Neutron Studies of Tb_(2)Mo_(2)O_(7)

摘要

We have used the new high energy resolution spectrometer (BaSiS), at the Spallation Neutron Source in Oak Ridge, to conclusively prove the existence of a low energy mode at 0.34(1) meV in the spin glass Tb_(2)Mo_(2)O_(7). This mode is reminiscent of the excitation observed in the ordered phases of both Tb_(2)Ti_(2)O_(7) and Tb_(2)Sn_(2)O_(7). The dynamical nature of the transition seen in the magnetization at approx 25 K suggests that this frustrated magnet shows a dynamic crossover between a high-temperature phase of poorly correlated, quickly relaxing spins to a low-temperature regime with much slower, short ranged spin correlations extending no further than to the next nearest neighbor. Existing theories explain the spin glass transition in terms of a phase transition and order parameters, and assume the existence of a distinct spin glass phase. There is no evidence for such a phase in Tb_(2)Mo_(2)O_(7).