Memory effects on the current induced propagation of spin textures in NdCo$_5$/Ni$_8$Fe$_2$ bilayers

TL;DR

This study demonstrates how memory effects in NdCo$_5$/Ni$_8$Fe$_2$ bilayers influence the guided propagation of spin textures, enabling reconfigurable magnetic racetracks controlled by magnetic history and external fields.

Contribution

It reveals the role of magnetic history and exchange bias in controlling spin texture propagation in bilayers, introducing a reconfigurable magnetic system for spintronic applications.

Findings

Guided vortex/antivortex propagation above a threshold current.

Propagation sense depends on topological charge and magnetic history.

Exchange-bias memory effect controls propagation direction.

Abstract

Bilayers of NdCo$_5$/Ni$_8$Fe$_2$ can act as reconfigurable racetracks thanks to the parallel stripe domain configuration present in the hard magnetic material with weak perpendicular anisotropy (NdCo$_5$), and its imprint on the soft magnetic layer (Ni$_8$Fe$_2$). This pattern hosts spin textures with well defined topological charges and establishes paths for their deterministic propagation under the effect of pulsed currents, which has been studied as a function of externally applied fields by using Magnetic Transmission X-ray Microscopy. The experiments show guided vortex/antivortex propagation events within the Ni$_8$Fe$_2$ above a threshold current of $3\cdot10^{11}$ A/m$^2$. Opposite propagation senses have been observed depending on the topological charge of the spin texture, both in the remnant state and under an applied external field. Micromagnetic simulations of our multilayer reveal that the guiding effect and asymmetric propagation sense are due to the magnetic history of the hard magnetic layer. An exchange-bias-based memory effect acts as a magnetic spring and controls the propagation sense by favoring a specific orientation of the in plane magnetization, leading to a system which behaves as a hard-soft magnetic composite with reconfigurable capabilities for a controlled propagation of magnetic topological textures.