Yoshio KOBAYASHI (小林 義男)

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Challenging Research (Exploratory), Fund Type: -, Overall Grant Amount: - (direct: 5000000, indirect: 1500000)
The results are listed as follows. (1) Controllable hysteresis in iron(II) spin-crossover materials. (2) Solid-state organic spin transition as a dynamic covalent chemistry. (3) Intramolecular solid-state organic spin transition. (4) Singlet/triplet ground spin-state switch in bisnitroxide materials. (5) Two-dimensional coordination polymers of rare-earth coordination materials. (6) Development of spin-crossover ligands carrying a radical group. In conclusion, we developed several room-temperature spin-crossover complexes and room-temperature organic spin-transition compounds. Furthermore, we studied the possibility of control of magnetic interactions and cooperativities and extension to high-dimensional magnetic networks. Several checkpoints of the present project have been cleared.

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 新学術領域研究(研究領域提案型), Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 4500000, indirect: 720000)
単結晶フッ化カルシウムを試料に、短寿命57Mn核をイオン注入したインビーム・メスバウアースペクトルを295Kと310Kで長時間観測した。スペクトル全体の概形がシングレットS1に収束する方向となった。室温近傍で観測したS1の線幅のブロードニングは、プローブ核として埋め込まれた57Fe核の最近接原子であるフッ化物イオンの局所場での揺らぎの結果であると示唆された。メスバウアー分光法は、プローブ核57Feの周囲の微視的な環境変化に敏感である。従来のフッ化物におけるフッ化物イオンの拡散挙動は、高温領域におけるマクロスコピックな実験データをもとに考察されてきた。本研究のような原子スケールでの挙動についての研究結果は例が少ない。この結果から、室温近傍でフッ化物イオンの長距離拡散を起こすためのlocal motionの前駆現象が起こっているのではないかと考えられる。
295Kおよび310Kの時間分割インビーム・メスバウアースペクトルの結果からシングレットの線幅を評価した。random-walkモデルに基づいたEinstein-Smoluchovskiの式を用いると、295Kにおける平均ジャンプ時間τと平均ジャンプ距離rは、それぞれ700nsと0.22nmとなり、メスバウアー分光による拡散係数Dは5.76E-15 m2/sとなった。この値は、トレーサー実験で得られた400℃（673 K）での拡散係数の約1/200に相当する。310Kにおいて同様の計算をすると、平均ジャンプ時間τと平均ジャンプ距離rは、それぞれ1400nsと0.31nmで、ジャンプ時間が長く、ジャンプ距離は大きくなっていることがわかった。本研究から、原子スケールで観察すると室温近傍でもフッ化物イオンはすでにイオン拡散の前駆的な挙動を示していることを初めて明らかにすることができた。

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Challenging Exploratory Research, Fund Type: -, Overall Grant Amount: - (direct: 3000000, indirect: 900000)
This study has been focused on cage-structured compounds expected to be a candidate of thermoelectric materials. Particularly, we have investigated cage-structured compounds having a magnetic guest atom, which is important for thermal insulation, in order to reveal relationships between thermal insulation and magnetic properties in cage-structured compounds. One of the important obtained in the present work is the fact that guest atomic motions in type-I clathrates, which correlate with thermal insulation, are more sensitive to number of their carriers than their ferromagnetic ordering.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 0, indirect: 0)
In-beam Mossbauer spectroscopy coupled with a radioactive nuclear beam enables to elucidate the electronic states and reaction products of the isolated iron atoms in gas matrices at low temperatures. The emission Mossbauer spectra of 57Fe obtained after 57Mn implantation into the gas matrices of argon, methane, and ethylene were measured at 18 K. It was found that Monovalent Fe+ with an excited state atomic configuration of 3d7 in the argon matrix, Fe(CH4)2+ species in the methane matrix, and Fe(C2H4) species in ethylene matrix were observed respectively, and assigned on the basis of the obtained Mossbauer parameters and the density functional theory calculations.

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 特定領域研究, Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 0, indirect: 0)
放射光の特徴であるエネルギー可変性、高輝度、パルス性を利用し、充填スクッテルダイト化合物における格子振動、電子状態、構造に関する研究を行った。
格子振動に関する研究では、SmRu4P12のSm-149核共鳴非弾性散乱および高分解能X線非弾性散乱を用いて、Pの正20面体に内包されたSm原子の振動モードの分散が非常に小さく、音響フォノンと反交差していることを実験的に証明した。それと同時に、同じ結晶構造を持ち金属絶縁体転移を示すPrRu4P12とは異なって、金属絶縁体転移では構造変化が起こらないことをフォノン分散の温度変化から明らかにした。また、Pよりのカゴのサイズの大きなLa0s4Sb12についても高分解能X線非弾性散乱を行ない、非充填化合物のIrSb3のフォノン分散との比較から、Sbの正20面体に内包されるLaの分散を実験的に検証するとともに、その非調和性についても調べた。
構造に関する研究では、前年度に調べたSm0s4Sb12のSmサイトの温度変化に伴う構造の変化の有無に関して放射光粉末X線回折を用いて調べた。その結果、温度を低下させるとともにイオン半径の大きな2価のSmイオンの3価のSmイオンに対する割合が増加するにもかかわらず、それを内包するSbのカゴが収縮することが明らかとなった。このことは、重い電子的振舞いが実現するために必要な伝導電子と4f電子の強い混成を実現することと関連していることを示唆している。

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 0, indirect: 0)
We have performed an in-beam Mossbauer spectroscopic experiment using a short-lived ^<57>Mn(T_<1/2>=1.5 min) beam, in order to study the production of the novel chemical species of ^<57>Fe atoms arising from ^<57>Mn implanted into solid oxygen. It is expected that the high electron affinity of oxygen favors the production of high valence states of Fe.
^<57>Mn particles were produced as a secondary RI beam following a nuclear projectile-fragmentation reaction of ^<58>Fe beams (E=63 MeV/nucleon) with Be production target, and separated by the in-flight isotope separator using RIPS(Riken Projectile-fragment Separator) in RIKEN Accelerator Research Facility. Subsequently, the ^<57>Mn was implanted into a solid O_2 sample after passing through an Al plate with an appropriate thickness to suppress the beam energy down to about 20 MeV/nucleon. The in-beam Mossbauer spectra were measured at 18, 32 and 40 K during the implantation of ^<57>Mn. The obtained spectrum at 18 K could be analyzed by 4 sets of Lorentzian doublet. From the basis of Mossbauer parameters of the isomer shifts and the quadrupole splittings and the ab-initio molecular orbital calculations, these 4 components were assigned to be Fe(O_2), FeO, and (O_2)Fe(O_2), and a chemical species in a higher oxidation state of Fe atoms. We discussed the reaction products between ^<57>Fe atoms arising from ^<57>Mn and a solid O_2 matrix, compared with the products of laser-ablated Fe atoms with O_2 gas isolated in the Ar matrix at low temperatures.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 3600000, indirect: -)
Transient field(TF) is an effective magnetic field acting on ions passing through ferromagnetic foils. Because of large TF strengths, a large number of nuclear magnetic moments have been measured for short-lifetime excited states on stable nuclei. Such measurements have been carried out using stable-ion beams at velocities v << Z^・ vo, since the velocity dependence of the TF strength B_ is well known in this region, where Z and vo denote the atomic number and the Bohr velocity. Taking into account the fact that radioactive-isotope beams produced in the projectile-fragmentation reaction have high velocities v 【greater than or equal】 Z^・ vo, it is important to determine the velocity dependence of B_ at a velocity of approximately Z^・ vo or higher. From measurements using E=135 MeV ^<22>Ne and ^<24>Mg beams obtained from the K=70 RIKEN AVF cyclotron and the targets consisting of two layers, Au and Gd, we have determined preliminary values of B_ strengths. Their values were smaller than the expected strengths from those determined in the lower velocity region. Theoretically, a sharp decrease in TF strength was predicted at velocities v【greater than or equal】Z^・ vo. The obtained strengths, however, are much larger than this prediction. It rather supports a recent model, with which a rather constant or even increasing trend of B_ strength is predicted at velocities v【greater than or equal】Z^・ vo. Moreover, this observation is in agreement with other measurements obtained at similar velocities. This finding allows us to measure the excited-state magnetic moments of unstable nuclei produced in the projectile-fragmentation reactions.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: competitive_research_funding, Overall Grant Amount: - (direct: 0, indirect: 0)
All of the Mossbauer spectra have been measured by using the Doppler modulation since the discovery of the Mossbauer effect. The Doppler moduration technique has contributed to the establishment of the Mossbauer spectoscopy as one of the most valuable experimental tools in the fields of not only the nuclear physics but also solid state chemistry. However, we should observe the Mossbauer resonance, if the Mossbauer energy level of source unclide is made to hyperfine split under applied external magnetic field and the energy of the emitted gamma-ray is equivalent to one of the energy difference between the excited and ground states of an absorber. In this research, we have developed the new measuring system under strong magnetic field without utilizing the Doppler effect in order to apply to the in-beam Mossbauer spectroscopy for magnetism investigations.
(1) Production of the Mossbauer gamma-rays detector (parallel Plate Avalanche Counter) and evaluation of the performance
(2) Evaluation of the cryostat with a superconducting solenoid magnet
(3)Measurement of the Mossbauer spectrum with magnetic modulation