Changes in the Onsager reaction field are used to account quantitatively for aging (the decrease in the magnetic susceptibility when cooling in zero field is halted below the glass temperature) and rejuvenation (the disappearance of aging phenomena on further cooling only to reappear at $T_w$ on heating) that characterize spin glasses. These effects must be caused by interactions between the spins since, absent the interactions, the magnetic properties of $N$ spins are just $N$ times the magnetic property of a single spin that cannot display aging. A spin introduced at an empty site with a nonzero field becomes polarized, and the polarized spin in turn polarizes its neighbors, thereby changing the local field. This additional field is the Onsager reaction field. Ma’s theory for the reaction field in spin glasses [PRB 22, 4484 (1980)] has been extended to provide a spin-glass model that can account for the experimental data.

• Received 14 July 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.027207