Larmor Resonance Research Articles

Beam Shift Modulation Based on Larmor Resonance in Graphene–VO2 Photonic Crystal

A new method to enhance the beam shift of Goos–Hänchen (GH) effect in a 1D photonic crystal based on Larmor resonance in terahertz (THz) region is proposed. Larmor resonance can enhance the surface plasmon resonance (SPR) effect, which enhances the GH effect. A 1D photonic crystal with a graphene–VO2 periodic structure is designed. As a result of different states at different temperatures, the SPR effect of graphene–VO2 periodic structure photonic crystals will change. In this structure, Larmor resonance caused by a strong magnetic field perpendicular to the incident surface will resonate with surface plasmons. It is found that the strength of the magnetic field required to enhance SPR is relative to the frequency of electromagnetic waves and the Fermi level. The enhancement of the GH effect by the Larmor resonance theory provides a new way for us to measure strong magnetic fields.

Magnetic Gradient Fluctuations from Quadrupolar 73Ge in Si / SiGe Exchange-Only Qubits

We study the time-fluctuating magnetic gradient noise mechanisms in pairs of Si/SiGe quantum dots using exchange echo noise spectroscopy. We find through a combination of spectral inversion and correspondence to theoretical modeling that quadrupolar precession of the $^{73}$Ge nuclei play a key role in the spin-echo decay time $T_2$, with a characteristic dependence on magnetic field and the width of the Si quantum well. The $^{73}$Ge noise peaks appear at the fundamental and first harmonic of the $^{73}$Ge Larmor resonance, superimposed over $1/f$ noise due to $^{29}$Si dipole-dipole dynamics, and are dependent on material epitaxy and applied magnetic field. These results may inform the needs of dynamical decoupling when using Si/SiGe quantum dots as qubits in quantum information processing devices.

NMR-like effect on the anisotropic magnetic moment of surface bound states in the topological superfluid He3−B

We present experimental observation of a phenomenon that we interpret as a NMR-like effect on an anisotropic magnetic moment of the surface Andreev bound states in topological superfluid $^{3}\mathrm{He}\text{\ensuremath{-}}\mathrm{B}$ at zero temperature limit. We show that an anisotropic magnetic moment formed near the horizontal surface of a mechanical resonator due to symmetry violation of the superfluid $^{3}\mathrm{He}\text{\ensuremath{-}}\mathrm{B}$ order parameter by the resonator's surface may lead to anomalous damping of the resonator motion in magnetic field. In difference to the classical NMR technique, here NMR was excited using own harmonic motion of the mechanical resonator and nuclear magnetic resonance was detected as a maximum in damping when the resonator's angular frequency satisfied the Larmor resonance condition.

Synthesized Gd2O3 nanoparticles as contrast agent

Introduction: Gd (III) ion has been known to be the best metal ion in the periodic table that can be used as a T1 MRI contrast agent. Gadolinium have 7 unpaired electrons and these electrons can make magnetic area. No other metal ions possess unpaired electron more than this. CAs based on the element Gd are classified as “positive”, by opposition to “negative” CAs. Nowadays, Gd (III) chelates is prevailing in clinical use because it can be generally used for all organ. Around 35% of all MRI exams occur with contrast agents, and Gd (III) complexes are by far the most widely used contrast agents in clinical practice. The presence of superparamagnetic iron oxide particles in a tissue significantly changes the local magnetic field. Therefore, the optimal conditions to achieve 1H Larmor resonance are very sensitively affected. Suspensions of USPIO and SPIO typically express R2/R1 larger than 2. Physical properties of this magnetic element nanostructure have not studied so much yet. In this paper we have synthesized nanoparticles of Gadolinium Oxide in Polyol method and we try to compare it with commercial MRI contrast agent. On the other hand, there are reports about the effects of hyperthermia through the applying of strong magnetic fields on iron oxide superparamagnetism nanostructures. Later this property was used to treat cancer. Materials and Methods: We use Gd(NO3)3.6H2O, DEG, PVP 1.300.000 and NaOH that prepared by Sigma Merck to synthesized nanoparticles. We have verified this structure using Transmission electron microscopy (TEM), Dynamic light scattering (DLS) and X-ray crystallography (XRD) tests. Also we use Hyperthermia to calculate the temperature rise in magnetic field. Then we study magnetic properties of these nanoparticles with VSM and MRI images and compare it with two conventional contrast agents: Dotarem and Gadovist. Results: The DLS and TEM results show a diameter of 5 nm for the particles, with homogenous distributions among the solution. The XRD pattern show that we have crystal of Gd2O3. However, VSM results show that the anisotropy of this nanoparticles is 5.4 ×10-3 (J/m3) and a superparamagnetic loop, this value means we could have better relaxation time compared to Dotarem and Gadovist in magnetic area. By calculate the values we could find the relaxation time of our nanoparticles are 100 time smaller than commercial contrast agents. Hyperthermia shows 14ᵒ temperature rise in 0.15 T magnetic area that it could be used in cancer treatment. Conclusion: At the end of paper, we put the same concentration of Dotarem, Gadovist and nanoparticles in MRI image. By the results that calculate in VSM we guess that the contrast of nanoparticles must be better than commercial contrast agents. The results show that the highest contrast among these three structures refers to nanostructures. These results were obtained based on Hydrogens relaxation. This can be the base of using this nanoparticles as a MRI contrast agent in future.

The QUAX proposal: a search of galactic axion with magnetic materials

Aim of the QUAX (QUaerere AXion) proposal is to exploit the interaction of cosmological axions with the spin of electrons in a magnetized sample. Their effect is equivalent to the application of an oscillating rf field with frequency and amplitude which are fixed by axion mass and coupling constant, respectively. The rf receiver module of the QUAX detector consists of magnetized samples with the Larmor resonance frequency tuned to the axion mass by a polarizing static magnetic field. The interaction of electrons with the axion-equivalent rf field produces oscillations in the total magnetization of the samples. To amplify such a tiny field, a pump field at the same frequency is applied in a direction orthogonal to the polarizing field. The induced oscillatory magnetization along the polarizing field is measured by a SQUID amplifier operated at its quantum noise level.

New shielding configurations for a simultaneous PET/MRI scanner at 7T

Understanding sources of electromagnetic interference are important in designing any electronic system. This is especially true when combining positron emission tomography (PET) and magnetic resonance imaging (MRI) in a multimodality system as coupling between the subsystems can degrade the performance of either modality. For this reason, eliminating radio frequency (RF) interference and gradient-induced eddy currents have been major challenges in building simultaneous hybrid PET/MRI systems. MRI requires negligible RF interference at the Larmor resonance frequency, while RF interference at almost any frequency may corrupt PET data. Moreover, any scheme that minimizes these interactions would, ideally, not compromise the performance of either subsystem. This paper lays out a plan to resolve these problems.A carbon fiber composite material is found to be a good RF shield at the Larmor frequency (300MHz in this work) while introducing negligible gradient eddy currents. This carbon fiber composite also provides excellent structural support for the PET detector components. Low frequency electromagnetic radiation (81kHz here) from the switching power supplies of the gradient amplifiers was also found to interfere with the PET detector. Placing the PET detector module between two carbon fiber tubes and grounding the inner carbon fiber tube to the PET detector module ground reduced this interference. Further reductions were achieved by adding thin copper (Cu) foil on the outer carbon fiber case and electrically grounding the PET detector module so that all 3 components had a common ground, i.e. with the PET detector in an electrostatic cage. Finally, gradient switching typical in MRI sequences can result in count losses in the particular PET detector design studied. Moreover, the magnitude of this effect depends on the location of the detector within the magnet bore and which MRI gradient is being switched. These findings have a bearing on future designs of PET/MRI systems.

Spin-orbit effects on the Larmor dispersion relation in GaAs quantum wells

We have studied the relevance of spin-orbit coupling to the dispersion 00009 relation of the Larmor resonance observed in inelastic light scattering and electron-spin resonance experiments on GaAs quantum wells. We show that the spin-orbit interaction, here described by a sum of Dresselhaus and Bychkov-Rashba terms, couples Zeeman and spin-density excitations. We have evaluated its contribution to the spin splitting as a function of the magnetic field $B$, and have found that in the small $B$ limit, the spin-orbit interaction does not contribute to the spin splitting, whereas at high magnetic fields it yields a $B$ independent contribution to the spin splitting given by $2(\lambda_R^2-\lambda_D^2)$, with $\lambda_{R,D}$ being the intensity of the Bychkov-Rashba and Dresselhaus spin-orbit terms.

Nuclei in Cooperation

We analyze and discuss two distinct resonance phenomena at high nuclear polarizations, which give independent experimental information about the exchange couplings, direct or indirect, between the nuclear spins in solids. In cases of more than one isotope with a nuclear spin, there is an isotopic-interference effect, sometimes referred to as a suppression-enhancement effect. Even in cases with just one spin species, one may observe harmonic lines of the ordinary Larmor resonance. By analyzing the shifts and intensities of the resonance lines as functions of the nuclear polarization, one can find the sign and magnitude of the exchange couplings. The focus of this paper is in experiments on nuclear magnetic ordering in pure metals. We present studies on copper, silver, rhodium, thallium, and gold, and discuss shortly our ongoing work on lithium.

Boron implantation doping of diamond

Spin polarized B12 nuclei were produced in a B11(d,p)12B nuclear reaction and recoil implanted into a type Ib diamond sample at doses below 1011 cm−2. β-radiation detected nuclear magnetic resonance spectra were measured directly after implantation at sample temperatures ranging from 300 to 800 K. The polarization asymmetry at the Larmor resonance yielded fractions of boron ions at sites of full tetrahedral symmetry of 12(1)% at 300 K, increasing to 17(2)% at 800 K. It is argued that these boron atoms are incorporated substitutionally by direct replacement collisions during the implantation process. The resonance spectra also showed additional boron at low-symmetry sites.

Temperature dependence of the EPR spectra of KNiF 3

The X-band EPR powder spectra of KNiF 3 has been measured from T N = 253 K to 530 K. A very broad asymmetric line was observed in all cases and, from a fitting procedure, the Larmor resonance fields H r and linewidths Δ H were obtained. While H r is constant and corresponds to g = 2.32 ± 0.04, the linewidth increases with temperature from 3.8 to 7.2 kOe. At temperature T > 1.4 T N, Δ H increases linearly with T suggesting that spin-lattice relaxation is dominated by one-phonon processes.

Proton and Deuteron Magnetic Resonance Study of Calcium Bromate Monohydrate

The proton magnetic resonance spectrum of calcium bromate monohydrate was obtained. Results indicate that there are two orientations of the water molecule in the crystal. The p–p distances are 1.58 ± 0.02 and 1.59 ± 0.02 Å, respectively. Their orientations with respect to the crystallographic axes were determined. The protonic spin–lattice relaxation times were measured as functions of orientation at room temperature and of temperature in a single crystal of calcium bromate monohydrate. The b crystallographic axis was the axis of rotation of the crystal. The relaxation time was essentially independent of orientation of the crystal in the external magnetic field. The temperature dependence was characteristic of 180° flipping motion of the H2O molecule whose activation energy was 6.7 ± 0.4 kcal/mole. Quadrupole splittings of the Larmor resonance for the deuterons in Ca(BrO3)2·D2O were measured for single crystals at room temperature. The D2O molecules execute flipping motion at this temperature. The coupling constants and asymmetry parameters for both nonequivalent D2O molecules were determined to be 124.0 ± 1.5 kc/sec and 0.759 ± 0.015, respectively. No dipolar splittings of the quadrupole lines were observed. The H2O molecules were determined to be hydrogen bonded to the O(5) and O(2) atoms in the crystal.

Deuteron Magnetic Resonance Study of Potassium Oxalate Monodeuterate

Quadrupole splittings of the Larmor resonance for the deuteron in potassium oxalate monodeuterate (K2C2O4·D2O) were measured for single crystals at temperatures from −50° to 95°C. The D2O molecule is stationary at room and lower temperatures. The coupling constant and asymmetry parameter were determined to be 209.7±2.5 kc/sec and 0.090±0.020, respectively. The z field-gradient axis is within 4.8°±2.0° of parallelism with the O—D bond while the y axis is in the a—c plane and within 4.6°±2.0° of being perpendicular to the DOD plane. The D2O molecule begins to 180° flip about its DOD bisector at 25°—50°C and higher. The coupling constant and asymmetry parameter of the flipping molecule are 114.2 kc/sec and 0.851, respectively. The z field-gradient axis is nearly perpendicular to the DOD plane while the y axis is nearly parallel to the D—D vector in its equilibrium position. Both axes are in the a—c plane and rotated away from perpendicularity and parallelism, respectively, by 4.6°±2.0°. The coupling constants of this and three other deuterates differ among themselves and they are markedly lower than the computed and measured values for the isolated D2O molecule. Reasons for these differences are discussed including hydrogen bond strengths and D2O motion. For this crystal the field gradient due to nearby ions was estimated on the basis of a simple model and it was found to augment the measured coupling constant by about 9%.

Wave Motion in a Plasma Based on a Fokker-Planck Equation

An isotropic Fokker-Planck collision model is introduced in Boltzmann's equations in order to study the small amplitude wave motion of an unbounded, fully ionized, neutral, two-component plasma in a uniform applied magnetic field. In the Laplace and Fourier transformed space the linearized Boltzmann's equations with Maxwell's equations are solved and the dispersion relation is constructed. Because the isotropic Fokker-Planck operators describe a diffusion process in velocity space while the previously considered Krook relaxation models do not, an infinite number of new Larmor resonance modes is found at arbitrary directions of propagation with respect to the applied magnetic field. These new resonances remain in the limit of long macroscopic wavelengths and small collision frequencies. At propagation parallel to the applied magnetic field new resonances are found for wavelengths large and small with respect to the mean free path. In other macroscopic ranges such as the cold plasma regime and the long wavelength magnetohydrodynamic regime the Krook and the isotropic Fokker-Planck models give the same results to lowest order.

Long-Wavelength Phenomena in a Plasma

The long-wavelength modes of excitation of a two-component plasma in a steady magnetic field are examined. Two linearized Boltzmann equations are given with collision terms which are coupled through the difference in temperatures and difference in velocities of the two gases. A formal means of classification of phenomena is described in terms of the nature of the roots about k = 0. Two types of behavior are uncovered: magnetohydrodynamics, which includes finite phase-speed phenomena near k = 0; and plasma electromagnetics, which includes infinite-phase-speed phenomena near k = 0. The dissipative effects of collisions are included. In the limit of vanishing collision frequency, roots previously obtained are recaptured. The relevance of the pertinent domains are discussed and the complex interplay between the ``fast'' and ``Alfvén'' modes of magnetohydrodynamics and the plasma-magnetic modes of the plasma electromagnetic domain is demonstrated. Equations macroscopic in appearance are derived which include the effects of the initial configuration. In the limit of large collision frequency these equations reduce to standard forms. The dispersion of the Nth-order Larmor resonance is given which includes the effect of the mass ratio.

Spin-spin relaxation and magnetic resonances in two copper tutton salts

The real and imaginary components χ′ and χ″ of the paramagnetic susceptibilities of CuCS 2(SO 4) 2. 6H 2O and Cu(NH 4) 2(SO 4) 2. 6H 2O have been studied at frequencies of 0.41, 1.21, 1.76 and 3.2 GHz. The powdered samples were placed in transmission cavities (cf. Fig. 1 and 2) and nearly all measurements have been carried out at 20°K. The accuracy of the absolute values is of the order of 5%. The exchange interaction in the Cs Tutton salt is small while in the NH 4 Tutton salt (Table IV) it is of the same order as the dipole-dipole interaction. This leads to a very different magnetic behaviour as may be seen from the figures 4–9, where χ″ is given in perpendicular magnetic fields, and χ″ as well as χ′ in parallel fields. In the figures 10–13 the data obtained in some of the fields have been plotted as a function of the frequency. In zero field (Fig. 10 and 11) reasonably good agreement with Gauss curves is found for the Cs Tutton salt. The high top value of χ″ and the negative values of χ′ at high frequencies are striking. A line shape function (Form. 6) for intermediate cases having the Gauss and Lorentz shapes as the two limits is proposed. The results for the NH 4 Tutton salt fit well with the shape function which is expected to apply in view of the ratio of exchange to dipole-dipole interaction derived from the specific heat of the spin system. The decrease of width of the χ″ curve in a perpendicular field due to truncation of the Hamiltonian of dipole-dipole interaction is observed for the Cs Tutton salt as well as a weak absorption band at half the field H L of the Larmor resonance (Fig. 4). The exchange narrowing of the Larmor resonance in the NH 4 Tutton salt is observed and, in accordance with the 10/3 factor, the width is found to decrease with increasing field (Fig. 7). In large parallel fields marked resonances at the Larmor frequency and the double Larmor frequency (at constant frequency occuring at the Larmor field and half the Larmor field) are observed in the Cs Tutton salt (Fig. 5, 6 and 13). The absolute values, as well as the ratio of the intensities agree satisfactorily with the formulae taking the hyperfine interaction of the copper nuclei into account, which have been developed by Dr. Caspers in his appendix. On the whole good agreement is found with the theoretical expectations a great part of which may be found in the appendix mentioned.