μSR-detected soft mode toward a possible phase transition in a disordered spin-gap system, (CH3)2CHNH3–Cu(ClxBr1−x)3

Abstract Measurements of the macroscopic properties have indicated that the bond-disordered spin-gap system (CH 3 ) 2 CHNH 3 –Cu(Cl x Br 1− x ) 3 is gapless when x is between 0.44 and 0.87. Using muon spin relaxation to investigate the microscopic properties of a sample with x =0.35, we observed a dynamical spin fluctuation, whose characteristic frequency decreased with decreasing temperature, indicating a magnetic ground state.