The effect of confinement on thermal fluctuations in nanomagnets

Abstract

We study the magnetization dynamics in nanomagnets excited by stochastic magnetic fields to mimic temperature in a micromagnetic framework. The effect of confinement arising from the finite size of the structures is investigated, and we visualize the spatial extension of the internal magnon modes. Furthermore, we determine the temperature dependence of the magnon modes and focus specifically on the low frequency edge modes, which are found to display fluctuations associated with switching between C-and S-states, thus posing an energy barrier. We classify this fluctuating behavior in three different regimes and calculate the associated energy barriers using the Arrhenius law.

Emergent anisotropy in magnetic metamaterials

“…The incident wavelength of the p-polarized incident laser was set to 659 nm with a spot size of 1 mm 2 , giving the response of approximately million discs. An external field with an amplitude of 40 mT was applied along the [10] and [11] directions, with a sweep rate of 0.11 Hz.…”

“…The in-plane cell size was defined as 0.5•l ex , were the exchange length, l ex is a material parameter defined by M sat and A ex [24]. The average magnetization | m | of the magnetic states in Table I were obtained by saturating disks placed on a 5×5 grid along [10] and [11] direction. This was followed by relaxing the systems to its minimum free energy, leading to a mixture of different states.…”

“…1. Top: Magnetization loops at 83 K and 276 K for mesospins with a diameter of 350 nm and magnetic field applied along [11] direction. The curves have been normalized to the net magnetization at 0 K, obtained by fitting the magnetization at 40 mT.…”

“…In these studies, the magnetic islands -mesospins -have been treated as indivisible building blocks without inner structure, with a classical order-disorder transition of the mesoscopic elements. It is only recently their inner degrees of freedom have been included in the description [9][10][11]. For disk-shaped mesospins, a collection of works addressed dynamics involving bistability of magnetization textures within, depending on geometry and temperature [12,13].…”

“…It was further shown that the size and shape of the mesospins determines also to which extent static internal magnetic textures, such as S-, C-, O-and vortex states, prevail [14][15][16][17]. A more detailed understanding of the role of thermal excitations in the magnetic texture was only recently developed [9,11]. In the light of this, systems allowing for the study of the effect of internal mesospin degrees of freedom on the collective order and thermal dynamics, have been shown to exhibit exotic order-disorder transitions [9,18].…”