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, C₃₆H₄₈Cu₂F₆N₈O₁₂ S₂ (TK91). According to the first principle Density Functional Theory calculations, the compound represents a 3D-coupled dimer system with intradimer coupling J₁/k_B~ 10 K and interdimer couplings J₂/k_B∼ J₃/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 TlCuCl₃ 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.