Calculation Of Magnetic Moment Research Articles

Nanogranular Phase Formation During Devitrification of Fe(NiCo)ZrB Amorphous Alloys

A comprehensive review of our recent experimental and theoretical developments in the processing of nanocrystalline soft magnetic materials made by crystallization of amorphous precursors and containing new nanocrystalline phases is given. The relationship between the structures of the metastable and equilibrium phases and their transformations are discussed. Nickel-rich amorphous precursors with stoichiometry Ni64Fe16Zr7B12Au1 were produced by melt-spinning technique and then heat-treated at temperatures ranged from 420 °C to 600 °C for one hour to form nanostructured alloy. The transformation from the amorphous state into the nanocrystalline state was investigated by the differential scanning calorimetry (DSC), the x-ray diffraction (XRD), the vibrating sample magnetometry (VSM) and Mossbauer techniques. The annealing favours the emergence of cubic FexNi23-xB6 crystalline grains (10-25 nm in diameter). Magnetic measurements made at 4.2-1100 K reveal rather high value of saturation magnetization (nearly 60 and 40 Am2/kg at 4.2 K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300 K 57Fe Mossbauer results which are well supported by the calculations of Ni and Fe magnetic moments in Ni23B6 and Fe23B6 phases, using the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. However, anomalous high magnetic moments of Fe and Co atoms were found in some inequivalent positions in the crystal structure.

A nonperturbative calculation of the electron's magnetic moment

In principle, the complete spectrum and bound-state wave functions of a quantum field theory can be determined by finding the eigenvalues and eigensolutions of its light-cone Hamiltonian. One of the challenges in obtaining nonperturbative solutions for gauge theories such as QCD using light-cone Hamiltonian methods is to renormalize the theory while preserving Lorentz symmetries and gauge invariance. For example, the truncation of the light-cone Fock space leads to uncompensated ultraviolet divergences. We present two methods for consistently regularizing light-cone-quantized gauge theories in Feynman and light-cone gauges: (1) the introduction of a spectrum of Pauli–Villars fields which produces a finite theory while preserving Lorentz invariance; (2) the augmentation of the gauge-theory Lagrangian with higher derivatives. In the latter case, which is applicable to light-cone gauge ( A + = 0 ), the A − component of the gauge field is maintained as an independent degree of freedom rather than a constraint. Finite-mass Pauli–Villars regulators can also be used to compensate for neglected higher Fock states. As a test case, we apply these regularization procedures to an approximate nonperturbative computation of the anomalous magnetic moment of the electron in QED as a first attempt to meet Feynman's famous challenge.

Hyperon radiative decays in the1/Ncexpansion

Using a recent calculation of transition magnetic moments in the 1/N_c expansion and a calculation showing the suppression of E2/M1 by powers of N_c, we compute the widths for the radiative decays Sigma^* --> Sigma gamma, Sigma^* --> Lambda gamma, and Xi^* --> Xi gamma.

Nanogranular FexNi23−xB6 phase formation during devitrificationof nickel-rich Ni64Fe16Zr7B12Au1 amorphous alloy

Nickel-rich amorphous precursors with chemical composition of Ni64Fe16Zr7B12Au1 were produced by melt-spinning technique and then heat treated at temperatures ranging from 435to600°C for 1h to form a nanostructure. Properties of the amorphous and the nanocrystalline samples were investigated by the differential scanning calorimetry, the x-ray diffraction (XRD), the vibrating sample magnetometry, and Mössbauer techniques. The annealing favors the emergence of cubic FexNi23−xB6 crystalline grains (10–25nm in diameter). Magnetic measurements made at 4.2–1100K reveal rather high value of saturation magnetization (nearly 60 and 40Am2∕kg at 4.2K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300K Fe57 Mössbauer effect results which are well supported by the calculations of Ni and Fe magnetic moments in Ni23B6 and Fe23B6 phases, using the spin polarized tight binding linear muffin-tin orbital method. However, anomalous high magnetic moments of Fe atoms were found in some inequivalent positions in the crystal structure.

Effects of Perturbative Exchanges in a QCD String Model

The QCD string model for baryons derived by Yu. A. Simonov and used for the calculation of baryon magnetic moments in a previous paper is extended to include also perturbative gluon and meson exchanges. The mass spectrum of the baryon multiplet is studied. For the meson interaction, either pseudoscalar or pseudovector coupling is used. Predictions are compared with the experimental data. Besides these exchanges, the influence of excited quark orbitals on the baryon ground state are considered by performing a multichannel calculation. The nucleon-Δ splitting increases due to the mixing of higher quark states, while the baryon magnetic momenta decrease. The multichannel calculation with perturbative exchanges is shown to yield reasonable magnetic moments, while the mass spectrum is close to experiment.

Solution of the Skyrme–Hartree–Fock–Bogolyubov equations in the Cartesian deformed harmonic-oscillator basis. (IV) HFODD (v2.08i): a new version of the program

We describe the new version (v2.07f) of the code HFODD which solves the nuclear Skyrme-Hartree-Fock or Skyrme-Hartree-Fock-Bogolyubov problem by using the Cartesian deformed harmonic-oscillator basis. In the new version, all symmetries can be broken, which allows for calculations with angular frequency and angular momentum tilted with respect to the mass distribution. The new version contains an interface to the LAPACK subroutine ZHPEVX.

Ab Initio STUDY OF THE MAGNETIC PROPERTIES AND CONDUCTIVE PROPERTIES OF BEST2[Fe(CN)5NO]

With the help of the ab initio method of the full potential linearized augmented-plan-wave, electronic band structure and its magnetic property for a charge transfer compound of bis (ethylenediselena)-tetrathiafulvalene (BEST) with [Fe(CN)5NO] anions are studied, where the exchange-correlation effects of electrons are accounted. The partial density of states and atomic spin magnetic moments are calculated and discussed. It is found that the π-electron of the iron atom in the t2g orbital mainly provides the magnetism. Because of the hybridization between oxygen and nitrogen, unpaired electrons localized at the nitric oxide radical contribute the magnetism to the compound. In particular, the calculations of spin magnetic moments reveal that the spin population (spin up and down) of C/Se/S altered in the organic donors, which may lead to antiferromagnetic exchange interactions. We also found that the π-electrons of the 2p-orbital of oxygen, the 2p-orbital of nitrogen, the t2g-orbital of iron, the 2p-orbital of selenium and the 2p-orbital of sulfur contribute to conductivity. These result reveal that the magnetism and conductivity are coexist in the titled compound. Our results are in good agreement with the experiment.

D+isversusd+id′time reversal symmetry breaking states in finite size systems

We report self-consistent quasiclassical calculations of spontaneous currents and magnetic moments in finite size unconventional superconducting systems, namely: (i) in isolated d-wave superconductor islands where, in addition to the dominant order parameter (with a d_{x^2-y^2} symmetry), a subdominant order parameter of s or d_{xy} symmetry is added; (ii) in grain boundary junctions between two arbitrarily oriented d-wave superconductors, and between a d-wave and an s-wave superconductor. We show that the profile of the spontaneous current density and the magnetic field distribution depend on the time-reversal symmetry breaking properties of the system. For the d_{x^2-y^2}+id_{xy} state, vortices appear near the edges of the finite size systems. We associate these vortices with the chiral nature of the mixed order parameter. The method developed here is quite general, and can be used for predicting properties of any finite size superconducting system.

MAGNETIC MOMENTS NEAR THE SHARP INTERFACES OF FERROMAGNETIC MATERIALS

Ab initio theoretical calculations of magnetic moments near the interfaces of 3d ferromagnetic transition metals were performed using the self-consistent interface Green's function technique based on linear-muffin-tin orbitals (LMTO) method within the tight-binding (TB) and atomic sphere approximation together with local-spin-density approximation. We have also made supercell spin-polarized (SP) band structure calculations of (1 0 0) Fe/Co interface in the framework of TB-LMTO method, in order to take into account structural deformations and estimate their influence on the magnetic moments near that interface. Our results for layer magnetic moments near Fe/Co, Fe/Ni and Ni/Co interfaces did not show any oscillating behavior, contrary to the recent findings for the magnetic moment profile near Fe/Co interface deduced from the perturbed angular correlation measurements of hyperfine fields. The reasons for this disagreement have been discussed and a comparison with earlier experimental and theoretical results was made.

An interpolation of the vacuum polarization function for the evaluation of hadronic contributions to the muon anomalous magnetic moment

We propose a simple parameterization of the two-point correlator of hadronic electromagnetic currents for the evaluation of the hadronic contributions to the muon anomalous magnetic moment. The parameterization is explicitly done in the Euclidean domain. The model function contains a phenomenological parameter which provides an infrared cutoff to guarantee the smooth behavior of the correlator at the origin in accordance with experimental data in e+ e- annihilation. After fixing a numerical value for this parameter from the leading order hadronic contribution to the muon anomalous magnetic moment the next-to-leading order results related to the vacuum polarization function are accurately reproduced. The properties of the four-point correlator of hadronic electromagnetic currents as for instance the so-called light-by-light scattering amplitude relevant for the calculation of the muon anomalous magnetic moment are briefly discussed.

Electronic and magnetic structures of Ni/Fe(0 0 1) overlayers: first-principles study

The electronic and magnetic structures are calculated for the Ni/Fe(0 0 1) overlayer system within the local-density approximation using the tight-binding linear muffin-tin orbital method in the atomic sphere approximation. Magnetic moment calculations of Ni/Fe n /Ni for n=(1,3,5,7,9,11) monolayers (ML) show that the coupling at the interface is ferromagnetic. The average value of the Fe magnetic moment is slightly enhanced as compared to its bulk value, and bulk Fe can be represented by at least 9 ML.

Epitaxial growth, alloying and magnetic structure of interfaces in Fe/Cr (0 0 1) superlattices

Fe/Cr(0 0 1) superlattices containing two-monolayers thick 57Fe probe layers at the Fe/Cr (Fe-on-Cr) or Cr/Fe (Cr-on-Fe) interfaces were studied using conversion electron Mössbauer spectroscopy (CEMS). For the interpretation of the CEMS data of superlattices annealed at different temperatures, we performed theoretical modeling of their chemical and magnetic structure. Roughness and interface alloying were introduced to the model by algorithms of epitaxial growth, which included ballistic deposition with subsequent floating of some atoms on the surface. Self-consistent calculations of magnetic moments within the periodic Anderson model confirmed the proportionality between hyperfine fields and magnetic moments. For the explanation of the evolution of CEM spectra versus annealing temperature, the difference in the melting points of bulk Fe and Cr has to be taken into account.

Calculations of magnetic moments for three-electron atomic systems.

The first fully correlated calculations of the magnetic moment in lithium are presented. Relative to the free-electron value, the Zeeman gJ factor for the ground state lithium gJ/g(e)-1 is calculated to a computational accuracy of 200 parts in 10(9), including relativistic and radiative corrections of orders alpha2, alpha2m/M, and alpha3. The isotope shifts in gJ are predicted precisely for various isotopes. The extensions to the first excited S state of lithium and the ground state of Be+ are made.

Maximum magnetic moment in field-cooled superconducting disk: application to paramagnetic Meissner effect

We have studied the magnetic moment in a superconducting sheet for fields perpendicular to the sample surface. We gave a method for calculation of the magnetic moment of the superconducting sample which has an arbitrary shape but is thin enough, by applying the recent calculations of maximum magnetic moments of a field-cooled superconducting disk. The magnetic moment can be obtained when we give the field component perpendicular to the surface of a circular region which covers the whole sample. Our result is useful in discussion of the magnitude of magnetic moment and the appearance of the paramagnetic Meissner effect due to the flux compression.

Shell Model Calculation of Magnetic Moments of Mirror Nuclei (A = 8 − 13)

Corrections to the magnetic moment due to the particle-hole excitations between major shells are estimated for the five mirror pairs in p-shell nuclei (A = 8 − 13). The observed value of the isoscalar part in the (A = 9, T = 3/2) pair is larger than the theoretical value given by the shell model calculation within the p-shell model space. This problem is found to be quite difficult to solve with harmonic oscillator-type wave functions and the standard parameter set for the one-boson exchange potential.

Effective magnetic dipole operators for 88Sr\\ and 90Zr closed-shell cores

Core-polarisation and meson-exchange current calculations have been performed at 88Sr and 90Zr closed-shell cores to determine the effective magnetic dipole operator for valence orbitals. The values obtained show considerable core- and orbit-dependency. The results are tested in shell-model calculations for magnetic moments in N=50 and N=51 nuclides and the comparison with experiment is satisfactory.

The calculation of magnetic components and moments from TMI: A case study from the Tuckers igneous complex, Queensland

This paper re-examines some largely forgotten methods that are eminently adaptable to modern computing environments. The methods were originally formulated before the advent of electronic computers and do not appear to have been fully developed, or given the attention they deserve. It is apparent that if an anomaly is small with respect to the geomagnetic field, which is usual, components of the anomaly can be derived from total magnetic intensity observations, or indeed, from any other component irrespective of its direction. Furthermore, for an isolated anomaly, integrals of first order moments of the components yield information such as the direction and magnitude of the total anomalous magnetic moment of the source. Improvements to the calculation of components are proposed that, i) compensate for the finite nature of survey areas, and ii) correct for the departure from a true potential field of total magnetic intensity anomalies.Examples of the application of the methods are derived from a survey flown by Aerodata over the Tuckers Range area of north Queensland. This survey was chosen because the magnetic properties of the lithologies giving rise to the magnetic anomalies have been thoroughly studied. The selected areas include the north margin and an outlier, which contain many anomalies showing effects of magnetic remanence of reverse polarity. The results of the methods used herein agree well with those expected from the measured magnetic properties and magnetic modelling. The calculation of the total moment of the north margin yielded a declination of 35.8° and an inclination of 39.0°. A comparison with the measured properties shows that the reverse remanence of the overprint zone appears to account for about 70% of the total anomaly over the north margin. Similarly, the outlier yielded a declination of 13.7° and an inclination of 4.5°. Over the outlier the overprinted zone appears to account for about 50% of the magnetic anomaly. It seems that magnetic interpretation could be significantly enhanced by developing these methods to their full potential and incorporating them in commercial packages.

Decuplet baryon magnetic moments in the chiral quark model

We present calculations of the decuplet baryon magnetic moments in the chiral quark model. As input we use parameters obtained in qualitatively accurate fits to the octet baryon magnetic moments studied previously. The values found for the magnetic moments of $\Delta^{++}$ and $\Omega^{-}$ are in good agreement with experiments. We finally calculate the total quark spin polarizations of the decuplet baryons and find that they are considerably smaller than what is expected from the non-relativistic quark model.

Properties of Iron Atoms at Grain Boundaries in Fe and Fe72Al28

ABSTRACTLocation of diffused 57Co atoms in single crystals, bicrystals and polycrystals of pure iron and Fe72Al28alloy were investigated by means of emission Mössbauer spectroscopy. To interpret the results, first principles calculations of iron atom magnetic moments and hyper-fine field were carried out. From comparison of M6ssbauer spectra of single crystals with those of bicrystals and polycrystals, an information about grain boundary positions occupied by diffusing atoms is obtained. It is shown that about 5% of the diffusing atoms at the {112} grain boundary of iron are located at the positions either having impurity atoms in the nearest neighbourhood or characterized by larger atomic spacing in comparison with the bulk. In the Fe72Al28 a dominating portion of diffusing atoms have different surrounding than in grain volume. An enrichment of grain boundaries by aluminum could explain their hyperfine parameters.

Electronic structure and magnetic properties of hard/soft multilayers

Magnetic properties of FePt/Fe multilayers of alternating hard and soft magnetic regions are calculated using linear-muffin-tin-orbitals and Green function methods. The changes in the magnetic properties of hard and soft phases with their relative thicknesses are studied via self-consistent calculations of local magnetic moments, effective exchange interaction parameters and the anisotropy energy. The calculations show that this system is a promising permanent-magnet candidate with large-energy product, uniaxial anisotropy, and high Curie temperature.