Neutral ρ meson in a strong magnetic field in the SU(2) lattice gauge theory

The correlation functions of vector and pseudoscalar currents have been calculated in the external strong magnetic field in SU(2) lattice gluodynamics. The masses of the neutral ρ meson with different spin projections s = 0, ±1 to the axis parallel to the external magnetic field B have been calculated. The ρ meson mass with zero spin s = 0 decreases with the growth of the magnetic field and the ρ meson masses with s = ±1 increase with the magnetic field.     

Spin interactions in a quantum ring containing a magnetic impurity

The exciton states in a CdTe semiconductor quantum ring containing a single magnetic impurity are considered in an external magnetic field. The electron-hole spin interaction and s,p-d interactions between electron, hole and magnetic impurity are also taken into account in the calculations. It is shown that due to the s,p-d spin interactions the ground state exciton energy splits into 12 doubly degenerated energy levels. The external magnetic field removes this degeneracy. A novel method is proposed here to determine the values of the strengths of s,p-d interactions. The optical spectrum of the system for different polarizations of the incident light and for different initial states of the magnetic impurity spin projection is also studied.     

Features of the Zeeman splitting of levels of the 1snp configurations of helium

The Zeeman splitting of the fine-structure levels of the 1s2p and 1s4p configurations of neutral helium in a magnetic field is calculated. The strengths of fields of intersection of magnetic sublevels are determined, and the field regions are found in which a constant energy gap between some sublevels is observed. The results are compared with the experimental data available in the literature.     

Transport phenomena in a partially lonized Lorentzian magnetoplasma

Some transport coefficients are evaluated for a homogeneous, partially ionized Lorentzian plasma in the presence of a uniform external magnetic field. The electronion collisions are taken into account by means of the modified Fokker-Planck equation and the electron-neutral collision frequency, ν_en is taken as velocity (ω) dependent or velocity independent, depending on the energy range under consideration. The variation of the transport coefficients with magnetic field is determined for ν_en ∝ ω^s (s being a positive or negative integer) and one finds that qualitatively this behavior does not change by changing either the collision frequency or the velocity dependence of the collision frequency; however for weak magnetic fields the magnitudes of these transport coefficients increase with the decrease in ν_en or s, whereas for strong magnetic fields the transverse components of the transport coefficients decrease and the Hall components tend to saturate with the decrease of either the collision frequency or s.     

The dc magnetic field,temperature and film thickness dependence of microwave surface resistance of YBCO and DyBCO thin films

We investigated the dc magnetic field and temperature dependences of the microwave surface resistance (R_s) of YBa₂Cu₃O_y (YBCO) and DyBa₂Cu₃O_y (DyBCO) superconducting thin films. The YBCO and DyBCO thin films, each with a thickness of 300, 500, or 700 nm, were deposited on MgO (1 0 0) substrates by the thermal co-evaporation method. The R_s was measured using the dielectric resonator method. A dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the superconducting thin films. The results showed that the R_s value had almost the same temperature dependence at various thicknesses in a zero-external field. The R_s of the YBCO and DyBCO thin films increased with the applied dc magnetic field. The DyBCO thin films showed weaker magnetic field dependence of R_s than the YBCO thin films. The R_s ratio (defined as R_s(5 T)/R_s(0 T)) linearly increased with the film thickness. These results show that pinning strength decreased with an increasing film thickness.     

Surface impedance of a superconducting slab in the mixed state: Effect of the surface barrier

The effect of the surface barrier on the surface impedance Z of a type-II superconductor slab with a finite thickness is investigated in dc magnetic fields H ₀, which are aligned parallel or perpendicular to the slab plane. It is demonstrated that, in a perpendicular geometry, the surface resistivity ρ_s=ReZ has a maximum when the depth of penetration of the ac magnetic field is of the order of the slab thickness (size effect). For a parallel orientation of the magnetic field H ₀, the effect of the Bean-Livingston surface barrier manifests itself as a decrease in the dissipative loss and a change in the field dependence of the surface resistivity characterized by a magnetic hysteresis. It is shown for the first time that, under the conditions of persistent trapped magnetic flux, the dependence ρ_s(H ₀) is a decreasing function, which is associated, in particular, with a nontrivial suppression of the size effect.     

Magnetic field and external pressure effects on the spiral order of polycrystalline MnCr2O4

In this paper, the magnetic and specific heat properties of polycrystalline MnCr₂O₄ were investigated, mainly by focusing on the spiral order transition around T_s. With increasing magnetic field, the magnetic anomaly around T_s in the M–T curve is gradually suppressed. However, an external magnetic field up to 5 T has no evident influence on the spiral magnetic transition as revealed by specific heat measurements. Upon cooling below T_s, AC susceptibility displays no frequency dependence, but the coercivity increases abruptly. Applying external pressure increases the coercivity at 5 K, implying the strengthening of the spiral order. It is suggested that with decreasing temperature across T_s, the spiral component develops in the direction perpendicular to the easy axis of the parent collinear ferri-magnetic phase and does not contribute to the saturation magnetization.     

Measurements of Hk and Ms in thin magnetic films by the angular dependence of the planar Hall effect

It is shown that the angular dependences of the planar Hall effect measured with infinite magnetic field and with magnetic field H⩾H_k have an intersection point and this fact is enough for measuring the anisotropy field H_k applying the method presented by Pastor, Ferreiro and Torres in J. Magn. Magn. Mat. 53 (1986) 349, 62 (1986) 101. The scaling of the Hall tension U proportional to M²_s in mV/Am^-1 gives a possibility for calculating the M_s-values of the films. These assumptions are verified for NiFe- and NiFeGe films with a uniaxial magnetic anisotropy.     

Field dependent central cell correction in germanium in a magnetic field

We report calculations of the energies of 1s and 2s donor levels in Ge as functions of magnetic field. The Ge 1s and 2s donor eigenstates in fields along the (111) and (100) directions were studied in the effective mass approximation by using variational wave functions. We have made none of the artificial assumptions invoked by previous authors for simplifyingsuch effective mass calculations. To account for the central cell shifts of these levels we generalize to the case of donors in Ge, in a model which has been very successful in predicting the magnetic field dependence of donor central cell corrections in GaAs. Our results cast some doubt on certain recent transition assignments of Gershenzon and Gol'tsman.     

On the rotational symmetry of the spin-spin correlation function of the two-dimensional Ising model

The spin-spin correlation function 〈s_oos_mn〉 of the two-dimensional Ising model is derived in the absence of a magnetic field. It is proved rigorously that this correlation function becomes rotationally symmetric near the critical point.     

Effect of magnetic field on the TC and magnetic properties for the aligned MnBi compound

In the compound MnBi, a first-order transition from the paramagnetic to the ferromagnetic state can be triggered by an applied magnetic field and the Curie temperature increases nearly linearly with an increase in magnetic field by ∼2 K/T. Under a field of 10 T, T_C increases by 20 and 22 K during heating and cooling, respectively. Under certain conditions a reversible magnetic field or temperature induced transition between the paramagnetic and ferromagnetic states can occur. A magnetic and crystallographic H-T phase diagram for MnBi is given. Magnetic properties of MnBi compound aligned in a Bi matrix have been investigated. In the low temperature phase MnBi, a spin-reorientation takes place during which the magnetic moments rotate from being parallel to the c-axis towards the basal plane at ∼90 K. A measuring Dc magnetic field applied parallel to the c-axis of MnBi suppresses partly the spin-reorientation transition. Interestingly, the fabricated magnetic field increases the temperature of spin-reorientation transition T_s and the change in magnetization for MnBi. For the sample solidified under 0.5 T, the change in magnetization is ∼70% and T_s is ∼91 K.     

High magnetic field studies of donor excitation spectra in InSb

The two lowest energy spectral lines of the shallow donors in InSb involving ground to excited state transitions are studied in photoconductivity using higher spectral resolution and stronger magnetic fields than achieved previously. The observed line positions are compared with recent calculations of the high field hydrogenic donor levels and difference of the order of the effective Rydberg R¹ at zero field are found at magnetic fields where the zero point cyclotron energy exceeds R¹ by two orders of magnitude. Central-cell components of the 1s–2p transition, corresponding to four donor species are resolved, and the magnetic field dependence of the relative chemical shifts are analysed. The broader 1s–2p₀ line undergoes a coupling at an interaction energy of 37 cm^-1, the origin of which is uncertain at present.     

Anisotropic contribution of magnetostriction to the elastic compliance constants in hexagonal materials: The Δs-effect

In this paper, we consider the single crystal analogue of the ΔE-effect in hexagonal materials with uniaxial magnetic anisotropy. We define Δs_ijld as the fractional change in the elastic compliance tensor s_ijkl in the demagnetized state relative to its value in the saturated state. The Δs-effect depends in general on the direction of the applied stress and the resulting magnetostrictive strain. We can show, however, that Δs_ijkl is always nonnegative when i=k and j=l. We then consider the measurements of the elastic constants in magnetic materials which have large magnetocrystalline anisotropy. The stresses applied in these measurements are not sufficient to rotate the magnetization away from the magnetically preferred direction, and hence cause no magnetostriction, and no Δs-effect. Therefore, it is not necessary to apply a saturating magnetic field along the easy axis in order to measure the true elastic constants in these materials.     

Microwave absorption in high-T c superconductors at high magnetic fields

In the mixed state of superconductors (H _c1?H?H _c2) the penetration of microwaves is governed by both, complex conductivity σ(T) and driven oscillation of vortices. In this paper, we show that an effective microwave conductivity can be derived and used to fit the field dependences of the surface resistanceR _s. The fit parameter is the upper critical field. Measurements on single crystals YBa₂Cu₃O_7-δ were made in magnetic fields (H∥c) up to 2.25 T, and in the temperature range from 70–100 K. The critical temperature for mean field superconductivity appears to be 89.3 K, while the apparent onset in the curve ofR _s(T) appears at about 92 K. The magnetic dependences ofR _s clearly demonstrate that one can separate the regions of mean field superconductivity from the region of fluctuations.     

The instability point H s of the Meissner state for large-κ superconductors

The critical field H _s corresponding to the emergence of vortices in a superconductor without a threshold is found near the transition temperature and in the limit as T→0 for an arbitrary value of the depairing factor Γ. In superconductors of the second kind, this field value coincides with the absolute instability point of the Meissner state. In large-κ superconductors, the order parameter tends to zero on the surface of the super-conductor if the external magnetic field reaches the value H _s. We obtain that H _s=H _cm (where H _cm is the thermodynamic critical field) for an arbitrary value of the depairing factor Γin the temperature region near T _c and at T=0.     

A buoyant flow structure in a magnetic field: Quasi-steady states and linear-nonlinear transitions

The confined evolution of a buoyant blob of fluid subject to a vertical magnetic field is investigated in the limit of low magnetic Reynolds number. When the applied magnetic field is strong, the rise velocity of the blob is small. As the vorticity diffuses along the magnetic field lines, a quasi-steady state characterised by a balance between the work done by buoyancy and Ohmic dissipation is eventually reached at time tqs∼(L²/δ²)τ, where L is the axial dimension of the fluid domain, δ is the radius of the buoyant blob and τ is the magnetic damping time. However, when the applied magnetic field is weak or the axial length is sufficiently large compared to the blob size, the growth of axial velocity eventually makes the advection of vorticity significant. The typical time for the attainment of this nonlinear phase is , where N₀ is the magnetic interaction parameter at time t=τ. The order-of-magnitude estimates for the timescales tqs and tnl are verified by computational experiments that capture both the linear and nonlinear phases.     

Flow-induced soliton lattice in superfluid 3He-A

It is shown that in the presence of superflow, υ_s, parallel to a strong magnetic field H (|H| ? 20 Oe), the uniform texture becomes unstable againts the formation of a one dimensional soliton lattice forυ_s ? υ_c2 (≈1 mm/s). The period of the resulting soliton lattice as well as the related NMR frequencies are determined as functions of υ_s.     

Magnetic surface reconstruction in thin film: Possibilities of production and exploitation

Various theoretical techniques are considered for the production of magnetic surface reconstruction (MSR) in ferromagnetic thin films. The problem is discussed within the framework of the surface field model assuming the existence of a unidirectional anisotropy on the surface described by an effective field K_s It is shown that knowledge of the conditions for the occurrence of MSR together with complementary information accessible from critical spin wave resonance permits the complete determination of the properties of the field K_s.     

Cascade-fluorescence spectroscopy on impact-excited He-atoms using level-crossing techniques

He atoms have been excited by 35 keV-Ne⁺ ions, and magnetic depolarization signals of the induced fluorescent light at 667.8nm (1s3d ¹ D-1s 2p ¹ P) have been investigated. By applying suitable electric fields in addition to the variable magnetic field, the complicated superposition structure of the depolarization signal resulting from cascade processes could be analyzed. Beside direct excitation of 1s 3d ¹ D (53%), cascade excitation through 1s4f (26%), 1s 5g (12%), and 1s5f-levels (6%) contributes significantly to the magnetic depolarization signal. From the signal widths the radiative lifetimes of the 1s4f-levels and 1s5g-levels have been deduced: τ(1s4f)=(74±3)ns, τ(1s5g)=(230±20)ns.     

Magnetic circular dichroism of the U center in KCl

The magnetic circular dichroism (MCD) and absorption spectrum of the U center in KCl have been measured at liquid helium temperature. The results are consistent with the usual ¹S(l s²) → ¹P(ls2p) assignment with the temperature independent MCD yielding an excited state magnetic moment only about 40 per cent that calculated for a hydride ion in an octahedral crystal field.