Giant Anomalous Hall Effect from Domain Wall Skew Scattering in Layered Antiferromagnet EuAl2Si2

Core Concepts

Giant anomalous Hall effect, originating from domain wall skew scattering, is observed in the layered antiferromagnet EuAl2Si2, opening new avenues for spintronics.

Abstract

Giant Anomalous Hall Effect from Domain Wall Skew Scattering in Layered Antiferromagnet EuAl2Si2

This research paper reports the observation of a giant anomalous Hall effect (AHE) in the layered antiferromagnet EuAl2Si2, attributed to a novel mechanism: domain wall (DW) skew scattering.

Background

• AHE, typically observed in ferromagnets, arises from the Berry curvature associated with the material's band structure.
• Antiferromagnets, with their zero net magnetization, were not expected to exhibit AHE.
• Recent studies have shown AHE in antiferromagnets with non-collinear spin structures, challenging the conventional understanding.

Key Findings

• EuAl2Si2 exhibits a giant AHE with an extrinsic anomalous Hall conductivity (σDWxy) reaching 1.51 × 104 S cm-1 at 2 K and 1.2 T.
• This value is two orders of magnitude larger than the intrinsic AHC from bulk and surpasses all previously reported AHC values in bulk materials.
• MFM measurements reveal a unique periodic stripe DW structure in EuAl2Si2.
• The DW density, and consequently the AHE, can be controlled by an external magnetic field.
• First-principles calculations and ARPES measurements confirm the presence of Weyl points near the Fermi level, a crucial factor for the observed giant AHE.

Mechanism

• The giant AHE is attributed to DW skew scattering, a mechanism where electrons passing through the DW experience asymmetric scattering due to the presence of Weyl points near the Fermi level.
• This effect is amplified in EuAl2Si2 due to the periodic nature of the DW structure and the proximity of the Weyl points to the Fermi level.

Significance and Implications

• This study provides the first experimental observation of giant AHE arising from DW skew scattering in an antiferromagnet.
• It establishes EuAl2Si2 as a model system for studying this novel AHE mechanism.
• The magnetic field controllability of the DW density and AHE in EuAl2Si2 holds potential for applications in spintronic devices, particularly in high-density data storage and processing.

Limitations and Future Research

• The study focuses on a specific material, EuAl2Si2. Further research is needed to explore the generality of this AHE mechanism in other antiferromagnets with similar characteristics.
• A deeper theoretical understanding of the DW skew scattering mechanism and its dependence on material parameters is crucial for optimizing the AHE in these materials.

This discovery opens new avenues for exploring and exploiting AHE in antiferromagnetic materials for next-generation spintronic applications.

Stats

The extrinsic anomalous Hall conductivity (σDWxy) reaches 1.51 × 104 S cm-1 at 2 K and 1.2 T.
The average distance between two neighboring DWs is approximately 0.975 µm at 0 T.
The DW density decreases nearly monotonically from 975 nm at 0 T to 232 nm at 4 T.
The mean free path l0 for F1 and F2 are estimated to be 17.5 nm and 31.9 nm respectively.

Quotes

"This is the first example of so large DWHE in an antiferromagnet originated from periodic stripe DW skew scattering, which definitely would prompt future exploration of large extrinsic AHE."
"Our observation of so large σDWxy in AFM EuAl2Si2 provides a paradigm of very large AHE caused by a new DW skew scattering mechanism."

Key Insights Distilled From

Giant domain wall anomalous Hall effect in an antiferromagnet

by Wei Xia, Bo ... at arxiv.org 10-21-2024

https://arxiv.org/pdf/2312.07336.pdf

Deeper Inquiries

How can the understanding of domain wall skew scattering in EuAl2Si2 be applied to engineer materials with even larger anomalous Hall effects?

This study reveals that the giant anomalous Hall effect (AHE) in EuAl2Si2 originates from the domain wall (DW) skew scattering mechanism, significantly amplified by the presence of Weyl points (WPs) near the Fermi level. This understanding provides a roadmap for engineering materials with even larger AHE:

Material Selection with High DW Density: Choosing materials that can host a high density of DWs is crucial. Layered antiferromagnets like EuAl2Si2, with weak interlayer coupling and strong anisotropy, are promising candidates. The material should ideally possess a high magnetic susceptibility to facilitate the formation of denser domains under an applied magnetic field, further enhancing the DWH effect.
Engineering Weyl Points Near Fermi Level: The presence of WPs near the Fermi level is essential for maximizing the skew scattering contribution. Band structure engineering through doping or strain can be employed to fine-tune the electronic structure and bring WPs closer to the Fermi level.
Controlling Domain Wall Periodicity: This study demonstrates that the periodicity of the stripe DW structure can be controlled by an external magnetic field. Fine-tuning this periodicity, potentially through nanostructuring or utilizing different substrates, could further enhance the AHE. A smaller periodicity, for instance, could lead to a higher density of DWs and thus a stronger AHE.
Exploring Other Material Systems: While this study focuses on EuAl2Si2, the principles discovered here can be extended to other material systems. Exploring other antiferromagnets, particularly those with layered structures and the potential to host WPs, could lead to the discovery of materials with even larger DW-driven AHE.
By systematically optimizing these factors, it is plausible to engineer materials exhibiting colossal anomalous Hall effects, opening doors to novel spintronic applications.

Could the observed giant AHE be attributed to other extrinsic mechanisms not considered in this study, such as the presence of spin chirality or non-coplanar spin clusters?

While the study strongly suggests DW skew scattering as the primary mechanism behind the giant AHE in EuAl2Si2, other extrinsic contributions cannot be entirely ruled out without further investigation.

Spin Chirality: The study doesn't delve into the potential role of spin chirality, a property often associated with non-coplanar spin structures. While EuAl2Si2 exhibits an A-type antiferromagnetic order, which is typically collinear, the presence of DWs introduces local non-collinearity. Investigating the presence and influence of spin chirality, particularly at the DWs, would be crucial to definitively rule out its contribution to the AHE.
Non-Coplanar Spin Clusters: Similarly, the potential formation of non-coplanar spin clusters, even if transient or localized, needs consideration. These clusters can act as scattering centers and contribute to the AHE. Advanced characterization techniques, such as spin-polarized scanning tunneling microscopy (SP-STM), could provide insights into the local spin arrangements and the potential presence of such clusters.
Further experimental and theoretical investigations are necessary to disentangle the potential contributions from spin chirality and non-coplanar spin clusters and definitively determine their role, if any, in the observed giant AHE.

What are the potential implications of this discovery for the development of low-power, high-speed spintronic devices based on antiferromagnetic materials?

The discovery of giant AHE driven by DW skew scattering in EuAl2Si2 holds significant implications for the development of next-generation spintronic devices, particularly those based on antiferromagnetic materials:

Low-Power Operation: Antiferromagnets are inherently less prone to generate stray magnetic fields, leading to reduced energy dissipation compared to their ferromagnetic counterparts. This inherent advantage, coupled with the giant AHE observed in EuAl2Si2, paves the way for developing ultra-low-power spintronic devices.
High-Speed Switching: Antiferromagnets exhibit significantly faster spin dynamics compared to ferromagnets, enabling high-speed operation. The ability to control the DW density and hence the AHE magnitude in EuAl2Si2 through an external magnetic field allows for rapid switching of the Hall resistance, a key requirement for high-speed memory and logic devices.
High-Density Integration: The periodic stripe DW structure observed in EuAl2Si2, with its controllable periodicity, offers a natural pathway for high-density data storage. Each DW can potentially represent a single bit of information, and the ability to tune the DW density with a magnetic field allows for writing and reading data at high densities.
Novel Device Concepts: The unique interplay between DWs, WPs, and AHE in EuAl2Si2 opens doors to novel device concepts. For instance, by manipulating the DW configuration, one could envision creating reconfigurable spintronic circuits or logic gates with functionalities determined by the DW arrangement.
The findings of this study provide a compelling case for further exploration of antiferromagnetic materials, particularly those hosting WPs and exhibiting controllable DW structures, for the development of energy-efficient, high-speed, and high-density spintronic devices.