Researchers have uncovered the magnetic properties and underlying mechanisms of a novel magnet using advanced optical techniques. Their study focused on an organic crystal believed to be a promising candidate for an "altermagnet"- a recently proposed third class of magnetic materials. Unlike conventional ferromagnets and antiferromagnets, altermagnets exhibit unique magnetic behavior.
Details of their breakthrough were published in the journal Physical Review Research on July 7, 2025.
"Unlike typical magnets that attract each other, altermagnets do not exhibit net magnetization, yet they can still influence the polarization of reflected light," points out Satoshi Iguchi, associate professor at Tohoku University's Institute for Materials Research. "This makes them difficult to study using conventional optical techniques."
To overcome this, Iguchi and his colleagues applied a newly derived general formula for light reflection to the organic crystal, successfully clarifying its magnetic properties and origin.
The group also comprised Yuka Ikemoto and Taro Moriwaki from the Japan Synchrotron Radiation Research Institute; Hirotake Itoh from the Department of Physics and Astronomy at Kwansei Gakuin University; Shinichiro Iwai from the Department of Physics at Tohoku University; and Tetsuya Furukawa and Takahiko Sasaki, also from the Institute for Materials Research.
The team's newly derived general formula for light reflection was based on Maxwell's equations and is applicable to a wide range of materials, including those with low crystal symmetry, such as the organic compound studied here.
This new theoretical framework also allowed the team to develop a precise optical measurement method and apply it to the organic crystal κ-(BEDT-TTF)₂Cu[N(CN)₂]Cl. They successfully measured the magneto-optical Kerr effect (MOKE) and extracted the off-diagonal optical conductivity spectrum, which provides detailed information about the material's magnetic and electronic properties.
The results revealed three key features in the spectrum: (1) edge peaks indicating spin band splitting, (2) a real component associated with crystal distortion and piezomagnetic effects, and (3) an imaginary component linked to rotational currents. These findings not only confirm the altermagnetic nature of the material but also demonstrate the power of the newly developed optical method.
"This research opens the door to exploring magnetism in a broader class of materials, including organic compounds, and lays the groundwork for future development of high-performance magnetic devices based on lightweight, flexible materials," adds Iguchi.