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

We present the results of measurements on a single crystal sample of scandium metal at temperatures down to 100 ?K using nuclear quadrupole resonance (NQR). We find two regimes 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 our sample is 90 +- 9 msec K-1. By observing deviations in the ratio of the intensities of adjacent nuclear spin transitions at the lowest attainable temperatures, we have been able to make a determination of the sign of the total electric field gradient present in the crystal. We find that the lowest energy state of the nuclear spin system corresponds to mI = +-7/2. A combination of these deviations and pulse NQR allows us to use this system as an absolute thermometer in the ?Kelvin regime.