Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 13: Poster:Schichten(1-23),Spinabh.Trsp(24-41),Exch.Bias(42-56),Spindyn.(57-67),Mikromag.(68-76),Partikel(77-90),Spinelektr.(91-97),Elektr.Theo.(98-99),Mikromag+PhasÜ+Aniso.(100-105),Magn.Mat.(106-118),Messmethod.(119-121),Obflm.+Abbverf.(122-123)

MA 13.84: Poster

Tuesday, March 9, 2004, 15:00–19:00, Bereich A

Magnetic relaxation of interacting ferromagnetic nanoparticle systems — •Xi Chen¹, S. Sahoo¹, S. Bedanta¹, O. Petracic¹, W. Kleemann¹, S. Cardoso², and P. P. Freitas² — ¹Angewandte Physik, Universität Duisburg-Essen, D-47048 Duisburg, — ²INESC, Rua Alves Redol 9-1, 1000 Lisbon, Portugal

The relaxation of the thermoremanent magnetisation of granular multilayers [Co₈₀Fe₂₀(t_n)/Al₂O₃(3 nm)]₁₀ is investigated by SQUID magnetometry at various nominal thicknesses t_n of the CoFe layers. In agreement with Monte Carlo simulations of random dipolarly interacting ferromagnetic nanoparticle systems [1] we find asymptotic stretched exponential decay for superspin glasses at low nanoparticle densities, t_n = 0.9 - 1.0 nm [2], while power law decay with finite asymptotic remanence is observed for superferromagnets at higher densities, t_n = 1.2 - 1.6 nm [3]. Efforts are put into localizing the marginal density, t_n ≈ 1.1 nm, where the stretched exponential is supposed to convert into a power law without remanence [1].

[1] M. Ulrich, J. Garcia-Otero, J. Rivas, and A. Bunde, Phys. Rev. B 67, 024416 (2003).

[2] S. Sahoo, O. Petracic, Ch. Binek, W. Kleemann, J. B. Sousa, S. Cardoso, and P. P. Freitas, J. Phys.: Condens. Matter 14, 6729 (2002).

[3] Xi Chen, W. Kleemann, O. Petracic, O. Sichelschmidt, S. Cardoso, and P. P. Freitas, Phys. Rev. B 68, 054433 (2003).