Localization of spin triplets in Tl1-xKxCuCl 3

Abstract

The effect of exchange randomness on field-induced magnetic ordering was investigated through specific heat measurements in Tl1-xK xCuCl3 with x ≤ 0.22. The isostructural parent compounds TlCuCl3 and KCuCl3 are coupled spin dimer systems with a gapped ground state and their field-induced antiferromagnetic ordering is described by the Bose-Einstein condensation (BEC) of spin triplets. Well-defined field-induced phase transitions were observed in Tl 1-xKxCuCl3. The critical exponent φ of the phase boundary defined by T(H) ∝ (H - Hc1/φ is reevaluated in TlCuCl3 as φ = 1.67 ± 0.07, which is close to φBEC = 3/2 derived from the magnon BEC theory. For x ≠ 0, the exponent φ decreases systematically with x. The phase boundary observed below 2 K for x > 0.1 approximates a linear function of temperature T. In the low-field region for H < Hc, no magnetic ordering is observed despite finite susceptibility. These properties are discussed in connection with the Bose glass phase argued by Fisher et al. © 2004 The Physical Society of Japan.