Cooling rate effect upon the field-cooled magnetization of an insulating spin-glass

Abstract

The field-cooled magnetization (FCM) of two cobalt aluminosilicate spin-glasses have been measured as a function of applied magnetic field and the rate of cooling through the spin-glass freezing temperature, Tf. For the lowest fields, a difference of ∼5% in the magnitude of the FCM for T<Tf was observed between the fastest cooling rate of ≳200 mK/s and the slowest rate of 1 mK/s. The magnitude of the FCM at a constant T<Tf did not change over a period of 8×104 s; and as long as the warming rate was the same as the cooling rate, the FCM was essentially ‘‘reversible.’’ These cooling rate effects show striking similarity to a real liquid-glass transition and suggest the FCM ‘‘plateau’’ may arise from the cooling rate being faster than the time necessary for the magnetic spins to relax to their true thermodynamic equilibrium.