Softening of breathing elastic mode and trigonal elastic mode in the disordered pyrochlore magnet NaCaCo 2 F 7

摘要: Here, the authors perform ultrasound velocity measurements in frustrated pyrochlore fluoride NaCaCo${}_{2}$F${}_{7}$, which exhibits spin freezing below ${T}_{f}$ $\ensuremath{\sim}$ 2.4 K with inherent presence of exchange disorder. In this cubic magnet, bulk modulus and trigonal shear exhibit anomalies at temperatures $\ensuremath{\sim}$20 down to ${T}_{f}$, reveal an occurrence magnetic field induced crossover from isostructural lattice instability toward a arising emergent dynamical spin-cluster state.