Aging and memory effects in zero-field-cooled collections of two-level subsystems

摘要

Numerical simulations of the temperature and time dependence of the moment of a collection of thermally activated, interacting two-level subsystems, explicitly prepared under zero-field-cooled (ZFC) conditions, are presented, which clearly demonstrate that such systems do indeed exhibit aging and memory effects analogous to those observed in collectively frozen spin glasses. In particular, if zero-field cooling at a constant cooling rate is interrupted temporarily by aging in zero field at a constant temperature T_a for a time Δt_a before the system is subsequently probed by the application of a magnetic field, then the aged moment, measured either as a function of temperature T on warming at a fixed rate, or as a function of observation time ln t at fixed temperature T_a, will lie below the unaged moment, and the difference between the aged and unaged response functions will exhibit an anomaly in the vicinity of either the aging temperature or the aging time, depending on the experiment which is performed.