Muon spin relaxation and rotation study on the solid solution of the two spin-gap systems (CH3)2CHNH3-CuCl3 and (CH3)2CHNH3-CuBr3

摘要

Muon-spin-rotation and relaxation studies have been performed on(CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$ with $x$=0.85 and 0.95, which aresolid solutions of the two isomorphic spin-gap systems(CH$_3$)$_2$CHNH$_3$CuCl$_3$ and (CH$_3$)$_2$CHNH$_3$CuBr$_3$ with differentspin gaps. The sample with $x$=0.85 showed a clear muon spin rotation underzero-field below $T_{\rm N}$=11.65K, indicating the existence of a long-rangeantiferromagnetic order. A critical exponent of the hyperfine field wasobtained to be $\beta$=0.33, which agrees with 3D-Ising model. In the othersample with $x$=0.95, an anomalous enhancement of the muon spin relaxation wasobserved at very low temperatures indicating a critical slowing down due to amagnetic instability of the ground state.