Dzyaloshinskii-Moriya induced inter-chain frustration in a new spin-chain compound

We present a first study of the Dzyaloshinski-Moriya spin-chain material K$_2$CuSO$_4$Br$_2$, highlighting the peculiar frustration of inter-chain couplings between nearest neighbor chains in this compound. Bulk magnetization and specific heat data are found well consistent with spin-chain models. Inelastic neutron scattering data support the pronounced one-dimensionality of the compound. In detail, intra-chain exchange amounts to $20.4$ K, yet magnetic long-range-order sets in only at $100$ mK. An extraordinary magnetic phase diagram is observed, which may be attributed to inter-chain frustration of helical intra-chain correlations. The relevant Dzyaloshinskii-Moriya exchange is evidenced by ESR-data. Funding by SNSF division 2 is acknowledged.