Linear magnetic birefringence in the quadratic-layer antiferromagnet K2MnF4

The linear optical birefringence of the quasi-Heisenberg antiferromagnet K₂MnF₄ has been determined between 5 and 300 K. A large magnetic contribution (LMB) is found at temperatures below 200 K. According to the earlier results with the iron-group difluorides the LMB can be related to the magnetic internal energy. Below 30 K the LMB of K₂MnF₄ obeys a T³-law. The temperature derivative of the LMB follows a course expected for the magnetic heat capacity of pronounced two-dimensional systems: a broad, rounded maximum above the three -dimensional transition point. At T_N a kink occurs in the LMB.     

Phenomenological analysis of the linear magnetic birefringence in dysprosium iron garnet

Experimental data on linear magnetic birefringence (LMB), previously reported at 1.15 μm wavelength in the 4.2-300 K temperature range and with an applied field up to 20 kOe, in dysprosium iron garnet (DyIG) are analyzed in terms of electric dipole transition within the three magnetic sublattices. Assuming that the garnet symmetry is cubic and that the contribution of the Fe³⁺ ions to LMB is the same as yttrium iron garnet (YIG), the 2nd order magneto-optical (MO) coefficient (Γ₂) of the Dy³⁺ ions is deduced. In the spontaneous state, Γ₂ is linear temperature dependent as previously found for the 1st order (MO) coefficient. It is shown that Γ₂ must be field dependent to explain the evolution of the LMB.     

Special features of linear magnetic birefringence in an α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>:Ga single crystal

Experimental investigations of the field dependence of the linear magnetic birefringence (LMB) in an α-Fe₂O₃:Ga single crystal are presented. It is established that during crystal magnetization in the basal plane near directions perpendicular to the С₂ axes in the region of magnetic field saturation, the LMB changes nonmonotonically. The observed special feature of the field LMB dependence is due to the reorganization of the magnetic α-Fe₂O₃:Ga structure during magnetization.     

Discrete binning: correspondence limit consistent analysis of classical probabilities using faux angular momenta and multi-polar harmonic moments to give ‘quantum-like’ probabilities

This paper develops discrete binning (DB) for N_i slices for classical probability functions for an arbitrary number of classical continuous variables, x_i , where 0 ≤?x_i ≤?1 or ?1 ≤?x_i ≤?1. Faux angular momenta, j_i , are introduced where 2j_i +?1 =?N_i , and the discrete probabilities for the various |j_im_i ? are calculated with a generalisation of the theory of Anderson and Aquilanti. Discrete probabilities are calculated from Legendre moments of the classical intensities with Clebsch–Gordan moments. The m_i may represent vibrational quanta, rotational angular momenta, or discrete values of the impact parameter, scattering angles and other variables. DB directly yields probabilities for different m_i , but in the correspondence limit (large j_i ) the discrete probabilities correspond to classical probabilities, I({x _{m i} }), at known discrete values {x _{m i} }. DB probabilities sum to unity, but some may be negative. Since the Clebsch–Gordan coefficients appropriate for this work are actually Gram (discrete Chebyshev) polynomials, DB is equivalent to compression and/or smoothing of data using Gram polynomials. For large N_i , DB and histogram binning (HB) provide equivalent probabilities and statistical errors. However, smoothing can often reduce the statistical errors for DB probabilities. DB is related to Legendre moment binning (LMB), but DB guides the most consistent implementation of LMB. The rule of three is introduced to provide finer resolution for DB, HB, and LMB analysis. This also leads to fractional slice binning (FSB), which is equivalent to Gaussian binning. The paper presents one-, two-, and three-dimensional examples, and spectroscopic plots are very useful for summarising the results.     

A contribution to the temperature dependence of the tunnel current of metal-dielectric-metal structures

Assuming the tunnel transfer of electrons, a general formula is derived for the current flowing between the metal electrodes of a metal-dielectric-metal structure. The formula is numerically solved for a rectangular barrier without image forces at absolute zero and several higher values of temperature. Though the temperature dependence of the tunnel current is very weak, it is possible to use it for determining the dielectric parameters. The metal-dielectric work function can be found from the maximum of the curvej _T /j ₀ vs.V, the thickness of the dielectric layer from the value ofj _T /j ₀ at zero voltage.     

Thermoluminescence properties of rare earth doped lithium magnesium borate phosphors

This paper reports the thermoluminescence (TL) properties of rare earth doped lithium magnesium borate (LMB) polycrystalline phosphor. LMB phosphor has been prepared by high temperature solid state diffusion method. Among all the rare earth doped LMB phosphors, terbium doped material has shown maximum TL sensitivity with a broad dosimetric glow peak at 240 °C. near the tissue equivalent TL phosphor with terbium dopant has about four times the TL sensitivity of TLD-100. The main dosimetric properties such as glow curve stability, TL response versus absorbed dose, post-irradiation storage stability, and reusability are investigated. This TL material has a linear dose response up to 10³ Gy, negligible storage fading and a simple annealing procedure for reuse. The TL emission spectra of LMB:Tb³⁺ showed broad green emission at 544 nm, which merged with host emission. The characteristic Tb³⁺ emissions are seen in the photoluminescence (PL) spectra.     

Catalytic reduction of methylene blue by sulfide ions in the presence of nanoAlMCM-41 material

This article reports the reduction of methylene blue (MB) by sulfide ions (S²⁻) in aqueous solution by a nanoAlMCM-41 catalyst. The results obtained showed that, under acidic conditions (pH=2) MB was reduced to the Leuco methylene blue (LMB) form by sulfide ions and by changing the pH between 2.0 and 7.0 a reduction of the MB dye to the MBH₂⁺ form was observed. In alkaline media (pH=8), a reduction of methylene blue by sulfide ions to the MBH₂⁺ form and demethylation of the dye was observed simultaneously. The demethylation of MB leads to a thionine dye product. Using nanoAlMCM-41 but with encapsulated CoS nanoparticles only causes demethylation of MB in aqueous solution.     

X-ray study of the PZT solid solutions near the morphotropic phase transition

In the solid solutions Pb(Zr_xTi_1?x)O₃ it is stated that for x ? 0.55 there is a morphotropic phase change. Thermodynamically, it is expected that there will be a region of x, in which the two phases coexist and obey the leverage law. By X-ray diffraction, we found that the two phases coexist for x between 0.49 and 0.64. In this range the lattice parameters do not change, and the leverage law is obeyed. We conclude that an adequate explanation of the particular properties of the PZT solutions has to be found.     

On the criterion of the crystal-liquid phase transition

A localization criterion is proposed for the crystal-liquid phase transition (PT). According to this criterion, the PT begins when the E _d/k _b T ratio reaches a boundary value E _d(s)/k _b T _m such that a solid phase is present above it and a liquid phase is present below it in a phase diagram. Here, E _d is the energy of atom delocalization, k _b is the Boltzmann constant, T is the temperature, and E _d(s) is the delocalization energy for a solid phase at melting point T _m. This criterion is shown to generalize the Lindemann criterion of melting to the case of crystallization and the Löven criterion of crystallization to the case of melting. This localization criterion is found to be applicable for both normally melting substances and substances that melt with a decrease in the specific volume upon the transition into a liquid phase. The relation of the localization criterion to the vacancy and diffusional criteria of the crystal-liquid PT has been studied. The inequality T _N < T _m, where T _N is the temperature of the onset of crystallization, is explained using the localization criterion. The calculated values of the T _N /T _m ratio coincide well with the experimental estimates. The maximum value of T _N /T _m is likely to be most probable in crystals with a bcc structure and a small value of the Grüneisen parameter. The T _N /T _m ratio is analyzed at the points in the PT where no change in the specific volume occurs and an entropy jump is nonzero.     

Effects of the velocity dependence of the collision frequency on the Dicke line narrowing

The effect of the velocity (v) dependence of the transport collision frequency ν_trv on the Dicke line narrowing is analyzed in terms of the strong-collision model generalized to velocity-dependent collision frequencies (the so-called kangaroo model). This effect has been found to depend on the mass ratio of the resonance (M) and buffer (M _b) particles, β = M _b/M: it is at a minimum for β ? 1 and reaches a maximum for β ? 3. A power-law particle interaction potential, U(r) ∝ r ^?n , is used as an example to show that, compared to ν_trv (v) = const (n = 4), the line narrows if ν_trv (v) decreases with increasing v (n < 4) and broadens if ν _trv (v) increases with v(n > 4). At β ? 3, the line width can increase [compared to ν_trv (v) = const] by 5 and 12% for the potentials with n = 6 and n ? 10, respectively; for the potentials with n = 1 (Coulomb potential) and n = 3, it can decrease by more than half and 6%, respectively. The line profile I(Ω) has been found to be weakly sensitive to ν_trv (v) at some detuning Ω_c of the radiation frequency Ω. Dicke line narrowing is used as an example to analyze the collisional transport of nonequilibrium in the resonance-particle velocity distribution in a laser field. The transport effect is numerically shown to be weak. This allows simpler approximate one-dimensional quantum kinetic equations to be used instead of the three-dimensional ones to solve spectroscopic problems in which it is important to take into account the velocity dependence of the collision frequency when the phase memory is preserved during collisions.     

Some remarks on the significant character of spectroscopic constants (triatomic linear molecules)

The influence of the H_v term on the values of the other spectroscopic constants B_v and D_v has been analyzed. The questions specifically considered are: When is it necessary to introduce it in the fit to reproduce satisfactorily the wavenumbers for the rotational structure of a given vibration-rotation transition? Even though this constant is not a significant parameter (H > 3δH, δH being the standard deviation) is it necessary to introduce it for extrapolations to very high J values? As a result of these considerations, it has been possible to define an experimental; protocol to determine “correct” spectroscopic constants.     

Theory of the period-doubling phenomenon of one-dimensional mappings based on the parameter dependence

A theory is presented of the period-doubling phenomenon of one-dimensional mappings of the form x_n+1 = F(x_n, r), which is different from that of Feigenbaum mainly in that it is based on the r dependence of various quantities rather than on their x dependence. Consequently, it enables us to evaluate, for example, the Lyapunov numbers of periodic orbits as a function of r as well as the Feigenbaum ratio. It is shown that the results of our theory are in good agreement with those of numerical simulations.     

Effect of the surface integral in the torque equation of the electromagnetic angular momentum on the Faraday rotation

A circularly polarized plane wave of infinite transverse extent (δ = ∞) has no spin angular momentum, while a realistic light does carry it. This paradox originates from the presence (δ = ∞) and absence (δ ≈ 0) of the surface integral in the total angular momentum J. The same holds for the torque equation of dJ/dt, so that δ is also connected with the relative Faraday rotation angle Θ_F/θ_F when a radius (a) of a cylindrical medium with optical activity is only a little larger than that (b) of light beam, where Θ_F is the Faraday rotation angle and θ_F is the intrinsic Faraday rotation angle of a medium. It is shown here that it is possible to estimate δ for a realistic light from the drastic variation in Θ_F/θ_F near b/a = 1.     

On the efficiencies of absorption heat pumps

Although commonly used, the coefficient of performance COP is not always an adequate measure to describe the effectiveness of a sorption heat pump. Equations for four different efficiencies are derived, discussed and compared for absorption heat pumps (AHP). A flow-sheeting computer program, developed for both design and evaluation simulations of arbitrarily complex absorption cycles, is used to exemplify the derived equations. The working fluid pair H₂OLiBr has been used in two different AHP configurations. The examples given clearly show that the COP can only be used to compare different AHPs operated at the same circulation ratio. The COP can be considered as an indicator of the effectiveness of heat exchange within and thermal insulation of a heat pump operated at a fixed circulation ratio. Nevertheless, it is an insufficient measure to compare different AHPs, even when they are operated at the same circulation ratio. On the other hand, the coefficient of performance for cooling Q_e/Q_g is better in this respect since it takes into account the real heat flow to the generator. The Carnot efficiency COP_rev takes into consideration both the real heat outputs from the absorber and condenser, and the temperature of heat sources and heat sinks. The thermodynamic efficiency E_th is shown to be a more logical measure of the heat pump efficiency, since it takes into account the real heat input the generator. The exergetic efficiency E_ex can be considered as an alternative to the thermodyanamic efficiency E_th but it offers a possibility to take into account any temperature level where heat energy may be considered worthless. However, both E_ex and E_th are not conventionally used since their numerical values are always less than 1.0. On the other hand, the exergetic index I_ex is directly related to E_ex but its numerical value shoul be considered as a more significant measure for evaluating the performance of AHP systems, since it properly takes into account the exergy losses which inevitably occur in the system. It may however be stressed that exergy analysis should be used as a compliment to the First Law analysis.     

Enhancing of the critical temperature of an in-plane FFLO state in heterostructures by the orbital effect of the magnetic field

It is well-known that the orbital effect of the magnetic field suppresses superconducting T _c . We show that for a system, which is in the Larkin-Ovchinnikov-Fulde-Ferrell (FFLO) state at zero external magnetic field, the orbital effect of an applied magnetic field can lead to the enhancement of the critical temperature higher than T _c at zero field. We concentrate on two systems, where the in-plane FFLO state was predicted recently. These are equilibrium S/F bilayers and S/N bilayers under nonequilibrium quasiparticle distribution. However, it is suggested that such an effect can take place for any plane superconducting system, which is in the in-plane FFLO state (or is close enough to it) at zero applied field.     

Probabilities for electronic transitions of molecular systems of high-temperature air components—I. The schumann-runge system of the O2-molecule and the first positive system of the N2-molecule

The results for absolute and relative probabilities for electronic transitions of the Schumann-Runge system of the O₂-molecule and the first positive system (1+) of the N₂-molecule published elsewhere have been critically analyzed. For the S-R system, statistical processing of the experimental results for absolute and relative probabilities on a joint basis made it possible to establish a new dependence of the electronic transition strength on the internuclear separations S_e(r_v′v″), which reliably describes the behaviour of S_e over the whole spectral range. For the (1+) system of the N₂-molecule, it has been shown that none of the published dependences S_e(r_v′v″) provide acceptable fits to the measured results on absolute intensities and life-times. In practical calculations, one should use the dependence given in Ref. 41, which is derived from relative intensities and corroborated by absolute intensity measurements.     

Trends in the density of states of hydrogen chemisorbed on the transition metal series

Extensive many-body calculations of the ground state properties of hydrogen chemisorbed on all 3d, 4d and 5d transition metal surfaces are performed. The trends of the location E_p of the discrete level under the bottom of the d-band are presented. It is found that, on going to the right of the series, E_p approaches the bottom of the d-band, eventually merges in it and detaches again from it for the last elements of the series.     

On the metastability of the Standard Model vacuum

If the Higgs mass m_H is as low as suggested by present experimental information, the Standard Model ground state might not be absolutely stable. We present a detailed analysis of the lower bounds on m_H imposed by the requirement that the electroweak vacuum be sufficiently long-lived. We perform a complete one-loop calculation of the tunnelling probability at zero temperature, and we improve it by means of two-loop renormalization-group equations. We find that, for m_H=115 GeV, the Higgs potential develops an instability below the Planck scale for m_t>(166±2) GeV, but the electroweak vacuum is sufficiently long-lived for m_t<(175±2) GeV.     

First-principles prediction of the magnetism of 3d transition-metal-doped Rocksalt MgO

Using first-principles band structure methods, we have systematically studied the electronic structures, magnetic stabilities, and half-metal properties of 3d transition-metal (TM) doped Rocksalt MgO compounds TMMg₃O₄ (TM=V, Cr, Mn, Fe, Co, and Ni). The calculations reveal that only CrMg₃O₄ has a ferromagnetic stability among the six compounds, which is explained by double-exchange mechanism. The magnetic stability is affected by the doping concentration of TM if the top valance band is composed of partially occupied t2g states. In addition, CrMg₃O₄ is a half-metallic ferromagnet. The origins of half-metallic and ferromagnetic properties are explored. The Curie temperature (Tc) of CrMg₃O₄ is 182 K. And it is hard for CrMg₃O₄ to deform due to the large bulk modulus and shear modulus, so it is a promising spintronic material. Our calculations provide the first available information on the magnetic properties of 3d TM-doped MgO.