Muon-spin relaxation measurements on the dimerized spin-1/2 chains NaTiSi2O6 and TiOCl

We report muon spin relaxation (μSR) and magnetic susceptibility investigations of two Ti3+ (S=1/2) chain compounds, NaTi Si2 O6 and TiOCl, each of which exhibits a spin gap at low temperature. From these we conclude that the spin gap in NaTi Si2 O6, which arises from orbital ordering at TOO =210 K, is temperature independent below TOO, with a value of 2Δ=700 (100) K. In TiOCl, we find thermally activated spin fluctuations corresponding to a spin gap 2Δ=440 (60) K below Tc1 =67 K. We can describe both the μSR and susceptibility data in terms of a model based on the dimerization of the Ti3+ chains. We also compare the methods used to extract the spin gap and the concentration of free spins within the samples from μSR and magnetic susceptibility data. © 2007 The American Physical Society