On the possible magnetic field dependence of the nickel carbonylation rate

The interaction of Ni with CO gas to produce Ni(CO)₄ at 1 atm pressure, has been studied as a function of time, temperature (25 < T < 95°C) and externally applied magnetic field (H ? 500 Oe). We find no significant magnetic field dependence of the nickel carbonylation rate, in sharp contrast with results previously reported by Krinchik et al. The activation energy for this reaction is found to be 0.21 ± 0.05 eV independent of magnetic field.     

Electric field dependence of the direct recombination rate in InSb

Using the approximation of drifted Maxwellians an analytic expression is derived for the electric field dependence of the direct recombination rate.     

Radio frequency magnetic field effects on electron-hole recombination

We present measurements of the spectrum (1--80 MHz) of the effect of a weak (approximately 500 microT) radio frequency magnetic field on the electron-hole recombination of radical ion pairs in solution. Distinct spectra are observed for the pyrene anion/dimethylaniline cation radical pair in which one or both of the radicals are perdeuterated. The radical pair mechanism is developed theoretically and shown to account satisfactorily for both the magnetic field effect and the associated magnetic isotope effect.     

The magnetic field dependence of the breathing artifact

Breathing causes ghost artifacts in magnetic resonance (MR) images. These ghosts are more conspicuous at high magnetic field strength due to (i) operational factors that affect the relative intensity of the individual ghosts and (ii) factors that affect the image intensity of the moving structures producing the ghosts. Both types of factors are identified and illustrated with images of a human subject. A brief theoretical analysis of the noiseless MR image of a point object in sinusoidal motion shows that the intensity structure of each ghost depends on the number of pixels over which the object moves. Generally, images with narrower pixels have ghosts with greater relative intensity. However, the breathing artifact is more apparent at high magnetic field strength primarily because the signal-to-noise ratio and the cotnrast between fat and muscle tissues are increased.     

The magnetic field dependence of the magnetisation of nickel

The magnetisation of a single crystal has been measured parallel to the easy direction as a function of field within the temperature range 4.2 to 300 K. The results are analysed in terms of spin-wave and single particle excitations and reveal an additional excitation of unknown origin.     

Temperature dependence of indirect-exciton luminescence in in-plane magnetic field

We report on a magneto-luminescence on a double quantum well subject to an in-plane magnetic field. The attention is paid to the properties of interwell excitons, which are indirect in the real space and which become indirect in the reciprocal space as well when a finite in-plane magnetic field is applied. Such indirect exciton states become optically inactive unless some relaxation mechanisms of their momentum appear. The experiment is carried out on a sample where, as reported previously, the radiative recombination of indirect excitons is possible due to their localization or via collisions with structural defects. The experimental data presented here, measured at various temperatures, favour the latter mechanism which is less sensitive to the system temperature in comparison with the former one.     

Enhancement of low energy electron-ion recombination in a magnetic field: influence of transient field effects

Electron-ion recombination observed in storage ring experiments shows a strong enhancement relative to what standard radiative recombination rates predict. We simulate the effect of a transient motional electric field induced by the merging of an electron and an ion beam in the electron cooler which opens an additional pathway for free-bound transitions of electrons. We show that the measured rate contains a significant contribution from radiative stabilization of Rydberg states formed by this transient motional electric field. The absolute excess recombination rates obtained are in good agreement with the experimental data. The scaling of the rate with the ion charge and the magnetic guiding field is analyzed.     

The velocity andZ dependence of the transient magnetic field in iron

The velocity dependence of the transient magnetic field in iron has been investigated for¹³⁴Ba at four initial velocities betweenv _i=0.8v ₀ andv _i=3.6v ₀ (v ₀=c/137). The present work confirms the linearv-dependence found for light ions (Z34). Existing data on transient fields were reanalyzed assuming a general validity of the linearv-dependence. The extractedZ-dependence shows a smooth, almost linearZ-dependence for ions withZ12. From the present work, with the calibration of the transient field from systematics, theg-factor of the first excited 2⁺ state in¹³⁴Ba is determined to beg=0.41(6).     

Analysis of the magnetic field dependence of the nuclear magnetic relaxation times in solid He

We have analyzed the field dependence of the magnetic relaxation time T₁ in solid He³ and find that the experimental data are in good agreement with the theory of Blume and Hubbard for the time dependence of the spin correlation function.     

Size effect in the magnetic field dependence of nonequilibrium electron tunneling

The electron bottleneck in normal metal-insulator-metal tunnel junctions due to nonequilibrium effects has been investigated in the presence of a magnetic field. The observed results are due to a new geometrical size effect and are explained in an extension of our nonequilibrium theory.     

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB

The structural and magnetic properties of as-grown 5–50 nm thin ion-beam sputter deposited transition metal–metalloid Co₂₀Fe₆₀B₂₀ (CFB) films are reported in this communication. A broad peak observed at 2θ∼45° in the glancing angle X-ray diffraction pattern revealed the formation of very fine nano-sized grains embedded in majority amorphous CFB matrix. Although no magnetic field is applied during deposition, the longitudinal magneto-optic Kerr effect measurements performed at 300 K in these as-grown films clearly established the presence of in-plane uniaxial magnetic anisotropy (K_u). It is argued that this observed anisotropy is strain-induced. This is supported by the observed dependence of direction of K_u on the angle between applied magnetic field and crystallographic orientation of the underlying Si(100) substrate, and increase in the coercivity with the increase of the film thickness.     

On possible light–torsion mixing in background magnetic field

The interaction of the light with propagating axial torsion fields in the presence of an external magnetic field has been investigated. Axial torsion fields appearing in higher derivative quantum gravity possess two states, with spin one and zero, with different masses. The torsion field with spin-0 state is a ghost that can be removed if its mass is infinite. We investigate the possibility when the light mixes with the torsion fields resulting in the effect of vacuum birefringence and dichroism. The expressions for ellipticity and the rotation of light polarization axis depending on the coupling constant and the external magnetic field have been obtained.     

Temperature and magnetic field dependence of superconductivity in nanoscopic metallic grains

We study pairing correlations in ultrasmall superconductor in the nanoscopic limit by means of a toy model where electrons are confined in a single, multiply degenerate energy level. We solve the model exactly to investigate the temperature and magnetic field dependence of number parity effect (dependence of ground state energy on evenness or oddness of the number of electrons). We find a different parity effect parameter to critical temperature ratio (4 rather than 3.5) which turns out to be consistent with exact solution of the BCS gap equation for our model. This suggests the equivalence between the parity effect parameter and the superconducting gap. We also find that magnetic field is suppressed as temperature increases.     

New magnetic field dependence of Landau levels in a graphenelike structure

We consider a tight-binding model on the honeycomb lattice in a magnetic field. For special values of the hopping integrals, the dispersion relation is linear in one direction and quadratic in the other. We find that, in this case, the energy of the Landau levels varies with the field B as epsilon(n)(B) ~ [(n+gamma)B](2/3). This result is obtained from the low-field study of the tight-binding spectrum on the honeycomb lattice in a magnetic field (Hofstadter spectrum) as well as from a calculation in the continuum approximation at low field. The latter links the new spectrum to the one of a modified quartic oscillator. The obtained value gamma=1/2 is found to result from the cancellation of a Berry phase.     

Hard axis magnetic field dependence on current-induced magnetization switching in MgO-based magnetic tunnel junctions

We conducted a detailed study of hard axis magnetic field (H_hard) dependence on current-induced magnetization switching (CIMS) in MgO-based magnetic tunnel junctions (MTJs) with various junction sizes and various uniaxial anisotropy fields. The decreases in critical current density (J_c) and the intrinsic critical current density (J_c0) estimated from the pulse duration dependence on J_c in CIMS are observed when applying H_hard for all MTJs. The decrease in energy barrier of CIMS is also observed except for the largest sample. These results indicate that the reduction of J_c is attributable to both the increase of spin-transfer efficiency and the decrease in energy barrier in the case of applying H_hard. The J_c0 decreases with increase in the mutual angle between the direction of magnetization and the easy axis (θ_f), which is consistent with the theoretical prediction proposed by Slonczewski. The degree of the reduction of J_c0 for the same value of H_hard decreases with decreasing size of MTJs. This behavior is considered to be related to not only decrease in θ_f due to the increase in anisotropy field in MTJs, but also to the increase in the variance of the initial angle of magnetization due to the thermally activated magnon excitation. The stable switching endurance related to CIMS was observed in a wide range of MTJ sizes when applying H_hard. Moreover, we proposed a new architecture and a new switching method considering write disturbance. These results would be useful for application to spin memory and other spin-electronic devices.     

Nonlinear field dependence of the Faraday effect in neodymium gallium garnet under high magnetic field

In this paper, we present a theoretical investigation on the Faraday effect in paramagnetic neodymium gallium garnet (Nd₃Ga₅O₁₂) by taking account of the SO and CF interactions, the superexchange interaction and the external magnetic field. It is demonstrated that under high magnetic field, the Faraday rotation (θ) is strongly nonlinear with the external magnetic field (H_e) while the coefficients of deeply dependent on the frequency of the incident light and temperature, and the Verdet constant V(θ/H_e) is also a function of H_e. Furthermore, theoretical calculations show that the reciprocity of the Faraday effect cannot be neglected under high magnetic field. The theoretical results are in good agreement with the experimental data.