Seeking for the electronic-structure origin of the unusual spin states in trivalent Co oxides

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05502
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics I
• Research Institution: Tokyo University of Science
• Principal Investigator: Saitoh Tomohiko 東京理科大学, 理学部第一部応用物理学科, 教授 (30311129)
• Co-Investigator(Kenkyū-buntansha): 小林 義彦 東京医科大学, 医学部, 講師 (60293122)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: コバルト酸化物 / 電子構造 / 光電子分光 / スピンクロスオーバー / バンド計算 / 強相関電子系 / 遷移金属酸化物 / 磁性

Outline of Final Research Achievements

We measured the electronic structure of perovskite-type Co oxides RCoO3 (R: rare earth) from the room temperature (RT) down to about 10 K by using hard x-ray photoemission spectroscopy (HAXPES). In particular, we have succeeded in the lowest-temperature measurements for the first time, which had never been done because of experimental difficulties. From our analysis, we found that (1) the temperature-dependent changes in the electronic structure of LaCoO3 cannot be explained by a superposition of the low-spin and the high-spin state (2) the electronic states that have not been seriously considered, such as Co 4sp and La 5p states, may contribute to the temperature-dependent changes in the Co 3d spin state. We have also confirmed this uniqueness of LaCoO3 by measuring HAXPES spectra of PrCoO3 from RT down to 20 K to RT, which showed no changes in accordance with its magnetic susceptibility measurement.

Free Research Field

強相関電子系の電子構造と磁性

Academic Significance and Societal Importance of the Research Achievements

LaCoO3の温度誘起スピンクロスオーバーの解明はノーベル物理学賞受賞のGoodenough博士も好んで追究した、60年以上に亘る未解明問題である。この現象は、Co 3dのスピン状態の温度変化が主な原因とされてきたが、本研究では、Co 3d状態のみを考えてきた従来の考え方に対して、Co 4spやLa 5pなどの別の電子状態も考慮する必要性を指摘した点で学術的意義がある。また、Co酸化物は充電池電極として広く応用されており、その電子構造の解明は、応用の為の基礎知識としても社会的意義がある。