[Paper Review] Altermagnetism: Exploring New Frontiers in Magnetism and Spintronics

Ling Bai, Wanxiang Feng+4 more|arXiv (Cornell University)|Jun 4, 2024

Magnetic properties of thin films4 citations

TL;DR

This review introduces altermagnetism—a novel collinear magnetic phase that breaks time-reversal symmetry and exhibits spin-split bands with vanishing net magnetization due to symmetry. It unifies features of ferromagnetism and antiferromagnetism, enabling unique spintronic phenomena such as large spin Hall effects and topological responses, with experimental validation in materials like MnSi and FeSi.

ABSTRACT

Recent developments have introduced a groundbreaking form of collinear magnetism known as "altermagnetism". This emerging magnetic phase is characterized by robust time-reversal symmetry breaking, antiparallel magnetic order, and alternating spin-splitting band structures, yet it exhibits vanishing net magnetization constrained by symmetry. Altermagnetism uniquely integrates traits previously considered mutually exclusive to conventional collinear ferromagnetism and antiferromagnetism, thereby facilitating phenomena and functionalities previously not achievable within these traditional categories of magnetism. Initially proposed theoretically, the existence of the altermagnetic phase has since been corroborated by a range of experimental studies, which have confirmed its unique properties and potential for applications. This review explores the rapidly expanding research on altermagnets, emphasizing the novel physical phenomena they manifest, methodologies for inducing altermagnetism, and promising altermagnetic materials. The goal of this review is to furnish readers with a comprehensive overview of altermagnetism and to inspire further innovative studies on altermagnetic materials which could potentially revolutionize applications in technology and materials science.

Motivation & Objective

• To provide a comprehensive overview of altermagnetism as a newly recognized magnetic phase in condensed matter physics.
• To highlight the physical mechanisms enabling time-reversal symmetry breaking and spin splitting without net magnetization.
• To identify and classify promising altermagnetic materials with potential for spintronic applications.
• To bridge theoretical predictions with experimental realizations of altermagnetism in quantum materials.
• To inspire future research by outlining unexplored functionalities and device concepts enabled by altermagnetism.

Proposed method

• Systematic analysis of electronic band structures in magnetic materials to identify alternating spin-splitting patterns.
• Application of group theory and time-reversal symmetry constraints to classify altermagnetic states based on crystal and magnetic space groups.
• Review of first-principles calculations (e.g., DFT) to predict and characterize altermagnetic order and spin textures.
• Synthesis and characterization of candidate materials such as MnSi, FeSi, and transition metal dichalcogenides to confirm altermagnetic behavior.
• Evaluation of spin transport properties, including spin Hall effect and spin-orbit coupling, in altermagnetic systems.
• Integration of experimental data with theoretical models to validate the existence and stability of altermagnetic phases.

Experimental results

Research questions

• RQ1 How can a magnetic state break time-reversal symmetry while maintaining zero net magnetization?
• RQ2 What are the distinct electronic and topological signatures that differentiate altermagnets from conventional ferromagnets and antiferromagnets?
• RQ3 Which materials host stable altermagnetic order, and what are their key electronic and structural features?
• RQ4 What novel spintronic effects can be engineered in altermagnetic materials due to their unique spin-split band structure?
• RQ5 How can altermagnetism be experimentally detected and distinguished from other magnetic phases?

Key findings

• Altermagnetism is a distinct magnetic phase characterized by alternating spin-split bands and broken time-reversal symmetry, yet with vanishing net magnetization due to spatial symmetry.
• Theoretical predictions of altermagnetism have been experimentally confirmed in materials such as MnSi and FeSi, demonstrating robust spin-splitting and time-reversal symmetry breaking.
• Altermagnets exhibit large intrinsic spin Hall conductivity, enabling efficient spin current generation without external magnetic fields.
• The interplay between spin splitting and band topology in altermagnets leads to emergent phenomena such as the spin Hall effect and chiral anomaly in transport.
• Materials like transition metal dichalcogenides and Heusler compounds are identified as promising candidates for hosting tunable altermagnetic order.
• The discovery of altermagnetism opens new pathways for designing spintronic devices with high efficiency, low power consumption, and topological protection.