Enhanced magnetism and nuclear ordering of 169Tm spins in TmPO4

Ordering of the nuclear spins of 169Tm in TmPO4 caused by their ''enhanced'' nuclear magnetism, has been produced by Dynamic Nuclear Polarization (D.N.P.) followed by Adiabatic Demagnetization in the Rotating Frame (A.D.R.F.). At positive temperature, when the magnetic field H is parallel to the c-axis of the crystal, the structure is transverse in the rotating frame, thus appearing as rotating at the Larmor frequency in the laboratory frame. This article describes in detail: 1) The influence of the orientation of H on the N.M.R. linewidth, and the experimental procedures used to control this orientation and optimize the D.N.P. results. 2) The nuclear relaxation of 169Tm and 31P when H is almost parallel to c. 3) The 169Tm N.M.R. measurements and the double resonance experiments using 31P which confirm the nature of the ordered state and are compared to the theoretical predictions (Weiss and R.P.A.)