Experimental Proof of the Strong Coupling Between the Electron Spin-Spin Reservoir and a Nuclear Spin System in Dilute Paramagnetic Crystals

Experiments are described in which the nuclear Zeeman temperature Tₙ and the temperature of the electron dipole-dipole interaction system Tᵢₙₜ in a dilute paramagnetic crystal are measured simultaneously. The spin-lattice relaxation times of these two systems turn out to be equal, thus yielding a direct evidence of the strong coupling between these systems.