Field-induced phase transition in a metalorganic spin-dimer system—a potential model system to study Bose–Einstein condensation of magnons

Abstract

We report on the results obtained from studying electron spin resonance, magnetic susceptibility, specific heat and thermal expansion experiments on a metalorganic spin-dimer system, C 36 H 48 Cu 2 F 6 N 8 O 12 S 2 (TK91). According to the first principle Density Functional Theory calculations, the compound represents a 3D-coupled dimer system with intradimer coupling J 1 / k B ∼ 10 K and interdimer couplings J 2 / k B ∼ J 3 / k B ∼ 1 K. The measurements have been performed on both pressed powder and single-crystal samples in external magnetic fields up to 12 T and at low temperatures down to ∼ 0.2 K. Susceptibility measurements reveal a spin-gap behavior consistent with the theoretical results. Furthermore, clear indications of a field-induced phase transition have been observed. A similar field-induced phase transition was also detected in an inorganic compound TlCuCl 3 and was interpreted as Bose–Einstein condensation (BEC) of magnons. The possibility of changing both the intradimer and interdimer couplings in TK91 by chemical substitutions makes the system a potentially good system to study BEC of magnons.