770 Oe), and effective damping constant (αeff ∼ 0.0143) for the BL2 configuration. Moreover, the strength of the nearest-neighbor exchange interaction Jeff in the BL2 configuration exhibits linear falloff with the increasing LCO layer thickness (2 nm ≤ t L C O ≤ 18 nm). This scenario is also consistent with the variation of the effective number of spins available per unit volume [10 cm−3 ≤ NV(×1022) ≤ 2 cm−3] with increasing tLCO. As tLCO approaches negligibly small values (<2 nm), the magnitude of Jeff/kB reaches its maximum ∼5.47 K (for LCO) and 21.93 K (for LSMO), which is in good agreement with Jeff/kB ∼ 5 ± 2 K (20 ± 2 K) for highly epitaxial LCO (LSMO) single layers. These results demonstrate that the layer sequence control of magnetic coupling across the interfaces opens a constructive approach for exploring the novel electronic devices. [ABSTRACT FROM AUTHOR]

We investigate a slowly rotating black hole solution in a novel Einstein–Maxwell-scalar theory, which is prompted by the classification of general Einstein–Maxwell-scalar theory. The gyromagnetic ratio of this black hole is calculated, and it increases as the second free parameter β increases, but decreases with the increasing parameter γ ≡ 2 α 2 1 + α 2 . In the Einstein–Maxwell-dilaton (EMD) theory, the parameter β vanishes but the free parameter α governing the strength of the coupling between the dilaton and the Maxwell field remains. The gyromagnetic ratio is always less than 2, the well-known value for a Kerr–Newman (KN) black hole as well as for a Dirac electron. Scalar hairs reduce the magnetic dipole moment in dilaton theory, resulting in a drop in the gyromagnetic ratio. However, we find that the gyromagnetic ratio of two can be realized in this Einstein–Maxwell-scalar theory by increasing β and the charge-to-mass ratio Q/M simultaneously (recall that the gyromagnetic ratio of KN black holes is independent of Q/M). The same situation also applies to the angular velocity of a locally non-rotating observer. Moreover, we analyze the period correction for circular orbits in terms of charge-to-mass ratio, as well as the correction of the radius of the innermost stable circular orbits. It is found the correction increases with β but decreases with Q/M. Finally, the total radiative efficiency is investigated, and it can vanish once the effect of rotation is considered. [ABSTRACT FROM AUTHOR]

We report angular dependent spin rectification spectra which are applied to studying spin excitations in single permalloy stripe. Based on planar Hall effect, those spin excitations generate special resonant dc Hall voltages, which have been characterized as functions of the amplitude and direction of applied magnetic field. Through high angular resolution 2D mappings, the evolutions of different spin excitation can be directly presented, and the dynamic magnetic parameters such as the gyromagnetic ratio, effective exchange field, as well as the quantized numbers of standing spin waves can be accurately determined through fitting the angular evolution of each resonance. [ABSTRACT FROM AUTHOR]

Sodium magnetic resonance imaging (23Na‐MRI) is a highly promising imaging modality that offers the possibility to noninvasively quantify sodium content in the tissue, one of the most relevant parameters for biochemical investigations. Despite its great potential, due to the intrinsically low signal‐to‐noise ratio (SNR) of sodium imaging generated by low in vivo sodium concentrations, low gyromagnetic ratio, and substantially shorter relaxation times than for proton (1H) imaging, 23Na‐MRI is extremely challenging. In this article, we aim to provide a comprehensive overview of the literature that has been published in the last 10–15 years and which has demonstrated different technical designs for a range of 23Na‐MRI methods applicable for disease diagnoses and treatment efficacy evaluations. Currently, a wider use of 3.0T and 7.0T systems provide imaging with the expected increase in SNR and, consequently, an increased image resolution and a reduced scanning time. A great interest in translational research has enlarged the field of sodium MRI applications to almost all parts of the body: articular cartilage tendons, spine, heart, breast, muscle, kidney, and brain, etc., and several pathological conditions, such as tumors, neurological and degenerative diseases, and others. The quantitative parameter, tissue sodium concentration, which reflects changes in intracellular sodium concentration, extracellular sodium concentration, and intra–/extracellular volume fractions is becoming acknowledged as a reliable biomarker. Although the great potential of this technique is evident, there must be steady technical development for 23Na‐MRI to become a standard imaging tool. The future role of sodium imaging is not to be considered as an alternative to 1H MRI, but to provide early, diagnostically valuable information about altered metabolism or tissue function associated with disease genesis and progression. Level of Evidence: 1 Technical Efficacy Stage: 1 [ABSTRACT FROM AUTHOR]

Objective: Considering the reported elevation of ω-6/ω-3 fatty acid ratios in breast neoplasms, one particularly important application of 13C MRS could be in more fully understanding the breast lipidome's relationship to breast cancer incidence. However, the low natural abundance and gyromagnetic ratio of the 13C isotope lead to detection sensitivity challenges. Previous 13C MRS studies have relied on the use of small surface coils with limited field-of-view and shallow penetration depths to achieve adequate signal-to-noise ratio (SNR), and the use of receive array coils is still mostly unexplored. Methods: This work presents a unilateral breast 16-channel 13C array coil and interfacing hardware designed to retain the surface sensitivity of a single small loop coil while improving penetration depth and extending the field-of-view over the entire breast at 7T. The coil was characterized through bench measurements and phantom 13C spectroscopy experiments. Results: Bench measurements showed receive coil matching better than -17 dB and average preamplifier decoupling of 16.2 dB with no evident peak splitting. Phantom MRS studies show better than a three-fold increase in average SNR over the entirety of the breast region compared to volume coil reception alone as well as an ability for individual array elements to be used for coarse metabolite localization without the use of single-voxel or spectroscopic imaging methods. Conclusion: Our current study has shown the benefits of the array. Future in vivo lipidomics studies can be pursued. Significance: Development of the 16-channel breast array coil opens possibilities of in vivo lipidomics studies to elucidate the link between breast cancer incidence and lipid metabolics. [ABSTRACT FROM AUTHOR]

We acquire ferromagnetic resonance (FMR) spectra for an out-of-plane magnetized yttrium iron garnet sample with a vector network analyzer at microwave frequencies ranging from 4.2 to 5.2 GHz. The applied static magnetic field varies from approximately 253.6 to 260.1 kA/m. Based on an empirical model for resonant features in the S21 spectrum produced by the excitation of multiple modes and instrumental effects, we predict measured values of S21-parameters. For each of many microwave frequencies, for each of multiple modes, we determine the resonant field value of the applied magnetic field, an amplitude, and an FMR linewidth. Based on the frequency-dependent resonant field values produced by excitation of the main mode, we determine the effective magnetization and the gyromagnetic ratio of the sample. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the study was to investigate whether incorrectly compensated eddy currents are the source of persistent X‐nuclear spectroscopy and imaging artifacts, as well as methods to correct this. Methods: Pulse‐acquire spectra were collected for 1H and X‐nuclei (23Na or 31P) using the minimum TR permitted on a 3T clinical MRI system. Data were collected in 3 orientations (axial, sagittal, and coronal) with the spoiler gradient at the end of the TR applied along the slice direction for each. Modifications to system calibration files to tailor eddy current compensation for each X‐nucleus were developed and applied, and data were compared with and without these corrections for: slice‐selective MRS (for 23Na and 31P), 2D spiral trajectories (for 13C), and 3D cones trajectories (for 23Na). Results: Line‐shape distortions characteristic of eddy currents were demonstrated for X‐nuclei, which were not seen for 1H. The severity of these correlated with the amplitude of the eddy current frequency compensation term applied by the system along the axis of the applied spoiler gradient. A proposed correction to eddy current compensation, taking account of the gyromagnetic ratio, was shown to dramatically reduce these distortions. The same correction was also shown to improve data quality of non‐Cartesian imaging (2D spiral and 3D cones trajectories). Conclusion: A simple adaptation of the default compensation for eddy currents was shown to eliminate a range of artifacts detected on X‐nuclear spectroscopy and imaging. [ABSTRACT FROM AUTHOR]

Double electron-electron resonance (DEER) is a pulse electron paramagnetic resonance (EPR) technique that measures distances between paramagnetic centres. It utilizes a four-pulse sequence based on the refocused Hahn spin echo. The echo decays with increasing pulse sequence length 2(τ1 Cτ2), where τ1 and τ2 are the two time delays. In DEER, the value of τ2 is determined by the longest inter-spin distance that needs to be resolved, and τ1 is adjusted to maximize the echo amplitude and, thus, sensitivity. We show experimentally that, for typical spin centres (nitroxyl, trityl, and Gd(III)) diluted in frozen protonated solvents, the largest refocused echo amplitude for a given τ2 is obtained neither at very short τ1 (which minimizes the pulse sequence length) nor at τ1 D τ2 (which maximizes dynamic decoupling for a given total sequence length) but rather at τ1 values smaller than τ2. Large-scale spin dynamics simulations based on the coupled cluster expansion (CCE), including the electron spin and several hundred neighbouring protons, reproduce the experimentally observed behaviour almost quantitatively. They show that electron spin dephasing is driven by solvent protons via the flip-flop coupling among themselves and their hyperfine couplings to the electron spin. [ABSTRACT FROM AUTHOR]

We report the magnetization, magnetic field dependence of direct current magnetoresistance (dc MR) and alternating current magnetoresistance (ac MR) in La1-xSrxMnO3 (x = 0.12, 0.18, and 0.20) in the frequency range f= 30 MHz to 3000 MHz, at room temperature. The ac MR is negative in all three compositions and shows a dramatic increase in magnitude compared to the dc MR when f = 30 MHz and in a magnetic field H = ±3 kOe. With increasing frequency of current, the sign of ac MR at 3 kOe progressively changes from negative to positive in all these samples which is initiated by appearance of two peaks at H = ±Hr. Line shape analysis of the data indicate that Hr increases linearly with f in x = 0.12 and 0.18. We attribute the two peak behavior at high frequencies to electron paramagnetic resonance in x = 0.12 and 0.18 samples. From the analysis, we obtain the gyromagnetic ratio γ/2π = 2.428 MHz/Oe and 2.690 MHz/Oe for x = 0.18 and 0.12 respectively. The smaller value of γ/2π in x = 0.18 possibly reflects short-range correlations among Mn-spins in the paramagnetic state. [ABSTRACT FROM AUTHOR]

The article focuses on a study which described giant nonreciprocity in transmitting surface acoustic waves on lithium niobate substrate coated with ferromagnet/insulator/ferromagnet multilayer structure. The structure is utilized with a unique asymmetric band diagram and expanded on magnetoelastic coupling theory to demonstrate how the magnetic bands couple with acoustic waves in a single direction. Results of the study are discussed. Materials and methods used are described.

La2/3Sr1/3MnO3 (LSMO) thin films of various thicknesses (6, 8, 10, 20, and 30 nm), capped by 7 nm‐thick Pt layer, are grown by pulsed laser deposition on SrTiO3 (001) substrates. X‐ray diffraction revealed that LSMO films are (001) oriented. Vibrating sample magnetometer is used to determine the magnetization at saturation and the magnetic dead layer thickness. This latter is around 3.4 nm, significantly thicker compared with the one induced at interfaces of Pt with ferromagnetic transition metals. Microstrip line ferromagnetic resonance (MS‐FMR) is used to extract the gyromagnetic ratio, which is found to increase with LSMO thickness. MS‐FMR revealed that the in‐plane magnetic anisotropy is dominated by a uniaxial contribution for the Pt capped film, whereas the noncapped 10 nm‐thick LSMO layer shows a fourfold anisotropy. Furthermore, the thickness dependence of the effective magnetization reveals the existence of a second‐order perpendicular anisotropy term, which is thickness‐dependent, and of a weak uniaxial interface anisotropy. The Gilbert damping coefficient is found to vary linearly with the inverse of the effective LSMO thickness due to spin pumping leading to relatively low spin mixing conductance of LSMO/Pt interface. [ABSTRACT FROM AUTHOR]

An unexpected deficit of the computed hyper fine coupling constant in normal formyl HCO radicals, compared to that expected based on the proton to deuteron gyromagnetic ratio of the DCO species, was observed in experimental electron paramagnetic resonance studies of HCO and DCO radicals in a CO solid matrix at cryogenic conditions. Still, the matrix was found to have only a small effect on the anisotropic parts of the magnetic parameter tensors. The underlying isotope effect between the lighter proton and the heavier deuteron on the motional dynamics was verified and elucidated by quantum chemical calculations. The experimental results obtained within a temperature range of 1.4 K–4.2 K require special attention due to the tunneling motions of the molecule and its constituent particles. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe, averaged over the dynamics of the low temperature CO matrix isolation, reveals a clear proton isotope effect under both classical and quantum conditions. [ABSTRACT FROM AUTHOR]

Purpose: Hyperpolarized 15N‐labeled molecules have been proposed as imaging agents for investigating tissue perfusion and pH. However, the sensitivity of direct 15N detection is limited by the isotope's low gyromagnetic ratio. Sensitivity can be increased by transferring 15N hyperpolarization to spin‐coupled protons provided that there is not significant polarization loss during transfer. However, complete polarization transfer would limit the temporal window for imaging to the order of the proton T1 (2‐3 s). To exploit the long T1 offered by storing polarization in 15N and the higher sensitivity of 1H detection, we have developed a pulse sequence for partial polarization transfer. Methods: A polarization transfer pulse sequence was modified to allow partial polarization transfer, as is required for dynamic measurements, and that can be implemented with inhomogeneous B1 fields, as is often the case in vivo. The sequence was demonstrated with dynamic spectroscopy and imaging measurements with [15N2]urea. Results: When compared to direct 15N detection, the sequence increased the signal‐to‐noise ratio (SNR) by a factor of 1.72 ± 0.25, where both experiments depleted ~20% of the hyperpolarization (>10‐fold when 100% of the hyperpolarization is used). Simulations with measured cross relaxation rates showed that this sequence gave up to a 50‐fold increase in urea proton polarization when compared to spontaneous polarization transfer via cross relaxation. Conclusion: The sequence gave an SNR increase that was close to the theoretical limit and can give a significant SNR benefit when compared to direct 13C detection of hyperpolarized [13C]urea. [ABSTRACT FROM AUTHOR]

We investigated the magnetic-field-dependent microwave absorption in polycrystalline La0.6Sr0.4Mn1-xGaxO3 samples (x = 0.0–0.3) over a wide frequency spectrum (f = 0.1–4 GHz) and up to a magnetic field of Hdc= 2.5 kOe at room temperature. The field dependence of microwave power absorption (ΔP) in each sample exhibits a peak at a critical value of Hdc and the peak moves towards higher fields as frequency increases. The shift is at a faster rate for x = 0.2 and 0.3 compared to x = 0.01 and 0.1. Based on the line shape analysis, we attribute the observed features to ferromagnetic resonance for x ≤ 0.1 and a combined effect of electron spin resonance and superparamagnetic resonance for x ≥ 0.2. Our results are also verified by magnetic resonance spectra recorded using a coplanar waveguide spectrometer. We extracted the gyromagnetic ratio, saturation magnetization, and anisotropy field in our samples. Frequency-tunable microwave absorption at resonance found in these materials will be of interest for high-frequency device applications. [ABSTRACT FROM AUTHOR]

The fluorine-19 nucleus was recognized early to harbor exceptional properties for NMR spectroscopy. With 100% natural abundance, a high gyromagnetic ratio (83% sensitivity compared to 1H), a chemical shift that is extremely sensitive to its surroundings and near total absence in biological systems, it was destined to become a favored NMR probe, decorating small and large molecules. However, after early excitement, where uptake of fluorinated aromatic amino acids was explored in a series of animal studies, 19F-NMR lost popularity, especially in large molecular weight systems, due to chemical shift anisotropy (CSA) induced line broadening at high magnetic fields. Recently, two orthogonal approaches, (i) CF3 labeling and (ii) aromatic 19F-13C labeling leveraging the TROSY (Transverse Relaxation Optimized Spectroscopy) effect have been successfully applied to study large biomolecular systems. In this perspective, we will discuss the fascinating early work with fluorinated aromatic amino acids, which reveals the enormous potential of these non-natural amino acids in biological NMR and the potential of 19F-NMR to characterize protein and nucleic acid structure, function and dynamics in the light of recent developments. Finally, we explore how fluorine NMR might be exploited to implement small molecule or fragment screens that resemble physiological conditions and discuss the opportunity to follow the fate of small molecules in living cells. [ABSTRACT FROM AUTHOR]

Equation‐of‐motion coupled‐cluster singles and doubles (EOM‐CCSD) calculations have been performed to determine coupling constants 1J(X–Y) for 65 molecules HmX–YHn, with X,Y ═ 1H, 7Li, 9Be, 11B, 13C, 15N, 17O, 19F, 31P, 33S, and 35Cl. The computed 1J(X–Y) values are in good agreement with available experimental data. The reduced coupling constants 1K(X–Y) have been derived from 1J(X–Y) by removing the dependence on the magnetogyric ratios of X and Y. Patterns are found for the reduced coupling constants on a 1K(X–Y) surface that are related to the positions of X and Y in the periodic table. [ABSTRACT FROM AUTHOR]

The classical model of the spinning particle is analyzed in detail in two versions – with single spinor and two spinors put on the trajectory. Equations of motion of the first version are easily solvable. The system with two spinors becomes nonlinear. Nevertheless, the equations of motion are analyzed in detail and solved analytically and numerically. In either case the trajectories are illustrated and their properties are discussed. There is also discussion of possible physical quantities associated with the spinning motions. Among others: the size of particles and their gyromagnetic ratios. [ABSTRACT FROM AUTHOR]

The article focuses on a switchable giant nonreciprocal frequency shift of propagating spin waves in interlayer exchange–coupled synthetic antiferromagnets; and mentions the sign of the frequency shift depends on relative configuration of two magnetizations, based on which we demonstrate an electrical switching of the nonreciprocity.

Ferrihydrite nanoparticles (2–3 nm in size), which are products of the vital activity of microorganisms, are studied by the ferromagnetic resonance method. The "core" of ferrihydrite particles is ordered antiferromagnetically, and the presence of defects leads to the appearance of an uncompensated magnetic moment in nanoparticles and the characteristic superparamagnetic behavior. It is established from the ferromagnetic resonance data that the field dependence of the frequency is described by the expression 2πν/γ = HR + H(T=0)A(1 − T/T*), where γ is the gyromagnetic ratio, HR is the resonance field, HA ≈ 7 kOe, and T* ≈ 50 K. The induced anisotropy HA is due to the spin-glass state of the near-surface regions. [ABSTRACT FROM AUTHOR]

Spectroscopic and biophysical methods for structural determination at atomic resolution are fundamental in studies of biological function. Here we introduce an approach to measure molecular distances in bio‐macromolecules using 19F nuclear spins and nitroxide radicals in combination with high‐frequency (94 GHz/3.4 T) electron–nuclear double resonance (ENDOR). The small size and large gyromagnetic ratio of the 19F label enables to access distances up to about 1.5 nm with an accuracy of 0.1–1 Å. The experiment is not limited by the size of the bio‐macromolecule. Performance is illustrated on synthesized fluorinated model compounds as well as spin‐labelled RNA duplexes. The results demonstrate that our simple but strategic spin‐labelling procedure combined with state‐of‐the‐art spectroscopy accesses a distance range crucial to elucidate active sites of nucleic acids or proteins in the solution state. [ABSTRACT FROM AUTHOR]

Ribonucleic acid oligonucleotides (RNAs) play pivotal roles in cellular function (riboswitches), chemical biology applications (SELEX‐derived aptamers), cell biology and biomedical applications (transcriptomics). Furthermore, a growing number of RNA forms (long non‐coding RNAs, circular RNAs) but also RNA modifications are identified, showing the ever increasing functional diversity of RNAs. To describe and understand this functional diversity, structural studies of RNA are increasingly important. However, they are often more challenging than protein structural studies as RNAs are substantially more dynamic and their function is often linked to their structural transitions between alternative conformations. NMR is a prime technique to characterize these structural dynamics with atomic resolution. To extend the NMR size limitation and to characterize large RNAs and their complexes above 200 nucleotides, new NMR techniques have been developed. This Minireview reports on the development of NMR methods that utilize detection on low‐γ nuclei (heteronuclei like 13C or 15N with lower gyromagnetic ratio than 1H) to obtain unique structural and dynamic information for large RNA molecules in solution. Experiments involve through‐bond correlations of nucleobases and the phosphodiester backbone of RNA for chemical shift assignment and make information on hydrogen bonding uniquely accessible. Previously unobservable NMR resonances of amino groups in RNA nucleobases are now detected in experiments involving conformational exchange‐resistant double‐quantum 1H coherences, detected by 13C NMR spectroscopy. Furthermore, 13C and 15N chemical shifts provide valuable information on conformations. All the covered aspects point to the advantages of low‐γ nuclei detection experiments in RNA. [ABSTRACT FROM AUTHOR]

Recently, we had reported the detection of electron paramagnetic resonance (EPR) from magnetoimpedance (MI) measurements in bulk La0.60Ca0.40MnO3 (LCMO) samples using radio frequency (rf) currents [U. Chaudhuri and R. Mahendiran, Appl. Phys. Lett. 115, 092405 (2019)]. Here, we report an alternative method which involves measuring the effective MI changes of a copper stripcoil that encloses the LCMO sample. Magnetoresistance (∆R/R0) and magnetoreactance (∆X/X0) of the sample were measured indirectly via the stripcoil for frequencies of current from f = 0.5 to 2.5 GHz. During the field sweep, ∆R/R0 shows an abrupt increase that is accompanied by a dip in ΔX/X0 at a critical value of dc magnetic field (Hc) when f ≥ 0.9 GHz. Hc increased linearly with frequency (f) of the current in the stripcoil, satisfying the EPR relation fr = (γ/2π)Hdc, where γ is the gyromagnetic ratio and fr is the resonance frequency. The same stripcoil and the sample were also used to measure microwave power absorption using a vector network analyzer. The features observed in both these techniques were strikingly similar to the results obtained from the direct MI measurement in LCMO, which confirms the electrical detection of EPR. [ABSTRACT FROM AUTHOR]