Magnetic properties of quantum spin system RbCuMoO studied by SR technique

Kawamura, Seiko   ; Tomiyasu, Keisuke*; Koda, Akihiro*; Sari P., D.*; Asih, R.*; Yoon, S. W.*; Watanabe, Isao*; Nakajima, Kenji  

RbCuMoO is a quantum spin system having zig-zag chains of the spin-1/2 Cu ions. Whereas the system is expected to exhibit an incommensurate spin-singlet state based on a ratio of the second neighbor ferromagnetic interaction to the first neighbor antiferromagnetic interaction , there is no report to bare a direct evidence for the spin-singlet ground state of this system. We carried out SR measurements on this system, to clarify its ground state and dynamics. In the zero-field measurement, the time spectra do not show changes with temperature from 300 K to 20 K, while the muon spin relaxation is enhanced below 20 K. The relaxation is again independent of temperature below 1.5 K. The result reveals that the ground state of RbCuMoO is nonmagnetic. Furthermore, the longitudinal-field SR measurements indicate characteristic behavior of the internal field and dynamics accompanying formation of the spin singlet.