Physics – Condensed Matter – Statistical Mechanics
Scientific paper
2007-01-31
Phys. Rev. B 75, 184432 (2007) (10 pages)
Physics
Condensed Matter
Statistical Mechanics
24 pages, 4 figures
Scientific paper
10.1103/PhysRevB.75.184432
We present an analytical method of calculating the mean first-passage times (MFPTs) for the magnetic moment of a uniaxial nanoparticle which is driven by a rapidly rotating, circularly polarized magnetic field and interacts with a heat bath. The method is based on the solution of the equation for the MFPT derived from the two-dimensional backward Fokker-Planck equation in the rotating frame. We solve these equations in the high-frequency limit and perform precise, numerical simulations which verify the analytical findings. The results are used for the description of the rates of escape from the metastable domains which in turn determine the magnetic relaxation dynamics. A main finding is that the presence of a rotating field can cause a drastic decrease of the relaxation time and a strong magnetization of the nanoparticle system. The resulting stationary magnetization along the direction of the easy axis is compared with the mean magnetization following from the stationary solution of the Fokker-Planck equation.
Denisov S. I.
Hänggi Peter
Sakmann Kaspar
Talkner Peter
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