A tiny spin change just flipped a famous quantum effect

Researchers at Osaka Metropolitan University have demonstrated that the Kondo effect behaves differently depending on the size of localized quantum spins. The team built on earlier work with a spin one half Kondo necklace by extending the system to spin one. They used an organic inorganic hybrid material made from organic radicals and nickel ions. The design relied on the RaX-D molecular framework to control crystal structure and magnetic interactions. Thermodynamic measurements on the spin one system showed a clear phase transition into a magnetically ordered state. Quantum analysis revealed that Kondo coupling creates an effective magnetic interaction between spin one moments that stabilizes order throughout the material. For decades the Kondo effect was understood to suppress magnetism by forming singlets. The new experiments show that this holds only for spin one half. When the spin is larger the same interaction promotes magnetic order instead. The work provides the first direct experimental evidence that the Kondo effect's role depends on spin size. Associate Professor Hironori Yamaguchi of the Graduate School of Science led the research. The results are reported in Communications Materials.