4C6 - Concentration and temperature dependences of spin-lattice relaxation times in ruby at helium temperatures: Relaxation in a zero magnetic field

The relaxation times T
1
for the grouud state levels in ruby were measured in the temperature range 4.2 to 1.6°K for the various concentrations of the
Cr^{3+}
ions
f
from 0.05 to 0.7 percent. The dependence
T_{1}(f)
of the form
T_{1}^{-1}(f) = T_{1}^{-1}(0) + T_{1}^{-1}(I)f ^{n}
with
n \simeq 2
has been obtained for the different transitions. The measurements of relaxation times for
\pm \frac{1}{2} \leftrightarrow \pm \frac{3}{2}
transition at zero magnetic field were especially aimed at establishing a form of dependence
T_{1}(f)
because of the absence of the cross relaxation effects in this case. The normal temperature dependence
T_{1} \propto T_{1}^{-1}
has been obtained at all concentrations in comparison with anomalous dependences observed at high concentrations by some researchers.