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論文

Incommensurate helimagnetic structure of Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ determined by single-crystal neutron diffraction

田中 誠也*; 鬼柳 亮嗣; 石川 喜久*; 天児 寧*; 飯山 拓*; 二村 竜祐*; 丸山 建一*; 内海 重宣*

Physical Review Materials (Internet), 7(1), p.014403_1 - 014403_11, 2023/01

https://doi.org/10.1103/PhysRevMaterials.7.014403
 被引用回数：0 パーセンタイル：0.00(Materials Science, Multidisciplinary)

Sc-substituted hexagonal ferrite Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ has an incommensurate helimagnetic structure. However, the incommensurate helimagnetic structure has not been sufficiently determined, and the mechanism via which the helimagnetism develops has not been studied. Time-of-flight single-crystal neutron diffraction measurements were performed on single-crystal samples of Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ with Sc concentrations of x = 0, 0.128, 0.153, and 0.193. The magnetic structure analyses revealed that the helimagnetic structure of Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ is a cone type whose base is in the ab plane and height is in the c-axis direction. The magnetic moments of Fe2(4$$e$$), Fe4(4$$f_{2}$$), and Fe5(12$$k$$) are aligned with distinct angles, leading to the helimagnetic structure of Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$, and can be explained by assuming that there is an antiferromagnetic superexchange interaction $$J_{5}$$ between Fe2(4$$e$$) and Fe5(12$$k$$) that is negligible in the x = 0 crystal. The shorter bond distance of Fe2-O1 in Sc-rich crystals revealed by the crystal structure analyses enhances the superexchange interaction $$J_{5}$$. The relatively strong $$J_{5}$$ leads to competition among the three superexchange interactions, $$J_{3}$$, $$J_{4}$$, and $$J_{5}$$, resulting in the development of the helimagnetic structure. These findings facilitate the understanding of the essentials of the basic magnetic material BaFe$$_{12}$$O$$_{19}$$.

論文

Magnetic phase diagram of helimagnetic Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ (0 $$leq$$ x $$leq$$ 0.2) hexagonal ferrite

丸山 建一*; 田中 誠也*; 鬼柳 亮嗣; 中尾 朗子*; 森山 健太郎*; 石川 喜久*; 天児 寧*; 飯山 拓*; 二村 竜祐*; 内海 重宣*; et al.

Journal of Alloys and Compounds, 892, p.162125_1 - 162125_8, 2022/02

https://doi.org/10.1016/j.jallcom.2021.162125
 被引用回数：2 パーセンタイル：12.81(Chemistry, Physical)

Hexagonal ferrite Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ is an important magnetic oxide material in both science and engineering because it exhibits helimagnetism around room temperature (300 K). In this study, the magnetic phase diagram of Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ consisting of ferri-, heli-, antiferro-, and paramagnetic phases has been completed through magnetization and neutron diffraction measurements. The magnetic phase transition temperature to paramagnetism decreases with the increase in x, and the temperature at which the magnetization reaches a maximum, which corresponds to the magnetic phase transition from heli- to ferrimagnetism, is determined for low x crystals. The temperatures at which helimagnetism appears are precisely determined by observing the magnetic satellite reflection peaks in neutron diffraction at various temperatures, which characterize helimagnetism. Based on these results, the magnetic phase diagram of the Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ system is constructed in the T-x plane. Helimagnetism appears at x $$>$$ 0.06, and magnetism with antiferromagnetic components appears as the extension phase of helimagnetism at x $$>$$ 0.19 through the coexistence region. The turn angle $$phi_{0}$$ of the helix for each x crystal is calculated from the relationship, $$phi_{0} = 2pidelta$$, where $$delta$$ is the incommensurability. The turn angle $$phi_{0}$$ decreases with the increase in temperature for the same x crystal, and increases with the increase in x at the same temperature. Furthermore, it is found that there are clear thresholds at which $$phi_{0}$$ cannot take values between 0$$^{circ}$$ < $$phi_{0}$$ < 90$$^{circ}$$ and 170$$^{circ}$$ < $$phi_{0}$$ < 180$$^{circ}$$.

論文

Flux growth and magnetic properties of helimagnetic hexagonal ferrite Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$ single crystals

内海 重宣*; 田中 誠也*; 丸山 建一*; 天児 寧*; 鬼柳 亮嗣; 中尾 朗子*; 森山 健太郎*; 石川 喜久*; 他9名*

ACS Omega (Internet), 5(38), p.24890 - 24897, 2020/09

https://doi.org/10.1021/acsomega.0c03671
 被引用回数：5 パーセンタイル：22.76(Chemistry, Multidisciplinary)

六方晶フェライトBa(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$の磁気構造を解明し、さらなる応用開発を進めるためには、大型の高品質な単結晶を育成することが重要な第一歩である。本研究では、Na$$_{2}$$O-Fe$$_{2}$$O$$_{3}$$フラックスを使用した自発結晶化法によって、さまざまなSc濃度$$x$$のBa(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$単結晶の育成に成功した。得られた結晶は、高品質の単相Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$であることがX線回折と元素分析により確認され、$$x$$ = 0.128結晶の77Kの磁化測定では、ヘリマグネティックな挙動を示すことがわかった。$$x$$=0.128結晶の中性子回折測定の結果、211K以下で磁気衛星反射が確認され、Ba(Fe$$_{1-x}$$Sc$$_{x}$$)$$_{12}$$O$$_{19}$$がヘリ磁性物質であることが確認された。

論文

Conduction-band electronic states of YbInCu$$_4$$ studied by photoemission and soft X-ray absorption spectroscopies

内海 有希*; 佐藤 仁*; 栗原 秀直*; 間曽 寛之*; 平岡 耕一*; 小島 健一*; 飛松 浩明*; 大河内 拓雄*; 藤森 伸一; 竹田 幸治; et al.

Physical Review B, 84(11), p.115143_1 - 115143_7, 2011/09

https://doi.org/10.1103/PhysRevB.84.115143
 被引用回数：12 パーセンタイル：45.97(Materials Science, Multidisciplinary)

典型的な価数揺動系であるYbInCu$$_4$$の価電子状態を、硬X線内殻光電子分光,軟X線吸収実験、及び軟X線光電子分光の温度依存性の実験から研究した。YbInCu$$_4$$の価数転移について、価電子帯からYb 4$$f$$状態への電荷移動で記述した。

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