Gyromagnetic Factor Research Articles

Anomalous magnetic moment of the positronium ion

We determine the gyromagnetic factor of the positronium ion, a three-body system consisting of two electrons and a positron, including first relativistic corrections. We find that the g-factor is modified by a term , exceeding 15 times the correction for a free electron. We compare this effect with analogous results found previously in atomic positronium and in hydrogen-like ions.

Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

10 nm and 50 nm Co2FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (Ta), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing Ta, while the uniaxial anisotropy field is nearly unaffected by Ta within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta. Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10−3 and 1.3×10−3 for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively).

Effect of the annealing temperature on dynamic and structural properties of Co2FeAl thin films

10 nm and 50 nm thick Co 2 FeAl (CFA) thin films have been deposited on thermally oxidized Si(001) substrates by magnetron sputtering using a Tantalum cap layer and were then ex-situ annealed at 415°C, 515°C and 615°C during 15 minutes in vacuum. X-rays diffraction indicates that films CFA are polycrystalline and exhibit an in-plane isotropy growth. Ferromagnetic resonance measurements, using a microstrip line (MS-FMR), reveal a huge interfacial perpendicular magnetic anisotropy and small in-plane uniaxial anisotropy both annealing temperature-dependent. The MS-FMR data also allow concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with annealing temperature. Finally, the FMR linewidth decreases with increasing annealing temperature due to the enhancement of the chemical order, and allow deriving a very low intrinsic damping parameter (1.3×10 −3 at 615°C).

Determination of Exciton Reduced Mass and Gyromagnetic Factor of Wurtzite (InGa)As Nanowires by Photoluminescence Spectroscopy under High Magnetic Fields

Semiconductor nanowires (NWs) have the prospect of being employed as basic units for nanoscale devices and circuits. However, the impact of their one-dimensional geometry and peculiar crystal phase on transport and spin characteristics remains largely unknown. We determine the exciton reduced mass and gyromagnetic factor of (InGa)As NWs in the wurtzite phase by photoluminescence (PL) spectroscopy under very high magnetic fields. For B perpendicular to the NW ĉ axis, the exciton reduced mass is 10% greater than that expected for the zincblende phase and no field-induced circular polarization of PL is observed. For B parallel to ĉ, an exciton reduced mass 35% greater than that of the zincblende phase is derived. Moreover, a circular dichroism of 70% is found at 28 T. Finally, an analysis of the PL line shape points at two Zeeman split levels, whose separation corresponds to an exciton gyromagnetic factor |g(e) - g(h,∥)| = 5.8. These results provide a quantitative estimate of the basic electronic and spin properties of NWs and may guide a theoretical analysis of the band structure of these fascinating nanostructures.

Covariant basis induced by parity for the(j,0)⊕(0,j)representation

In this work, we build a covariant basis for operators acting on the $(j,0)\oplus(0,j)$ Lorentz group representations. The construction is based on an analysis of the covariant properties of the parity operator, which for these representations transforms as the completely temporal component of a symmetrical tensor of rank $2j$. The covariant properties of parity involve the Jordan algebra of anti commutators of the Lorentz group generators which unlike the Lie algebra is not universal. We make the construction explicit for $j=1/2,1$ and $3/2$, reproducing well-known results for the $j=1/2$ case. We provide an algorithm for the corresponding calculations for arbitrary $j$. This covariant basis provides an inventory of all the possible interaction terms for gauge and non-gauge theories of fields for these representations. In particular, it supplies a single second rank antisymmetric structure, which in the Poincar\'e projector formalism implies a single Pauli term arising from gauge interactions and a single (free) parameter $g$, the gyromagnetic factor. This simple structure predicts that for an elementary particle in this formalism all multipole moments, $Q^{l}_{E}$ and $Q^{l}_{M}$, are dictated by the complete algebraic structure of the Lorentz generators and the value of $g$. We explicitly calculate the multipole moments, for arbitrary $j$ up to $l=8$. Comparing with results in the literature we find that only the electric charge and magnetic moment of a spin $j$ particle are independent of the Lorentz representation under which it transforms, all higher multipoles being representation dependent. Finally we show that the propagation of the corresponding spin $j$ waves in a electromagnetic background is causal.

Top anomalous magnetic moment and the two-photon decay of the Higgs boson

We compute the dependence of the Higgs to two-photon decay rate ${\ensuremath{\Gamma}}_{h\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$ on the top quark gyromagnetic factor ${g}_{t}$ in the heavy top limit and evaluate the expected change for one-loop SM correction to ${g}_{t}$. Our results are general and allow consideration of further modifications of ${g}_{t}$, and we predict the resultant ${\ensuremath{\Gamma}}_{h\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$.

GROUND STATE MAGNETIC PROPERTIES OF ODD NEUTRON DY ISOTOPES

Using the quasiparticle phonon nuclear model (QPNM) and taking into account the spin–spin interaction, the effects of the spin polarization on spin gyromagnetic factors (gs) as well as the intrinsic magnetic moments (gK) of the deformed odd neutron155-165Dy isotopes were studied. The calculated values of gsand gKare in fair agreement with the experiment as well as with other microscopic calculations. Our calculations indicated that because of the core polarization, the gsfactors of the nucleons in the nucleus reduce noticeably from its free nucleon value and the spin–spin interactions play an important role in the explanation of the quenching of the gsfactors. A very good reproduction of the phenomenological quenching of gsfactor from its free values [Formula: see text] is obtained for155-165Dy .

Collectivity of neutron-rich magnesium isotopes investigated by projected shell model calculations

The abnormally large collectivity of neutron-rich magnesium isotopes in the “island of inversion” has not been well understood. It has been commented that the unexpectedly large deformations observed in the magnesium isotopes are attributed to the neutron f7/2 intruder orbits involved remarkably even in the ground states, which points to nuclear force directly. Recently, a new isospin-dependent Nilsson potential was suggested to improve the calculations of the ground states of magnesium isotopes. With the improved Nilsson potential, in the present work we investigate the collectivity of excited states by using the projected shell model. To avoid the collapse of the BCS pairing, which occurs in weak pairing, we improved pairing calculations by using the Lipkin-Nogami approach. The collectivity and the erosion of the N = 20 shell in neutron-rich magnesium isotopes are discussed by calculating spectra and electric quadrupole transitions. The gyromagnetic factors are calculated and compared with existing data to get insight into the configurations of collective states at different spins. A two-quasineutron K π = 6 + state in 38 Mg is predicted to be a possible isomer with an excitation energy lower than the I π = 6 + member of the ground-state band.

Gyromagnetic factors in the even Ru and Pd chains

Recent g -factor measurements in even Ru and Pd isotopes have significantly improved the accuracy of the \( g(2^{+}_{1})\) factors in the lighter nuclei of both isotopic chains and enhanced the systematics, thus enabling a detailed test of current nuclear models. It has been performed paying particular attention to the IBA-2 model and to the dependence of the calculated g factors on the parameters of the M1 operator.

Renormalization of the QED of self-interacting second order spin $ \frac{1}{2} $ fermions.

We study the one-loop level renormalization of the electrodynamics of spin 1/2 fermions in the Poincar\'e projector formalism, in arbitrary covariant gauge and including fermion self-interactions, which are dimension four operators in this framework. We show that the model is renormalizable for arbitrary values of the tree level gyromagnetic factor g within the validity region of the perturbative expansion, \alpha g^2 << 1. In the absence of tree level fermion self-interactions, we recover the pure QED of second order fermions, which is renormalizable only for |g|=2. Turning off the electromagnetic interaction we obtain a renormalizable Nambu-Jona-Lasinio-like model with second order fermions in four space-time dimensions.

Temperature dependence of electron magnetic resonance spectra of iron oxide nanoparticles mineralized in Listeria innocua protein cages

Electron magnetic resonance (EMR) spectroscopy was used to determine the magnetic properties of maghemite (γ-Fe(2)O(3)) nanoparticles formed within size-constraining Listeria innocua (LDps)-(DNA-binding protein from starved cells) protein cages that have an inner diameter of 5 nm. Variable-temperature X-band EMR spectra exhibited broad asymmetric resonances with a superimposed narrow peak at a gyromagnetic factor of g ≈ 2. The resonance structure, which depends on both superparamagnetic fluctuations and inhomogeneous broadening, changes dramatically as a function of temperature, and the overall linewidth becomes narrower with increasing temperature. Here, we compare two different models to simulate temperature-dependent lineshape trends. The temperature dependence for both models is derived from a Langevin behavior of the linewidth resulting from "anisotropy melting." The first uses either a truncated log-normal distribution of particle sizes or a bi-modal distribution and then a Landau-Liftshitz lineshape to describe the nanoparticle resonances. The essential feature of this model is that small particles have narrow linewidths and account for the g ≈ 2 feature with a constant resonance field, whereas larger particles have broad linewidths and undergo a shift in resonance field. The second model assumes uniform particles with a diameter around 4 nm and a random distribution of uniaxial anisotropy axes. This model uses a more precise calculation of the linewidth due to superparamagnetic fluctuations and a random distribution of anisotropies. Sharp features in the spectrum near g ≈ 2 are qualitatively predicted at high temperatures. Both models can account for many features of the observed spectra, although each has deficiencies. The first model leads to a nonphysical increase in magnetic moment as the temperature is increased if a log normal distribution of particles sizes is used. Introducing a bi-modal distribution of particle sizes resolves the unphysical increase in moment with temperature. The second model predicts low-temperature spectra that differ significantly from the observed spectra. The anisotropy energy density K(1), determined by fitting the temperature-dependent linewidths, was ∼50 kJ/m(3), which is considerably larger than that of bulk maghemite. The work presented here indicates that the magnetic properties of these size-constrained nanoparticles and more generally metal oxide nanoparticles with diameters d < 5 nm are complex and that currently existing models are not sufficient for determining their magnetic resonance signatures.

Electromagnetic currents of elementary particles from a second order formalism

We use a second order formalism based on Poincaré symmetry, and known as Covariant Projector Formalism to calculate the electromagnetic currents of spin 1/2, spin 1 and spin 3/2 particles. We restrict to parity conserving processes and obtain the currents in terms of the gyromagnetic factor g alone. This parameter is then fixed by calculating the forward Compton scattering cross section. In the end we reproduce the Dirac moments for the electron from a more general second order Lagrangian, we also reproduce the Standard Model results for the W boson. In the spin 3/2 case we show that the RS current is incomplete as it does not include the spin 1 piece of the vector-spinor representation. As a consequence, when we calculate the spin 3/2 EM moments, instead of the universal value g = 2, we find g = 2/3 as the gyromagnetic ratio for a Rarita-Schwinger particle.

Constraining the variation of fundamental constants at z ∼ 1.3 using 21-cm absorbers

We present high resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) and 21-cm absorption spectra obtained with the Giant Metrewave Radio Telescope (GMRT) and the Green Bank Telescope (GBT) of five quasars along the line of sight of which 21-cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsec scale radio images of these quasars obtained with the Very Large Baseline Array (VLBA). We use the data on four of these systems to constrain the time variation of x = g_p*alpha^2/mu where g_p is the proton gyromagnetic factor, alpha is the fine structure constant, and mu is the proton-to-electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross-correlation analysis and repeated Voigt profile fitting. In two cases we also confirm our results by analysing optical spectra obtained with the Keck telescope. We find the weighted and the simple means of Delta_x / x to be respectively -(0.1 +/- 1.3)x10^-6 and (0.0 +/- 1.5)x10^-6 at the mean redshift of <z> = 1.36 corresponding to a look back time of ~ 9 Gyr. This is the most stringent constraint ever obtained on Delta_x / x. If we only use the two systems towards quasars unresolved at milliarcsec scales, we get the simple mean of Delta_x / x = + (0.2 +/- 1.6)x10^-6. Assuming constancy of other constants we get Delta_alpha / alpha = (0.0 +/- 0.8)x10^-6 which is a factor of two better than the best constraints obtained so far using the Many Multiplet Method. On the other hand assuming alpha and g_p have not varied we derive Delta_mmu / mu = (0.0 +/- 1.5)x10^-6 which is again the best limit ever obtained on the variation of mu over this redshift range. [Abridged]

Acceleration and vacuum temperature

The quantum fluctuations of an "accelerated" vacuum state, that is vacuum fluctuations in the presence of a constant electromagnetic field, can be described by the temperature $\TEH$. Considering $\TEH$ for the gyromagnetic factor $g=1$ we show that $\TEH(g=1)=\THU$, where $\THU$ is the Unruh temperature experienced by an accelerated observer. We conjecture that both particle production and nonlinear field effects inherent in the Unruh accelerated observer case are described by the case $g=1$ QED of strong fields. We present rates of particle production for $g=0,1,2$ and show that the case $g=1$ is experimentally distinguishable from $g=0,2$. Therefore, either accelerated observers are distinguishable from accelerated vacuum or there is unexpected modification of the theoretical framework.

Local environment of optically active Nd3+ions in the ultratransparent BaMgF4ferroelectric crystal

A comprehensive study of the site location of Nd${}^{3+}$ ions in the BaMgF${}_{4}$ ultratransparent ferroelectric crystal is presented. By combining different low-temperature optical spectroscopies and electron paramagnetic resonance, the crystal field energy levels of Nd${}^{3+}$ ions and the gyromagnetic factors are experimentally determined. These results are employed to perform the crystal field analysis of Nd${}^{3+}$ ions considering a Cs point symmetry. The crystal field calculation yields a small root-mean-square deviation of 18 cm${}^{\ensuremath{-}1}$ and reveals a large crystal field strength (621 cm${}^{\ensuremath{-}1}$), verifying the assignment of the Ba${}^{2+}$ cationic site as the location for Nd${}^{3+}$ ions in this fluoride host. The results suggest a slight displacement of Nd${}^{3+}$ from the barium regular site with a rearrangement of the fluorine ions around it. The work gives a deep insight into the properties of the Nd${}^{3+}$-doped BaMgF${}_{4}$ crystal, a ferroelectric widely ultra-transparent material with potential applications as optical device operating in the Vacuum Ultraviolet-Ultraviolet and midinfrared spectral regions.

Structural and magnetic properties of Co2MnSi thin films

AbstractCo2MnSi (CMS) films of different thicknesses (20, 50, and 100 nm) were grown by radio frequency (RF) sputtering on a‐plane sapphire substrates. Our X‐rays diffraction (XRD) study shows that, in all the samples, the cubic 〈110〉 CMS axis is normal to the substrate and that six well defined preferential in‐plane orientations are present. Static and dynamic magnetic properties were investigated using vibrating sample magnetometry (VSM) and microstrip line ferromagnetic resonance (MS‐FMR), respectively. From the resonance measurements versus the direction and the amplitude of an applied magnetic field, most of the magnetic parameters are derived, i.e.: the magnetization, the gyromagnetic factor, the exchange stiffness coefficient, and the magnetic anisotropy terms. The in‐plane anisotropy results from the superposition of two terms showing a twofold and a fourfold symmetry, respectively. The observed behavior of the hysteresis loops is in agreement with this complex form of the in‐plane anisotropy.

Renormalization of the QED of second-order spin12fermions

In this work we study the renormalization of the electrodynamics of spin 1/2 fermions in the Poincar\'e projector formalism which is second order in the derivatives of the fields. We analyze the superficial degree of divergence of the vertex functions of this theory, calculate at one-loop level the vacuum polarization, fermion self-energy and \gamma-fermion-fermion vertex function and the divergent piece of the one-loop contributions to the \gamma-\gamma-fermion-fermion vertex function. It is shown that these functions are renormalizable independently of the value of the gyromagnetic factor g which is a free parameter of the theory. We find a photon propagator and a running coupling constant \alpha (q^2) that depend on the value of g. The magnetic moment form factor contains a divergence associated to g which disappears for g=2 but in general requires the coupling g to be renormalized. A suitable choice of the renormalization condition for the magnetic form factor yields the one loop finite correction \Delta{g}=g\alpha/2\pi. For a particle with g=2 we recover results of Dirac theory for the photon propagator, the running of \alpha (q^2) and the one-loop corrections to the gyromagnetic factor.

Equal coupling strength approach to spin precession effects concerning Rashba and Dresselhaus spin–orbit interactions in the presence of in-plane magnetic fields

The influence of Rashba and Dresselhaus spin–orbit interactions on the electronic properties of quasi one-dimensional systems like InAs quantum wires is discussed in the presence of in-plane magnetic fields. One shows that equal coupling strength conditions are provided specifically by the commutativity of two-dimensional constituents of velocity and current operators. The interesting point is that equal strength spin–orbit couplings one deals with proceed in conjunction with related spin conservations, which amounts to account for selected orientations of the magnetic field. Accordingly, the in-plane magnetic fields should be directed solely along the bisectrices. Other angles may be conceivable, but in this case spin conservations alluded to above are lost. Such results open the way to a consistent derivation of the equal coupling strength limit of the energy, which leads in turn to the derivation of novel spin-precession effects. A related effective gyromagnetic factor has also been established.

Studies on the Gyromagnetic Factors of the Tetragonal NdBa2Cu3O6.1

The electron paramagnetic resonance (EPR) g factors g (ayen) and g (aSyen) of the tetragonal NdBa2Cu3O6.1 are theoretically studied using the perturbation formulas of the g factors for a 4f (3) ion in tetragonal symmetry. In the calculations, the influences of the admixtures of various energy levels are considered, while the tetragonal field parameters are determined from the local structural data of Nd3+ site using the superposition model. The theoretical g factors are in reasonable agreement with the observed values. The positive anisotropy g (aSyen) - g (ayen) is attributable to the elongation of the oxygen cube around Nd3+ along the C (4) axis in NdBa2Cu3O6.1. The magnitude (average) of the g factors for NdBa2Cu3O6.1 is lower than that for the previously observed NdBa2Cu3O7-delta (0 <delta < 1). This can be ascribed to the different oxygen amount and the dissimilar local environments around Nd3+ under different preparation conditions and parameters. Further, the lowest Kramers doublet of the present NdBa2Cu3O6.1 is the unresolved I" (7,8), while that of NdBa2Cu3O7 is I" (6).

Gyromagnetic factors and atomic clock constraints on the variation of fundamental constants

We consider the effect of the coupled variations of fundamental constants on the nucleon magnetic moment. The nucleon g-factor enters into the interpretation of the measurements of variations in the fine-structure constant, alpha, in both the laboratory (through atomic clock measurements) and in astrophysical systems (e.g. through measurements of the 21 cm transitions). A null result can be translated into a limit on the variation of a set of fundamental constants, that is usually reduced to alpha. However, in specific models, particularly unification models, changes in alpha are always accompanied by corresponding changes in other fundamental quantities such as the QCD scale, Lambda_QCD. This work tracks the changes in the nucleon g-factors induced from changes in Lambda_QCD and the light quark masses. In principle, these coupled variations can improve the bounds on the variation of alpha by an order of magnitude from existing atomic clock and astrophysical measurements. Unfortunately, the calculation of the dependence of g-factors on fundamental parameters is notoriously model-dependent.