[Paper Review] Current-induced fragmentation of antiferromagnetic domains

M. S. Wörnle, Pol Welter+8 more|arXiv (Cornell University)|Dec 11, 2019

Advanced Electron Microscopy Techniques and Applications21 citations

TL;DR

This study reveals that current pulses induce nano-scale fragmentation of antiferromagnetic domains in CuMnAs films, a process controlled by current amplitude and independent of current direction. Simultaneous scanning NV magnetometry and resistance measurements show that this fragmentation correlates strongly with large resistive switching signals—up to 20% at room temperature—while the fragmented state retains memory of the original domain pattern and relaxes back toward it.

ABSTRACT

Electrical and optical pulsing allow for manipulating the order parameter and magnetoresistance of antiferromagnets, opening novel prospects for digital and analog data storage in spintronic devices. Recent experiments in CuMnAs have demonstrated giant resistive switching signals in single-layer antiferromagnetic films together with analog switching and relaxation characteristics relevant for neuromorphic computing. Here we report simultaneous electrical pulsing and scanning NV magnetometry of antiferromagnetic domains in CuMnAs performed using a pump-probe scheme. We observe a nano-scale fragmentation of the antiferromagnetic domains, which is controlled by the current amplitude and independent on the current direction. The fragmented antiferromagnetic state conserves a memory of the pristine domain pattern, towards which it relaxes. Domain fragmentation coexists with permanent switching due to the reorientation of the antiferromagnetic moments. Our simultaneous imaging and resistance measurements show a correlation between the antiferromagnetic domain fragmentation and the largest resistive switching signals in CuMnAs.

Motivation & Objective

• To investigate the microscopic origin of giant resistive switching in antiferromagnetic CuMnAs films under electrical pulsing.
• To determine whether current-induced domain fragmentation contributes to the large resistive changes observed in previous studies.
• To explore the interplay between domain fragmentation and Néel vector reorientation in antiferromagnetic order parameter switching.
• To establish the role of current density and pulse duration in driving domain texture evolution using in situ nanoscale magnetic imaging.
• To assess the memory and relaxation dynamics of fragmented antiferromagnetic domains after current pulsing.

Proposed method

• Employed scanning nitrogen-vacancy (NV) magnetometry to image the nanoscale magnetic stray field of antiferromagnetic domains in CuMnAs microdevices with sub-100 nm spatial resolution.
• Used a pump-probe scheme with electrical current pulses and time-resolved NV measurements to track domain evolution during and after pulsing.
• Calibrated the NV center’s sensitivity and orientation using ODMR spectroscopy with applied magnetic bias fields to determine the sign and magnitude of the in-plane magnetic stray field component.
• Applied Gaussian low-pass filtering (σ = 24 nm) to stray field maps to enhance morphological clarity and reduce noise.
• Quantified the magnetic stray field amplitude using the root mean square (RMS) of B_NV(x,y) over the field map, with uncertainty estimated via jackknife resampling.
• Correlated the measured magnetic stray field patterns with concurrent electrical resistance measurements to link domain structure to resistive switching behavior.

Experimental results

Research questions

• RQ1 Does current pulsing induce structural changes in antiferromagnetic domain textures beyond Néel vector reorientation?
• RQ2 How is the domain fragmentation in CuMnAs related to the magnitude of resistive switching signals?
• RQ3 Is the current-induced domain fragmentation dependent on current direction or solely on current amplitude?
• RQ4 Does the fragmented antiferromagnetic state retain a memory of the original domain configuration, and if so, how does it relax?
• RQ5 How do the spatial inhomogeneities in current density across a cross-shaped microdevice affect domain fragmentation?

Key findings

• Current pulses induce nano-scale fragmentation of antiferromagnetic domains in CuMnAs, with the extent of fragmentation controlled by current amplitude and independent of current direction.
• The fragmented domain state correlates strongly with the largest resistive switching signals observed—up to 20% at room temperature and ~100% at 30 K—exceeding conventional anisotropic magnetoresistance effects by 2–3 orders of magnitude.
• The fragmented domain pattern preserves a memory of the original pristine domain configuration and gradually relaxes back toward it over time, as confirmed by time-resolved NV imaging.
• Domain fragmentation coexists with 180° Néel vector reorientation in some regions, indicating that multiple switching mechanisms operate simultaneously.
• Spatially non-uniform current density distribution across the cross-shaped microdevice leads to inhomogeneous domain fragmentation, as revealed by correlated current and magnetic field mapping.
• The RMS of the magnetic stray field, a quantitative measure of domain texture complexity, increases significantly after pulsing and correlates with peak resistive switching, confirming the role of domain fragmentation in signal amplification.