Neutron scattering study of magnetic ordering and excitations in the doped spin-gap system Tl(Cu1-xMgx)Cl3 -: art. no. 184424

Neutron elastic and inelastic scattering measurements have been performed in order to investigate the spin structure and the magnetic excitations in the impurity-induced antiferromagnetic ordered phase of the doped spin gap system Tl(Cu1-xMgx)Cl-3 with x = 0.03. The magnetic Bragg reflections indicative of the ordering were observed at Q = (h,0,l) with integer h and odd l below T-N = 3.45 K. It was found that the spin structure of the impurity-induced antiferromagnetic ordered phase on average in Tl(Cu1-xMgx)Cl-3 with x = 0.03 is the same as that of the field-induced magnetic ordered phase for Hparallel tob in the parent compound TlCuCl3. The triplet magnetic excitation was clearly observed in the a*-c* plane and the dispersion relations of the triplet excitation were determined along four different directions. The lowest triplet excitation corresponding to the spin gap was observed at Q = (h,0,l) with integer h and odd l, as observed in TlCuCl3. It was also found that the spin gap increases steeply below T-N upon decreasing temperature. This strongly indicates that the impurity-induced antiferromagnetic ordering coexists with the spin gap state in Tl(Cu1-xMgx)Cl-3 with x = 0.03.