Proton polarization and relaxation in dilute paramagnetic crystals by rotational cooling I. yttrium ethyl sulfate doped with Yb and Dy ions

Abstract

The method of proton polarization by means of rotational cooling is employed in crystals of Y (C 2H 5SO 4) 3 · 9H 2O doped with Yb 3+ and Dy 3+ ions. The decay of the proton polarization is observed as a function of magnetic field H(1 kOe≲ H ≲ 10 kOe), temperature T (0.05 K ≲ T ≲ 1 K) and concentration of the rare-earth ions c(0.07% ≲ c ≲ 3%). For an explanation of the results on proton spin-lattice relaxation times the inclusion of the dipole-dipole reservoir (D.D.R.) of the paramagnetic ions is required. The influence of the concentration of the Yb or Dy ions on the maximum obtainable proton polarization is discussed. The electron spin-lattice relaxation appears to be mainly determined by the direct process.