Quantum Dissipation Theory of Slow Magnetic Relaxation Mediated by Domain-Wall Motion in the One-Dimensional Chain Compound [Mn (hfac)2 BN OH]

Based on a quantum dissipation theory of open systems, we present a theoretical study of slow dynamics of magnetization for the ordered state of the molecule-based magnetic complex [Mn (hfac)2 BN OH] composed from antiferromagnetically coupled ferrimagnetic (5 2,1) spin chains. Experimental investigations of the magnetization process in pulsed fields have shown that this compound exhibits a metamagnetic AF-FI transition at a critical field in the order of the interchain coupling. A strong frequency dependence for the ac susceptibility has been revealed in the vicinity of the AF-FI transition and was associated with an AF-FI interface kink motion. We model these processes by a field-driven domain-wall motion along the field-unfavorable chains correlated with a dissipation effect due to a magnetic system-bath coupling. The calculated longitudinal magnetization has a two-step relaxation after the field is switched off and are found in good agreement with the experiment. The relaxation time determined from the imaginary part of the model ac susceptibility agrees qualitatively with that found from the remanent magnetization data. © 2006 The American Physical Society.The authors would like to thank E. Z. Kuchinskii for discussions. This work was partly supported by Grant No. NREC-005 of US CRDF Civilian Research and Development Foundation. Two of the authors V.E.S. and A.S.B. thank the Foundation Dynasty Moscow for support