Aging, Rejuvenation, and Memory Effects in Single Crystal Spin Glass

Spin glasses are a prototype of complex systems for which dynamics can be studied experimentally only out of equilibrium. We are systematically studying the phenomena of aging, rejuvenation, and memory, common to many glassy systems.  We use ac susceptibility measurements made on a single crystal of CuMn with a 7.91% concentration of manganese and a T_g of 41 K. Aging occurs when the temperature is held fixed, leading to a relaxation or decrease of the susceptibility [1]. Rejuvenation occurs when the sample “forgets” that it aged and returns to a reference cooling curve (hence it gets “younger”) [1]. In the memory effect, after temperature cycling, the heating curve seems to “remember” its previous cooling history [1]. In this talk, we discuss these effects with a focus on rejuvenation and our attempts to understand its underlying mechanisms both through a droplet model (in the form of Bray-Moore temperature chaos [2]) and a hierarchical model. The ac frequency was 1 Hz and the ac field was 5 Oe.  The temperatures investigated ranged from 37 K to 8.5 K. Our data show that both the rejuvenation and memory results appear to favor a temperature dependent hierarchical model.

 

[1] Jonason, K., et al. "Memory and chaos effects in spin glasses." Physical Review Letters 81.15 (1998): 3243.

[2] Bray, Alan J., and Michael A. Moore. "Chaotic nature of the spin-glass phase." Physical review letters 58.1 (1987): 57.