title: Experimental evidence for violation of the fluctuation-dissipation theorem in a superspin glass.
abstract: We present the experimental observation of the fluctuation-dissipation theorem 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(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.
authors.affiliation: Service de Physique de l'Etat Condensé (CNRS/URA 2464), DSM/IRAMIS/SPEC, CEA Saclay, F-91191 Gif/Yvette Cedex, France. katsuyoshi.komatsu@cea.fr
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Komatsu
authors.forename: Denis
authors.initials: D
authors.lastname: L'Hôte
authors.forename: Sawako
authors.initials: S
authors.lastname: Nakamae
authors.forename: Vincent
authors.initials: V
authors.lastname: Mosser
authors.forename: Marcin
authors.initials: M
authors.lastname: Konczykowski
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Dubois
authors.forename: Vincent
authors.initials: V
authors.lastname: Dupuis
authors.forename: Regine
authors.initials: R
authors.lastname: Perzynski