Ground States of Double Spin Chain Systems TlCuCl3, NH4CuCl3 and KCuBr3

Abstract

The magnetic susceptibilities of S = 1/2 double spin chain systems, TlCuCl3, NH4CuCl3 and KCuBr3, which are isomorphous with KCuCl3 have been measured using single crystals and polycrystals. The exchange interactions in a double chain can be described by a Heisenberg spin ladder with an additional diagonal interaction. It is found for TlCuCl3 and KCuBr3 that with decreasing temperature the susceptibilities for different external field directions exhibit broad maxima at 38 K and 130 K, respectively, and decrease exponentially to zero as observed in KCuCl3. This result indicates that their ground state is a spin singlet with an excitation gap. This behavior is attributed to the quantum effect characteristic of the spin ladder system. For NH4CuCl3, the susceptibility of polycrystals displays a round maximum at 4.5 K and decreases with a tendency toward zero, which implies the nonmagnetic ground state. © 1997, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.