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Kofu Group

member
Professor KOFU, Maiko

Research Subjects

  • Dynamics of hydrogen atoms and hydrogen-containing molecules in a wide range of materials
  • Excitation characteristics of spin glasses
  • Spin dynamics of single-molecule magnets
  • Development of neutron scattering instruments and challenges to new measurements

We study the dynamics of atoms, molecules, and spins in various materials using neutron scattering techniques, to discover novel phenomena and universality inherent in a wide range of materials. Neutron is a powerful probe to detect hydrogen atoms. Observation of hydrogen quantum dynamics and proton/hydride ion conduction is one of our major research interests. Hydrogen is known as a quantum atom, but the quantum nature of hydrogen is rarely manifested. We will try new measurement techniques, such as coherent/incoherent separation of light hydrogen using polarized neutrons, and find dynamics that have not been captured so far. Functional liquids, monolayer ice with frustration, spin glass, and single-molecule magnets (which behave like nanomagnets) are also within our scope. Since these studies require measurements in a wide dynamic range, we use neutron spectrometers from around the world and develop neutron scattering spectrometers.

Hydrogen state in palladium hydride nanoparticles studied by neutron diffraction, inelastic, and quasielastic scattering. Our comprehensive studies showed that some hydrogen atoms near the surface of the nanoparticles are accommodated at the tetrahedral sites, in contrast to the accommodation at the octahedral sites in bulk, and exhibit highly anharmonic vibrations and fast diffusion processes.
Bose-scaled Localized magnetic excitation was commonly observed in spin glasses with different properties such as spin-freezing temperature (Tf), morphology (crystalline or amorphous), and electronic properties (insulator or metal). The excitation is highly reminiscent of the "boson peak" in structural glasses. The broad spectrum with the high-energy tail can be attributed to elementary excitations in a multitude of metastable states (spin clusters) with different sizes and spin configurations.

Publications and Research Highlights