Abstract
We have numerically solved the Landau-Lifshitz-Gilbert (LLG) equation in its standard and inertial forms to study the magnetization switching dynamics in a $3d$ thin film ferromagnet. The dynamics is triggered by ultrashort magnetic field pulses of varying width and amplitude in the picosecond and Tesla range. We have compared the solutions of the two equations in terms of switching characteristic, speed and energy analysis. Both equations return qualitatively similar switching dynamics, characterized by regions of slower precessional behavior and faster ballistic motion. In case of inertial dynamics, ballistic switching is found in a 25 % wider region in the parameter space given by the magnetic field amplitude and width. The energy analysis of the dynamics is qualitatively different for the standard and inertial LLG equations. In the latter case, an extra energy channel, interpreted as the kinetic energy of the system, is available. Such extra channel is responsible for a resonant energy absorption at THz frequencies, consistent with the occurence of spin nutation.
Highlights
The traditional method of writing information to magnetic hard disk drives consists of reversing the magnetization direction via the application of magnetic fields produced by external currents and localized via a so-called “write-head.”
Geritts et al [5] demonstrated instead a technique by which ultrafast magnetization reversal can be achieved using picosecond-long magnetic field pulses transverse to the magnetization direction
From our LLG and iLLG simulations we explored the different switching dynamics triggered by ultrafast magnetic field pulses of different full-width at half-maximum (FWHM) and amplitude in the ps and Tesla ranges
Summary
The traditional method of writing information to magnetic hard disk drives consists of reversing the magnetization direction via the application of magnetic fields produced by external currents and localized via a so-called “write-head.” In order to achieve efficient switching, the magnetic field is applied nearly antiparallel to the direction of the initial magnetization state, and the switching process obtained is often referred to as “damped” switching [1–3]. In order to achieve efficient switching, the magnetic field is applied nearly antiparallel to the direction of the initial magnetization state, and the switching process obtained is often referred to as “damped” switching [1–3]. The switching time in this process is limited by the macroscopic relaxation time of the magnetization of the order of 100 ps, and correctly described by the standard Landau Lifhitz Gilbert (LLG) equation [4]. Geritts et al [5] demonstrated instead a technique by which ultrafast magnetization reversal can be achieved using picosecond-long magnetic field pulses transverse to the magnetization direction. Such a switching technique was reported in other studies [6,7]. At the same time, a series of experiments performed
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