Giant magnetic field dependence of the coupling between spin chains inBaCo2V2O8

Abstract

We use nuclear magnetic resonance to map the complete low-temperature phase diagram of the antiferromagnetic Ising-like spin-chain system ${\mathrm{BaCo}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ as a function of the magnetic field applied along the chains. In contrast to the predicted crossover from the longitudinal incommensurate to the transverse antiferromagnetic ordered phase, we find a sequence of three magnetically ordered phases between the critical fields $3.8$ and $22.8 \mathrm{T}$. Their origin is traced to the giant magnetic field dependence of the total effective coupling between spin chains, found to vary by a factor of 24. We explain this interesting phenomenon as emerging from a combination of nontrivially coupled spin chains and incommensurate spin fluctuations in the chains treated as Tomonaga-Luttinger liquids.