Spin structure at zero magnetic field and field-induced spin reorientation transitions in a layered organic canted antiferromagnet bordering a superconducting phase

Kohsuke Oinuma, Naoki Okano, Hitoshi Tsunakawa, Shinji Michimura, Takuya Kobayashi, Hiromi Taniguchi, Kazuhiko Satoh, Julia Angel, Isao Watanabe, Yasuyuki Ishii, Hiroyuki Okamoto, and Tetsuaki Itou
Phys. Rev. B 102, 035102 – Published 1 July 2020

Abstract

We attempted to assign the spin structure of a layered organic antiferromagnet, κ-(d8-BEDT-TTF)2Cu[N(CN)2]Br, which is a key material located closest to the Mott boundary at ambient pressure among this family of compounds, by investigating its macroscopic magnetization thoroughly, motivated by a recent successful assignment of the spin structure of an isostructural material, κ-(BEDT-TTF)2Cu[N(CN)2]Cl [BEDT-TTF and d8-BEDT-TTF are bis(ethylenedithio)tetrathiafulvalene and its deuterated molecule, respectively]. We measured the isothermal magnetization after careful choice of the measurement temperatures and cooling speed at around 80 K, so that the magnetism of the antiferromagnetic phase can be effectively extracted. Consequently, we observed hysteresis loops signifying ferromagnetism and steplike behavior when the magnetic field applied parallel to the crystallographic b and a axes was swept, respectively. The possible spin structure consistent with these results was discussed in terms of probable interactions between the spins, such as exchange interactions and the Dzyaloshinskii-Moriya interaction. Eventually, we asserted that κ-(d8-BEDT-TTF)2Cu[N(CN)2]Br has a spin structure with the easy axis being the c axis and the net canted moment parallel to the b axis, which is surprisingly different from that of κ-(BEDT-TTF)2Cu[N(CN)2]Cl. We suggested that this difference originates from the difference of the sign of the interlayer interaction between the two materials. We also elucidated the overall picture of the magnetization processes of this material under the magnetic fields parallel to the three principle axes, which are also in contrast to those of κ-(BEDT-TTF)2Cu[N(CN)2]Cl. In particular, the spin-reverse transition at which half of the spins rotate by 180 was not induced by the b-axis magnetic field, as in the case of κ-(BEDT-TTF)2Cu[N(CN)2]Cl, but by the a-axis magnetic field. Finally, numerical simulations and magnetic symmetry analysis enabled us to confirm the validity of the spin structures proposed for the two antiferromagnets under zero and high magnetic fields.

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  • Received 21 November 2019
  • Revised 18 June 2020
  • Accepted 19 June 2020

DOI:https://doi.org/10.1103/PhysRevB.102.035102

©2020 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Kohsuke Oinuma, Naoki Okano2, Hitoshi Tsunakawa2, Shinji Michimura2, Takuya Kobayashi2, Hiromi Taniguchi2,*, and Kazuhiko Satoh2

  • Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan

Julia Angel and Isao Watanabe3

  • Meson Science Laboratory, Nishina Center for Accelerator-Based Science, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako 351-0198, Japan

Yasuyuki Ishii

  • Department of Physics, College of Engineering, Shibaura Institute of Technology, Saitama 337-8570, Japan

Hiroyuki Okamoto

  • Faculty of Medicine, Kanazawa University, Kodatsuno 5-11-89, Kanazawa 920-0942, Japan

Tetsuaki Itou

  • Department of Applied Physics, Tokyo University of Science, Tokyo 125-8585, Japan

  • *taniguchi@phy.saitama-u.ac.jp

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Issue

Vol. 102, Iss. 3 — 15 July 2020

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