• Ozerov, M.; Zvyagin, A.A.; Cizmar, E.; Wosnitza, J.; Feyerherm, R.; Xiao, F.; Landee, C.P.; Zvyagin, S.A.: Spin dynamics in S=½ chains with next-nearest-neighbor exchange interactions. Physical Review B 82 (2010), p. 014416/1-5

10.1103/PhysRevB.82.014416
Open Access Version

Abstract:
Low-energy magnetic excitations in the S= 1/2 chain compound [(C6H9N2)CuCl3]CuCl3 [known as (6MAP)CuCl3] are probed by means of tunable-frequency electron spin resonance. Two modes with asymmetric (with respect to the hν =gμ_B B line) frequency-field dependences are resolved, illuminating the striking incompatibility with a simple uniform S= 1/2 Heisenberg chain model. The unusual ESR spectrum is explained in terms of the recently developed theory for S= 1/2 chains, suggesting the important role of next-nearest neighbor interactions in this compound. Our conclusion is supported by model calculations for the magnetic susceptibility of (6MAP)CuCl3, revealing a good qualitative agreement with experiment.