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AM: Magnetismus

AM 9: Poster: Magnetowid. (1-17), Dü. Schichten (18-34), Oberfl
ächenmag. (35,36), Mikr. Methoden (37-45), Mikromag. (46-58), Phasenüberg. (59-77), Spektroskop. (78-91), Nanokr.Mat.(92-96), Anisotrop. (97-101), Schmelzen(102-104),Sonst/postdeadl.(105-109)

AM 9.28: Poster

Dienstag, 27. März 2001, 14:45–19:00, Foyer S 3

Magnetic critical behavior of dipolar interacting ferromagnetic nanoparticles in discontinuous Co₈₀Fe₂₀/Al₂O₃ multilayers — •S. Sahoo¹, O. Sichelschmidt¹, O. Petracic¹, Ch. Binek¹, W. Kleemann¹, G.N. Kakazei², Yu.G. Pogorelov², J.B. Sousa², S. Cardoso³, and P.P. Freitas³ — ¹Laboratorium für Angewandte Physik, Gerhard-Mercator-Universität, D-47048 Duisburg — ²IFIMUP, Departamento de Fisica, Universidade de Porto, 4169-007 Porto, Portugal — ³INESC, Rua Alves Redol 9-1, 1000, Lisbon, Portugal

Discontinuous metal insulator multilayers (DMIMs) Co₈₀Fe₂₀(t) /Al₂O₃(3 nm)₁₀ of CoFe granules embedded in Al₂O₃ spacer layers are studied by SQUID magnetometry and ac susceptometry. Zero field ac susceptibility studies on samples with 0.9 ≤ t ≤ 1.6nm reveal the existence of a low temperature super spin glass state. It is manifested by a characteristic frequency dispersion of the peaks of both Re(χ_ac) and Im(χ_ac) vs T. The glass transition temperature T_g and the critical exponents, zν and γ, are obtained from the temperature dependence of the relaxation time, τ , and the non-linear susceptibility, χ₃, respectively. Moreover a superferromagnetic state is evidenced for samples with t ≥ 1.05nm from a second peak in Re(χ_ac) at T = T_SFM > T_g. In order to study the influence of the dimensionality we investigated the 3D to 2D crossover by subsequent reduction of the number of DMIM bilayers.