The spin structures of interlayer coupled magnetic films with opposite chirality

S P Kang,N J Kim,J W Choi,B C Min,H Y Kwon,C Won

doi:10.1038/s41598-018-20800-8

Abstract

Using Monte-Carlo simulations and micromagnetic simulations, we reveal how the spin structural correlation and the skyrmion dynamics are affected by the interlayer coupling in a chiral magnetic bilayer system, in which the two layers have opposite chirality. The interaction through interlayer coupling between chiral magnetic structures influences the static and dynamics properties profoundly. The competition between the Dzyaloshinskii-Moriya interaction and the interlayer interaction allows multiple magnetic structures to be energetically stable, which includes sole skyrmion states (skyrmion appears in only one of the layers) and skyrmion pair states (coupled skyrmions in top and bottom layers). When current driven spin transfer torques are applied to each state, the sole skyrmion state is mainly propelled by a spin transfer torque causing the skyrmion hall effect, but the skyrmion pair state is propelled by a torque from skyrmion-skyrmion interaction and not influenced by the skyrmion hall effect. Also upon application of an external magnetic field, we found the skyrmions in a skyrmion pair state extinguish in an exclusive way, as the annihilation of a skyrmion in one of the layers stabilizes the once paired skyrmion in the other layer, i.e. the skyrmion lattice sites have only one skyrmion in either layer.

Highlights

Spintronics using magnetic skyrmions has been intensively studied in recent years[1,2,3,4,5,6,7,8,9]
The scale of a chiral structure is determined by the strength of DM interaction and the chirality of the structure is determined by the direction of DM vector that is related to the symmetry of the system[17,18]
The dynamics of the sole skyrmion and the skyrmion pair are distinctive; When the STT in two layers are identical, the sole skyrmion is mostly influenced by the adiabatic STT and exhibit the SkHE, while the skyrmion pair is propelled by the non-adiabatic spin transfer torque(STT) without SkHE

Summary

Introduction

Spintronics using magnetic skyrmions has been intensively studied in recent years[1,2,3,4,5,6,7,8,9]. A skyrmion is topologically stable because spatially twisted magnetization provides a topological number and it cannot be destroyed or generated without a topological transition. It is highly mobile with small spin currents since its current induced translational motion does not accompany the dissipation of energy[10,11]. One of the methods to control the chirality is using interlayer coupled magnetic bilayer systems. We discuss how interlayer coupling affects the spin structure of a bilayer system in which the two layers have opposite chirality (opposite DM interaction). The competition between the DM interaction energy and the interlayer coupling energy results in complex spin structures, in which sole skyrmion states and paired skyrmion states coexist. The skyrmions in the paired skyrmion states are annihilated in a special exclusionary way, showing potential for use of these systems in spin logic circuit

Methods

Results

Conclusion