High-Field Magnetization Processes of Double Spin Chain Systems KCuCl₃ and TlCuCl₃

Abstract

High-field magnetization processes of S=1/2 double spin chain systems KCuCl₃ and TlCuCl₃ have been measured up to 39, T at 4.2 and 1.7, K for both systems and at 1.0 and 0.5, K for TlCuCl₃ using single crystals. A transition from a singlet ground state with an excitation gap to a gapless magnetic state with finite susceptibility occurs at H_c-- 20, T and 6, T for KCuCl₃ and TlCuCl₃, respectively. The critical field H_c depends on the external field direction due to the anisotropy of the g-factor. The excitation gap Δ is evaluated as Δ/k_B=31.1, K for KCuCl₃ and 7.5, K for TlCuCl₃. Although the antiferromagnetic interactions in TlCuCl₃ are stronger than those in KCuCl₃, which can be seen from the slope of the magnetization curves above H_c, the excitation gap in TlCuCl₃ is about a quarter of that of KCuCl₃. It is observed that the transition field H_c increases with increasing temperature.