Ammonium ions in alkali metal halide crystals: Tunnelling and spin relaxation

Abstract

We have used low energy inelastic neutron scattering spectroscopy to examine the tunnelling spectroscopy of the ammonium ion in the (NH₄)_0.02Rb_xK_0.98−xI system. The concentration of different species were varied as x increased, this was followed systematically and the first consistent assignment scheme for these features is given. Differences were also found for the relaxation rate of the spin temperature inversions that could be generated in these species. At a critical concentration—about x = 0.04 mole fraction—the relaxation rates of the species changed dramatically.