[Paper Review] Crystal design of altermagnetism

Zhiyuan Zhou, Xingkai Cheng+4 more|arXiv (Cornell University)|Mar 12, 2024

Geomagnetism and Paleomagnetism Studies4 citations

TL;DR

This paper demonstrates crystal design as a novel strategy to engineer altermagnetism by distorting CrSb films to break glide and magnetic mirrors on the (0001) plane, enabling precise control over altermagnetic symmetry. It achieves room-temperature spontaneous anomalous Hall effect and enables field-free, 100% switching of the Néel vector by designably locking exchange-coupling torques and Dzyaloshinskii-Moriya (DM) torques via crystal symmetry engineering.

ABSTRACT

Symmetry plays a fundamental role in condensed matter. The unique entanglement between magnetic sublattices and alternating crystal environment in altermagnets provides a unique opportunity for designing magnetic space symmetry. There have been extensive experimental efforts concentrated on tuning the Neel vector to reconstruct altermagnetic symmetry. However, it remains challenging to modulate the altermagnetic symmetry through the crystal aspect. Here, the crystal design of altermagnetism is successfully realized, by breaking glide mirrors and magnetic mirrors of the (0001) crystallographic plane in CrSb films via crystal distortion. We establish a locking relationship between altermagnetic symmetry and the emergent Dzyaloshinskii-Moriya (DM) vectors in different CrSb films, realizing unprecedentedly room-temperature spontaneous anomalous Hall effect in an altermagnetic metal. The concept of exchange-coupling torques is broadened to include both antiferromagnetic exchange-coupling torque and DM torque. Their relationship is designable, determining electrical manipulation modes, e.g., field-assisted switching for CrSb(1-100)/Pt and field-free switching for W/CrSb(11-20). Particularly, the unprecedentedly field-free 100-percent switching of Neel vectors is realized by making these two torques parallel or antiparallel, dependent on Neel vector orientation. Besides unravelling the rich mechanisms for electrical manipulation of altermagnetism rooted in broadened concept of exchange-coupling torques, we list other material candidates and propose that crystal design of altermagnetism would bring rich designability to magnonics, topology, etc.

Motivation & Objective

• To overcome the challenge of electrically manipulating altermagnetic order through crystal symmetry control.
• To establish a designable framework linking altermagnetic symmetry to emergent Dzyaloshinskii-Moriya (DM) vectors.
• To realize field-free, 100% switching of the Néel vector in altermagnetic metals using engineered exchange-coupling torques.
• To extend the concept of exchange-coupling torques to include both antiferromagnetic and DM contributions for tunable electrical switching modes.

Proposed method

• Crystal distortion of CrSb films is applied to break glide mirrors and magnetic mirrors on the (0001) crystallographic plane.
• Symmetry analysis is used to identify the emergence of Dzyaloshinskii-Moriya (DM) vectors linked to altermagnetic order.
• The locking relationship between altermagnetic symmetry and DM vectors is engineered to control the Néel vector orientation.
• Exchange-coupling torques and DM torques are designed to be parallel or antiparallel, enabling field-free switching.
• Theoretical modeling and symmetry analysis are used to predict and validate electrical manipulation modes in different heterostructures.
• Material candidates are proposed based on symmetry compatibility and potential for enhanced topological and magnonic responses.

Experimental results

Research questions

• RQ1 Can crystal symmetry engineering be used to control altermagnetic order and its associated Dzyaloshinskii-Moriya vectors?
• RQ2 How can the interplay between antiferromagnetic exchange-coupling torque and Dzyaloshinskii-Moriya torque be tuned for electrical switching?
• RQ3 What role does crystal distortion play in enabling field-free, 100% Néel vector switching in altermagnetic metals?
• RQ4 Can room-temperature spontaneous anomalous Hall effect be achieved through symmetry-controlled altermagnetism?
• RQ5 What are the design principles for identifying new altermagnetic materials with tunable electrical manipulation properties?

Key findings

• Crystal distortion of CrSb(1-100) films breaks glide and magnetic mirrors on the (0001) plane, enabling control over altermagnetic symmetry.
• A locking relationship is established between altermagnetic symmetry and emergent Dzyaloshinskii-Moriya (DM) vectors, leading to a spontaneous anomalous Hall effect at room temperature.
• Field-free, 100% switching of the Néel vector is achieved in W/CrSb(11-20) by aligning exchange-coupling and DM torques in parallel or antiparallel configurations.
• The concept of exchange-coupling torques is broadened to include both antiferromagnetic and DM contributions, enabling designable electrical manipulation modes.
• The study identifies new material candidates for altermagnetism based on symmetry and crystal structure compatibility.
• The results demonstrate unprecedented control over altermagnetic order through crystal design, with implications for magnonics and topological quantum materials.