Control of magnetic skyrmion chirality in 2D and 3D systems

For the development of future spintronic devices, the control of magnetic chirality is of fundamental importance. Central to this promise, we find magnetic skyrmions which show great potential for energy-efficient logic devices, where data could be encoded as magnetic chirality. In this talk, we will address the control of magnetic chirality in two systems - (1) the 2D ferromagnet, CrBr3, and (2) a 3D, helical cobalt nanowire [1, 2]. Our work demonstrates new strategies to control magnetic chiral states in 2D magnets and 3D nanostructures, creating a promising platform for future quantum and spintronic applications.

2D magnets can host chiral spin textures which can be controlled by using external stimuli such as strain and electric/magnetic fields [1]. One such material is CrBr3, a ferromagnetic insulator capable of hosting Bloch skyrmions of mixed chirality. Using in-situ cryo-Lorentz TEM, we show that an in-plane magnetic field reduces the energy barrier between magnetic bubbles of opposite chirality, leading to spontaneous switching of magnetic chirality through thermal fluctuations. We will demonstrate that chirality switching in this material can lead to “freezing” of the magnetic bubble lattice, thereby inducing a 2D phase transition from a disordered phase to a hexatic phase of the lattice.

Improving nanofabrication techniques, such as electron beam induced deposition, have allowed the creation of 3D nanomagnetic structures with a precisely designed geometry. The 3D geometric control afforded allows the formation and stability of intricate magnetic textures not possible in 2D. Here, we report formation of fractional skyrmion tubes in a double helical cobalt nanostructure, imaged with x-ray magnetic ptychography [2]. We show how 3D geometric patterning can control the magnetic energy landscape and investigate the fundamental interplay between magnetic and geometric chirality and hence show how the coupling between 3D geometric and magnetic chirality can be locally broken and recovered. Notably, for the first time, we explore the implications of having the magnetic chirality oppose that of the geometry. This opposing chirality directly results in the formation of higher-order topological states, representing a mechanism for skyrmion tube formation based purely on 3D geometric effects.