Activation volumes in thin film and particulate systems

We consider magnetization reversal and decay in thin film and particulate m agnetic systems where thermally activated processes are important. We prese nt measurements on the activation volumes associated with magnetization rev ersal in CoCrPt thin films. We find that the measured activation volume V-* goes through a minimum as the film thickness is decreased from 17.5 to 5.5 nm. We have modeled this behavior qualitatively by assuming that the energ y barrier to thermally activated reversal varies as 1/H, as has been predic ted for incoherent nucleation processes and thermally activated domain-wall motion. This model also predicts that V-* varies as T-2 at high temperatur e in qualitative agreement with measurements on several systems. This behav ior is contrasted with that predicted on the basis of coherent rotation of the magnetization in single-domain particles. (C) 2000 American Institute o f Physics. [S0021-8979(00)44708-0].