A groundbreaking discovery has revealed that a minute alteration in quantum spin size can fundamentally reverse the famous Kondo effect. This change transforms its established role from suppressing magnetism to actively fostering it, opening new frontiers in condensed matter physics. Led by Associate Professor Hironori Yamaguchi, researchers at Osaka Metropolitan University demonstrated this pivotal shift, challenging decades of scientific understanding.
For decades, the Kondo effect, a crucial phenomenon in condensed matter physics, has been understood primarily as a mechanism that quenches magnetism. It describes how localized quantum spins interact with mobile electrons, often leading to a non-magnetic ground state by forming entangled singlets. This intricate interaction is central to understanding the collective behaviors of quantum particles in various materials.
However, isolating these core spin interactions from other electronic behaviors, such as charge motion and orbital effects, has historically posed a significant challenge. Theoretical models, like Sebastian Doniach’s 1977 Kondo necklace model, simplified this complexity to explore quantum states, though experimental realization of such a pure spin system remained elusive for nearly fifty years. The new findings now provide a clear experimental context for these theoretical questions.
Unveiling the spin size dependency
The pivotal question driving this research concerned whether the Kondo effect’s behavior remains constant across all spin sizes. Associate Professor Hironori Yamaguchi’s team at Osaka Metropolitan University answered this by engineering a novel Kondo necklace. They utilized an organic-inorganic hybrid material, precisely controlling its crystal structure and magnetic interactions through a molecular design framework called RaX-D. This allowed them to meticulously study the Kondo effect spin change.
Previously, the team successfully constructed a spin-1/2 Kondo necklace. Their latest work, detailed in a recent report via ScienceDaily on January 21, 2026, extended this system by increasing the localized spin from 1/2 to 1. Thermodynamic measurements of this spin-1 system clearly indicated a phase transition into a magnetically ordered state. Quantum analysis confirmed that the Kondo coupling, for spin-1 moments, created an effective magnetic interaction, stabilizing long-range magnetic order across the material.
Redefining magnetism in quantum materials
This groundbreaking result overturns the long-held view that the Kondo effect primarily suppresses magnetism by locking spins into singlets. For many years, physicists considered this effect as a mechanism for demagnetization. However, the new findings demonstrate that when the localized spin exceeds 1/2, the same Kondo interaction no longer weakens magnetism but actively promotes it, forming ordered magnetic states.
By providing direct experimental evidence from a clean, spin-only platform, the researchers have identified a clear quantum boundary. The Kondo effect consistently forms local singlets for spin-1/2 moments, yet it stabilizes magnetic order for spin-1 and higher spins. According to Britannica, understanding such fundamental interactions is crucial for advancing condensed matter physics. This discovery fundamentally alters our understanding of how quantum matter organizes itself.
The identification of a quantum principle dependent on spin size within the Kondo effect opens up an entirely new research avenue in quantum materials. The ability to precisely switch quantum states between nonmagnetic and magnetic regimes by merely controlling spin size offers a powerful new design strategy. This insight could accelerate the development of next-generation quantum technologies, from advanced sensors to novel data storage solutions, by leveraging these previously unrecognized magnetic behaviors.
