Magnetic properties of alpha-Mn under high pressure, Anomalous Hall effect and quantum critical phenomena

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01042
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: Okayama University
• Principal Investigator: Kobayashi Tatsuo 岡山大学, 環境生命自然科学学域, 教授 (80205468)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: マンガン / 磁気秩序 / 高圧 / 異常ホール効果 / NMR / 中性子回折

Outline of Final Research Achievements

Zero-field NMR was performed in the antiferromagnetic (AFM) phase of α-Mn. The analyzable spectra was successfully measured for the first time. As a result, it was revealed that the site II splits into two sites, and the sites III and IV split into four sites due to the AFM order. This confirms that the AFM phase has a lower symmetry than the previously known spin structure.
Neutron diffraction experiments were performed on the weakly ferromagnetic phase under high pressure to determine the spin structure. The spontaneous magnetization expected from the determined magnetic structure is 0.020μB/Mn, which is in excellent agreement with the magnitude of the observed spontaneous magnetization. This magnetic structure is ferrimagnetic with the same symmetry as the ferromagnetic one, strongly supporting the appearance of the anomalous Hall effect due to the Berry phase.

Free Research Field

物性実験

Academic Significance and Societal Importance of the Research Achievements

α-Mnの反強磁性相におけるNMRについては，50年前に指摘された中性子散乱実験との不一致を明確なものとする実験結果が得られた。この論文はJ.Phys.Soc.Jpn.のEditors’choiceに選ばれた。スピン構造の決定には至っていないが，単体元素磁性体でスピン構造が決定されていない物質はほかに例がなく，学術的に大きな意義がある。
高圧下における弱い強磁性相のスピン構造が強磁性と同じ対称性を有したフェリ磁性であることは，この相で現れる異常ホール効果の出現機構がベリー位相に起因していることを強く支持する結果であり学術的に重要な意義がある。