Dipolar Zeeman mixing in weak magnetic fields: An experiment with ice protons

The evolution of the longitudinal magnetization of nuclear spins in a cw high-frequency magnetic field has been measured using a SQUID magnetometer at liquid-helium temperatures in magnetic fields H ₀ of up to 57 Oe. The time T _m for thermal mixing of the Zeeman and dipolar systems has been found to range between 0.05 and 4×10² s. For T _m>1 s the function T _m(H ₀) is exponential. The proton NMR spectra near the fundamental and twice the Larmor frequency have been obtained. The shift in the resonance with respect to the Larmor frequency is close to the theoretical prediction. Zh. éksp. Teor. Fiz. 114, 1006–1017 (September 1998) Deceased.