Hydrogen recombination in the early Universe in the presence of a magnetic field

Hydrogen recombination in the earlyUniverse in the presence of amagnetic field is studied. An equation for the recombination temperature in the presence of a magnetic field is obtained. The limiting cases of weak and strong magnetic fields are examined. A critical field above which the system being considered is in the atomic-hydrogen phase at any temperature is shown to exist. The relative shift of the recombination temperature in a magnetic field is estimated, and it is shown that this shift is small.     

NMR Knight shift studies in SmSn3 — Extension to low temperatures

The ¹¹⁹Sn Knight shift in SmSn3 has been measured in the temperature range 15—300 K, and it is found that the 4f-contribution to the Knight shift does not show a sign reversal in this temperature interval. The range of crystal field parameters for which simultaneous fit to the magnetic susceptibility and the extended Knight shift results in SmSn3 is obtained can be substantially narrowed from that reported earlier.     

Spin and dispersion of a massive Dirac neutrino in a magnetized plasma

The total energy shift of a polarized massive Dirac neutrino in an electron–positron plasma in a constant magnetic field is investigated. The calculation in the Feynman gauge is performed for the first time by using the Matsubara temperature Green functions. The dependence of the dispersion relation and the anomalous magnetic moment of the neutrino on the magnetic field strength, spin, energy, direction of motion, neutrino mass, and the plasma parameters is analyzed. The results of investigations for the massive neutrino in the limiting case are compared with those obtained earlier by other authors for the massless left neutrino.     

Photoluminescence of EuSe and the magnetic polaron model

We report on extensive new measurements relating to the near-infrared photoluminescence of EuSe first reported by Busch and Wachter in 1966. The emission and excitation spectra are obtained as functions of temperature and external magnetic field. The total red shift is 0.13 eV in the excitation spectrum (in good agreement with the absorption-edge shift), and 0.25 eV in the emission spectrum. At 4.3°K an external magnetic field of 11 kOe quenches the yield to about 30% of its field-free value. The experimental results are discussed in relation to photoconductivity and optical absorption measurements. An intrinsic and localized model for the luminescence is proposed, in which the emission takes place by radiative recombination of a localized magnetic polaron with a hole in the europium 4f-shell.     

Structural Peculiarities and Magnetic Properties of Nanoscale Terbium in Tb/Ti and Tb/Si Multilayers

The structure and the magnetic properties of rf-sputtered nauoscale Tb in [Tb/Ti]n and [Tb/Si] multilayers have been studied experimentally. It is found that the structure of Tb layers changes, transforming from a fine-crystalline state of Tb into an amorphous state as the magnetic layer thickness decreases. The observed displacement of a magnetic ordering temperature to the lower temperature range and the shift of magnetic hysteresis obtained in the ZFC-FC terms may be caused by the size effect and the amorphization. Both the first and the second suppress the exchange interaction and decrease the crystalline magnetic anisotropy. The type of material of nonmagnetic spacers between the Tb layers plays a certain role in these changes.     

Temperature dependence of phase shift in ferrite phase shifters

Reciprocal ferrite phase shifters exhibit a pronounced dependence of phase shift upon temperature. In a sample of magnesium-copper-chromium ferrite it is shown that the temperature dependence of the phase shift is basically determined by the temperature dependence of the microwave magnetic permeability.In conclusion the authors wish to thank G. I. Yudin for making the measurements of phase shift and its dependence on the field for various temperatures.     

Temperature effects on the magnetoplasmon spectrum of a weakly modulated graphene monolayer

In this work, we determine the effects of temperature on the magnetoplasmon spectrum of an electrically modulated graphene monolayer as well as a two-dimensional electron gas (2DEG). The intra-Landau band magnetoplasmon spectrum within the self-consistent field approach is investigated for both the aforementioned systems. Results obtained not only exhibit Shubnikov-de Haas (SdH) oscillations but also commensurability oscillations (Weiss oscillations). These oscillations are periodic as a function of inverse magnetic field. We find that both the magnetic oscillations, SdH and Weiss, have a greater amplitude and are more robust against temperature in graphene compared to a conventional 2DEG. Furthermore, there is a π phase shift between the magnetoplasmon oscillations in the two systems which can be attributed to Dirac electrons in graphene acquiring a Berry's phase as they traverse a closed path in a magnetic field.     

Temperature investigations of the spatial spin-modulated structure of multiferroic BiFeO<Subscript>3</Subscript> by means of Mössbauer spectroscopy

The results from ⁵⁷Fe Mössbauer spectroscopic studies of multiferroic BiFeO₃ in a range of tem-peratures including that of the magnetic phase transition are presented. The Mössbauer spectra are processed and analyzed by reconstructing the hyperfine magnetic field distributions and interpreting the spectra with a cycloid-type spatial spin-modulated structure model. The temperature dependences of the hyperfine spectrum parameters (the Mössbauer line shift, the quadrupole shift, and the isotropic and anisotropic contributions to the hyperfine magnetic field) are obtained, along with the anharmonicity parameter of an incommensurate spin wave.     

Study of the [Fe(OMe)(dpm)2]2 dimer in the presence of a magnetic field by using Mössbauer spectroscopy

We present a Mössbauer study of a S = 0 ground state magnetic Fe(III)-dimer in the presence of an applied 5 T longitudinal magnetic field, between 7.6 and 33 K. The values obtained for the isomer shift and the quadrupolar splitting are comparable with the ones of Fe(III) ions coordinated to eight oxygen ions. Regarding the spin dynamics, both intramultiplet and intermultiplet transitions are considered. In the chosen temperature range the rate of the former transitions is constant, within the errors, while the rate of the latter ones quickly increases with the temperature.     

Energy of free and bound excitons in GaAs in a magnetic field

We have measured in photoluminescence the energy shift of free, weakly and tightly bound excitons in high purity GaAs in magnetic fields up to 12T. In the weak binding limit we find a surprising result: the mass obtained from the magnetic shift is the electron-heavy hole reduced mass in contrast to the results obtained from k · p calculation in zincblende type semiconductors in zero magnetic field. In the tight binding limit the mass deduced from the magnetic shift is the effective electron mass.     

Local magnetic susceptibility of the positive muon in the quasi-one-dimensional S=1/2 antiferromagnet dichlorobis (pyridine) copper (II)

We report muon spin rotation measurements of the local magnetic susceptibility around a positive muon in the paramagnetic state of the quasi-one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II). Signals from three distinct sites are resolved and have a temperature dependent frequency shift which is significantly different than the magnetic susceptibility. This difference is attributed to a muon induced perturbation of the spin 1/2 chain. The obtained frequency shifts are compared with transfer matrix density-matrix renormalization-group numerical simulations.     

Magnetic phase transitions in Fe80-xNixCr20 (14 ⩽ x ⩽ 30) alloy studied by using 57Fe Mössbauer spectroscopy

This paper reports ⁵⁷Fe Mössbauer spectroscopic studies of the polycrystalline samples of the substitutionally disordered, isostructural (fcc), ternary alloy system Fe_80-xNi_xCr₂₀ for x = 30, 26, 19 and 14 in the temperature range of 10–295 K. The data have been analyzed in terms of the magnetic phase transitions occurring in these alloys by examining the temperature dependence of the various Mössbauer parameters like line‐width, center shift, resonance area, distribution of hyperfine field, P(H), and the average hyperfine field 〈H〉. An estimate of the magnetic transition temperature T _C is made for the alloys with x = 30 and 26 and these results are compared with those previously obtained by magnetic measurements and neutron diffraction experiments. The data for the second order Doppler shift have been analyzed to estimate the Debye temperature ΘD for alloys with x = 30 and 26.     

Analysis of the influence of various effects on frequency shifts of the acetylene saturated absorption lines

Frequency shifts of the acetylene saturated absorption lines at 1.5\,$\mu$m with temperature, gas pressure and laser power have been investigated in detail. The second-order Doppler effect, the recoil effect, the Zeeman effect, the pressure shift and the power shift are taken into consideration. The magnitudes of those shifts caused by various effects are evaluated. In order to reproduce the stability of $5.7\times10^{ - 14}$ obtained by Edwards, all necessary conditions are given. The results show that when there is a larger external magnetic field, the Zeeman shift could not be neglected, so that the shield should be employed. And the design of a long cavity is advantageous to reduce the influence of the second-order Doppler effect. The results also show that at least $\pm $2.5\du\ temperature control for cavity can effectively prevent several effects and improve the frequency stability.     

Impurity cyclotron resonance in InGaAs/AlAs superlattice under ultra high magnetic fields

We have carried out cyclotron resonance (CR) measurements of (InGaAs)₈/(AlAs)₈ superlattice (SL) to investigate electronic properties of the SL under pulsed ultra-high magnetic fields. The magnetic fields up to 160 T were generated by using the single-turn-coil technique. Clear CR signals were obtained in the transmission of far-infrared laser through the SL at room temperature and lower temperature. We observed a shift of CR peak to lower magnetic field caused by transition from free-electron CR to impurity CR below 90 K. Compared with the previous works of GaAs/AlAs SL, the peak shift was small and the transition temperature was low. This result suggests that a binding energy of the impurity in the InGaAs/AlAs SL is smaller than the GaAs/AlAs SL.     

Exchange bias with Fe substitution in LaMnO<Subscript>3</Subscript>

We observe the negative shift of the magnetic hysteresis loop at 5 K, while the sample is cooled in external magnetic field in case of 30% of Fe substitution in LaMnO₃. The negative shift and training effect of the hysteresis loops indicate the phenomenon of exchange bias. The cooling field dependence of the negative shift increases with the cooling field below 7.0 kOe and then, decreases with further increase of cooling field. The temperature dependence of the negative shift of the hysteresis loops exhibits that the negative shift decreases sharply with increasing temperature and vanishes above 20 K. Temperature dependence of dc magnetization and ac susceptibility measurements show a sharp peak (T_p) at 51 K and a shoulder (T_f) around 20 K. The relaxation of magnetization shows the ferromagnetic and glassy magnetic components in the relaxation process, which is in consistent with the cluster-glass compound.     

Analysis of the influence shifts of the acetylene of various effects on frequency saturated absorption lines

Frequency shifts of the acetylene saturated absorption lines at 1.5μm with temperature, gas pressure and laser power have been investigated in detail. The second-order Doppler effect, the recoil effect, the Zeeman effect, the pressure shift and the power shift are taken into consideration. The magnitudes of those shifts caused by various effects are evaluated. In order to reproduce the stability of 5.7 × 10^-14 obtained by Edwards, all necessary conditions are given. The results show that when there is a larger external magnetic field, the Zeeman shift could not be neglected, so that the shield should be employed. And the design of a long cavity is advantageous to reduce the influence of the second-order Doppler effect. The results also show that at least 4-2.5℃ temperature control for cavity can effectively prevent several effects and improve the frequency stability.     

Ferromagnetic resonance in amorphous ferromagnet

The peculiarities of the ferromagnetic resonance of an amorphous ferromagnet in which a certain number of atoms forms the two-level systems are studied. The logarithmic dependence upon the temperature and the applied magnetic field of the frequency shift of the ferromagnetic resonance is obtained. The comparison of this theoretical dependence with experimental results gives a chance of the direct examination of the idea of the existence of the two-level systems. The dependence upon the temperature and the magnetic field of the frequency linewidth is also calculated.     

Finite temperature corrections to fleid theory: Electron mass and magnetic moment,and vacuum energy

A finite temperature formalism which maintains Lorentz covariance is rederived and compared to other approaches. It is used to obtain the order-α temperature shifts in the electron mass and magnetic moment, vacuum energy. The mass and magnetic moment shifts, for kT ? m, are of order $\text{α(}\text{kT}\text{m}\text{)}{}^2$ and hence beyond the present experimental observation limits. An explicit form for the general temperature mass shift is obtained.     

Mössbauer studies of spatial spin-modulated structure and hyperfine interactions in multiferroic Bi<Superscript>57</Superscript>Fe<Subscript>0.10</Subscript>Fe<Subscript>0.85</Subscript>Cr<Subscript>0.05</Subscript>O<Subscript>3</Subscript>

Results of Mössbauer investigations on ⁵⁷Fe nuclei in multiferroic material Bi⁵⁷Fe_0.10Fe_0.85Cr_0.05O₃ in the temperature range from 5.2 to 300 K are presented. Bulk rhombohedral samples were obtained by solidstate synthesis at high pressure. Mössbauer spectra were analyzed using the model of spatial incommensurate spin-modulated structure of the cycloidal type. Information on the influence of substituting Cr cations for Fe cations on hyperfine spectral parameters was obtained: the shift and quadrupolar shift of a Mössbauer line, and isotropic and anisotropic contributions into the hyperfine magnetic field. The anharmonicity parameter m of the spatial spin-modulated structure increases almost 1.7 times at 5.2 K when BiFeO₃ is doped with chromium. The data on m were used for calculation of the uniaxial magnetic anisotropy constants and their temperature dependences for pure and chromium-doped BiFeO₃.     

Ⅱ—Ⅵ族稀磁半导体ZnSe／Zn1—xMnxSe超晶格中的应力效应

本文通过Ⅱ－Ⅵ族稀磁半导体超晶格ＺｎＳｅ／Ｚｎ１－ｘＭｎｘＳｅ的光致发光谱的测量，对其应力效应进行了讨论。样品的组分ｘ＝０．２，０．３，０．４，测量温度为Ｔ＝１１￣３００Ｋ。结果表明：由于应力效应，ＺｎＳｅ／Ｚｎ１－ｘＭｎｘＳｅ超晶格中的激子能量随ｘ值增加而发生红移。在相同组分下，不同阱、垒宽度比使应力的分布产生明显变化，从而影响超晶格中激子能量。实验与理论计算结果相一致。超晶格中光致发光峰随温度