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論文

Magnetically induced electric polarization in Ba$$_{3}$$Fe$$_{2}$$O$$_{5}$$Cl$$_{2}$$ with tunable direction in three dimensions

阿部 伸行*; 塩澤 俊介*; 松浦 慧介*; 佐賀山 基*; 中尾 朗子*; 大原 高志; 徳永 祐介*; 有馬 孝尚*

Physical Review B, 101(18), p.180407_1 - 180407_5, 2020/05

 被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)

The correlation between magnetism and electric polarization in a chiral insulating magnet Ba$$_{3}$$Fe$$_{2}$$O$$_{5}$$Cl$$_{2}$$ has been investigated. The temperature dependence of magnetic susceptibility shows an anomaly at 564 K, suggesting the onset of antiferromagnetic order of Fe$$^{3+}$$ moments. Electric polarization appears in a magnetic field below TN due to the spin-direction-dependent metal-ligand hybridization. The direction of the electric polarization can be controlled in three-dimensional space by changing the direction of an external magnetic field. This compound also shows an antiferromagnetic-to-weak-ferromagnetic transition accompanied by a structural phase transition at 140 K.

論文

Phase-transition kinetics of magnetic skyrmions investigated by stroboscopic small-angle neutron scattering

中島 多朗*; 稲村 泰弘; 伊藤 崇芳*; 大石 一城*; 大池 広志*; 賀川 史敬*; 吉川 明子*; 田口 康二郎*; 加倉井 和久*; 十倉 好紀*; et al.

Physical Review B, 98(1), p.014424_1 - 014424_5, 2018/07

 被引用回数:4 パーセンタイル:55.32(Materials Science, Multidisciplinary)

MnSi中に発生する磁気スキルミオンの相転移の挙動を中性子小角散乱ストロボスコピック測定により観測した。温度を50K/秒という速度で急激に変化させている間に13マイクロ秒の時間分解能で中性子小角散乱パターンの時間変化を測定することに成功し、その結果、温度の上昇によって磁気スキルミオンが消滅する様子や、急速な冷却過程で生成されたスキルミオンが本来存在できない低温まで過冷却状態で残る様子などが明らかとなった。

論文

Magnetic excitations in the orbital disordered phase of MnV$$_2$$O$$_4$$

松浦 慧介*; 佐賀山 基*; 上原 周*; 新居 陽一*; 梶本 亮一; 蒲沢 和也*; 池内 和彦*; Ji, S.*; 阿部 伸行*; 有馬 孝尚*

Physica B; Condensed Matter, 536, p.372 - 376, 2018/05

 被引用回数:1 パーセンタイル:87.78(Physics, Condensed Matter)

We have investigated the temperature dependence of magnetic dynamics in a spinel-type vanadium oxide MnV$$_2$$O$$_4$$ by inelastic neutron scattering. The scattering intensity of excitation around 20 meV disappears in the collinear intermediate-temperature cubic-ferrimagnetic phase, which reveals that this excitation should be peculiar to the orbital ordered phase. We have found a weakly dispersive mode emergent from a non-integer wavevector $$(1.4,1.4,0)$$ at 56 K, which lies in the cubic-ferrimagnetic phase between non-coplanar ferrimagnetic and paramagnetic phases. This indicates that the probable presence of an incommensurate instability in the simple collinear structure.

論文

Spin-orbital correlated dynamics in the spinel-type vanadium oxide MnV$$_{2}$$O$$_{4}$$

松浦 慧介*; 佐賀山 基*; 上原 周*; 新居 陽一*; 梶本 亮一; 蒲沢 和也*; 池内 和彦*; Ji, S.*; 阿部 伸行*; 有馬 孝尚*

Physical Review Letters, 119(1), p.017201_1 - 017201_6, 2017/07

 被引用回数:7 パーセンタイル:33.51(Physics, Multidisciplinary)

We investigate the magnetic dynamics in the spinel-type vanadium oxide MnV$$_2$$O$$_4$$. Inelastic neutron scattering around 10 meV and a Heisenberg model analysis have revealed that V$$^{3+}$$ spin-wave modes exist at a lower-energy region than previously reported. The scattering around 20 meV cannot be reproduced with the spin-wave analysis. We propose that this scattering could originate from the spin-orbital coupled excitation. This scattering is most likely attributable to V$$^{3+}$$ spin-wave modes, entangled with the orbital hybridization between $$t_{2g}$$ orbitals.

論文

Magnetoelectric coupling in the honeycomb antiferromagnet Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$

Khanh, N. D.*; 阿部 伸行*; 佐賀山 基*; 中尾 朗子*; 花島 隆泰*; 鬼柳 亮嗣; 徳永 祐介*; 有馬 孝尚*

Physical Review B, 93(7), p.075117_1 - 075117_6, 2016/02

 被引用回数:50 パーセンタイル:6.02(Materials Science, Multidisciplinary)

The magnetic structure and magnetoelectric effect have been investigated for single crystals of the antiferromagnet Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$. Single-crystal neutron diffraction and magnetic susceptibility measurement have revealed that the magnetic structure is different from a collinear arrangement with spin parallel to the trigonal axis as proposed previously. Co$$^{2+}$$ magnetic moments are found to be almost lying in the basal plane, which lowers the magnetic symmetry to $$C2/c'$$ with the propagation vector $$k$$ = 0. Associated with the magnetic phase transition, a sharp anomaly in the dielectric constant and displacement current indicate the appearance of the magnetoelectric below Neel temperature TN with a large coupling constant up to 30 ps/m. The existence of off-diagonal components in a magnetoelectric tensor indicate the formation of ferrotoroidic order in Co$$_{4}$$Nb$$_{2}$$O$$_{9}$$. Such a magnetoelectric effect can be ascribed to the reduction of symmetry caused by simple antiferromagnetic order in a honeycomb network.

論文

Large trigonal-field effect on spin-orbit coupled states in a pyrochlore iridate

植松 大介*; 佐賀山 基*; 有馬 孝尚*; 石川 洵*; 中辻 知*; 高木 英典*; 吉田 雅洋*; 水木 純一郎; 石井 賢司

Physical Review B, 92(9), p.094405_1 - 094405_6, 2015/09

 被引用回数:15 パーセンタイル:32.98(Materials Science, Multidisciplinary)

The half-filled topmost valence band of Ir$$^{4+}$$ in several iridates such as Sr$$_2$$IrO$$_4$$, IrO$$_2$$, and CaIrO$$_3$$ has been proposed to originate mainly from the spin-orbit coupled $$J_{rm eff}=1/2$$ states. In pyrochlore iridates $$R_2$$Ir$$_2$$O$$_7$$ ($$R$$: rare earth), some exotic electronic states are theoretically proposed by assuming $$J_{rm eff}=1/2$$ states. However, the octahedral coordination around Ir is trigonally distorted, which may affect the energy level scheme of Ir $$5d$$ states. Here, we report spectra of resonant elastic and inelastic X-ray scattering in Eu$$_2$$Ir$$_2$$O$$_7$$ at the Ir $$L$$ edges. A large suppression of the magnetic scattering signal at the Ir $$L_{rm II}$$ edge supports the $$J_{rm eff}=1/2$$ picture rather than the $$S=1/2$$ one. The inelastic scattering spectrum indicates that the magnitude of the trigonal field on the Ir$$^{4+}$$ states is evaluated to be comparable to the spin-orbit interaction. The energy diagram of the $$5d$$ state is proposed based on the simple cluster model.

論文

Multi-spin-state dynamics during insulator-metal crossover in LaCoO$$_3$$

土居 篤典*; 藤岡 淳*; 福田 竜生; 筒井 智嗣*; 奥山 大輔*; 田口 康二郎*; 有馬 孝尚*; Baron, A. Q. R.*; 十倉 好紀*

Physical Review B, 90(8), p.081109_1 - 081109_4, 2014/01

 被引用回数:15 パーセンタイル:35.4(Materials Science, Multidisciplinary)

The phonon dynamics of spin-state crossover for perovskite LaCoO$$_3$$ was investigated using infrared and inelastic X-ray spectroscopy. We observed that the Co-O bond stretching phonons couples to the thermally excited spin-state. The momentum dispersion of the optical mode is anomalously dispersionless (less than 3 meV), and this supports the spin-state disproportionation scenario. The steep enhancement of spin-state fluctuation compared to the charge gap suggests the density dependent spin state disproportionation; a simple low spin (LS)/high spin (HS)- or LS/intermediate spin (IS)-state disproportionation is realized at the initial stage with dilute HS- (or IS-) state density, while the complex spin-state disproportionation involving all of the LS-, IS- and HS-state is formed when the density of HS- (or IS-) state is enhanced.

論文

Soft phonon mode coupled with antiferromagnetic order in incipient-ferroelectric Mott insulators Sr$$_{1-x}$$Ba$$_x$$MnO$$_3$$

酒井 英明*; 藤岡 淳*; 福田 竜生; Bahramy, M. S.*; 奥山 大輔*; 有田 亮太郎*; 有馬 孝尚*; Baron, A. Q. R.*; 田口 康二郎*; 十倉 好紀*

Physical Review B, 86(10), p.104407_1 - 104407_11, 2012/09

 被引用回数:23 パーセンタイル:26.22(Materials Science, Multidisciplinary)

Infrared optical and inelastic X-ray scattering spectra have been systematically investigated in combination with first-principles calculations for paraelectric and antiferromagnetic perovskite Sr$$_{1-x}$$Ba$$_x$$MnO$$_3$$ single crystals, which are close to a ferroelectric transition arising from off-center displacement of magnetic Mn$$^{4+}$$ ions. One optical phonon rapidly softens toward zero frequency at room temperature with increasing $$x$$. This soft-mode behavior is also reproduced by the first-principles calculations, from which we have predicted the vibration mode of all the optical phonons. Below the antiferromagnetic-transition temperature, the soft mode hardens with decreasing temperature and then resoftens toward the lowest temperature.

論文

Emergent phenomena in perovskite-type manganites

田口 康二郎*; 酒井 英明*; 奥山 大輔*; 石渡 晋太郎*; 藤岡 淳*; 福田 竜生; 橋爪 大輔*; 賀川 史敬*; 高橋 陽太郎*; 島野 亮*; et al.

Physica B; Condensed Matter, 407(11), p.1685 - 1688, 2012/06

 被引用回数:3 パーセンタイル:82.41(Physics, Condensed Matter)

Perovskite-type manganites exhibit various interesting phenomena arising from complex interplay among spin, charge, orbital, and lattice degrees of freedom. As the respective examples, perovskite-type YMnO$$_3$$ and Sr$$_{1-x}$$Ba$$_x$$MnO$$_3$$ are discussed. In the YMnO$$_3$$, the ferroelectric lattice distortion associated with the $$E$$-type spin order is observed for the first time. Displacement-type ferroelectricity with off-center magnetic ions is discovered for Sr$$_{0.5}$$Ba$$_{0.5}$$MnO$$_3$$, which shows both large polarization value and strong coupling between ferroelectricity and magnetism.

論文

Multiferroic $$M$$-type hexaferrites with a room-temperature conical state and magnetically controllable spin helicity

徳永 祐介*; 金子 良夫*; 奥山 大輔*; 石渡 晋太郎*; 有馬 孝尚*; 脇本 秀一; 加倉井 和久; 田口 康二郎*; 十倉 好紀*

Physical Review Letters, 105(25), p.257201_1 - 257201_4, 2010/12

 被引用回数:206 パーセンタイル:1.73(Physics, Multidisciplinary)

Magnetic and magnetoelectric (ME) properties have been studied for single crystals of Sc-doped $$M$$-type barium hexaferrites. Magnetization ($$M$$) and neutron diffraction measurements revealed that by tuning Sc concentration a longitudinal conical state is stabilized up to above room temperatures. ME measurements have shown that a transverse magnetic field ($$H$$) can induce electric polarization ($$P$$) at lower temperatures and that the spin helicity is nonvolatile and endurable up to near the conical magnetic transition temperature.

論文

Critical competition between two distinct orbital-spin ordered states in perovskite vanadates

藤岡 淳*; 安江 俊夫*; 宮坂 茂樹*; 山崎 裕一*; 有馬 孝尚*; 佐賀山 基*; 稲見 俊哉; 石井 賢司; 十倉 好紀*

Physical Review B, 82(14), p.144425_1 - 144425_12, 2010/10

 被引用回数:43 パーセンタイル:13.5(Materials Science, Multidisciplinary)

We have investigated the spin/orbital phase diagram in the perovskite orthovanadate $$R$$VO$$_3$$ ($$R$$ = Eu, Y, Dy, and Ho) by measurements of magnetization, dielectric constant, specific heat, Raman scattering spectra, and X-ray diffraction, focusing on the interplay between the V $$3d$$ spin and the $$4f$$ moment of the $$R$$ ion. The results cannot be uniquely explained in terms of the exchange interaction between the V $$3d$$ spin and the $$R$$-ion $$4f$$ moment. By comparing this phase diagram with the spin/orbital ordering in TbVO$$_3$$, it is evident that the critical competition between the C-type spin/G-type orbital ordered phase and the G-type spin/C-type orbital ordered one depends not only on the GdFeO$$_3$$-type lattice distortion but also on the presence of the $$4f$$ moment of the $$R$$ ion. The magnetic field induced phase transition of the spin/orbital ordering is achieved concomitantly with polarizing $$R$$ $$4f$$ moments for DyVO$$_3$$ and HoVO$$_3$$. The results cannot be uniquely explained in terms of the exchange interaction between the V $$3d$$ spin and the $$R$$-ion $$4f$$ moment. The coupling of the $$R$$ $$4f$$ moment polarization with the lattice distortion tied with the orbital ordering of the V $$3d$$ sublattice may also be relevant to this field induced phase transition.

論文

Magnetic-field-induced polarization flop in multiferroic TmMn$$_{2}$$O$$_{5}$$

福永 守*; 坂本 勇馬*; 木村 宏之*; 野田 幸男*; 阿部 伸行*; 谷口 耕治*; 有馬 孝尚*; 脇本 秀一; 武田 全康; 加倉井 和久; et al.

Physical Review Letters, 103(7), p.077204_1 - 077204_4, 2009/08

 被引用回数:46 パーセンタイル:12.41(Physics, Multidisciplinary)

We discovered a reversible electric polarization flop from the $$a$$ axis ($$P_a$$) to the $$b$$ axis ($$P_b$$) in multiferroic TmMn$$_{2}$$O$$_{5}$$ below 5 K by applying a magnetic field of approximately 0.5 T along the $$c$$ axis. This phenomenon is the first example of the rare-earth ($$R$$) compound $$R$$Mn$$_{2}$$O$$_{5}$$. This magnetic-field-induced polarization flop corresponds to a magnetic phase transition from one incommensurate magnetic (ICM) $$P_a$$ phase to another ICM $$P_b$$ phase, which is equivalent to an ICM $$P_b$$ phase above 5 K under no magnetic field. The spin chirality in the $$bc$$ plane, which was observed in the $$P_b$$ phase by polarized neutron diffraction, disappeared in the ICM $$P_a$$ phase. This indicates that the polarization in the ICM phases of TmMn$$_2$$O$$_5$$ was induced by an $$S_i times S_j$$ type interaction.

論文

Unconventional ferroelectric transition in the multiferroic compound TbMnO$$_{3}$$ revealed by the absence of an anomaly in $$c$$-polarized phonon dispersion

梶本 亮一; 佐賀山 基*; 佐々井 健蔵*; 福田 竜生; 筒井 智嗣*; 有馬 孝尚*; 廣田 和馬*; 三井 由佳利*; 吉澤 英樹*; Baron, A. Q. R.*; et al.

Physical Review Letters, 102(24), p.247602_1 - 247602_4, 2009/06

 被引用回数:11 パーセンタイル:39.64(Physics, Multidisciplinary)

TbMnO$$_{3}$$ exhibits a spontaneous electric polarization along $$mathbf{c}$$ concomitantly with a spiral spin ordering modulated along $$mathbf{b}$$ below $$T$$$$_{rm c}$$ = 28 K. We have performed inelastic X-ray scattering measurements on a single crystal of TbMnO$$_{3}$$ to clarify whether phonon anomalies related to the ferroelectricity exist. We measured transverse modes, especially the Mn-O-Mn bending mode polarized along $$mathbf{c}$$ and propagating along $$mathbf{b}$$, which we expect is most relevant to the ferroelectricity. However, no anomaly was found in the phonon dispersion below 50 meV across $$T$$$$_{rm c}$$. The present result suggests that the mechanism of ferroelectricity in TbMnO$$_3$$ is different from that of a conventional displacive-type ferroelectric. The weak coupling between electric polarization and lattice in TbMnO$$_{3}$$ strongly suggests that the ferroelectricity is mainly derived from the spiral spin ordering.

論文

Magnetic-field-induced transition in the lattice modulation of colossal magnetoelectric GdMnO$$_3$$ and TbMnO$$_3$$ compounds

有馬 孝尚*; 後藤 剛史*; 山崎 裕一*; 宮坂 茂樹*; 石井 賢司; 坪田 雅己; 稲見 俊哉; 村上 洋一*; 十倉 好紀*

Physical Review B, 72(10), p.100102_1 - 100102_4, 2005/09

 被引用回数:112 パーセンタイル:4.74(Materials Science, Multidisciplinary)

強磁場下での単結晶放射光X線回折実験を磁気誘電化合物GdMnO$$_3$$とTbMnO$$_3$$で行った。低温で磁場の印加によって誘起される${bf P}$//aの強誘電相は斜方晶のb軸方向へのq=1/2と1/4の整合な格子変調によって特徴づけられる。この格子変調は変調ベクトル(0 1/4 1)の反強磁性スピン配列によるものである。スピン構造の変化は直接磁場誘起誘電相転移と関係づけられる。なぜなら、いかなる(0 1/4 1)の整合スピン変調はPbnm空間群を持つ歪んだペルブスカイトの${it a}$軸に垂直な映心面を壊すからである。

論文

X-ray diffraction experiments under pulsed magnetic fields above 30T

稲見 俊哉; 大和田 謙二; 松田 康弘*; 上田 勇治*; 野尻 浩之*; 村上 洋一*; 有馬 孝尚*; 太田 寛人*; Zhang, W.*; 吉村 一良*

Nuclear Instruments and Methods in Physics Research B, 238(1-4), p.233 - 236, 2005/08

 被引用回数:8 パーセンタイル:44.85(Instruments & Instrumentation)

通常強磁場下でのX線回折実験は超伝導マグネットを用いて行われ、このため、最大磁場は15Tとなっている。この限界を超えるため、われわれは、パルス磁場を組み込んだX線回折システムを構築した。8T近傍で起こるPr$$_{0.6}$$Ca$$_{0.4}$$MnO$$_3$$の構造相転移と26T近傍で起こるYbInCu$$_4$$の価数転移をデモンストレーションとして示す。

論文

Application of a portable pulsed magnet to synchrotron radiation experiments

松田 康弘*; 上田 勇治*; 野尻 浩之*; 高橋 俊晴*; 稲見 俊哉; 大和田 謙二; 村上 洋一; 有馬 孝尚*

Physica B; Condensed Matter, 346-347, p.519 - 523, 2004/04

 被引用回数:47 パーセンタイル:13.47(Physics, Condensed Matter)

高磁場下での放射光実験を行うために、非常に小型のキャパシターバンクと小型のパルスマグネットを開発した。長さ1msで20Tのパルス磁場を1kJのエネルギーで発生できた。ミリ波領域での電子スピン共鳴とX線回折実験を行うことができた。

口頭

Inelastic X-ray scattering study of phonons in the multiferroic compound TbMnO$$_3$$

梶本 亮一; 佐賀山 基*; 佐々井 健蔵*; 福田 竜生; 筒井 智嗣*; 有馬 孝尚*; 廣田 和馬*; 三井 由佳利*; 吉澤 英樹*; Baron, A. Q. R.*; et al.

no journal, , 

An inelastic X-ray scattering study on a single crystal of TbMnO$$_3$$ was performed to reveal whether phonon anomaly related to the appearance of the ferroelectricity exists. We have measured the transverse modes, especially the Mn-O-Mn bending mode, polarized along the $$c$$ axis propagating along the $$b$$ axis, because these modes are expected to be most relevant to the spontaneous electric polarization along the $$c$$ axis concomitantly with the spiral spin ordering modulated along the $$b$$ axis. However, no anomaly in phonon dispersions was observed even below the ferroelectric transition temperature below 50 meV. The present result suggests that the mechanism of ferroelectric transition in $$R$$MnO$$_3$$ is different from that of a conventional displacive-type ferroelectric.

口頭

Neutron scattering activities on multiferroic systems; Neutron diffraction experiments on hexaferrites

加倉井 和久; 脇本 秀一; 石渡 晋太郎*; 奥山 大輔*; 西 正和*; 徳永 祐介*; 有馬 孝尚*; 田口 康二郎*; 十倉 好紀*

no journal, , 

The discovery of magnetoelectric (ME) effects caused by a cycloidal spin order has initiated an intense research on new class of ME materials. Among them one interesting class of materials is the hexaferrites such as Y-type (A$$_{2}$$Me$$_{2}$$Fe$$_{12}$$O$$_{22}$$: Me=transition metal), M-type (AFe$$_{12}$$O$$_{19}$$: A=Pb, Ca, Sr, Ba, etc.), where types of elementary blocks and their stacking order are different. These materials show a variety of complex magnetic ordering. In this presentation recent neutron diffraction experiments on multiferroic hexaferrites performed at the JRR-3 Neutron Science Facility of Japan Atomic Energy Agency (JAEA) are reported.

口頭

Polarised neutron spectrometer, POLANO, at J-PARC attempts at understanding novel magnetism

大山 研司*; 横尾 哲也*; 伊藤 晋一*; 鈴木 純一*; 岩佐 和晃*; 佐藤 卓*; 吉良 弘*; 坂口 佳史*; 猪野 隆*; 奥 隆之; et al.

no journal, , 

We aim at constructing a polarisation analysis neutron spectrometer at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC) based on a collaboration of KEK and Tohoku Univ. The proposed instrument, named POLANO, is designed as a compact chopper spectrometer with a rotary detector bank ($$L_{1}$$ = 17.5 m, $$L_{2}$$ = 2.5 m). At the first phase of the project, we will concentrate the $$E_{i} < $$ 30 meV region using a fan type bender supermirror spin analyser because rich scientific targets in basic and application materials science exist in this region. In the second phase, we will try to install a $$^{3}$$He spin filter analyser for the $$E_{f} >$$ 100 meV region. This project passed in the final board of J-PARC on SEP-2011, and the construction has been authorized already.

口頭

中性子強吸収体SmBaMn$$_{2}$$O$$_{6}$$の結晶・磁気構造研究

鬼柳 亮嗣; 山田 重樹*; 青木 博*; 佐賀山 基*; 茂吉 武人*; 中尾 朗子*; 有馬 孝尚*

no journal, , 

RE$$_{1-x}$$AE$$_{x}$$MnO$$_{3}$$(RE=3価の希土類、AE=2価のアルカリ土類)で表されるMn酸化物は、巨大磁気抵抗に代表される様々な物性を示す物質群として盛んに研究が行われている。SmBaMn$$_{2}$$O$$_{6}$$はAサイトが秩序化したダブルペロブスカイト型構造をもち、380Kで電荷-軌道の秩序化、200K付近で電荷-軌道秩序の再編と反強磁性相転移を起こす。また、10K付近においても帯磁率に異常が観測されている。本研究では、SmBaMn$$_{2}$$O$$_{6}$$の反強磁性相や相転移の詳細を調べるため、J-PARC/MLFの単結晶装置SENJUを用いて単結晶回折実験を行った。測定の結果、中性子吸収断面積の非常に大きなSmが入っているにも関わらず、広い範囲の逆格子マップを得ることができ、180K以下で磁気超格子反射が観測された。また、超格子反射の温度変化により、200K付近の反強磁性相転移温度と電荷-軌道秩序の再編の温度はわずかに異なることが明らかとなった。

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