Dresden 2003 – scientific programme

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MA: Magnetismus

MA 6: Magnetische Partikel / Cluster

MA 6.12: Talk

Monday, March 24, 2003, 18:00–18:15, HSZ/04

Non-equilibrium dynamics of interacting superparamagnetic particles in discontinuous Co₈₀Fe₂₀/Al₂O₃ multilayers — •S. Sahoo¹, O. Petracic¹, Ch. Binek¹, W. Kleemann¹, P. Nordblad², S. Cardoso³, and P. Freitas³ — ¹Laboratorium für Angewandte Physik, Gerhard-Mercator-Universität, 47048 Duisburg, Germany — ²Department of Material Science, Uppsala University, Box 534, SE-75121 Uppsala, Sweden — ³INESC, Rua Alves Redol 9-1, 1000 Lisbon, Portugal

Random dipolar interactions and anisotropies of ferromagnetic nanoparticles in discontinuous magnetic multilayer systems [Co₈₀Fe₂₀(t)/ Al₂O₃(3 nm)] with t = 0.9 nm give rise to a low temperature collective superspin glass (SSG) state as evidenced by the critical slowing down of relaxation and the divergence of the nonlinear susceptibility. Magnetization relaxation measurements show that the system ages, i.e. the magnetic response depends on its thermal history and on the length of time it has been kept at constant temperature in the spin glass phase. Furthermore, the system memorizes the structure of a quasi-equilibrium state reached after an intermittent stop-and-wait protocol. These observations indicate that the system approaches equilibrium during aging and can be explained by a growing correlation length between the superspins.