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論文

Magnetic and transport properties of the pseudobrookite Al$$_{1-x}$$Ti$$_{2+x}$$O$$_{5}$$ single crystals

高濱 隆成*; 有薗 実駿*; 犬童 代梧*; 吉永 汰正*; 寺倉 千恵子*; 竹下 直*; 白崎 巧*; 野田 正亮*; 桑原 英樹*; 梶本 亮一; et al.

JPS Conference Proceedings (Internet), 38, p.011114_1 - 011114_6, 2023/05

We investigated the transport and magnetic properties of single crystals of the pseudobrookite Al$$_{1-x}$$Ti$$_{2+x}$$O$$_{5}$$ for $$0 le x le 1$$ grown using a floating zone. We found a correlation of spin-singlet Ti$$^{3+}$$-Ti$$^{3+}$$ dimers even in the conductive $$alpha$$ and $$lambda$$ phases which develops with increasing $$x$$. The development of the dimer correlation suppresses the magnetic susceptibility at the low temperature and enhances the electric conductivity perhaps due to the suppression of the magnetic scattering at the isolated Ti$$^{3+}$$ ions. The compound shows the best conductivity in the $$lambda$$ phase near the phase boundary between the $$lambda$$ and $$beta$$ phases where the dimer correlation is much developed. Some exotic conductive state may be realized under the background of fluctuation of the spin-singlet dimer in the $$lambda$$ phase near the phase boudary.

論文

Structural, magnetic, transport, and thermoelectric properties of the pseudobrookite AlTi$$_{2}$$O$$_{5}$$-Ti$$_{3}$$O$$_{5}$$ system

高濱 隆成*; 石井 透依*; 犬童 代梧*; 有薗 実駿*; 寺倉 千恵子*; 十倉 好紀*; 竹下 直*; 野田 正亮*; 桑原 英樹*; 斎木 琢夫*; et al.

Physical Review Materials (Internet), 4(7), p.074401_1 - 074401_11, 2020/07

 被引用回数:6 パーセンタイル:40.97(Materials Science, Multidisciplinary)

We investigated the structural, magnetic, transport, and high-temperature thermoelectric properties of single crystals of the pseudobrookite Al$$_{1-x}$$Ti$$_{2+x}$$O$$_{5}$$ for $$0 le x le 1$$ grown using a floating zone. We found a correlation of spin-singlet Ti$$^{3+}$$-Ti$$^{3+}$$ dimers coupled with the lattice even in the conductive $$alpha$$ and $$lambda$$ phases which develops with increasing $$x$$. This developing dimer correlation reduces the number of unpaired Ti$$^{3+}$$ ions, which makes the compound more conductive owing to the suppression of disorder for $$x$$ up to about 0.75. The dimer fluctuation causes a critical enhancement of the magnetic susceptibility at around 150 K in the $$lambda$$ phase near the boundary ($$x sim 0.9$$) between the $$lambda$$ and the $$beta$$ phases. Such a correlation of the spin-singlet Ti$$^{3+}$$-Ti$$^{3+}$$ dimers may produce a high Seebeck coefficient in the conductive $$alpha$$ and $$lambda$$ phases leading to a large thermoelectric power factor at high temperatures.

論文

Time-of-flight elastic and inelastic neutron scattering studies on the localized 4d electron layered perovskite La$$_5$$Mo$$_4$$O$$_{16}$$

飯田 一樹*; 梶本 亮一; 水野 雄介*; 蒲沢 和也*; 稲村 泰弘; 星川 晃範*; 吉田 幸彦*; 松川 健*; 石垣 徹*; 河村 幸彦*; et al.

Journal of the Physical Society of Japan, 86(6), p.064803_1 - 064803_6, 2017/06

 被引用回数:1 パーセンタイル:12.14(Physics, Multidisciplinary)

The magnetic structure and spin wave excitations in the quasi-square-lattice layered perovskite compound La$$_5$$Mo$$_4$$O$$_{16}$$ were studied by a combination of neutron diffraction and inelastic neutron scattering techniques using polycrystalline sample. Neutron powder diffraction refinement revealed that the magnetic structure is ferrimagnetic in the $$ab$$ plane with antiferromagnetic stacking along the $$c$$-axis. The inelastic neutron scattering results display strong easy-axis magnetic anisotropy along the $$c$$-axis due to the spin-orbit interaction in Mo ions. The model Hamiltonian consisting of in-plane anisotropic exchange interactions, the interlayer exchange interaction, and easy-axis single-ion anisotropy can explain our inelastic neutron scattering data well. Strong Ising-like anisotropy and weak interlayer coupling compared with the intralayer exchange interaction can explain both the high-temperature magnetoresistance and long-time magnetization decay recently observed in La$$_5$$Mo$$_4$$O$$_{16}$$.

口頭

磁場中中性子回折実験によるLa$$_5$$Mo$$_4$$O$$_{16}$$の磁気構造の研究

梶本 亮一; 飯田 一樹*; 中尾 朗子*; 茂吉 武人*; 松田 雅昌*; Ye, F.*; 水野 雄介*; 勝藤 拓郎*

no journal, , 

La$$_{5}$$Mo$$_{4}$$O$$_{16}$$は二次元正方格子上に配列したMo$$^{4+}$$イオンとMo$$^{5+}$$イオンがイジング性の強いフェリ磁性秩序を示す。最近、その磁化は磁場に対して大きなヒステリシスを示し、かつ、いくつかの磁化の値で滞留点を示すことが明らかになった。そこで本研究では、この特徴的な磁化過程がどのような磁気構造の変化に対応しているのか調べるため、中性子回折装置SENJUおよびCORELLIを用いて磁場中単結晶中性子回折実験を行った。磁場による磁気Bragg反射位置の変化は実験の分解能の範囲では観測されなかったが、磁場により層間強磁性・層間反強磁性の反射の強度がそれぞれ増大、減少する様子が観測された。これらの反射強度の磁場変化は磁化の変化と対応しており、La$$_5$$Mo$$_4$$O$$_{16}$$の特徴的な磁化の振る舞いは層間強磁性・反強磁性の磁気構造のドメインの、体積分率の変化によるものであることが示唆される。

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