Article

# Vortex core magnetization dynamics induced by thermal excitation

Applied Physics Letters (Impact Factor: 3.52). 12/2011; 100(11). DOI: 10.1063/1.3694757

Source: arXiv

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**ABSTRACT:**The dynamics of gyrotropic vortex motion in a thin circular nanodisk of soft ferromagnetic material is considered. The demagnetization field is calculated using two-dimensional Green's functions for the thin-film problem and fast Fourier transforms. At zero temperature, the dynamics of the Landau-Lifshitz-Gilbert equation is simulated using fourth-order Runge-Kutta integration. Pure vortex initial conditions at a desired position are obtained with a Lagrange multipliers constraint. These methods give accurate estimates of the vortex restoring force constant kF and gyrotropic frequency, showing that the vortex core motion is described by the Thiele equation to very high precision. At finite temperature, the second-order Heun algorithm is applied to the Langevin dynamical equation with thermal noise and damping. A spontaneous gyrotropic motion takes place without the application of an external magnetic field, driven only by thermal fluctuations. The statistics of the vortex radial position and rotational velocity are described with Boltzmann distributions determined by kF and by a vortex gyrotropic mass mG=G2/kF, respectively, where G is the vortex gyrovector.Physical review. B, Condensed matter 09/2012; 86(10). · 3.66 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We demonstrate a lossless switching between vortex and collinear magnetic states in circular FePd disks arranged in a square lattice. Above a bifurcation temperature (Te) we show that thermal fluctuations are enough to facilitate flipping between the two distinctly different magnetic states. We find that the temperature dependence of the vortex annihilation and nucleation fields can be described by a simple power law relating them to the saturation magnetization.New Journal of Physics 05/2014; 16(5):053002. · 4.06 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**It has recently been shown that domain walls in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(1 1 0) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting the systems to a thermal gradient we observe a temperature dependent movement of the domain wall as well as changes of the spatial magnetization profile of the system. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. The material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy and the exchange interaction, and shows that the larger DW velocities are found for materials with low magnetic anisotropy. The relatively slow DW motion of the Fe/W(1 1 0) system is hence primarily caused by its large magnetic anisotropy.Physical Review B 08/2013; 90(1). · 3.66 Impact Factor

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