Cole-Cole Analysis of the Superspin Glass System Co₈₀Fe₂₀/Al₂O₃

Authors

• O. Petracic, Laboratorium für Angewandte Physik, Gerhard-Mercator-Universität Duisburg
• Sarbeswar Sahoo, Laboratorium für Angewandte Physik, Gerhard-Mercator-Universität DuisburgFollow
• Christian Binek, University of Nebraska-LincolnFollow
• Wolfgang Kleemann, Laboratorium für Angewandte Physik, Gerhard-Mercator-Universität DuisburgFollow
• J.B. Sousa, IFIMUP, Departamento de Fisica, Universidade de Porto, 4169-007 Porto, Portugal
• Susana Cardoso de Freitas, INESCFollow
• P.P. Freitas, INESC

Document Type

Article

Date of this Version

4-9-2003

Comments

Published in Phase Transitions 76:4–5 (2003), pp. 367–375. Copyright © 2003 Taylor & Francis Ltd. Used by permission. http://www.tandf.co.uk/journals/titles/01411594.asp

Abstract

Ac susceptibility measurements were performed on discontinuous magnetic multi-layers [Co₈₀Fe₂₀ (t)/Al₂O₃ (3 nm)] ₁₀, t = 0.9 and 1.0 nm, by Superconducting Quantum Interference Device (SQUID) magnetometry. The CoFe forms nearly spherical ferromagnetic single-domain nanoparticles in the diamagnetic Al₂O₃ matrix. Due to dipolar interactions and random distribution of anisotropy axes the system exhibits a spin-glass phase. We measured the ac susceptibility as a function of temperature 20 ≤ T ≤ 100 K at different dc fi elds and as a function of frequency 0.01 ≤ f ≤ 1000 Hz. The spectral data were successfully analyzed by use of the phenomenological Cole–Cole model, giving a power-law temperature dependence of the characteristic relaxation time τ_c and a high value for the polydispersivity exponent, α ≈ 0.8, typical of spin glass systems.