Cole-Cole analysis of the superspin glass system Co80Fe20/Al2O3
Petracic, O. · Sahoo, S. · Binek, Ch. · Kleemann, W. · Sousa, J. B. · Cardoso, S. · Freitas, P. P.
Original · EN
Ac susceptibility measurements were performed on discontinuous magnetic multilayers [Co80Fe20(t)/Al2O3(3nm)]x10, t = 0.9 and 1.0nm, 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 < 100K at different dc fields and as a function of frequency 0.01 < f < 1000Hz. The spectral data were successfully analysed by use of the phenomenological Cole-Cole model, giving a power-law temperature dependence of the characteristic relaxation time tauc and a high value for the polydispersivity exponent, alpha = 0.8, typical of spin glass systems.
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