Current sheets in the Earth’s magnetosphere and in laboratory experiments: The magnetic field structure and the Hall effect

The main characteristics of current sheets (CSs) formed in laboratory experiments are compared with the results of satellite observations of CSs in the Earth’s magnetotail. We show that many significant features of the magnetic field structure and the distributions of plasma parameters in laboratory and magnetospheric CSs exhibit a qualitative similarity, despite the enormous differences of scales, absolute values of plasma parameters, magnetic fields, and currents. In addition to a qualitative comparison, we give a number of dimensionless parameters that demonstrate the possibility of laboratory modeling of the processes occurring in the magnetosphere.     

Effect of a longitudinal strong magnetic field on the polarization characteristics of H α emission

The effect of the magnetic field whose direction is parallel to the direction of the collision-induced alignment on the polarization characteristics of emission of ensembles of excited particles is considered. Concrete calculations were performed for the emission corresponding to the transitions between the levels of the fine structure of the states of atomic hydrogen with n=3 and n=2.     

On the way to ‘optical doping’ of electronically low-dimensional polymer systems with strong charge and spin correlations

We discuss the concept of optical manipulation of the charge and spin density in polymer systems with strong-correlation phenomena by attaching pendant chromophores to the polymer backbone. In the process of identifying suitable functional groups for future inclusion in polymers, we study here boron–nitrogen-linked ferrocene derivatives. We investigate the metal-to-ligand charge transfer between a ferrocene donor and -acceptor units across the B–N bridges. On the basis of photophysical measurements, including picosecond time-resolved spectroscopy, we identify that the initial relaxation of the excited states depends critically on the degree of structural rigidity, and can be tuned by more than an order of magnitude (20–800 ps). PACS 42.70.Jk; 75.50.-Xx; 78.47.+p; 82.53.Hn     

Change in the microhardness of nonmagnetic crystals after their exposure to the Earth’s magnetic field and AC pump field in the EPR scheme

Changes in the microhardness of ZnO, triglycine sulfate (TGS), and potassium acid phthalate (KAP) crystals after their exposure to crossed ultralow magnetic fields, i.e., the Earth’s field B _Earth ≈ 50 μT and the alternating-current field \(\tilde B \approx 3 \mu {\rm T}\) orthogonal to it, have been revealed. In ZnO crystals, the microhardness increases, whereas in TGS and KAP, it decreases. A maximum change (10–15%) is reached within 1–3 h after magnetic treatment; then, the microhardness gradually recovers to its initial value for the first day. After a sufficient pause, the effect is completely reproduced under the same conditions. The resonant frequency of the pump field \(\tilde B\) corresponds to the EPR condition with a g-factor close to two. The magnetic memory exhibits a strong anisotropy: for each of the crystals, a direction is found, which, being coincident with the Earth’s magnetic field vector B _Earth, causes complete or partial suppression of the effect. In ZnO and TGS crystals, these are symmetry axes 6 and 2, respectively. In the KAP crystal, it is the direction in the cleavage plane orthogonal the 2 axis. Possible physical mechanisms of the observed phenomena have been discussed.     

Induced fractional zero-point angular momentum for charged particles of the Bohm–Aharonov system by means of a “spectator” magnetic field

An induced fractional zero-point angular momentum of charged particles by the Bohm–Aharonov (BA) vector potential is realized via a modified combined trap. It explores a “spectator” mechanism in this type of quantum effects: In the limit of the kinetic energy approaching one of its eigenvalues the BA vector potential alone cannot induce a fractional zero-point angular momentum at quantum mechanical level in the BA magnetic field-free region; But when there is a “spectator” magnetic field the BA vector potential induces a fractional zero-point angular momentum. The “spectator” does not contribute to such a fractional angular momentum, but plays essential role in guaranteeing non-trivial dynamics at quantum mechanical level in the required limit. This “spectator” mechanism is significant in investigating the BA effects and related topics in both aspects of theory and experiment.     

Distortions of magnetic order parameters due to “charged” edges of atomic steps at the ferromagnet—antiferromagnet interface

Distortions of the magnetic order parameters due to the presence of uncompensated antiferromagnetic spins near the edges of atomic steps at the interface between the ferromagnetic film and the antiferromagnetic substrate with compensated atomic planes parallel to the interface have been studied. It has been demonstrated that such “charged” linear defects do not give rise to domains in the film or substrate, as was suggested in some models of the exchange bias. The cases of large and small strengths of random fields arising due to the presence of uncompensated spins near the step edges have been investigated.     

Dipolar magnetic field and fermi contact field at the μ+ site in α-Fe at very low temperatures

In a longitudinal ⁺SR experiment on a high-purity-Fe single crystal sphere magnetically saturated in a 111 direction damped oscillations (wiggles) were observed in a temperature range 30 mK to 600 mK and in a certain regime of applied magnetic fieldsB _appl. Meassurements of the wiggle frequency as a function ofB _appl give us directly the Fermi fieldB _Fermi=(–1.13±0.02)T and the dipolar magnetic field ¦B _dip ¦=(0.66±0.03)T.B _dip was used to determine the prefactor in the Arrhenius law obeyed by the ⁺ hopping rate between 100 K and 1000 K. A comparision with the corresponding values for protons and deuterons suggests diffusion via the adiabatic mechanism.     

Quantum model of the magnetic dynamics of single-domain particles for describing their magnetization curves and Mössbauer spectra in a weak magnetic field

A universal approach to describing the equilibrium magnetization curves and relaxation Mössbauer spectra of magnetic nanoparticles is proposed for consistent analysis of magnetometry and gamma-resonance experimental data, based solving a quantum-mechanical problem for a particle with spin S that has intrinsic magnetic anisotropy and is positioned in an external magnetic field.     

Centrality dependences of the pseudorapidity distributions of charged particles in Au+Au collisions at RHIC energies

By employing the Glauber model, we give the centrality dependences of the numbers of participants and binary nucleon-nucleon collisions in nucleus-nucleus collisions. By taking into account the energy loss of the participants in their multiple collisions, we then present the pseudorapidity distributions of charged particles in nucleus-nucleus collisions as a function of beam energy and impact parameter. Finally, we analyze the centrality dependence of the pseudorapidity of the charged particles in Au＋Au collisions at energies from √SNN=19.6 to 200 GeV. The theoretical results are in good agreement with the experimental observations of the RHIC-PHOBOS collaboration.     

Search for heavy charged particles and for particles with anomalous charge in e+e? collisions at LEP

Using the OPAL data accumulated in 1991–1993 amounting to 74 pb^–1 of integrated luminosity, corresponding to 1.64×10⁶ selected multi-hadronic events, a search has been performed for charged particles with unusual mass or unusual charge. The mass was determined from a combination of momentum and ionization energy loss measurements. No isolation criteria were applied to the tracks examined, so that both isolated particles and particles produced in jets were valid candidates. For particles with chargeQ/e=–1, one candidate with a mass of approximately 4.2 GeV/c² was found, which is compatible with the background rate expected according to a Monte Carlo simulation. The implications of this search for the mass limits of a conjectured stable or quasi-stable charged gluino composite are discussed. Limits are also presented for the production of fractionally-charged particles withQ/e=±2/3 and ±4/3 as well as for particles withQ/e=±2.     

Influence of the static high magnetic field on the liquid–liquid phase separation during solidifying the hyper-monotectic alloys

Magnetic in-situ quenching refers to fixing and quenching the sample at a static high magnetic field (SHMF) up to 18 T; it has been achieved by a specially designed facility. Zn-7wt%Bi and Zn-10wt%Bi hyper-monotectic melts were quenched under different magnetic flux densities to investigate the influence of SHMF on the liquid–liquid phase separation process in solidifying hyper-monotectic alloys. Because this separation is mainly caused by the growth of minority phase droplets (Bi droplets in the present study), and such growth is attributed to the diffusion of Bi element and the coalescence between the droplets, the influence of SHMF on the growth of Bi droplets was analyzed. Results show that the imposed SHMF prevented the formation of layered structure in the Zn-10wt%Bi alloy and refined the Bi particles in the Zn-7wt%Bi alloy, which indicates that the SHMF retarded the liquid–liquid phase separation during solidifying the hyper-monotectic alloys. Indeed, the two motions of droplets in determining the coalescence, Marangoni migration and Stocks sedimentation, were slowed down by the applied SHMF. Analytical estimations of the magnitude of such damping effect have been made and show that the 18 T SHMF could reduce the speed of Stokes sedimentation and Marangoni migration of the minority phase droplets by about 95.5 % and 62.4 %, respectively.     

Lowering of magnetic field intensity at the surfaces of α-Fe2O3 and FeBO3 single crystals

Depth-selective conversion electron Mössbauer spectroscopy was used to study magnetic properties of the thin surface layers of the α-Fe₂O₃ and FeBO₃ single crystals. An analysis of the experimental spectra indicates that the magnetic properties of the layers at a depth of more than ～100 nm from the surface are similar to the properties of crystal bulk, and the corresponding spectra consist of narrow lines. The lines gradually broaden as the crystal surface is approached. The spectra of the ～10-nm-thick surface layers consist of broad lines, indicating a wide distribution δ=2.1 T of the effective magnetic field about its mean value of 32.2(4) T. The experimental spectra were used to determine the effective magnetic fields (H _eff) for the iron ions situated in the surface layers of thickness ～100 nm. The effective fields in these layers were found to gradually decrease at room temperature (291 K) as the crystal surface was approached. The H _eff values in the 2.4(9)-nm-thick surface layer of the α-Fe₂O₃ crystal and 4.9(9)-nm layer of FeBO₃ are 0.7(2) and 1.2(3)%, respectively, smaller than for the nuclei of the ions in the bulk of these crystals.     

Anisotropic resonant magnetoplasticity of NaCl crystals in the Earth’s magnetic field

Resonant relaxation of the dislocation structure under the action of crossed magnetic fields, i.e., constant magnetic field of the Earth (B _Earth) and alternating radio-frequency field ( $\tilde B$ ), has been experimentally studied in a series of dielectric (NaCl) crystals with various compositions of impurities under variations in the frequency, direction of the pumping field $\tilde B$ , and orientation of the samples in the Earth’s magnetic field. The frequency dependence of the dislocation path length l(ν) exhibits peaks with various heights (l _max) and resonant frequencies (ν_res). The maximum resonant effect has been observed for dislocations with the direction L orthogonal to the plane of crossed magnetic fields in a configuration of mutually perpendicular vectors {L, $\tilde B$ , B _Earth} belonging, together with sample edges {a, b, c}, to the 〈100〉 system. Variation of the concentration C of calcium impurity in crystals of the NaCl_Ca series only influenced the resonant peak height as $l_{\max } \propto 1/\sqrt C $ . Rotation of the magnetic field $\tilde B$ in the (b, c) plane from direction $\tilde B$ ⊥ B _Earth to $\tilde B$ ∥ B _Earth also did not influence the frequency of the resonance but changed its amplitude. Depending on the crystal type, this influence changed from rather insignificant (in crystals of the NaCl_LOMO series) to complete suppression of the effect for $\tilde B$ ∥ B _Earth (in the NaCl_Nik series). The resonant frequency ν_res is sensitive to orientation of the sample with respect to B _Earth. Upon rotation of the crystal by the angle θ = ∠(c, B _Earth) about the a ⊥ B _Earth edge, the initial peak for dislocations L ‖ a at the crystal orientation θ = 0 and the frequency ν _res ⁰ is replaced by a pair of peaks at frequencies ν_{1, 2} ≈ ν _res ⁰ cosθ_{1, 2}, where θ₁ = 90° ? θ and θ₂ = θ. Previously, these peaks were observed separately in NaCl_Nik crystals for $\tilde B$ ∥ c and $\tilde B$ ∥ b. In the present study, these peaks have been observed simultaneously for both orientations of $\tilde B$ in NaCl_LOMO and NaCl_Ca crystals, where the resonance is not completely suppressed for $\tilde B$ ∥ B _Earth.     

Study of the stability of charged particle dynamics in a Penning–Malmberg–Surko trap with a rotating field

The solutions of equations characterizing the dynamics of charged particles in electromagnetic Penning–Malmberg traps with a rotating transverse electric field are presented and analyzed. The equations of motion are transformed in a way that makes it possible to distinguish between the motions of magnetron and cyclotron particles, reduce the system of equations to a stationary one, and conclude that asymptotically Lyapunov stable solutions of these equations are lacking in a certain parameter interval. This allows one to optimize the confinement of charged particles in such traps.     

Measurement of the yields of positively charged particles at an angle of 35° in proton interactions with nuclear targets at an energy of 50 GeV

Momentum spectra of cumulative particles in the region of high transverse momenta (P _T ) in pA → h ⁺ + X reactions were obtained for the first time. The experiment in which this was done was performed at the SPIN setup (Institute for High Energy Physics, Protvino) in a beam of 50-GeV protons interacting with C, Al, Cu, and W nuclei. Positively charged particles were detected at a laboratory angle of 35° and in the transverse-momentum range between 0.6 and 3.7 GeV/c. A strong dependence of the particle-production cross section on the atomic number was observed. A comparison with the results of calculations based on the HIJING and UrQMD models was performed in the subcumulative region.     

Evolution of magnetic domain structure of martensite in Ni–Mn–Ga films under the interplay of the temperature and magnetic field

Ferromagnetic shape memory Ni-Mn-Ga films with 7M modulated structure were prepared on MgO （001） substrates by magnetron sputtering. Magnetization process with a typical two-hysteresis loop indicates the occurrence of the reversible magnetic field-induced reorientation. Magnetic domain structure and twin structure of the film were controlled by the in- terplay of the magnetic and temperature field. With cooling under an out-of-plane magnetic field, the evolution of magnetic domain structure reveals that martensitic transformation could be divided into two periods： nucleation and growth. With an in-plane magnetic field applied to a thermomagnetic-treated film, the evolution of magnetic domain structure gives evidence of a reorientation of twin variants of martensite. A microstructural model is described to define the twin structure and to produce the magnetic domain structure at the beginning of martensitic transformation; based on this model, the relationship between the twin structure and the magnetic domain structure for the treated film under an in-plane field is also described.     

Application of Blanc’s law at arbitrary electric field to gas density ratios

Application of Blancs law for drift velocities of electrons and ions in gas mixtures at arbitrary reduced electric field strengths E/n₀ was studied theoretically and by numerical examples. Corrections for Blancs law that include effects of inelastic collisions were derived. In addition we have derived the common mean energy procedure that was proposed by Chiflikyan in a general case both for ions and electrons. Both corrected common E/n₀ and common mean energy procedures provide excellent results even for electrons at moderate E/n₀ where application of Blancs law was regarded as impossible. In mixtures of two gases that have negative differential conductivity (NDC) even when neither of the two pure gases show NDC the Blancs law procedure was able to give excellent predictions.     

Influence of static magnetic field intensity on the separation and migration of Fe-rich bulks in an immiscible (Fe–C)–Cu alloy

In this study, we solidified an immiscible pseudo-binary (Fe–C)–50mass%Cu alloy in a static magnetic field and observed macro morphologies as a function of the magnetic flux density. The experimental result shows that the Fe-rich phase exhibits a single bulk when the alloy is solidified at a low magnetic flux density, while it is separated in to two smaller bulks at high magnetic flux densities and the distance between the bulks becomes larger with the increase of the magnetic flux density. The possible reason for the separation of the Fe-rich phase was simply proposed. As far as the migration of separated Fe-rich phase bulks is concerned, the thermoelectric effect between the Fe-rich and Cu-rich metals was considered, from which the thermoelectric body force could be exerted upon the Fe-rich droplets. The higher the body force is produced, the larger the distance will be covered due to the migration of the droplets. Further analysis reveals that the convection attributed to the thermoelectric effect may contribute to the migration of the Fe-rich droplets at a low magnetic field and become negligible at high magnetic flux densities.