Low-temperature nuclear quadrupole resonance studies of antimony and application to thermometry

The spin-lattice retaxation time, {dollar}Tsb1{dollar}, of finely divided powdered metallic antinomy immersed in liquid {dollar}sp3{dollar}He was measured using pulsed Nuclear Quadrupole Resonance (NQR) techniques. In this technique, the nuclear quadrupole resonant antinomy nuclei were saturated using an RF pulse. The recovery back to equilibrium was monitored using short inspection pulses and the magnetization recovery follows a recovery curve characterized by the relaxation time {dollar}Tsb1{dollar}.; {dollar}Tsb1{dollar} measurements were performed at temperatures ranging from 150 mK to 1.25 mK. Temperatures down to 11 mK were achieved by using a dilution refrigerator. Lower temperatures were achieved using adiabatic nuclear demagnetization of a copper bundle starting at 8.5 Tesla (7.5 Tesla average field over the copper bundle). The sample was cooled by immersion in liquid {dollar}sp3{dollar}He which is in thermal contact with silver sinter packed in the bottom of a silver cell. This cell was bolted onto a cold plate attached to the copper bundle.; It was found that a low temperatures starting near 75 mK, the measured total relaxation was significantly enhanced with respect to the Korringa relaxation, the dominant relaxation mechanism expected for a metal at these temperatures. This enhancement is attributed to a surface relaxation mechanism mediated by the surface {dollar}sp3{dollar}He atoms.; In systems immersed in liquid {dollar}sp3{dollar}He, a surface relaxation mechanism is present due to a modulation of the interaction between the solid-like {dollar}sp3{dollar}He atoms on the surface and the surface spins. This modulation is due to the quantum zero-point motion of the {dollar}sp3{dollar}He atoms on the surface. This phenomenon has been well studied in insulating systems using Nuclear Magnetic Resonance.; The measurements undertaken in this study demonstrate that this phenomenon is present in a metallic and quadrupolar system. This surface relaxation mechanism becomes the dominant relaxation mechanism at low temperatures. Considering the surface and bulk spins as belonging to different phases, a two phase relaxation analysis was used to extract the surface relaxation parameters. This work helps explain previous relaxation measurements by other groups, on powdered metals (with spin {dollar}Ine 0{dollar}) immersed in liquid {dollar}sp3{dollar}He. In these studies, anomalies were reported whose features are consisted with the surface relaxation mechanism discussed in this work.; Using magnetic field perturbed NQR, the intensity ratio of two transitions was studied from 1.4 mK to 0.25 mK. The intensity ratio was observed to change as a function of temperature. A comparison is made with the expected Boltzmann distribution. This intensity ratio can be used as a self-calibrating, absolute thermometer for the ultra-low temperature region.