  We report muon spin relaxation (muSR) and magnetic susceptibility
investigations of two Ti3+ chain compounds which each exhibit a spin gap at low
temperature, NaTiSi2O6 and TiOCl. From these we conclude that the spin gap in
NaTiSi2O6 is temperature independent, with a value of 2*Delta=660(50)K, arising
from orbital ordering at Too = 210K; the associated structural fluctuations
activate the muon spin relaxation rate up to temperatures above 270K. In TiOCl
we find thermally activated spin fluctuations corresponding to a spin gap
2*Delta=420(40)K below Tc1=67K. We also compare the methods used to extract the
spin gap and the concentration of free spins within the samples from muSR and
magnetic susceptibility data.
