N. Cavadini, D. Andreica, F. N. Gygax, A. Schenck, K. Krämer, H.-U. Güdel, H. Mutka and A. Wildes
Local spin susceptibility in KCuCl₃
Physica B 335, 37-40 (2003)                 

Abstract: S = 1/2 KCuCl₃ has a singlet ground state with a finite spin energy gap D = 31 K to triplet excited states. The bulk magnetic susceptibility vanishes for T << D according to the singlet nature of the ground state. Astonishingly, recent muon spin relaxation (mSR) measurements reveal fluctuating internal fields down to T = 5 K, with the onset of a quasi-static regime below T = 5 K. The presence of free electronic magnetic moments and their possible freezing at low T contradicts the bulk picture of KCuCl₃. By means of polarized neutron scattering and mSR measurements on single crystals of the same batch, the nature of the local spin susceptibility is studied. The claims of a substantial muon influence in KCuCl₃ are reinforced.