Cole-Cole analysis of the superspin glass system Co80Fe20/Al2O3

TL;DR

This study uses Cole-Cole analysis on ac susceptibility data to investigate the spin-glass behavior of CoFe/Al2O3 multilayers, revealing a power-law relaxation and high polydispersivity characteristic of spin glasses.

Contribution

It applies Cole-Cole modeling to analyze ac susceptibility in magnetic multilayers, providing insights into their spin-glass dynamics and relaxation properties.

Findings

Power-law temperature dependence of relaxation time tau_c

High polydispersivity exponent alpha = 0.8

Confirmation of spin-glass phase behavior

Abstract

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 tau_c and a high value for the polydispersivity exponent, alpha = 0.8, typical of spin glass systems.