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論文

Massive Dirac magnons in the three-dimensional honeycomb magnetic oxide FeTiO

Chung, J.-H.*; Kwangwoo, S.*; Yokoo, Tetsuya R.; 植田大地*; 今井正樹; Kim, H.-S.; Kiem, D. H.; Han, M. J.*; 社本真一

Scientific Reports (Internet), 15, p.5978_1 - 5978_10, 2025/02

https://doi.org/10.1038/s41598-025-90478-2

被引用回数：0 パーセンタイル：0.00(Multidisciplinary Sciences)

Two dimensional honeycomb ferromagnets host massless Dirac magnons which are a bosonic analogue of Dirac fermions in graphene. The Dirac magnons may become massive and topological when the time-reversal symmetry breaks and an energy gap opens up at the Dirac point, which was experimentally observed in Cr $^{3+}$ -based van der Waals magnets. Here, we investigate the spin wave excitations in the magnetic oxide FeTiO with Fe $^{2+}$ electrons (). Using inelastic neutron scattering, we observe two magnon bands separated by a 1.2-meV gap at the Dirac points indicating that its Dirac magnons are massive. Using the linear spin-wave and density functional theory calculations, we find that the spin-orbit-coupled antisymmetric Dzyaloshinskii-Moriya exchanges can best account for the observed Dirac gap opening. The associated Berry curvature and Chern number () indicate that FeTiO hosts topological spin excitations via time-reversal symmetry breaking of Dirac magnons.

論文

Quantum critical behavior of the hyperkagome magnet MnCoSi

山内宏樹; Sari, D. P.*; 安井幸夫*; 坂倉輝俊*; 木村宏之*; 中尾朗子*; 大原高志; 本田孝志*; 樹神克明; 井川直樹; et al.

Physical Review Research (Internet), 6(1), p.013144_1 - 013144_9, 2024/02

https://doi.org/10.1103/PhysRevResearch.6.013144

-Mn-type family alloys Mn have three-dimensional antiferromagnetic (AFM) corner-shared triangular network. The antiferromagnet MnRhSi shows magnetic short-range order (SRO) over a wide temperature range of approximately 500 K above the Nel temperature $T_{rm N}$ = 190 K. MnCoSi has the smallest lattice parameter and the lowest $T_{rm N}$ in the family compounds. The quantum critical point (QCP) from AFM to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 of MnCoSi is only 140 K, quantum critical behavior is observed in MnCoSi as the enhancement of the electronic specific heat coefficient . We study how the magnetic SRO appears in MnCoSi by using neutron scattering, SR, and physical property measurements. The experimental results show that the neutron scattering intensity of the magnetic SRO does not change much regardless of the suppressed magnetic moment in the long-range magnetic ordered state compared to those of MnRhSi. The initial asymmetry drop ratio of SR above $T_{rm N}$ becomes small, and the magnetic SRO temperature $T_{SRO}$ is suppressed to 240 K. The results suggest that the MnCoSi is close to the QCP in the Mn system.

論文

Single-crystal neutron diffraction study of the heavy-electron superconductor CeNiGe $_{3}$

池田陽一*; 植田大地*; 吉澤英樹*; 中尾朗子*; 宗像孝司*; 大原高志

Journal of the Physical Society of Japan, 84(12), p.123701_1 - 123701_5, 2015/12

https://doi.org/10.7566/JPSJ.84.123701

被引用回数：6 パーセンタイル：43.19(Physics, Multidisciplinary)

特異な反強磁性秩序化を示すことが知られているheavy-electron超伝導体であるCeNiGe $_{3}$ について、MLFのSENJUを用いて単結晶中性子回折測定を行った。相転移温度の5K以下で測定を行ったところ、以前の粉末試料を用いた回折測定では伝搬ベクトルとして $k_{1}$ =(1,0,0)と $k_{2}$ =(0,0.41,1/2)が観測されたのに対して、単結晶試料を用いた測定では $k_{2}$ =(0,0.41,1/2)のみが観測された。このことから、CeNiGe $_{3}$ の常圧における磁気特性は伝搬ベクトル $k_{2}$ のみによって特徴づけられることが示唆された。