Localized magnetic excitations in the fully frustrated dimerized magnet BaCoSiOCl

Kurita, Nubuyuki*; Yamamoto, Daisuke*; Kanesaka, Takuya*; Furukawa, Nobuo*; Kawamura, Seiko   ; Nakajima, Kenji   ; Tanaka, Hidekazu*

Magnetic excitations of the effective spin =1/2 dimerized magnet BaCoSiOCl have been probed directly via inelastic neutron scattering experiments. We observed five types of excitation, which are all dispersionless within the resolution limits. The scattering intensities of the three low-lying excitations were found to exhibit different -dependences. Detailed analysis has demonstrated that BaCoSiOCl is a two dimensional spin dimer system described only by a single dimer site, where the triplet excitations are localized owing to the almost perfect frustration of the interdimer exchange interactions and the undimerized spins, even in small concentration, make an essential contribution to the excitation spectrum.