Spin dynamics in the low-dimensional magnet TiOCl
  We present detailed ESR investigations on single crystals of the low-dimensional quantum magnet TiOCl. The anisotropy of the g-factor indicates a stable orbital configuration below room temperature, and allows to estimate the energy of the first excited state as 0.3(1) eV ruling out a possible degeneracy of the orbital ground state. Moreover, we discuss the possible spin relaxation mechanisms in TiOCl and analyze the angular and temperature dependence of the linewidth up to 250 K in terms of anisotropic exchange interactions. Towards higher temperatures an exponential increase of the linewidth is observed, indicating an additional relaxation mechanism. 
D. V. Zakharov, J. Deisenhofer, H.-A. Krug von Nidda, P. Lunkenheimer,   J. Hemberger, M. Hoinkis, M. Klemm, M. Sing, R. Cla...