Measurement of the nuclear spin diffusion coefficient in CaF2

Measurements are reported of the spin-lattice relaxation time T1 at 80°K and at room temperature for F19 spins in CaF2 doped with one U3+ ion per 9×103 fluorine atoms. T1 was found to be strongly dependent on the orientation of magnetic field with respect to the crystalline axes. Observation at 80°K of the recovery of nuclear magnetization for very short times after saturation indicated a t12 behavior, as predicted by Blumberg for the diffusion-limited regime of relaxation via paramagnetic impurities. The magnetization which starts out proportional to t12 consists of spins near a paramagnetic impurity, i.e. those relaxed by direct contact with the paramagnetic ions rather than by diffusion of Zeeman energy via the nuclear dipoledipole interaction. The latter measurements, coupled with the T1 measurements, yield values for the effective spin-diffusion coefficient of 0.77×10-12 cm2/sec when the dc magnetic field is in the [111] direction, and 4.2×10-12 cm2/sec when it is in the [100] direction. These results are in disagreement with present theories, which predict little variation in the effective diffusion coefficient with orientation of the applied field. © 1968 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe