# Mesure de relations de fluctuation-dissipation dans un verre de spin

Abstract : This PhD work presents an original experimental setup allowing to measure and compare spontaneous magnetization fluctuations and the corresponding response to a magnetic field. This quantitative comparison allows, via the Fluctuation-Dissipation theorem (FDT), a absolute determination of the sample's temperature, when it is at thermal equilibrium. For glassy systems, the "effective temperature"---an extension of temperature preserving the formalism of the FDT for systems with weak-entropy production---is now accessible. A spin glass sample ($CdCr_{1,7}In_{0,3}S_4$) extensively characterized allows the measurement. The deeply aging, non-stationary regime, is investigated; the necessary measurement of the spontaneous fluctuations is very delicate (the amplitude of these fluctuations corresponds to the sample's response to variations of the order of $1/10^6$ of the earth's magnetic field).
The results show first of all a quasi-stationary dynamics, as previously obtained. The strongly aging regime is now also reached. However, the measures can not be directly translated into term of effective temperature, the coexistence of quasi-stationary and aging dynamics being experimentally systematically observed. A scaling analysis is used to separate these two contributions. Subject to the validity of this analysis, the measures confirms the main predicted characteristics of the effective temperature. In particular, no dependence on the age of the system is found.
However, the different known models do not allow to explain completely all the characteristics of the measured effective temperature, and some of them seem still paradoxical...
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https://tel.archives-ouvertes.fr/tel-00002055
Contributor : Didier Hérisson <>
Submitted on : Friday, November 29, 2002 - 1:36:39 PM
Last modification on : Friday, March 5, 2021 - 3:00:35 PM
Long-term archiving on: : Friday, April 2, 2010 - 8:02:19 PM

### Identifiers

• HAL Id : tel-00002055, version 1

### Citation

Herisson Didier. Mesure de relations de fluctuation-dissipation dans un verre de spin. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2002. Français. ⟨tel-00002055⟩

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