Observation of light-induced anisotropy in ferric borate by acoustic resonance

A light-induced anisotropy of two-fold symmetry in the magnetically easy c-plane has been observed at 77 K in c-plane platelets of FeBO₃ using the method of acoustic resonance. The anisotropy field is shown to be negative (positive) in the direction of the net magnetization during illumination in those samples for which the susceptibility increases (decreases) with light.     

Observation of one phonon transitions in terbium by nuclear resonance fluorescence

For the first time the resonance absorption of a Mössbauer line by inducing one phonon transitions in the absorber has been observed. In the experiment the 58 keV transition of ¹⁵⁹Tb was used to study the phonon spectrum of terbium.     

Observation of intermolecular double-quantum coherence signal dips in nuclear magnetic resonance

The correlated spectroscopy revamped by asymmetric Z-gradient echo detection (CRAZED) sequence is modified to investigate intermolecular double-quantum coherence nuclear magnetic resonance signal dips in highly polarized spin systems. It is found that the occurrence of intermolecular double-quantum coherence signal dips is related to sample geometry, field inhomogeneity and dipolar correlation distance. If the field inhomogeneity is refocused, the signal dip occurs at a fixed position whenever the dipolar correlation distance approaches the sample dimension. However, the position is shifted when the field inhomogeneity exists. Experiments and simulations are performed to validate our theoretic analysis. These signal features may offer a unique way to investigate porous structures and may find applications in biomedicine and material science.     

Observation of critical behaviors in squaric acid by H nuclear magnetic resonance

¹H nuclear magnetic resonance (NMR) was employed in order to investigate the phase transitions in a two-dimensional antiferroelectric system, squaric acid (H₂C₄O₄). As a result, in addition to the critical behaviors around the long range order phase transition, similar behaviors were observed at higher temperatures where a short range order phase transition presumably takes place.     

Muonium acoustic resonance

Theoretical consideration is given to the effect of ultrasonic oscillations on the spin polarization of the positive muon of muonium present in matter. The resonant action of the periodic acoustic perturbation on the muonium hyperfine structure levels is shown to result in characteristic oscillations and to modify the muon spin precession pattern considerably. The possibilities for experimental detection of the muonium acoustic resonance are discussed     

Monium acoustic resonance in alpha-quartz

The effect of acoustic oscillations of the -quartz crystalline lattice on the behaviour of muonium polarization has been studied experimentally. It is shown that when the frequency of the standing ultrasound wave coincides with one of the muonium quadrupole interaction frequencies a specific broadening of the muonium line occurs; that is a muonium acoustic resonance is observed. The possibilities of using this effect for investigating properties of solids by the SR method are discussed.     

Nuclear acoustic resonance in metals

A comprehensive quantum theoretical treatment of nuclear acoustic resonance (NAR) in metals is presented for the first time. Basic equations describing the NAR-absorption and NAR-dispersion are derived from the sound induced perturbation Hamiltonian Ih(t) by applying a generalized form of the Kubo susceptibility. It is shown that in metals, where a sound wave may induce nuclear magnetic dipole and nuclear electric quadrupole transitions simultaneously, the appearance of interference terms enables one to determine not only the absolute values but also the signs of the gradient-elastic tensor components. Explicit expressions are displayed for the dipolar, quadrupolar and interference contributions to the generalized NAR susceptibility in cubic metals. As an example the derivative of the expected⁹³Nb NAR-absorption line (|m|=1) is calculated for different signs of the gradient elastic tensor componentS ₄₄.     

Doppler-shifted acoustic cyclotron resonance in tungsten

Doppler-shifted cyclotron resonances have been observed acoustically in high purity tungsten single crystals. The resulting Fermi surface area derivatives agree generally with those obtained from magnetomorphic size effect experiments and with calculations based on an empirical model fitted to de Haas-van Alphen data. Certain non-central orbit zones of the latter model are modified to fit both sets of results. The resulting correction to the hole octahedron sheet is minimal, the modified electron jack has a more spherical shape, and the necks are slightly further away from the zone center. The dimensions of the re-parameterised model agree better with the results obtained from other Fermi surface measurements.     

Nuclear acoustic quadrupole resonance in CsBr

Nuclear acoustic resonance is used to measure the deformation in single crystal of CsBr. The measured relative deformation is estimated to be 0.1 per cent and the ratio of the bromine and cesium anti-shielding factors is 1.6.     

Diffusion in nuclear quadrupole resonance

With the aid of the method of random trajectories, formulas have been obtained for the first time for diffusion damping of the amplitudes of nuclear quadrupole spin echo signals because of molecular vibration-rotation in a two-frequency four-pulse program for spin 5/2 and zero asymmetry parameter. The formulas are similar to the result of Hahn for diffusion in NMR.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 14–16, June, 1985.     

Nuclear acoustic resonance in Cu-Mn single crystals

Cu⁶³ nuclear acoustic resonance signals have been observed between 300 and 2°K in single crystals of the dilute alloy Cu-Mn. The sensitivity does not decrease at low temperature, as it is the case for pure metals. The line width broadening due to the magnetic impurities is isotropic.     

Nuclear acoustic resonance in a liquid metal

The first observation of direct nuclear acoustic resonance (NAR) in a bulk liquid is reported. The measurements were performed with pure gallium. The line shape and angular dependence of the absorption signal are in good agreement with the theory for spin phonon coupling via the nuclear magnetic dipole moment.     

Detection of acoustic emission and simultaneous observation of nuclear quadrupole resonance in the α ⇋ β phase transition of paradichlorobenzene

Acoustic emission has been observed in the α ? β transition of monocrystalline samples of paradichlorobenzene. No acoustic emission has been detected in the β → α transition of single crystals nor in the α ? β transitions in polycrystalline samples. The simultaneous observation of acoustic emission and Nuclear Quadrupole Resonance when several α ? β transition cycles are carried out reveals some features of this solid state phase transition.     

Near-zero-field nuclear magnetic resonance

We investigate nuclear magnetic resonance (NMR) in near zero field, where the Zeeman interaction can be treated as a perturbation to the electron mediated scalar interaction (J?coupling). This is in stark contrast to the high-field case, where heteronuclear J?couplings are normally treated as a small perturbation. We show that the presence of very small magnetic fields results in splitting of the zero-field NMR lines, imparting considerable additional information to the pure zero-field spectra. Experimental results are in good agreement with first-order perturbation theory and with full numerical simulation when perturbation theory breaks down. We present simple rules for understanding the splitting patterns in near-zero-field NMR, which can be applied to molecules with nontrivial spectra.     

Dynamic nuclear spin resonance in n-GaAs

The dynamics of optically detected nuclear magnetic resonance is studied in n-GaAs via time-resolved Kerr rotation using an on-chip microcoil for rf field generation. Both optically allowed and optically forbidden NMR are observed with a dynamics controlled by the interplay between dynamic nuclear polarization via hyperfine interaction with optically generated spin-polarized electrons and nuclear spin depolarization due to magnetic resonance absorption. Comparing the characteristic nuclear spin relaxation rate obtained in experiment with master equation simulations, the underlying nuclear spin depolarization mechanism for each resonance is extracted.     

Electromagnetic acoustic resonance and materials characterization

This paper reviews the operation principles and several applications of electromagnetic acoustic resonance (EMAR). EMAR is an emerging ultrasonic spectroscopy technique for nondestructive and noncontact materials characterization, relying on the use of electromagnetic-acoustic transducers (EMATs) and the superheterodyne circuitry for processing the received reverberation signals excited by long radio-frequency (RF) bursts. The transduction occurs through the Lorentz force mechanism and, for ferrous metals, the dynamic response of magnetostriction and the magnetic force as well. Weak coupling of the EMATs is now essential to realize the high accuracy of measuring ultrasonic velocities and attenuation in conducting materials. High signal to noise ratio is achieved by receiving the overlapping coherent echoes at resonant frequencies. Small changes in the related material properties are well detectable. The spectral response can be interpreted for simple geometries such as plate, cylinder and sphere. EMAR has been proven to be powerful for industrial purposes because of its robustness, the omission of surface preparations and the capacity for simple measurement in a short time. Stress application varies the propagation velocities of ultrasonics and then shifts the resonant frequencies in longitudinal and shear modes in the parallel-sided geometries. Promising applications include the two-dimensional stress distribution in thin plates, the axial stress in railroad rails and the residual stresses around the weldments. In addition, the attenuation is precisely measurable at resonant frequencies and can evaluate the grain size of polycrystalline metals. Furthermore, the EMAR technique serves for developing the basic research on the effects of the metallurgical changes on ultrasonics, leading to the damage estimation of the fatigued, crept or thermally aged metal parts.