Experimental Evidence of Fluctuation-Dissipation Theorem Violation in a Superspin Glass

Abstract

We present the experimental observation of the fluctuation-dissipation theorem (FDT) violation in an assembly of interacting magnetic nanoparticles in the low temperature superspin glass phase. The magnetic noise is measured with a two-dimension electron gas Hall probe and compared to the out of phase ac susceptibility of the same ferrofluid. For "intermediate" aging times of the order of 1 h, the ratio of the effective temperature $T_{\mathrm{eff}}$ to the bath temperature T grows from 1 to 6.5 when T is lowered from $T_g$ to 0.3 $T_g$, regardless of the noise frequency. These values are comparable to those measured in an atomic spin glass as well as those calculated for a Heisenberg spin glass.

References in corpus (4)

• Spin glass behavior in an interacting gamma-Fe2O3 nanoparticle system
• Observation of superspin glass state in magnetically textured ferrofluid (gamma-Fe2O3)
• Growth of a dynamical correlation length in an aging superspin glass
• Aging and effective temperatures near a critical point

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• Financial Brownian particle in the layered order book fluid and Fluctuation-Dissipation relations