Gyromagnetic Ratio Research Articles

Generalization of the Landau–Lifshitz–Gilbert equation by multi-body contributions to Gilbert damping for non-collinear magnets

We propose a systematic and sequential expansion of the Landau–Lifshitz–Gilbert equation utilizing the dependence of the Gilbert damping tensor on the angle between magnetic moments, which arises from multi-body scattering processes. The tensor consists of a damping-like term and a correction to the gyromagnetic ratio. Based on electronic structure theory, both terms are shown to depend on e.g. the scalar, anisotropic, vector-chiral and scalar-chiral products of magnetic moments: e i ⋅ e j , (n ij ⋅ e i )(n ij ⋅ e j ), n ij ⋅ (e i × e j ), , e i ⋅ (e j × e k ) …, where some terms are subjected to the spin–orbit field n ij in first and second order. We explore the magnitude of the different contributions using both the Alexander–Anderson model and time-dependent density functional theory in magnetic adatoms and dimers deposited on Au(111) surface.

A Multifunctional Contrast Agent for 19F-Based Magnetic Resonance Imaging.

Magnetic resonance imaging, MRI, relying on 19F nuclei has attracted much attention, because the isotopes exhibit a high gyromagnetic ratio (comparable to that of protons) and have 100% natural abundance. Furthermore, due to the very low traces of intrinsic fluorine in biological tissues, fluorine labeling allows easy visualization in vivo using 19F-based MRI. However, one of the drawbacks of the available fluorine tracers is their very limited solubility in water. Here, we detail the design and preparation of a set of water-compatible fluorine-rich polymers as contrast agents that can enhance the effectiveness of 19F-based MRI. The agents are synthesized using the nucleophilic addition reaction between poly(isobutylene-alt-maleic anhydride) copolymer and a mixture of amine-appended fluorine groups and polyethylene glycol (PEG) blocks. This allows control over the polymer architecture and stoichiometry, resulting in good affinity to water solutions. We further investigate the effects of introducing additional segmental mobility to the fluorine moieties in the polymer, by inserting a PEG linker between the moieties and the polymer backbone. We find that controlling the polymer stoichiometry and introducing additional segmental mobility enhance the NMR signals and narrow the peak profile. In particular, we assess the impact of the PEG linker on T2* and T1 relaxation times, using a series of gradient-recalled echo images with varying echo times, TE, or recovery time, TR, respectively. We find that for equivalent concentrations, the PEG linker greatly increases T2*, while maintaining high T1 values, as compared to polymers without this linker. Phantom images collected from these compounds show bright signals over a background with high intensities.

Quantitative 23 Na-MRI of the intervertebral disk at 3 T.

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.

Effect of interfacial spin mixing conductance on gyromagnetic ratio of Gd substituted Y3Fe5O12

Due to its low intrinsic damping, Y3Fe5O12 and its substituted variations are often used for ferromagnetic layer at spin pumping experiment. Spin pumping is an interfacial spin current generation in the interface of ferromagnet and non-magnetic metal, governed by spin mixing conductance parameter G↑↓. G↑↓ has been shown to enhance the damping of the ferromagnetic layer. The theory suggested that the effect of G↑↓ on gyromagnetic ratio only comes from its negligible imaginary part. In this article, we show that the different damping of ferrimagnetic lattices induced by G↑↓ can affect the gyromagnetic ratio of Gd-substituted Y3Fe5O12.

Ferromagnetic resonance and spin-wave exchange stiffness of FeGaB/Al2O3 multilayer thin film stack for microwave applications

In this article, we have illustrated the deposition of multilayer film stack of Ta (5 nm)/[FeGaB (15 nm)/Al2O3 (3 nm)] n/Ta (3 nm)/Al2O3 (2 nm); n = 1,5, and 10, onto Si substrates, and studied magnetodynamic properties with multilayer thickness and temperature dependence. The results of surface morphology of thin film stacks suggest dipolar coupling generates for n = 5 and 10 thin film stack, which influence the ferromagnetic absorption results. From results of ferromagnetic resonance spectroscopy (FMR), the resonance peak for each excitation frequency provides the effective magnetization, the gyromagnetic ratio and damping factor. The damping factor for multilayer stack n = 1 shows a lower value compared to the other two samples. The multilayer stack provides perpendicular surface magnetic anisotropy (ks) from thickness dependence of effective magnetization. The analysis of spin-wave resonance spectra at multiple frequencies allows manipulate the exchange stiffness (D) of multilayer film stack n = 5 and n = 10 and temperature dependence the exchange stiffness follows the itinerant-electron model (T2 law) and suggests electron - magnon scattering exists in the thin film stack.

CW-EPR spectra of P1 centers in HPHT diamond in the vicinity of Rabi resonance: possible standard for [formula omitted] evaluation in EPR and DNP enhanced NMR spectroscopies

Synthetic commercial type-IIa diamond crystal containing low concentration of P1 (Ns0) centers ([Ns0] <1ppm) was examined as a possible calibration standard for evaluating microwave magnetic field intensity (B1) in the spectrometer cavity. The reliability of this standard was experimentally and theoretically tested by employing two different types of microwave cavities with different distributions of B1 values. The procedure relies on the ordinary continuous wave electron paramagnetic resonance (CW-EPR) with magnetic field modulation (ωrf/2π=100 kHz) applied under the regime of the microwave power (PMW) saturation of the out-of-phase first harmonic signal. The power saturation procedure for PMW∼B11/2 was analyzed with respect to the change of spectral lineshape when Rabi frequency (ω1=γB1, γis the electron gyromagnetic ratio) approaches to ωrf. The phenomenon of the inversion of sideband lines while passing the Rabi resonance condition (ω1=ωrf) was analyzed. In specific, from the simulation of the experimental lineshapes in the close vicinity of Rabi resonance (ω1≈ωrf) the correspondingB1 can be assigned. For the chosen diamond crystal low value of B1≈3.6µT at Rabi resonance was determined what makes it a convenient standard for DNP enhanced NMR spectroscopy which requires relatively small B1.

Dynamics of a Spin-Exchange Relaxation-Free Comagnetometer for Rotation Sensing

We investigate the dynamics of the spin-exchange relaxation-free (SERF) comagnetometer for rotation sensing. The transient and steady-state models of the rotation response are established by solving a set of Bloch equations. The transient responses of the comagnetometer with inertial rotation input and magnetic field input are compared. The effects of the pump-laser power density on the transient response are studied and the results indicate that the transient response reaches the fastest when the pumping rate equals the product of the gyromagnetic ratio and polarization field factor of the electron spins. The measuring range of the comagnetometer is investigated by experiment and simulation, which suggests that the measuring range can be improved by increasing the relaxation rates of the electron spins and nuclear spins and the ratio of the Fermi-contact field of the electron spins to that of the nuclear spins. The theory and method presented here pave the way for the practical application of SERF comagnetometers for rotation sensing.

Tunable gyromagnetic augmentation of nuclear spins in diamond

Nuclear spins in solids exhibit long coherence times due to the small nuclear gyromagnetic ratio. This weak environmental coupling comes at the expense of slow quantum gate operations, which should be as fast as possible for many applications in quantum information processing and sensing. In this work, we use nitrogen-vacancy (NV) centers in diamond to probe the nuclear spins within dark paramagnetic nitrogen defects (P1 centers) in the diamond lattice. The gyromagnetic ratio of the P1 nuclear spin is augmented by hyperfine coupling to the electron spin, resulting in greatly enhanced coupling to radiofrequency control fields. We then demonstrate that this effect can be tuned by variation of an external magnetic field. Our work identifies regimes in which we are able to implement fast quantum control of dark nuclear spins, and lays the foundations for further inquiry into rapid control of long-lived spin qubits at room temperature.

Spinning gauged boson and Dirac stars: A comparative study

Scalar boson stars and Dirac stars are solitonic solutions of the Einstein–Klein-Gordon and Einstein-Dirac classical equations, respectively. Despite the different bosonic vs. fermionic nature of the matter field, these solutions to the classical field equations have been shown to have qualitatively similar features [1]. In particular, for spinning stars the most fundamental configurations can be in both cases toroidal, unlike spinning Proca stars that are spheroidal [2]. In this paper we gauge the scalar and Dirac fields, by minimally coupling them to standard electromagnetism. We explore the impact of the gauge coupling on the resulting solutions. One of the most relevant difference concerns the gyromagnetic ratio, which for the scalar stars takes values around 1, whereas for Dirac stars takes values around 2.

Slowly rotating black holes in the novel Einstein\u2013Maxwell-scalar theory

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 beta increases, but decreases with the increasing parameter gamma equiv frac{2 alpha ^{2}}{1+alpha ^2}. In the Einstein–Maxwell-dilaton (EMD) theory, the parameter beta vanishes but the free parameter alpha 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 beta 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 beta but decreases with Q/M. Finally, the total radiative efficiency is investigated, and it can vanish once the effect of rotation is considered.

The role of epitaxial strain on the electronic and magnetic structure of La0.7Sr0.3MnO3/LaCoO3 bilayers

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 ≤tLCO≤ 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 (&amp;lt;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.

On the double copy for spinning matter

We explore various tree-level double copy constructions for amplitudes including massive particles with spin. By working in general dimensions, we use that particles with spins s ≤ 2 are fundamental to argue that the corresponding double copy relations partially follow from compactification of their massless counterparts. This massless origin fixes the coupling of gluons, dilatons and axions to matter in a characteristic way (for instance fixing the gyromagnetic ratio), whereas the graviton couples universally reflecting the equivalence principle. For spin-1 matter we conjecture all-order Lagrangians reproducing the interactions with up to two massive lines and we test them in a classical setup, where the massive lines represent spinning compact objects such as black holes. We also test the amplitudes via CHY formulae for both bosonic and fermionic integrands. At five points, we show that by applying generalized gauge transformations one can obtain a smooth transition from quantum to classical BCJ double copy relations for radiation, thereby providing a QFT derivation for the latter. As an application, we show how the theory arising in the classical double copy of Goldberger and Ridgway can be naturally identified with a certain compactification of mathcal{N} = 4 Supergravity.

From Angstroms to Nanometers: Measuring Interatomic Distances by Solid-State NMR.

Internuclear distances represent one of the main structural constraints in molecular structure determination using solid-state NMR spectroscopy, complementing chemical shifts and orientational restraints. Although a large number of magic-angle-spinning (MAS) NMR techniques have been available for distance measurements, traditional 13C and 15N NMR experiments are inherently limited to distances of a few angstroms due to the low gyromagnetic ratios of these nuclei. Recent development of fast MAS triple-resonance 19F and 1H NMR probes has stimulated the design of MAS NMR experiments that measure distances in the 1-2 nm range with high sensitivity. This review describes the principles and applications of these multiplexed multidimensional correlation distance NMR experiments, with an emphasis on 19F- and 1H-based distance experiments. Representative applications of these long-distance NMR methods to biological macromolecules as well as small molecules are reviewed.

Development and Preclinical Study of Free Radical Imaging Using Field-Cycling Dynamic Nuclear Polarization MRI.

Free radicals, such as metabolic intermediates, reactive oxygen species, and metal enzymes, are key substances in organisms, although they can also cause various oxidative diseases. Thus, in vivo free radical imaging should be considered as the ultimate form of metabolic imaging. Unfortunately, electron spin resonance (ESR) imaging has inherent disadvantages, such as free radicals with large linewidths generating blurred images and the presence of two or more free radicals resulting in a complicated imaging procedure. Dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) is a noninvasive imaging method to visualize in vivo free radicals, theoretically, with the same resolution as the MRI anatomical resolution, and fixed low-field DNP-MRI provides unique information on oxidative diseases and cancer. However, the large gyromagnetic ratio of the electron spin, which is 660-fold greater than that of a proton, requires field cycling, wherein the external magnetic field should be varied during DNP-MRI observations. This causes difficulties in developing a DNP-MRI system for clinical purposes. We developed a novel field-cycling DNP-MRI system for a preclinical study. In the said system, the magnetic field is switched by rotationally moving two magnets, with a magnetic flux density of 0.3 T for MRI and 5 mT for ESR. The image quality was examined using various pulse sequences and ESR irradiation using nitroxyl radical as the phantom, and the optimum conditions were established. Using the system, we performed a preclinical study involving free radical imaging by placing the free radicals under the palm of a human hand.

Gyromagnetic ratio of oriented hcp Co1−x Ir x soft magnetic films

The gyromagnetic ratio γ is a key quantity that determines spin and magnetic properties. In this study, γ is investigated via the electric detection of ferromagnetic resonance and first-principles calculations for c-axis oriented hcp-Co1−x Ir x () soft magnetic films with easy-plane magnetocrystalline anisotropy. γ increases linearly from 19.13 GHz kOe−1 for pure Co film to 19.32 GHz kOe−1 at x= 0.23, which is in agreement with the calculated result. The calculations reveal that the primary reason for the variation of γ 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 3d unoccupied minority states moving towards the Fermi level, which is induced by the local lattice distortion centered at Ir. Our findings provide the important γ 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.

The effect of a polarizing magnetic field on the dynamic properties and the specific absorption rate of a ferrofluid in the microwave range

ABSTRACT 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, f res , and the corresponding maximum absorption at a frequency, f max , were determined. From the H dependence of both f res and the ratio of f max /f res , we determined the anisotropy field, H A , the anisotropy constant K eff , the gyromagnetic ratio, , the damping parameter, , the spectroscopic splitting factor, g, and the internal magnetic viscosity, . Also, the theoretical Néel relaxation time, , 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 ρ F , as opposed to using just the density of the dispersed solid particles, ρ S . 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.

Robust finite-temperature magnetization dynamics in ferrimagnetic Gdx(FeCo)1−x (x = 0 ∼ 0.44) nanospheres across angular-momentum and magnetization compensation points: An atomistic model simulation

We explored robust magnetization dynamics in ferrimagnetic Gdx(FeCo)1−x nanospheres of Gd compositions ranging from x = 0 to 0.44 at finite T = 0 – 1200 K temperatures using two-sublattice atomistic simulations based on the stochastic Landau-Lifshitz-Gilbert equation. It was found that the magnetization compensation and angular-momentum compensation temperatures vary remarkably with x and that the former temperature is always lower than the latter. Also, it was found that neither compensation temperature exists below a specific Gd composition of x = 0.22, but above which, both exist and increase with x. The ferromagnetic resonance (FMR) frequency remarkably increases at the angular momentum compensation composition, whereas the FMR frequency does not reach zero at the magnetization compensation composition. The significant difference in the FMR frequency between the two characteristic compensation points is ascribed to the contrasting effective gyromagnetic ratios of Gd and FeCo. Our present atomistic simulation study well reproduced the earlier experimental observations of such dynamic behaviors at both the angular-momentum and magnetization compensation points, which observations cannot be explained by the existing Kittel and Wangsness models. This work provides a better understanding of robust dynamic behaviors of ferrimagnetic nanospheres as functions of temperature and constituent sublattice composition, especially at and near the characteristic compensation points.

The Intermolecular NOE Depends on Isotope Selection: Short Range vs Long Range Behavior.

The nuclear Overhauser effect (NOE) is a powerful tool in molecular structure elucidation, combining the subtle chemical shift of NMR and three-dimensional information independent of chemical connectivity. Its usage for intermolecular studies, however, is fundamentally limited by an unspecific long-ranged interaction behavior. This joint experimental and computational work shows that proper selection of interacting isotopes can overcome these limitations: Isotopes with strongly differing gyromagnetic ratios give rise to short-ranged intermolecular NOEs. In this light, existing NOE experiments need to be re-evaluated and future ones can be designed accordingly. Thus, a new chapter on intermolecular structure elucidation is opened.

Effect of oxygen growth-pressure on microstructural and magnetic properties of pulse laser deposited epitaxial YIG thin films

We investigated the effect of oxygen growth-pressure on the structural and magnetic properties of epitaxial YIG thin films. YIG films were grown on single crystalline GGG substrates with (111) orientations by pulse laser deposition technique. In-situ oxygen-gas pressure variations in the range of 0.0025–0.15 mbar was adopted to demonstrate the perfect growth. Structural analysis confirmed that the films were single crystalline in nature. Atomic force microscopy analysis indicated that roughness of the films decreases with increase of oxygen pressure. Saturation magnetization was enhanced by a factor of 17% over increase of oxygen pressure. Through angular dependent ferromagnetic resonance (FMR) measurements along film’s in-plane (φ-variation) and out-of-plane (θ-variation) geometries, resonance fields [HrθH,φH] and FMR linewidths [∆HrθH,φH] were obtained. Using theoretical analysis important material parameters such as; saturation magnetization, gyromagnetic ratio, uniaxial anisotropy, cubic anisotropy and Gilbert damping were evaluated. We have obtained lowest Gilbert damping ~4.37×10−5 for 0.15 mbar oxygen pressure deposited YIG film.

Orbit topology analyzed from π phase shift of magnetic quantum oscillations in three-dimensional Dirac semimetal

With the emergence of Dirac fermion physics in the field of condensed matter, magnetic quantum oscillations (MQOs) have been used to discern the topology of orbits in Dirac materials. However, many previous researchers have relied on the single-orbit Lifshitz-Kosevich (LK) formula, which overlooks the significant effect of degenerate orbits on MQOs. Since the single-orbit LK formula is valid for massless Dirac semimetals with small cyclotron masses, it is imperative to generalize the method applicable to a wide range of Dirac semimetals, whether massless or massive. This report demonstrates how spin-degenerate orbits affect the phases in MQOs of three-dimensional massive Dirac semimetal, NbSb2 With varying the direction of the magnetic field, an abrupt π phase shift is observed due to the interference between the spin-degenerate orbits. We investigate the effect of cyclotron mass on the π phase shift and verify its close relation to the phase from the Zeeman coupling. We find that the π phase shift occurs when the cyclotron mass is half of the electron mass, indicating the effective spin gyromagnetic ratio as g s = 2. Our approach is not only useful for analyzing MQOs of massless Dirac semimetals with a small cyclotron mass but also can be used for MQOs in massive Dirac materials with degenerate orbits, especially in topological materials with a sufficiently large cyclotron mass. Furthermore, this method provides a useful way to estimate the precise g s value of the material.