T1 relaxation times were measuring using a saturation recovery sequence (saturation with 64 90° pulses separated by 1 ms), again using a 40 μs solid echo for detection. Relaxation time constants were obtained by fitting spectral integrals to a general exponential recovery function. Conversion between set temperatures and actual sample temperatures was done by independent calibration experiments using ethylene glycol. Uncertainties in the final absolute sample temperatures are estimated to be ±5 K. Further details of the analysis and temperature calibration can be found in the data archive.