Scientists at the University of California San Diego have pioneered a computational technique that enables precise modeling and prediction of these complex spin structures using quantum mechanics calculations. Their breakthrough findings were published on Feb. 19 in Advanced Functional Materials.
"The helical spin structures in two-dimensional layered materials have been experimentally observed for over 40 years. It has been a longstanding challenge to predict them with precision," said Kesong Yang, professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering and senior author of the study. "The helical period in the layered compound extends up to 48 nanometers, making it extremely difficult to accurately calculate all the electron and spin interactions at this scale."
To overcome this challenge, the research team analyzed how the total energy of a chiral helimagnet changes as the spin rotation varies between atomic layers. Utilizing first-principles quantum mechanics calculations, they successfully mapped the key features of these intricate spiraling formations. "Rather than modeling the entire system at a large length scale, we chose to focus on how spin rotation affects the total energy of the system," explained Yun Chen, a nanoengineering Ph.D. student and the study's first author. "By using a small supercell and designing optimized spin configurations, we were able to obtain highly accurate results."
The team applied their method to chiral helimagnets containing chromium, a metal renowned for its magnetic properties. Their computational approach enabled them to predict three crucial parameters: the helix wavevector, which determines the tightness of the spin spiral; the helix period, or the length of one full turn of the spiral; and the critical magnetic field, the external field strength needed to modify the helimagnet's structure.
"This is exciting because we can now precisely model these complex spin structures using quantum mechanics calculations, opening new opportunities for designing better materials," said Yang.
Research Report:First-Principles Approach for Predicting Chiral Helimagnetism
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