Directional temperature of hot electrons in InSb under electric and magnetic fields

Directional differences in electron temperature are observed in n-type indium antimonide between E ∥ H and E ⊥ H geometries of electric and magnetic fields. Effects are reported in far-infrared cyclotron resonance for electrons at the donor level as well as the conduction band.     

Experimental and theoretical investigation of fmr in (111) thin garnet films with applied uniaxial stress

Analytical expressions for the resonance field shiftδH caused by an applied stressσ are deduced forH _e ∥ [¯1¯12] in the film plane, taking into account also the quadratic terms (～σ²) besides the dominant linear terms (～σ). The linear part ofδH=f(σ) forH _e andσ lying in the film plane depends only on the relative angle betweenH _e andσ, so that for the measurement of magnetostriction constants it is not necessary to have crystallographically oriented thin films.δH forH _e perpendicular to the film is very sensitive to deviations from the perpendicular direction. Both magnetostriction constants λ₁₁₁ and λ₁₀₀ were evaluated on (111) thin YIG ∶ Mn film.     

Response of an isolated magnetic grain suspended in a liquid to a rotating field

We have studied the response of an isolated uniaxial magnetic grain suspended in a liquid to an applied fieldh rotating with frequencyω. In the presence of an applied static field (H?h), at low frequencies (i.e. for fast relaxation), the easy axis followsh, while at high frequencies the behavior is similar to that of a bulk sample. In zero static field, the response of a ferromagnetic grain is more complicated; there exists a critical frequencyω _e below which a steady state is reached, with the easy axis followingh. Forω>ω _e the mechanical behavior depends crucially on the initial conditions. Finally, a superparamagnetic grain has a (different) critical frequencyω _e, below which it reacts similarly to the ferromagnetic particle, while forω>ω _e it does not follow steadily the rotating field, but can only oscillate about its initial position.     

High-frequency susceptibility and ferromagnetic resonance in multidomain thin films of the yttrium-iron garnet type

The field dependence of the high-frequency susceptibility and the ferromagnetic resonance were experimentally studied in a thin (d≈0.1 µm) (111)-oriented single-crystal film of substituted yttrium-iron garnet with the factor q?1. It was shown that the anomaly in the high-frequency susceptibility observed in a magnetic field H parallel to the normal to the film surface in the magnetization saturation region (H≈H_s) has a dual nature; more specifically, this anomaly is associated with an abrupt collapse of the stripe domain structure and a ferromagnetic resonance in the experimental configuration H ∥ [111] and h ⊥ H. In this case, the film transition from the inhomogeneous multidomain state to the homogeneous (single-domain) state at the point H≈H_s has no indications of a second-order phase transition. The experimental frequency-field dependence of ferromagnetic resonance (FMR) in the sample under study, having a characteristic minimum at the point ω₀=5 MHz and H_FMR=H_s, agrees qualitatively and quantitatively with calculations. The influence of the cubic magnetic anisotropy and the film thickness on the FMR spectrum and the orientation of the spontaneous magnetization in domains with respect to the film plane in the zero field H was theoretically studied.     

Polarization fluctuations in regions bounded by equi-potentials

It is shown that the integral of <{P(rτ), P(r')}>· n? as a function of r over a volume V_e bounded by an equi-potential is independent of r' and of V_e and is determined solely by [?(ω)?1] · n? provided the dielectric constant is local and that V_e is of macroscopic dimensions.     

Half-field and normal electron spin resonance study of the quasi-two dimensional magnetic crystal Mn(CHOO)2·2H2O

We have studied the normal electron spin resonance at the Larmor frequency as well as the half-field resonance of the quasi two dimensional magnetic crystal Mn(CHOO)₂·2H₂O at 35 GHz and room temperature. There are two groups of Mn²⁺ ions referred as A and B in this compound. The A ions lie in parallel (100) planes and have a strong exchange interaction within the plane. On the other hand, the B ions which lie in the adjacent parallel planes have no exchange interaction in the plane. We have measured the line width of the normal resonance from the A ions as a function of θ and φ where θ is the angle between the d.c. magnetic field H₀ and the a-axis of the crystal, which is very nearly perpendicular to the (100) plane and φ is the azimuthal angle of H₀ in the bc plane with respect to the b-axis. We also measured the intensity of the half-field resonance as a function of φ. We have calculated the second moments of the normal resonance line as a function of θ and φ. There is a satisfactory agreement between the calculated and the observed θ dependence of the line widths. The intensity of the half-field resonance has a maximum at φ = 40° whereas in an ideal 2d magnet, the maximum intensity is expected at φ = 45°. The ESR line width, because of the spindynamics in a 2 dimensional magnetic crystal, has an angular dependence of the form (3 cos²θ ? 1)². The observed dependence of the line width in Mn(COOH)₂·2H₂O seems to follow the same angular dependence when corrected for the contribution from the nearest neighbor B ions.     

A study of the effective line width in lithium ferrites using magneto microwave Kerr effect

A new technique to determine the effective line width ΔH_eff using the dimensional resonance phenomenon observed in magneto-microwave Kerr-effect experiment is discussed. This effect depends on the Permeability tensor components and the damping parameter α. The components of permeability tensor μ have been calculated theoritically and the damping parameter α is determined from experimental data. The measurements have been made at 24 GHz on three samples of lithium ferrite and their effective line widths have been obtained both in the partially magnetised and the saturated states of magnetisation. It has been found that ΔH_eff for two states of magnetisation are different. Further, the value of ΔH_eff obtained are higher than expected at this frequency. This suggests the possibility of additional relaxation mechanisms at dimensional resonance.     

Inversion-asymmetry-induced interband magneto-optical transitions in HgTe

The first evidence of linear-k term effects in HgTe is reported. New resonance structures observed in interband Γ₆ → Γ₈ magnetoabsorption spectra, for H ∥ [111], can be unambiguously identified with inversion asymmetry- induced transitions.     

The photoelectron spectra of tricyclo[3.3.0.02,6]Octene and tricyclo[3.3.0.02,6]Octane

The photoelectron spectra of tricyclo[3.3.0.0^2,6]octene (1) and tricyclo[3.3.0.0^2,6]octane (2) have been recorded. The first bands in these spectra are correlated with orbitals which are linear combinations of the Walsh orbitals and of the olefinic π-orbital. This assignment is based on a zero differential overlap molecular orbital model as well as on the results of extended Hückel calculations. The resonance integral <π|H|W > for 1 is found to be ?1.34 eV.     

Magnetic field investigation of the acoustic impedance resonance near 2Δ(T) in 3He-A

The acoustic impedance resonance near 2Δ(T) in ³He-A has been studied in magnetic fields up to H = 0.72 T with H?q?. It now appears that the resonance reported by Meisel et al. is independent of ?, q? orientation and satisfies ω(T) = a_ξΔ(T), where Δ(T) is the maximum in the weak coupling axial state gap and a_ξ = 1.8.     

Resonance mechanism of the production of electron-positron pairs in a strong magnetic field

The Compton-like process γe ^± → e ^± e ⁺ e ^? involving the production of an electron-positron pair in the interaction of an ultrarelativistic electron with a soft x-ray photon in the vicinity of the polar cap of a magnetar is considered. It is shown that the amplitude for this reaction has a resonance character. A simple analytic expression is obtained for the electron-absorption coefficient. Possible astrophysical implications of the resonance process γe ^± → e ^± e ⁺ e ^? are discussed.     

Nuclear magnetic resonance in noncollinear antiferromagnet Mn3Al2Ge3O12

The ⁵⁵Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice antiferromagnet Mn₃Al₂Ge₃O₁₂ has been studied in the frequency range of 200–640 MHz in the external magnetic field H ‖ [001] at T = 1.2 K. Three absorption lines have been observed in fields less than the field of the reorientation transition H _c at the polarization h ‖ H of the rf field. Two lines have been observed at H > H _c and h ⊥ H. The spectral parameters indicate that the magnetic structure of manganese garnet differs slightly from the exchange triangular 120-degree structure. The anisotropy of the spin reduction and (or) weak antiferromagnetism that are allowed by the crystal symmetry lead to the difference of ≈3% in the magnetization of sublattices in the field H < H _c. When the spin plane rotates from the orientation perpendicular to the C ₃ axis to the orientation perpendicular to the C ₄ axis, all magnetic moments of the electronic subsystem decrease by ≈2% from the average value in the zero field.     

Nuclear quadrupole resonance in C-nitro compounds

The nitrogen-14 nuclear quadrupole resonance spectra of CH₃NO₂ and of C₆H₅NO₂ were measured at 77°K. The results are: CH₃NO₂: e²qQ/h = 1694.6 kHz, η = 0.4240 and C₆H₅NO₂: e²qQ/h = 1424.9 kHz, η = 0.4039.     

Magnetostriction domain structure in a periodic system of magnetoelastic and elastic nonmagnetic layers

The spectrum of magnetoelastic waves in a periodic structure of alternating ferromagnetic and nonmagnetic layers was studied. In the case of ferromagnetic layers with easy magnetization axes parallel to the layer surfaces, an orientational phase transition induced by an external tangential magnetic field H_e was considered. The formation of an inhomogeneous phase with a spatially modulated order parameter, which is caused by the magnetization being coupled through magnetostriction to lattice strains near the interfaces separating the magnetoelastic from elastic media, is predicted. It is shown that at a certain critical field in excess of the orientational phase transition field in the system without magnetostriction, a magnetoelastic wave propagating in a direction parallel to the in-plane magnetization vector M becomes unstable at finite values of the wave vector and condenses into a magnetostriction domain structure. A phase diagram in the (L, T, H_e) coordinates is constructed, and the regions of existence of thermodynamically equilibrium collinear, canted, and domain phases are established (L and T are the thicknesses of the ferromagnetic and nonmagnetic layers, respectively).     

A low-lying resonance in the spectrum of H II. The 2P state

The wave function containing 20 parameters and the corresponding energy of the 2¹P state of H^- were calculated. As is well known this state lies in the H^- continuum. The inclusion of this state in the expansion of the continuum wave function can drastically influence the cross-section of an electron scattered by a hydrogen atom in the energy region involved. This bound pseudo-state will, in any case, influence the continuum absorption coefficient, but it may be insufficient to guarantee a peak in this absorption coefficient or in any e^-H experiment. Anyway, a new 2¹P virtual state of H^- is obtained with an energy of approximately -0.92 Ry. The exact position of the resonance needed to account for the occurrence of the interstellar line at 6180 Å is -0.9079 Ry. Since this resonance must lie very near the position of the bound state, our results support the identification of the broad feature at 6180 Å as a transition in H^-.     

Magnetic structure of the quasi-one-dimensional frustrated antiferromagnet LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> with Spin <Emphasis Type="Italic">S</Emphasis> = 1/2

The magnetic properties of LiCu₂O₂ single-crystal samples without twinning are investigated using electron spin resonance and nuclear magnetic resonance spectroscopy. The experimental results obtained are described in terms of the model of a planar spiral antiferromagnet for the orientation of the magnetic field H ‖ b or H ‖ c and the model of a collinear spin-modulated antiferromagnet for the orientation of the static magnetic field H ‖ a.     

Ultrasonic attenuation determination of Hc1 and Hc2 for ErRh4B4 at 1.5 K

The attenuation coefficient of longitudinal sound waves propagating in ErRh₄B₄ has been measured as a function of applied magnetic field where the propagation direction (q) of the sound waves was oriented either parallel or perpendicular to H_applied. For both orientations there is evidence of a type II-1 superconducting transition at H_c1 for T ≈ 1.5 K. In addition, when q ⊥ H an increase in attenuation is evident at H_c2, which does not appear when q 6 H, consistent with theories developed by Tachiki et al. utilizing supercurrent screening of the internal magnetic fields.     

Limits for two-photon ande + e − decay widths of positron-electron scattering resonances for√s=1.78 to 1.92 MeV

Motivated by the observation of energy- and momentum-correlatede ⁺ e ^? pairs in heavy ion collisions, a search for resonances ine ⁺ e ^? scattering at the corresponding energies has been made. Thee ⁺ e ^? decay channel is analyzed in a time window from ～ 10^?13 s to ～ 10^?11 s with a set-up optimized for low-background detection of delayede ⁺ e ^? decays. The two-photon decay channel of a hypothetical resonance is investigated by measuring the two-photon annihilation-in-flight excitation function. New upper limits for the partiale ⁺ e ^? decay width Γ_ee of a few meV are derived for total centre-of-mass energies √s between 1.78 and 1.92 MeV, taking into account the dilepton as well as the two-photon decay of a neutral resonance.     

Single crystal magnetization studies of DySb

High resolution magnetization measurements in single crystal-spherical DySb samples have been performed versus T in fields to 23.6 kOe. Measurements with H along principal crystallographic and 〈11$\text{2}$〉 directions are interpreted in terms of the intermediate metamagnetic phase having the HoP structure. Magnetization components parallel and perpendicular to the applied field for field rotations in (110) and (111) crystallographic planes have been measured and are interpreted in terms of a simple model with a single critical field. For H ∥ 〈110〉, M and H are collinear. The (M - H - T) phase diagram has been determined for H ∥ 〈110〉. The metamagnetic transition is 1st order below a critical point P_c = (8.5 K, 14.7 kOe) becoming 2nd order above. Field induced order for T >T_N is observed in agreement with the results of Brun et al. The absence of hysteresis in M_∥(θ) for H in (110) and (111) planes is interpreted as evidence for the tunneling model in DySb.