The University of Dublin | Trinity College -- Ollscoil Átha Cliath | Coláiste na Tríonóide
Trinity's Access to Research Archive
Home :: Log In :: Submit :: Alerts ::

TARA >
School of Engineering >
Electronic & Electrical Eng >
Electronic & Electrical Eng (Scholarly Publications) >

Please use this identifier to cite or link to this item: http://hdl.handle.net/2262/30602

Title: Effect of an oblique magnetic field on the superparamagnetic relaxation time. II. Influence of the gyromagnetic term
Author: COFFEY, WILLIAM THOMAS
Author's Homepage: http://people.tcd.ie/wcoffey
Keywords: Electronic & Electrical Engineering
Issue Date: 1998
Citation: Coffey, W.T., Crothers, D.S.F., Dormann, J.L., Geoghegan, L.J., Kennedy, E.C., 'Effect of an oblique magnetic field on the superparamagnetic relaxation time. II. Influence of the gyromagnetic term' in Physical Review B - Condensed Matter and Materials Physics, 58, 6, (1998), pp 3249 - 3266
Series/Report no.: Physical Review B - Condensed Matter and Materials Physics
58
6
Abstract: The effect of a uniform magnetic field applied at an oblique angle to the easy axis of magnetization on the superparamagnetic (longitudinal or Néel) relaxation time is investigated by numerically solving the Fokker-Planck equation for the smallest nonvanishing eigenvalue. It is demonstrated that the reciprocal of the asymptotic formula for the Kramers escape rate in the intermediate to high damping limit for general nonaxially symmetric potentials when applied to the present problem, yields an acceptable asymptotic approximation to the Néel time for moderate to high values of the damping. Alternatively the corresponding Kramers low dissipation formula (energy controlled diffusion) provides an acceptable approximation for very small values of the damping. The effect of the gyromagnetic term which gives rise to coupling between the longitudinal and transverse modes of motion generally corresponds to an increase of the smallest nonvanishing eigenvalue and so to a decrease of the Néel relaxation time. The integral relaxation time or area under the slope of the curve of the decay of the magnetization is also evaluated. It is demonstrated that for sufficiently high values of the uniform field (much less, however, than that required to destroy the bistable nature of the potential) the reciprocal of the lowest nonvanishing eigenvalue (proportional to the Néel time, or the time of reversal of the magnetization) and the integral relaxation time may differ exponentially from one another signifying the contributions of modes other than that associated with the overbarrier (Néel) relaxation process to the overall relaxation process. The overall behavior is qualitatively similar (apart from the azimuthal dependence) to that of the axially symmetric case which arises due to the depletion of the shallower of the two potential wells by the uniform field, so that the fast processes in the deeper of the two wells may come to dominate the relaxation process at sufficiently high values of the uniform field.
Description: PUBLISHED
URI: http://hdl.handle.net/2262/30602
Appears in Collections:Electronic & Electrical Eng (Scholarly Publications)

Files in This Item:

File Description SizeFormat
Effect of an oblique.pdfpublished (publisher copy) peer-reviewed368.5 kBAdobe PDFView/Open


This item is protected by original copyright


Please note: There is a known bug in some browsers that causes an error when a user tries to view large pdf file within the browser window. If you receive the message "The file is damaged and could not be repaired", please try one of the solutions linked below based on the browser you are using.

Items in TARA are protected by copyright, with all rights reserved, unless otherwise indicated.

 

Valid XHTML 1.0! DSpace Software Copyright © 2002-2010  Duraspace - Feedback