Browsing by Author "Iida, K"

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    Electron doping effects on the spin spectroscopy of BaFe2-xNixAs2 superconductors
    (International Conference on Neutron Scattering, 2017-07-12) Luo, HQ; Gong, DL; Xie, T; Lu, XY; Kamazawa, K; Iida, K; Kajimoto, R; Ivanov, AS; Adroja, DT; Kulda, J; Danilkin, SA; Deng, GC; Li, SL; Dai, PC
    High-temperature superconductivity in iron pnictides emerges from electron or hole doped parent compounds with antiferromagnetic order, which is argued to be associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons. With more than 6 years\' efforts, we have used time-of-flight neutron spectroscopy to extensively map out the spin excitations in the electron-doped BaFe2-xNixAs2 especially around the overdoped zone boundary of superconductivity. We have found that the high energy spin fluctuations survive in the extremely high doping x=0.6 far beyond the superconducting dome, but the low energy spin excitations including the spin resonance mode is very sensitive to the electron dopings, by finally forming a large spin gap just after the disappearance of superconductivity in the overdoped regime. Further polarized neutron analysis indicate that the spin gap actually is anisotropic, and the longitudinal mode of spin fluctuations, as a hallmark of the itinerant magnetism from Fermi surface nesting, is totally eliminated together with the hole pockets near the electron-overdoped zone boundary of superconductivity.Our results suggest that the strong fluctuations from local moments give framework for magnetic interaction, while itinerant spin excitations originated from Fermi surface nesting are crucial to the superconductivity in iron pnictides.
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    Giant magnetic in-plane anisotropy and competing instabilities in Na3Co2SbO6
    (American Physical Society, 2022-12-02) Li, XT; Gu, YC; Chen, Y; Garlea, VO; Iida, K; Kamazawa, K; Li, YM; Deng, GC; Xiao, Q; Zheng, XQ; Ye, Z; Peng, YY; Zaliznyak, IA; Tranquada, JM; Li, Y
    We report magnetometry data obtained on twin-free single crystals of Na3Co2SbO6, which is considered a candidate material for realizing the Kitaev honeycomb model for quantum spin liquids. Contrary to a common belief that such materials can be modeled with the symmetries of an ideal honeycomb lattice, our data reveal a pronounced twofold symmetry and in-plane anisotropy of over 200%, despite the honeycomb layer’s tiny orthorhombic distortion of less than 0.2%. We further use magnetic neutron diffraction to elucidate a rich variety of field-induced phases observed in the magnetometry. These phases manifest themselves in the paramagnetic state as diffuse scattering signals associated with competing ferromagnetic and antiferromagnetic instabilities, consistent with a theory that also predicts a quantum spin liquid phase nearby. Our results call for theoretical understanding of the observed in-plane anisotropy and render Na3Co2SbO6 a promising ground for finding exotic quantum phases by targeted external tuning. © Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
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    Tetrahedral triple-Q magnetic ordering and large spontaneous hall conductivity in the metallic triangular antiferromagnet Co1/3TaS2
    (Springer Nature, 2023-12-15) Park, P; Cho, W; Kim, C; An, Y; Kang, YG; Avdeev, M; Sibille, R; Iida, K; Kajimoto, R; Lee, KH; Ju, W; Cho, EJ; Noh, HJ; Han, MJ; Zhang, SS; Batista, CD; Park, JG
    The triangular lattice antiferromagnet (TLAF) has been the standard paradigm of frustrated magnetism for several decades. The most common magnetic ordering in insulating TLAFs is the 120° structure. However, a new triple-Q chiral ordering can emerge in metallic TLAFs, representing the short wavelength limit of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the first example of tetrahedral triple-Q magnetic ordering with the associated topological Hall effect (non-zero σxy(H = 0)). We also present a theoretical framework that describes the emergence of this magnetic ground state, which is further supported by the electronic structure measured by angle-resolved photoemission spectroscopy. Additionally, our measurements of the inelastic neutron scattering cross section are consistent with the calculated dynamical structure factor of the tetrahedral triple-Q state. © 2024 Springer Nature Limited.
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    Weak trimerization in the frustrated two-dimensional triangular Heisenberg antiferromagnet LuyY1−yMnO3
    (American Physical Society, 2023-06-02) Yano, S; Wang, CW; Gardner, JS; Chen, WT; Iida, K; Mole, RA; Louca, D
    To understand the 2D triangular Heisenberg antiferromagnetic system, we investigated the magnetic structures and the dynamics of LuyY1-yMnO3 in detail. The substitutions are adjusted to the Mn atomic position close to xMn=13. The neutron powder diffraction data claims that the magnetic structure of LuyY1-yMnO3 is described as a mixture of Γ3 (P63′cm′) and Γ4 (P63′c′m) at the xMn position for y=0.15, 0.30, and 0.45. The ratio of Γ3 and Γ4 depends on temperature and composition and the fraction of Γ3 increases upon cooling, while no clear trimerization was observed at the xMn position. We estimated exchange parameters from the analysis of the low-energy part of the spin waves. The results showed a weak trimerization effect on cooling because the nearest-neighbor exchange interaction is slightly enhanced. The temperature dependence of the spin-wave dispersion around the Γ point shows that the spin gap closes with increasing temperature because the exchange interactions in the nearest Mn-Mn neighbor become smaller. Gapless diffusive magnetic excitation from a Mn triangular lattice has been observed in a wide range in Q and E space of LuyY1-yMnO3. We found that Lu0.3Y0.7MnO3 could be an ideal case to investigate the trimerization, frustrated magnetism, and magnetoelastic coupling often observed in two-dimensional triangular lattice Heisenberg antiferromagnet systems. ©2023 American Physical Society