Magnetic vortex core reversal by excitation with short bursts of an alternating field

Abstract

The vortex state, characterized by a curling magnetization, is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of micrometre size and below. The interplay between the magnetostatic and the exchange energy favours an in-plane, closed flux domain structure. This curling magnetization turns out of the plane at the centre of the vortex structure, in an area with a radius of about 10 nanometres--the vortex core. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. The sense of gyration is determined by the vortex core polarization. Here we report on the controlled manipulation of the vortex core polarization by excitation with small bursts of an alternating magnetic field. The vortex motion was imaged by time-resolved scanning transmission X-ray microscopy. We demonstrate that the sense of gyration of the vortex structure can be reversed by applying short bursts of the sinusoidal excitation field with amplitude of about 1.5 mT. This reversal unambiguously indicates a switching of the out-of-plane core polarization. The observed switching mechanism, which can be understood in the framework of micromagnetic theory, gives insights into basic magnetization dynamics and their possible application in data storage.

Symmetry breaking in the formation of magnetic vortex states in a permalloy nanodisk

“…With two possible orientations of c and p, four different ground states of a magnetic vortex can occur 7,8 . The magnetic vortex structure constitutes a fascinating topological structure for fundamental studies of nanoscale spin behaviour and offers great potential as a novel concept in data storage technologies [9][10][11][12][13][14][15] . A priori, one would expect the energy of the four states to be degenerate.…”

Chirality control via double vortices in asymmetric Co dots

“…Magnetic vortices in sub-micron sized dots have gained considerable interests in recent years due to their unique reversal mechanisms, fascinating topological properties, and potential applications in information storage, [1][2][3][4][5][6] spin-torque oscillators, 7,8 magnetic memory and logic devices, 9 and targeted cancer-cell destruction strategies. 10 Vortices are one type of topological defects characterized by an in-plane magnetization with a clockwise (CW) or counter-clockwise (CCW) chirality and a central core with an out-of-plane magnetization (up or down polarity).…”

Experimental observation of switching in ferromagnetic nanoscale double disks

“…[1][2][3] The hysteresis curve measured for an applied in-plane magnetic field shows zero remanence and the magnetization reversal involves nucleation of a vortex, shift of the vortex's center perpendicular to the applied field and annihilation of the vortex. 4 The reversal of the out of plane center by means of microwave-or ac-current excitation is currently an interesting topic 5,6 which offers the possibility to use the up and down orientation of vortex's center in memory applications. Here we address experimentally the question whether different modes of switching can be achieved if two ferromagnetic disks overlap forming a peanut shaped structure.…”