Muon spin rotation and relaxation studies on the solid solution of the two spin-gap systems (C H3) 2 CHN H3 -Cu Cl3 and (C H3) 2 CHN H3 -Cu Br3

Muon-spin-rotation and -relaxation studies have been performed on (C H3) 2 CHN H3 Cu (Clx Br1-x) 3 with x=0.85 and 0.95, which are solid solutions of the two isomorphic spin-gap systems (C H3) 2 CHN H3 Cu Cl3 and (C H3) 2 CHN H3 Cu Br3 with different spin gaps. The sample with x=0.85 showed a clear muon spin rotation under zero-field below TN =11.65 K, indicating the existence of a long-range antiferromagnetic order. A critical exponent of the hyperfine field was obtained to be β=0.33, which agrees with 3D-Ising model. In the other sample with x=0.95, an anomalous enhancement of the muon spin relaxation was observed at very low temperatures indicating a critical slowing down due to a magnetic instability of the ground state.