Planar hall effect in gadolinium thin films near the curie point

The orientational and thermal dependences of planar Hall effect in Gd thin films deposited in an ultra-high vacuum were studied between 100 and 300 K. The critical exponent of magnetization as estimated from these measurements is $\text{β =}\text{1}\text{3}$.     

Impedance and magnetic properties of CoFeCrSiB amorphous ribbons near the curie point

The influence of temperature on the magnetic properties and magnetoimpedance of Co₆₄Fe₃Cr₃Si₁₅B₁₅ and Co₆₇FCr₃Si₁₅B₁₂ amorphous ribbons having different Curie points are studied. The impedance and its component are found to change greatly when the ribbons pass into the paramagnetic state. This finding can be used to determine the Curie point of ferromagnets and design high-sensitivity thermal transducers.     

The equilibrium domain structure of TGS in the vicinity of the curie point

The domain structure (DS) formed under strictly defined conditions favourable for the occurrence of the equilibrium domain structure was studied with TGS crystals in the temperature region fromT ₁=T _c–0·3° toT ₂=T _c–5°. It was shown that even at temperatures a few tenths of a degree belowT _c a regular plate DS exists and preserves the same character in the whole temperature region investigated; the domain widthw, however, increases with decreasing temperature. The average values ofw were determinated atT ₁ andT ₂ and the domain wall energy densities were calculated. The value of increases by more than two orders of magnitude when temperature drops fromT ₁ toT ₂; this is in qualitative agreement with Zhirnov's theory of domain walls.The author is indebted to Dr. J. Fousek for proposing this study and many valuable discussions, to Dr. V. Janovec and Dr. V. Dvoák for helpful advices.     

Mössbauer investigations of the surface state of hexagonal ferrites Sr-M near the curie point

The temperature dependence of the parameters of the hyperfine interaction in the surface layers and in the bulk of macroscopic crystals of hexagonal ferrites of the type Sr-M (SrFe₁₂O₁₉) is investigated by the method of simultaneous gamma-, x-ray, and electron Mössbauer spectroscopy. It is shown experimentally that the transition of an ≈ 200 nm thick surface layer of macroscopic ferromagnets to the paramagnetic state occurs at a temperature 3° below the Curie point (T _c) for the bulk of the crystal. It was established that the transition temperatureT _c(L) of a thin layer localized at a depthL from the surface of the crystal increases away from the surface and reaches the valueT _c at the lower (away from the surface) boundary of the so-called “critical” surface layer. A nonuniform state in which the bulk region of the crystal is magnetically ordered while the surface region is disordered is observed nearT _N.     

On the dissymmetry of mossbauer spectra in iron-nickel alloys

Valuable information about the disappearance of magnetism in the invar region (concentration of 30–45 pct of nickel) may be obtained by the examination of Mössbauer spectra.^I–5 However, it appears that some characteristics of these spectra are already present in non invar spectra have not been taken in account up to now: even in a 50 pct alloy, the six lines have anomalous widths and heights, and it is the aim of this note to put a quantitative interpretation of this fact, letting for the future the extension to invar spectra.     

原子光谱中同位素位移和超精细结构分裂

利用共线快离子束-激光光谱学方法测量了钕离子所有7个稳定同位素(A=142～146,148,150)之间的同位素位移和两个奇同位素(A=143,145)的超精细结构分裂．     

Electric hyperfine interactions in ferromagnetic binary alloys above the curie temperature

In the frame of an unscreened point charge model we calculated all possible electric field gradients for first neighbor atom arrangements in disordered binary fcc alloys. With these values and a distribution of isomer shifts we fit experimental spectra of nearly disordered alloys.     

Reinvestigation of the quadrupole hyperfine structure in rotational spectra of chloroiodomethane

The b-type Q-branch transitions of chloroiodomethane were remeasured and the quadrupole hyperfine structures were reinvestigated by a new method to improve the discrepancies in the hyperfine spectra observed and calculated in a previous work. The χ values of the off-diagonal element of ³⁵Cl and ³⁷Cl were determined. The nuclear quadrupole coupling constants were revised to be χ_aa = −1421.9 ± 1.9, χ_bb = 392.6 ± 1.0, χ_cc = 1029.3 ± 2.1, and {χ_ab} = 1174.9 ± 1.7 MHz of iodine; χ_aa = −31.1 ± 1.1, χ_bb = −9.0 ± 0.6, χ_cc = 40.1 ± 1.2, and {χ_ab} = 53.6 ± 4.2 MHz of ³⁵Cl for ³⁵Cl species; χ_aa = −1418.4 ± 2.5, χ_bb = 386.5 ± 2.7, χ_cc = 1031.9 ± 3.6, and {χ_ab} = 1181.8 ± 1.7 MHz of iodine; and χ_aa = −21.1 ± 1.7, χ_bb = −8.5 ± 0.9, χ_cc = 29.6 ± 1.9, and {χ_ab} = 34.6 ± 1.4 MHz of ³⁷Cl for ³⁷Cl species, respectively.     

运用光电流光谱测定钬原子能级的超精细结构

用自制钬空心阴极灯,运用光电流光谱技术在569nm～600nm谱区内首次测定了元素钬的9条谱线,确定其相应跃迁能级,及超精细结构常数.     

Reinvestigation of the quadrupole hyperfine structure in rotational spectra of 3-lodopropene

Quadrupole hyperfine structure of 3-iodopropene has been reinvestigated by the use of two methods, (1) Two-Level Approximation, and (2) Direct Solution of the Energy Matrix, to improve the discrepancies between the observed and calculated hyperfine spectra reported in a previous work (J. Mol. Spectrosc.66, 421–427 (1977)). Appreciable improvement can be found in the discrepancies between the observed and calculated spectra. By means of these two methods, the χ values of CH₂ICHCH₂ have been revised to be: |χ_ab| = 1160 MHz and χ_zz = ?1920 MHz, respectively.     

Paramagnetic resonance linewidth of EuO near the curie temperature

Measurements of the EPR linewidth ΔH of EuO at 9 GHz are reported in the temperature range of 66–300° K, with particular attention to the region near T_c (69.6° K). Comparison with the earlier data of Eastman at 25 GHz in the critical region shows considerable suppression of ΔH at 25 GHz. The temperature-dependent behavior of ΔH in EuO at 9 GHz is similar to the observations in CrBr₃ and it is in qualitative agreement with the zero-field predictions of Huber and Maleev. The quantitative discrepancies are believed to be due to the effect of the resonance magnetic field on EPR spin dynamics near T_c and an inadequate decoupling of the four-spin correlation functions used in the theories.     

Use of sturmian expansions in calculations of the hyperfine structure of atomic spectra

A procedure for calculating hyperfine structure (HFS) parameters using the basis of Sturmian functions is developed. The procedure is used to calculate the HFS parameter a _4d ⁵ of the 4d ⁵ levels of the niobium atom. The contributions of the continuous spectrum and higher orders of the perturbation theory are quantitatively estimated by comparing the numerical values of the parameter a _4d ¹⁰ obtained in the framework of the perturbation theory with the results of direct calculations by the configuration interaction method. Comparison of the results of relativistic and nonrelativistic calculations allows the contribution of relativistic effects to HFS parameters to be found.     

Anomalous resistivity near curie temperature due to the critical scattering

Critical behavior of the temperature derivative of the electrical resistivity at the Curie temperature is treated in general. It is shown by treating the sum rule in the correlation function rigorously that, for a large Fermi wave vector, the divergence is similar to that of specific heat both below and above the Curie temperature, but for a small Fermi wave vector, the de Gennes—Friedel region appears at higher temperatures. Comparison with other divergent mechanisms are also done.     

Magnetic interaction and the critical dynamics above the curie point

It is shown that near T_c, where 4πχ ? 1 magnetic interaction completely change the long-wave critical dynamics of the ferromagnets and the new dynamic critical exponent is z_d = (5 - η)/2 - ν^-1 ≈ 1.     

On the critical dynamics of isotropic ferromagnets below the curie point

The transport coefficients for isotropic Heisenberg ferromagnets are evaluated by mode-mode coupling theory forT≦ T _c. Near the critical point the results agree with dynamical scaling. In the hydrodynamic critical regime the longitudinal width depends crucially on the analytic form of the static longitudinal susceptibility. In the region where the ξ/q term dominates the width of the longitudinal peak is proportional to \(q^2 \xi ^{ - 1/2} \) , whereq and ξ are respectively the wave number and critical correlation length. When the Ornstein Zernike term dominates the width is \(q\xi ^{ - 3/2} \) . The damping of the transverse modes is \(q^4 \xi ^{3/2} (a + b\log (1/q\xi ))\) . If one accounts for the critical exponentn the above expressions are to be multiplied by \(\xi ^{\eta /2} \) . These frequency independent transport coefficients are valid in the neighborhood of the resonances. For larger frequencies the frequency dependent forms are evaluated.     

Correlations and spectra of an intermittent chaos near its onset point

A one-parameter family of piecewise-linear discontinuous maps, which bifurcates from a periodic state of periodm, (m=2, 3,...) to an intermittent chaos, is studied as a new model for the onset of turbulence via intermittency. The onset of chaos of this model is due to the excitation of an infinite number of unstable periodic orbits and hence differs from Pomeau-Manneville's mechanism, which is a collapse of a pair of stable and unstable periodic orbits. The invariant density, the time-correlation function, and the power spectrum are analytically calculated for an infinite sequence of values of the bifurcation parameter which accumulate to the onset point _c from the chaos side - _c > 0. The power spectrum near=0 is found to consist of a large number of Lorentzian lines with two dominant peaks. The highest peak lies around frequency=2/m with the power-law envelope l/¦-(2/m)¦⁴. The second-highest peak lies around o = 0 with the envelope l/¦¦². The width of each line decreases as, and the separation between lines decreases as/lg3^–1. It is also shown that the Liapunov exponent takes the form-/m and the mean lifetime of the periodic state in the intermittent chaos is given bym ^–1(ln ^–1+1).     

Born-Oppenheimer breakdown effects and hyperfine structure in the rotational spectra of SbF and SbCl

Pure rotational spectra have been measured for the ground electronic states of SbF and SbCl. The molecules were prepared by laser ablation of Sb metal in the presence of SF₆ or Cl₂, respectively. Their spectra were measured with a cavity pulsed jet Fourier transform microwave spectrometer. Although both molecules have two unpaired electrons, they are subject to Hund’s coupling case (c), and have X₁0⁺ ground states. The spectra have been interpreted with the formalism of ¹Σ⁺ molecules. For both molecules spectra of several isotopomers have been measured in the ground and first excited vibrational states. Large hyperfine splittings attributable to both nuclear quadrupole coupling and nuclear spin-rotation coupling have been observed. A Dunham-type analysis has produced unusually large Born-Oppenheimer breakdown parameters, which are interpreted in terms of the electronic structures of the molecules.