Chiral ESR spectroscopy with circularly polarized microwave on a SQUID magnetometer

2020 Fiscal Year Final Research Report

• Project/Area Number: 18H01955
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 32020:Functional solid state chemistry-related
• Research Institution: Osaka City University
• Principal Investigator: Shiomi Daisuke 大阪市立大学, 大学院理学研究科, 准教授 (40260799)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: ESR / 円偏波 / SQUID / キラリティー / キラル磁性体 / マイクロ波

Outline of Final Research Achievements

A novel spectroscopic method and instrumentation of ESR have been developed focusing on chiral magnetic systems. The measurement system is based on the static longitudinal magnetization detected on a conventional SQUID magnetometer, to which a circularly polarized microwave is introduced with a cylindrical waveguide. The waveguide suitable for the circularly polarized microwave in the V- or Q/Ka-band was designed on the basis of electromagnetic field simulations. With these system, ESR signals from an achiral organic radical were observed at cryogenic temperatures. It has been found from the analysis of the ESR signals that the irradiated microwave was contaminated with linearly polarized wave; the amplitude ratio of left- and right-handed polarized waves were 0.3/0.7 (V-band) and 0.4/0.6 (Q/Ka-band). Possible causes of the elliptic contamination are ascribed to the reflection or the higher-order modes of the polarized microwave and a volume effect inherent in the sample.

Free Research Field

物理化学・磁気化学

Academic Significance and Societal Importance of the Research Achievements

ESR（電子スピン共鳴）は，磁性体の評価手段として強力な方法である．これに円偏波の電磁波を使えるようになれば，これまで「ESRの眼」から隠されていた構造キラリティーに関する情報が得られる可能性がある．円偏波を使ってESRを検出するには，これまで技術的な困難があったが，定常的な縦磁化を検出するという斬新な方法をとることでこれを克服することに挑戦した．円偏波を照射しつつ縦磁化を検出できる装置系を設計し製作した．完成した装置で電磁波偏波の形を評価した結果，大きく「だ円形」に歪んでいることがわかった．この原因として，装置内部での偏波の反射や装置の歪み，或いは試料の大きさと波長との関係が考えられる．