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Influence of the gyromagnetic term in the effect of an oblique magnetic field on the superparamagnetic relaxation time |
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| Institution: | 1. Department of Microelectronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland;2. Department of Applied Mathematics and Theoretical Physics, The Queen''s University of Belfast, Belfast BT7 INN Northern Ireland, UK;3. Laboratoire de Magnétisme et d''Optique del''Université de Versailles, UKA 151 Bâtiment Fernrat, 45 Avenue des États Unis, 78035 Versailles Cedex, France;1. Departamento de Construcciones Arquitectónicas 1, Escuela Técnica Superior de Arquitectura, Universidad de Sevilla, 5 Avenida Reina Mercedes, n_ 2, 41012, Sevilla, Spain;2. CERIS, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal;1. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China;2. Dongfang Turbine Co., Ltd., Deyang 618000, China |
| Abstract: | The effect of a uniform magnetic field applied at an oblique angle ψ to the easy axis of magnetization on the superparamagnetic (longitudinal or Néel) relaxation time is illustrated by considering the simplest possible case where the field is applied normal to the easy axis. This is accomplished by numerically solving the Fokker-Planck equation for the smallest non-vanishing eigenvalue λ1. It is demonstrated that the asymptotic formula for the Kramers escape rate for general non-axially symmetric potentials evaluated for the particular case ψ = π/2 yields an acceptable asymptotic approximation to the behaviour of λ1 for sufficiently high-potential barrier heights and a wide range of values of the dimensionless damping factor. The effect of the gyromagnetic term which gives rise to coupling between the longitudinal and transverse modes of motion corresponds to an increase (higher when the dimensionless damping factor a is smaller) of the smallest non-vanishing eigenvalue λ1 and so to a decrease of the Néel relaxation time τ. |
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