Abstract
Magnetization dynamics can be coherently controlled by THz laser excitation, which can be applied in ultrafast magnetization control and switching. Here, transient magnetization dynamics are calculated for excitation with THz magnetic field pulses. We use the ansatz of Smit and Beljers, to formulate dynamic properties of the magnetization via partial derivatives of the samples free energy density, and extend it to solve the Landau-Lifshitz-equation to obtain the THz transients of the magnetization. The model is used to determine the magnetization response to ultrafast multi- and single-cycle THz pulses. Control of the magnetization trajectory by utilizing the THz pulse shape and polarization is demonstrated.
Highlights
The partial derivatives of the free energy density are given by Fφφ = μ0MS(Hext + HA), Fθθ = μ0MS(Hext + MS + HA), and Fφθ = 0 with HA = 2Ku/(μ0MS)
An analytical model for transient magnetization dynamics of a homogeneously magnetized sample based on the Landau-Lifshitz equation with Gilbert damping is derived
The solution to the equation of motion is formulated via the partial derivatives of the free energy density and is given for multi- and single-cycle THz laser pulses
Summary
Lars Bocklage[1,2] received: 26 November 2015 accepted: 19 February 2016 Published: 09 March 2016. It was shown that ultrafast magnetization dynamics are described by the LLG as long as the interactions are non-thermal and arise from a time-variation of the effective field[6,7,18] This holds for THz laser pulses[6,7]. We solve the LLG in spherical coordinates and the effective magnetic field is expressed via the derivatives of the free energy density[19,20] similar to the formulation of the ferromagnetic resonance by Smit and Beljers[21] In this way we derive a general solution for transient magnetic states that are independent of actual sample properties and of the explicit knowledge of the internal fields.
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