Seminar by Professor Shinji MIWA (The University of Tokyo)
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This talk reviews recent studies on spintronic devices based on chiral systems. The first half focuses on the chiral antiferromagnet Mn3Sn. In this material, a specific noncollinear magnetic structure, known as negative spin chirality, gives rise to a ferroic magnetic ordering of cluster octupole polarization. This polarization generates a substantial Berry curvature due to magnetic Weyl points in momentum space. We have successfully grown epitaxial thin films of Mn₃Sn using molecular beam epitaxy and achieved current-induced full switching of the octupole polarization. Moreover, we have observed a tunnel magnetoresistance effect in an all-antiferromagnetic tunnel junction composed of Mn3Sn/MgO/Mn3Sn. These unique properties of octupole polarization suggest promising avenues for future spintronic devices.
The second half of the talk concerns organic chiral molecules. In recent years, an increasing number of studies have reported a wide range of CISS-related phenomena. Despite significant experimental evidence, a comprehensive theoretical understanding of CISS remains lacking, posing a major challenge to both practical applications and further scientific progress. In our work, we employed a chiral electrolyte, either (1S)-(+)- or (1R)-(−)-camphor-10-sulfonic acid, to carry out time-resolved magnetoresistance measurements. Our results suggest that the key mechanism behind CISS is a magnetic interaction between the chiral molecules and the ferromagnetic electrode, similar to interlayer exchange coupling. We found that the electric current does not directly induce spin polarization; rather, it acts as a probe of the system. Instead, spin polarization appears to be driven by the molecular vibrations of the chiral molecules, which is a concept consistent with thermally driven spin polarization observed even in the absence of an applied bias current.
The second half of the talk concerns organic chiral molecules. In recent years, an increasing number of studies have reported a wide range of CISS-related phenomena. Despite significant experimental evidence, a comprehensive theoretical understanding of CISS remains lacking, posing a major challenge to both practical applications and further scientific progress. In our work, we employed a chiral electrolyte, either (1S)-(+)- or (1R)-(−)-camphor-10-sulfonic acid, to carry out time-resolved magnetoresistance measurements. Our results suggest that the key mechanism behind CISS is a magnetic interaction between the chiral molecules and the ferromagnetic electrode, similar to interlayer exchange coupling. We found that the electric current does not directly induce spin polarization; rather, it acts as a probe of the system. Instead, spin polarization appears to be driven by the molecular vibrations of the chiral molecules, which is a concept consistent with thermally driven spin polarization observed even in the absence of an applied bias current.
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