Investigation of the H Spin-Lattice Relaxation in Polycrystalline NH4Re04 Induced by Mechanical Sample Rotation

Measurements of the proton spin-lattice relaxation time, Tx , in polycrystalline NH4Re04 have shown that mechanical sample rotation in the static magnetic field reduces 2\ for proton magnetic resonance frequencies within the range 30 — 42 MHz. The rotation induced proton spin-lattice relaxation times, ?Y, were measured at different Larmor frequencies, sample rotation frequencies, and temperatures. At room temperature Tx' increases with increasing proton Larmor frequency. The dependence of 7\' on sample rotation frequency and temperature is small. The "normal" proton 7\ times were determined as a function of temperature at 30 and 42 MHz. From these measurements an average activation energy of 2.4 kcal/mole was obtained for the NH4+ reorientation. The "normal" spin-lattice relaxation behavior was observed to be non-exponential at 30 MHz above 200 K and at 42 MHz above 260 K and is nearly independent on temperature above 300 K.