What is the physical significance of frequency dependent freezing temperature shift during AC susceptibility measurement? Why only spin-glass can show this typical behavior unlike other magnetic phases?
Because the freezing temperature Tf relation on frequency f can de described by Vogel-Fulcher law:
f=f0exp(-Ea/kb(Tf-Tf0))
ehere f0, Tf0 are fitting aprameters, Ea is an activation energy and kb is Boltzmann constant.
When you perform measurements at different frequencies you "observe" spin systems in different time intervals (time windows). At high frequency the measurement time is fast and the time window is short thus there is a little chance to observe changes in a system of spins. At low frequency the time of measurements is long (long time windows) and you can observe relaxation or changes in a system of spins, which seems to be "frozen" at high frequencies. Thus at high frequency the system can be "frozen" like below freezing temperature, whereas it can exhibit relaxation at lower frequency and behave like above freezing temperature.
Best regards,
Bartek
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