Thermoremanent magnetization as a probe of the field-quenched states in spin glasses

The aging process for spin glasses has been characterized by barrier hopping between states of similar magnetization, with the maximum barrier height surmounted proportional to the logarithm of the waiting time ${\mathit{t}}_{\mathit{w}}$. We investigate the microscopic nature of the decay of the irreversible component of the magnetization upon a change in magnetic field. In particular, we examine transitions between states with magnetizations associated with the initial and final values of the magnetic field, and their related barrier heights. We employ a field cycling protocol during the waiting time to determine which states (barriers) are occupied upon a change of magnetic field. We find that the rapid component of magnetization change is associated with transitions between states of low barrier heights (we surmise of energy less than the change in overall Zeeman energy), and the slow component of magnetization change [decay of the thermoremanent magnetization (TRM)] is associated with diffusion from states at larger barrier heights to the ‘‘sink’’ associated with the (rapid) small barrier height transitions. The transitions between states of differing magnetization are limited to transitions between states of similar (small) barrier heights. We believe these observations account for the microscopics of spin-glass dynamics during the time decay of the TRM.