'A Semiconductor Revolution Is Coming... UNIST Opens Path to Signal Control with "Third Type of Magnetism" Material'

A breath of fresh air is entering the semiconductor process, which had previously reached a dead end. The discovery by UNIST of the existence of a "third type of magnetism" and the principle of signal control is emerging as a ray of hope for future device technology.

A domestic research team has succeeded in reversing the direction of the conversion signal by changing the alignment direction of spins within a gyrotropic magnetic material.

This achievement is being hailed as a breakthrough that opens the door to the development of low-power spin semiconductor devices capable of switching current without complex structures or strong magnetic fields.

On December 10, the team led by Professor Jungwoo Yoo of the Department of Materials Science and Engineering and Professor Changhee Son of the Department of Physics at UNIST announced that they had experimentally demonstrated the reversible control of spin-charge conversion within a ruthenium oxide gyrotropic magnetic material.

Research team, (from left) Professor Jungwoo Yoo, Professor Changhee Son, Dr. Hyunjung Jung, Researcher Gimok So. Provided by UNIST

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Ruthenium oxide has recently attracted attention in the semiconductor field as a "gyrotropic magnet," a third type of magnetic material that combines the advantages of ferromagnetic and antiferromagnetic materials. Theoretically, this material can be used to create spin semiconductors that surpass the speed limits of conventional semiconductor devices and maximize energy efficiency. However, in order to create electronic devices such as semiconductors from magnetic materials, it is essential to convert the "spin" signal into a current signal that can be recognized by circuits-a process known as spin-charge conversion. For gyrotropic magnetic materials, however, an established control technology for this process has been lacking.

The research team experimentally demonstrated that by adjusting the N?el vector-the direction of spin alignment inside the material-the direction (polarity) of spin-to-charge conversion can be completely reversed. In other words, they proved that simply rotating the magnetic alignment state inside the material by 180 degrees can reversibly switch the output electric signal between positive (+) and negative (-). This principle enables clear distinction and control of the "0" and "1" states of non-volatile memory devices, which retain information even without external power supply.

Previously, controlling such signal conversion typically required building complex multilayer structures or applying strong external magnetic fields.

The research team validated these findings by fabricating a device of their own design. They created a device by sequentially stacking ruthenium oxide (RuO₂) and cobalt iron boron (CoFeB) thin films on a titanium dioxide (TiO₂) substrate, and conducted experiments in which spin signals generated by temperature differences in the cobalt iron boron thin film were injected into the ruthenium oxide. The team then measured the conversion of spin signals into charge signals within the ruthenium oxide.

The joint research team explained, "This study experimentally confirmed that spin signals in gyrotropic magnets can be reversibly controlled. Such principles could be applied to the design of next-generation spin-based logic or memory devices."

Spin-charge conversion signal of chiral magnet flipped according to the direction of the N?el vector.

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This research has been supported since September 2024 by the "Grand Challenge R&D Project" of the Ministry of Science and ICT. This project is an innovative Korean research and development system designed to rapidly advance high-difficulty, high-impact basic science research that would be difficult to achieve using conventional approaches. With this support, the research team completed the entire process-from material synthesis to device fabrication, measurement, and publication-in just over a year, achieving outstanding results.

Kim Dongho, Lead Program Manager at the Grand Challenge Strategy Center, which oversees this project, stated, "This achievement is a representative example of innovative, challenge-driven research that boldly embraced risk without fear of failure. We will continue to provide strong support so that this technology can develop into a core strategic technology for Korea's semiconductor industry in the future."

This research was conducted with Hyunjung Jung, Researcher in the Department of Materials Science and Engineering at UNIST (currently a postdoctoral researcher at GIST InnoCore), and Gimok So, Researcher in the Department of Physics, as co-first authors. The results were published in Nano Letters, a globally recognized journal in the field of nanoscience and materials, on November 25.

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