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Summary of Research Projects (Supports in 2003
Fiscal Year)
| Subjects |
Study of Quantum Dynamics of Single Molecular Magnets by Using Ultra
Low Temperature ESR in Dilution Refrigerators |
| Representative researcher |
Tohoku University Hiroyuki NOJIRI |
| Joint researcher |
Okayama University Yasuhiro MATSUDA |
| Akita University Takuo SAKON |
| Dynamical properties of single molecular magnets with triangular networks have been studied by using fast sweeping magnetic fields and ESR technique. In antiferromagnetic spin triangles, a half step magnetization phenomenon has been found at the level crossing between the doubly degenerated ground state and the excited quartet. The appearance of half step, which is absent in isothermal magnetization curve, indicates that an adiabatic quantum mechanical motion of spin is realized in fast sweeping magnetic fields. The symmetry and the structure of the tunneling gaps are analyzed by using a spin Hamiltonian including Dzyaloshinsky-Moriya interaction. We found that the thermal relaxation is well suppressed in fast sweeping magnetic fields, because the spin system is decoupled from thermal fluctuations of the environment. The present fast sweeping technique opens a new way to study quantum dynamical magnetization process in single molecular magnets.
Short range correlation effect in a spin polyhedron named Keplerate with gigantic number of spin states has been also investigated by magnetization and ESR. In low temperature, we found a drastic change of ESR spectrum associated with a broad anomaly of specific heat. This phenomenon has been interpreted as "quasi ordering" in antiferromagnetic spin polyhedron. |
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