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 to the bath temperature grows from 1 to 6.5 when is lowered from to 0.3 , 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.
- Received 14 October 2010
DOI:https://doi.org/10.1103/PhysRevLett.106.150603
© 2011 American Physical Society