Observation of Magnetic Radial Vortex Nucleation in a Multilayer Stack with Tunable Anisotropy

Abstract

Recently discovered exotic magnetic configurations, namely magnetic solitons appearing in the presence of bulk or interfacial Dzyaloshinskii-Moriya Interaction (i-DMI), have excited scientists to explore their potential applications in emerging spintronic technologies such as race-track magnetic memory, spin logic, radio frequency nano-oscillators and sensors. Such studies are motivated by their foreseeable advantages over conventional micro-magnetic structures due to their small size, topological stability and easy spin-torque driven manipulation with much lower threshold current densities giving way to improved storage capacity, and faster operation with efficient use of energy. In this work, we show that in the presence of i-DMI in Pt/CoFeB/Ti multilayers by tuning the magnetic anisotropy (both in-plane and perpendicular-to-plane) via interface engineering and postproduction treatments, we can stabilize a variety of magnetic configurations such as Néel skyrmions, horseshoes and most importantly, the recently predicted isolated radial vortices at room temperature and under zero bias field. Especially, the radial vortex state with its absolute convergence to or divergence from a single point can potentially offer exciting new applications such as particle trapping/detrapping in addition to magnetoresistive memories with efficient switching, where the radial vortex state can act as a source of spin-polarized current with radial polarization.

Collective antiskyrmion-mediated phase transition and defect-induced melting in chiral magnetic films

“…In ultra-thin systems with interface-induced anisotropic DMIs, such as Ir/Co/Pt multilayers 23 , 24 , skyrmions form even at room temperature and in zero external magnetic field due to strong PMA. Additionally, it has been shown numerically 25 and experimentally 26 that a new type of magnetic solitons, namely radial vortices, also occur in the presence of weak in-plane anisotropy. Contrarily, antiskyrmion lattices have only been observed in bulk systems such as Mn–Pt–Sn 27 , and some of the current research is focused on stabilizing antiskyrmions in a wider range of materials, including thin films 28 .…”

Skyrmion Formation in Nanodisks Using Magnetic Force Microscopy Tip

“…It was found that confinement due to geometry can increase the stability of the skyrmion significantly [9]. Therefore, low-dimensional patterned structures can serve as hosts of reconfigurable magnetic states stable at room temperature [10,11]. Measuring and controlling the nucleation of skyrmions in patterned geometries still remains an important task [10,12,13].…”

Helicity of magnetic vortices and skyrmions in soft ferromagnetic nanodots and films biased by stray radial fields

“…Radial vortices [ Fig. 1(c)], for which γ = 0, π, can be stabilized by the interfacial Dzyaloshinskii-Moriya interaction (IDMI) [24,25], or in vertical stacks of nanodots with antiferromagnetic interlayer exchange coupling [26,27]. Other vortices having γ = 0, ±π/2, π are often called "unconventional vortices" [28].…”