ToF inelastic neutron scattering studies on quantum spin systems (CuCl)LaO ( = Nb, Ta)

Kawamura, Seiko   ; Nakajima, Kenji  ; Inamura, Yasuhiro; Tsujimoto, Yoshihiro*; Kitada, Atsushi*; Takeiri, Fumitaka*; Kageyama, Hiroshi*; Ajiro, Yoshitami*; Nishi, Masakazu*; Kakurai, Kazuhisa

The magnetic ground state of (CuCl)LaNbO has been suggested to be a spin-singlet state with an excitation gap of meV, while (CuCl)LaTaO has an antiferromagnetic (AFM) ground state. The systems are suspected to be a frustrated quantum spin system due to the competition between the nearest and next-nearest exchange interactions. We have studied magnetic excitation in these systems by ToF inelastic neutron scattering technique. The measurements were performed on powder samples of (CuCl)LaNbO and (CuCl)LaTaO at a disk-chopper-type spectrometer AMATERAS in J-PARC. In both systems, a band-like excitation was observed at meV. The dependence of the intensity of magnetic excitation around 2 meV for (CuCl)LaNbO well reproduces that observed at a triple-axis spectrometer, exhibiting characteristics of spin-singlet dimers. On the other hand, (CuCl)LaTaO in the AFM state exhibits a different dependence.