Octupole model advances simulations of antiferromagnet motion

Researchers at the University of Illinois Urbana-Champaign say they have built the first micromagnetic model for antiferromagnets based on magnetic multipoles, giving device designers a new way to simulate materials seen as candidates for spintronics. The work, published in Applied Physics Reviews, focuses on how complex magnetic domains move at scales too large for atom-by-atom calculations alone.

The team, from the university’s Grainger College of Engineering, said the framework offers a theoretical and computational basis for studying antiferromagnetic materials in future electronics that use electron spin. Spintronic devices rely on an electron’s magnetic orientation rather than its electric charge, according to the university.

Materials researchers have studied antiferromagnets for spintronics because they can show ultrafast spin behavior and remain stable in outside magnetic fields, the Illinois team said. Their spin structures, however, can be difficult to control and model, leaving a gap between basic materials research and practical device design.

Modeling noncollinear antiferromagnets

Micromagnetic simulations are common tools for examining spin dynamics in ferromagnets, according to the university, but an equivalent approach has not been fully established for antiferromagnets. The Illinois researchers targeted noncollinear antiferromagnets, a class with rotating spin structures that can be easier to manipulate than other antiferromagnetic arrangements.

Axel Hoffmann, a professor of materials science and engineering and senior author of the paper, said the goal was to create a numerical tool for studying larger-scale domain behavior that is hard to reach with atomistic simulations alone. He worked with postdoctoral researcher Myoung-Woo Yoo on the model.

The researchers used Mn3Sn as a representative noncollinear antiferromagnetic material, according to the university. They based the micromagnetic model on a magnetic octupole moment, treating that multipole as an effective way to represent the material’s magnetic order.

At the micrometer scale, the model reproduced domain-wall dynamics and other spatially nonuniform magnetic textures, the team reported. The researchers said those effects could not be described by existing analytic models.

The study also identified domain-wall deformation and an effective inertial mass, according to the university. The team said those findings add detail to the mesoscopic dynamics of magnetic multipoles in antiferromagnets.

Next steps for spin textures

Hoffmann said the work shows magnetic multipoles can serve as order parameters for micromagnetic simulations of these systems. The researchers said the model could help guide spintronic technologies for information processing, signal generation and data storage.

The current framework assumes a fixed magnetic spin texture, Yoo said. The researchers plan to extend the model because real spins can depart slightly from the ideal triangular arrangement used in the study.

Yoo said those deviations can add angular momentum and produce high-frequency spin dynamics. The Illinois team said future work will add that effect to the model and compare the simulations with experimental results.

The paper, “Micromagnetic simulations for magnetic multipoles,” was authored by Myoung-Woo Yoo and colleagues and published in Applied Physics Reviews.

This story draws on original reporting from Phys.org.