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

Katsuyoshi Komatsu (1) , D. L'Hote (1) , Sawako Nakamae (1) , Vincent Mosser (2) , Marcin Konczykowski (3) , Emmanuelle Dubois (4) , V. Dupuis (4) , Régine Perzynski (4)

1 SPEC - UMR3680 - Service de physique de l'état condensé
2 ITRON - itron
3 LSI - Laboratoire des Solides Irradiés - Irradiated Solids Laboratory
4 PECSA - Physicochimie des Electrolytes, Colloïdes et Sciences Analytiques

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 $T_{\rm eff}$ 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.

Mots clés: Fluctuation Disspipation Theorem Violation Superspin Glass

Domaines: Systèmes désordonnés et réseaux de neurones [cond-mat.dis-nn]

Katsuyoshi Komatsu, D. L'Hote, Sawako Nakamae, Vincent Mosser, Marcin Konczykowski, et al.. Experimental Evidence of Fluctuation-Dissipation Theorem Violation in a Superspin Glass. Physical Review Letters, 2011, 106, pp.150603. ⟨10.1103/PhysRevLett.106.150603⟩. ⟨hal-00527460v2⟩