Field-induced magnetic ordering in TlCuCl 3: lattice deformation and features of first-order transition

Abstract

We present NMR and strain-gauge study of a zigzag chain spin-gap material TlCuCl 3 which undergoes a field-induced long-range magnetic ordering transition regarded as a magnon Bose–Einstein condensation (BEC). Deformation of the crystal lattice at the magnetic transition is inferred from the temperature dependence of the quadrupole shift of Cl and direct strain-gauge measurements, implying strong spin–phonon coupling. A λ-like singularity in spin-lattice relaxation rate at the transition reveals enhancement of electron spin fluctuations as precursor to transverse Néel order.