Determination of the electric field gradient and relaxation time measurements in scandium metal at very low temperature

Abstract

Results are presented of measurements on a single crystal sample of scandium metal at temperatures down to 100 {mu}K using nuclear quadrupole resonance (NQR). Two regimes are found in the relaxation curves; an initial fast relaxation, followed by a slower relaxation consistent with the three exponential recovery expected for an I = 7/2 system in zero external magnetic field. The Korringa constant for this longer time relaxation in the sample is 90 {plus minus} 9 msec K{sup {minus}1}. By observing deviations in the ratio of the intensities of adjacent nuclear spin transitions at the lowest attainable temperatures, the authors were able to make a determination of the sign of the total electric field gradient present in the crystal. Results show that the lowest energy state of the nuclear spin system corresponds to m{sub I} = {plus minus} 7/2. A combination of these deviations and pulse NQR allows this system to be used as an absolute thermometer in the {mu}Kelvin regime.