GROUND-STATE AND ENERGY-GAP OF QUANTUM DOUBLE SPIN CHAIN SYSTEM - KCUCL3 FAMILY

The magnetic properties of the S = 1/2 double-spin chain systems, KCuC l3 and TlCuCl3, have been investigated by susceptibility and magnetiza tion measurements using single crystals. The present systems are descr ibed as Heisenberg spin ladders with an additional diagonal interactio n. The susceptibility results indicate that the ground states of the p resent systems are spin singlets with finite excitation gaps. It is fo und that the phase transition from the singlet ground state to the mag netic state occurs at H-c approximate to 20 and 5 T for KCuCl3 and TlC uCl3, respectively. (C) 1998 Elsevier Science B.V. All rights reserved .