Figure 2.

Power dependence of NO and Gd $\mathit{\pi }$ pulses. Transient nutation experiments were performed at different spectral positions of the NO–Gd ruler at 10 K. Data were recorded at 12, 6, and 0 dB attenuation (columns 1 to 3), varying the arbitrary waveform generator (AWG) amplitude. The fourth column shows the correlation of the extracted $\mathit{\pi }$ pulse lengths (first minimum of the nutation transient) and the AWG pulse amplitude (in percent) for the different main attenuator settings (in decibels). All extracted $\mathit{\pi }$ pulse lengths are given in Table S2 (part B). The transients shown in (a) were recorded on the spectral maximum of the Gd, and those in (b) were recorded on the maximum of the NO spectrum, which is 10.4 mT lower in magnetic field than the maximum of the Gd for the utilized sample (see Fig. ) using a shot repetition time (srt) of 1000  $\mathrm{\mu }$ s (if not stated differently). (a) In our setup, 12 dB attenuation and 80 % AWG amplitude correspond to a 30 ns Gaussian $\mathit{\pi }$ pulse on Gd. Doubling the power (6 dB) always requires halving the AWG amplitude to keep the same $\mathit{\pi }$ pulse length (highlighted in black for a $\approx$  30 ns $\mathit{\pi }$ pulse). (b) A srt of 1000  $\mathrm{\mu }$ s makes the nutation experiments more sensitive to Gd at 10 K (see relaxation data given in Figs. S1 to S3 and Table S3 to S4; part B). At 0 dB main attenuation and 20 % AWG amplitude, the nutation of the NO also becomes visible (black). Prolonging the srt to 400 000  $\mathrm{\mu }$ s at 20 % amplitude slightly increases the amplitude of the NO nutation with respect to the nutation of Gd (gray). A pulse amplitude of 80 % also gives 30 ns $\mathit{\pi }$ pulse length (green), which corresponds to a $\mathit{\pi }$ pulse on the NO spins.