A study of the relaxation mechanism of a KAl(SO₄)₂·12H₂O single crystal by observation of its³⁹K and²⁷Al spin–lattice relaxation processes

Abstract

The spin–lattice relaxation processes of the 39K and 27Al nuclei in KAl(SO4)2·12H2O crystals were studied; we found that these processes can be described by linear combinations of two and three exponential functions, respectively. From these results, we conclude that the discontinuity in the curve of the spin–lattice relaxation rate near Tc (= 360 K) corresponds to the first-order phase transition of the crystal. In the case of the 39K nucleus, the relaxation rate increases as the temperature increases. The relaxation rate of the 27Al nucleus decreases below Tc as the temperature increase, while above Tc its relaxation rate increases with increasing temperature. The temperature dependences of these spin–lattice relaxation rates can be described with the power law . Least square fits of the relaxation rates at temperatures below Tc indicate that k = 2 for the 39K nucleus and k = 7 for the 27Al nucleus. From these results, we conclude that the 39K and 27Al spin–lattice relaxations occur from Raman relaxation processes.

Activation Energy of69Ga,71Ga, and75As Nuclei in GaAs:Mn2+Single Crystal

“…As nuclei, it is important to know whether the relaxation rate is located on the slow side of the minimum or on the fast side of the minimum as a function of the inverse temperature. The general behavior of the spinlattice relaxation rate for random motions of the Arrhenius type with a correlation time τ c can be described in terms of regions of fast and slow motions as follows [28]: crystal, the spin-lattice relaxation time is in the slow motion region in the experimental temperature range.…”