Scientists have discovered the mechanisms behind the enhanced magnetic properties of a new machine-learning-identified iridium-doped iron-cobalt alloy. Why is this significant?
Magnetic materials are essential to modern technology, playing a critical role in electric motors, magnetic sensors, and other devices. High-magnetization ferromagnets are particularly important for advancing next-generation spintronics and efficient motor technologies. Among these materials, iron-cobalt (Fe-Co) alloys are widely used due to their strong magnetic properties.
However, performance improvements have reached limitations, requiring new approaches to enhance their capabilities.
Previous studies have shown that Fe-Co alloys doped with heavier elements can exhibit significantly higher magnetization when grown as epitaxial films. Recent advances in computational techniques, such as integrating machine learning with ab initio calculations, have accelerated the search for new material compositions.
One such material, iridium (Ir)-doped Fe-Co alloy (Fe-Co-Ir), was identified through machine learning and has demonstrated enhanced magnetic moments — exceeding those of conventional Fe-Co alloys. Until now, the underlying mechanisms responsible for these improvements have remained unclear, particularly regarding the role of Ir doping in influencing magnetic properties.
To address this, a research team led by Assistant Professor Takahiro Yamazaki from the Department of Material Science and Technology at Tokyo University of Science (TUS) implemented a novel approach. They used high-throughput X-ray magnetic circular dichroism (XMCD) on compositionally graded single-crystal thin films.
“Unlike previous studies which used polycrystalline thin films, we utilized compositionally graded single-crystal Fe-Co-Ir thin films, offering a more controlled environment for probing the mechanisms behind their enhanced magnetic properties,” Asst. Prof. Yamazaki explains. “Furthermore, using the world’s largest synchrotron radiation facility, SPring-8, we performed XMCD measurements to systematically investigate their magnetic properties.”
The team also included Mr. Takahiro Kawasaki and Prof. Masato Kotsugi from TUS, Dr. Yuma Iwasaki and Dr. Yuya Sakuraba of the National Institute of Materials Science (NIMS), Dr. Naomi Kawamura of the Japan Synchrotron Radiation Research Institute, and Prof. Takuo Ohkochi of the University of Hyogo.
Using the advanced technology at NIMS, the team first fabricated compositionally graded thin films in which the amount of Ir doping increased linearly from one end, consisting of pure Fe-Co alloy, to the other end consisting of Fe-Co alloy with 11 at% Ir.
The team then performed X-ray magnetic circular dichroism (XMCD) measurements on these films, using the soft and hard X-rays. Soft X-rays have lower energy than hard X-rays and are better suited for studying lighter metals like Fe and Co, while hard X-rays are more suitable for studying heavy metals like Ir.
This approach provided a more detailed understanding of each element’s contribution to the material’s magnetic behavior.
The results revealed significant improvements in the magnetic moments of Fe and Ir due to Ir doping. The magnetic moment of Fe increased by 1.44-fold and Ir by 1.54-fold at 11 at% Ir concentration compared to that at 1 at% Ir concentration.
To further validate and understand the origin of these enhancements, the team conducted ab initio calculations. Fe and Co belong to a class of elements known as 3d transition metals, where their outermost electrons occupy the 3d atomic orbitals, while Ir belongs to 5d transition metals.
The theoretical analysis supported the experimental findings and revealed that Ir addition leads to increased electron localization and stronger spin-orbit coupling between 3d electrons of Fe and Co and 5d electrons of Ir. This interaction results in enhanced magnetic moments, primarily through increased contributions of orbital magnetic moments.
Their study was published in the journal Physical Review Materials on March 12, 2025.
Filed Under: Electric Motor, Technology News