E. B. Genio

NMR studies of the orientational ordering in dilute solid N2-Ar mixtures

We report the results of NMR studies of the orientational ordering of15N2 molecules in solid N2-Ar mixtures for N2 concentrations in the 40–50% range. For samples with 50%15N2 a new phase distinct from the quadrupolar glass phase for the hcp structure has been observed. In this new phase, the local orientational order parameters were found to have very closely the same value at each site in contrast to the very broad distribution of order parameters observed in the quadrupolar glass state for the hcp lattice at higher concentrations (57–77%).

Nuclear spin relaxation of powdered metallic antimony in liquid 3He

Nuclear spin relaxation studies have been carried out to determine the surface relaxation of powdered Sb immersed in liquid3He. The surface relaxation mechanism was observed to be significantly more effective than the bulk Korringa relaxation rate for temperatures T < 75 mK. This surface relaxation is attributed to the modulation of the dipole-dipole interaction between the Sb spins at the metal surface and the3He spins in the solid-like layer on the surface by the quantum zero-point motion of these3He atoms. The total relaxation has been analyzed in terms of the surface relaxation and the spin diffusion through the bulk of the Sb particles. The experimental results are in excellent agreement with the theory developed for this system. Replacement of the3He by4He removes the surface relaxation component and restores the relaxation rates to the bulk value.

Coupling of the Nuclear Spin Alignment of Quadrupolar Nuclei to 3He at Interfaces

Measurements of the relaxation of nuclear spin alignments have been carried out using NQR spin echo studies of powdered antimony in contact with liquid3He. This system differs from previous studies of the relaxation and magnetization coupling of3He at surfaces because the magnetizations < Sz>≃ 0. The spin alignments < Sz2 > are the relevant dynamical variables. The analysis of the experimental results shows that the coupling of the nuclear spin alignment of the antimony nuclei to the magnetization of the3He nuclei is determined by the spectral density of the fluctuations of the spin-spin dipolar couplings at the interface. This power density is attributed to the zero-point motions (atom-atom and atom-vacancy exchange) of the3He atoms on the surface of the metal particles.

A new orientational glass in low concentration N2−Ar solid mixtures

NMR studies of the orientational ordering of15N2 molecules in solid N2−Ar mixtures have been carried out for the first time for low N2 concentrations. We have observed a new phase, that appears to be an orientational glass, in which the molecular axes are frozen in random directions at each crystal site but for which the mean alignment with respect to each local axis is a maximum. This is to be contrasted to the case for higher N2 concentrations, 0.57<x(N2)<0.77, for which a true quadrupolar glass is observed with a broad distribution of both local molecular axes and the mean alignment with respect to those axes. The formation of the new phase is believed to occur only for the cubic lattice structure at low N2 concentrations, while the quadrupolar glass occurs for the hcp structure.

Molecular glasses: NMR and dielectric susceptibility measurements

We review the properties of simple diatomic molecular glasses as explored by nuclear magnetic resonance techniques and measurements of the dielectric susceptibility. We focus on the behavior of classical molecular rotors formed by solid N2–Ar mixtures and discuss the time dependent behavior in terms of replica symmetry breaking theories.

Ultra-Low Temperature Thermometry Using Zeeman Perturbed NQR

AbstractWe report the results of measurements of the magnetic field perturbed nuclear quadrupole resonance (NQR) lines of powdered Sb immersed in liquid3He at low temperatures. The magnetic field was used to separate the frequencies of the allowed transitions between the

Nuclear spin-lattice relaxation times of metallic antimony at low temperatures

I_Z = \pm \frac{1}{2}

Zero sound spectroscopy of3He-B below 250 μK

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