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Ferromagnetic Precession

Working Group 2.52

The ferromagnetic precession is usually described using the Landau-Lifshitz-Gilbert-Equation (LLG):

In the LLG M is the magnetization of the ferromagnet, Heff is the effective field, |γ| is the gyromagnetic ratio, MS is the saturation magnetization and α is the Gilbert damping parameter.

The right hand side of the LLG has two terms, the precession term and the damping term. The precession term (-|γ|.M×Heff) can be derived from the quantum mechanic time evolution of the spin operator whereas the damping term (-α/MS .M×dM/dt) is of purely phenomenological origin.

The action of the two terms is sketched in Fig.2. The precession term induces the precession of the magnetization M about the effective field whereas the damping term leads to the convergence of the precession cone towards the effective field. The higher the value of the Gilbert damping parameter the faster the convergence of M towards Heff.

Fig 2: Sketch of the damped precession of the magnetization M under the influence of an effective field Heff.