Magnetic Resonance with Strong Radio-Frequency Fields in Solids

In order to explain nuclear magnetic resonance signals in solids, Redfield has proposed that, when a strong rf magnetic field is applied, the spin system can be described by the existence of a spin temperature in the rotating frame, that can be different from the lattice temperature. In the present work, we observe the fluorine resonance in a single crystal of Ca${\mathrm{F}}_2$, with the dc field in the [111] direction. In our method of observation, the passage through the line is slow, but the modulation is fast, compared to the spin-lattice relaxation time. The signal is recorded after lock-in detection. It is shown that this technique permits one to study separately the behavior of the spin system when isolated from the lattice, and the effect of the spin-lattice relaxation.