Magnetism
Rapid proliferation of electronic gadgets brings many benefits to people around the world in terms of communication and entertainment. On the other hand, these devices account for a growing portion of the energy household consumption and overall world consumption of electricity. Increasing the energy efficiency of these devices could have a far greater and immediate impact than gradual switch to renewable energy sources. The advances in the area of spintronics are therefore very important. Here we focus on local spin distribution and spin dynamics in nanosize magnetic objects.
In our article we investigate fundamental processes that govern magnetic vortex nucleation in sub-100nm mesoscopic magnets. Confinement leads to fundamental changes in physical behavior of materials due to increased role of the surface. In mesoscopic magnetic materials such changes in the energy landscape could lead to novel magnetic spin configurations such as vortices. Equilibrium properties of these new topological states are governed by both the properties of the magnetic material and the geometry of the object. On the other hand, confinement also leads to distinct dynamic behavior of the new topological states, since the available energy levels are very much limited. The transition probabilities between different states can thus be controlled by careful engineering of the geometry of the mesoscopic object.
The magnetization of disks in zero field can be oriented in-plane, out-of-plane, or vortex state can be created, depending on the disk diameter and thickness. In the disk the flux-closure magnetic state reduces the long range stray fields, i.e. reduces the magnetostatic interaction between neighboring disks. Therefore, such disk magnetic systems have a potential for high-density magnetic storage elements, with bits represented by chirality and polarity of a basic vortex state.
Here we analyze the mechanisms that establish specific chirality and polarity values in such Pacman-like nanomagnet by taking a closer look at energies and dynamics that govern the switching processes. We show that the polarity and the chirality of the vortex core nucleated in can be deterministically set by application in-plane field only. This is a promising finding to consider if using Pac-man like nanomagnet as a memory element in bit-patterned media or as a generator of magnetic vortices of desired polarity and chirality for microwave applications.
