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論文

Theory of the spin Seebeck effect influenced by crystal-field excitations in Tb$$_3$$Fe$$_5$$O$$_{12}$$

森 道康; Tomasello, B.*; Ziman, T.*

Physical Review B, 111(1), p.014407_1 - 014407_12, 2025/01

The spin Seebeck effect (SSE) is a phenomenon of thermoelectric generation that occurs within a device consisting of a bilayer of a metal and a ferromagnet. When Tb$$_3$$Fe$$_5$$O$$_{12}$$ (TbIG) is substituted for the ferromagnet, the effect goes to zero at low temperatures, yet it increases to positive values with the application of a magnetic field. This is opposite to the expectation that the SSE should be suppressed by a magnetic field due to the increase in ${the}$ magnon gap. In this paper, the crystal-field excitations (CFE) in TbIG are calculated within a mean field theory exploiting the parameters of Terbium Gallium Garnet Tb$$_3$$Fe$$_5$$O$$_{12}$$ (TGG) from the neutron-scattering experimental literature. Like TGG, the primitive cell of TbIG hosts twelve Tb sites with six inequivalent magnetic sublattices, but due to the net $$[111]$$-molecular field from the tetrahedral and octahedral Fe ions, these can be classified into two distinct groups, the $$mathbf{C}$$ and the $$mathbf{C'}$$ sites, which account for the "double umbrella" magnetic structure. We show that when an external magnetic field is applied along the [111] direction of the crystal, the lowest CFE of the $$mathbf{C}$$ sublattices decreases. As a consequence of the magnetic field dependence of the lowest CFE, we find that at low temperatures the SSE in TbIG can result enhanced by an applied magnetic field.

論文

Observation of nonreciprocal diffraction of surface acoustic wave

新居 陽一*; 山本 慧; 菅野 将誠*; 前川 禎通*; 小野瀬 佳文*

Physical Review Letters, 134(2), p.027001_1 - 027001_5, 2025/01

While the rectification phenomenon caused by the simultaneous breaking of time reversal and spatial inversion symmetries has been extended to a wide range of (quasi)particles and waves, the nonreciprocal diffraction, which is the imbalance of upward and downward deflections, was previously observed only for photons and remained to be extended to other (quasi)particles. Here, we present evidence of the nonreciprocal diffraction of surface acoustic wave (SAW) utilizing a magnetoelastic grating on a SAW device. Asymmetric diffraction intensities were observed when the ferromagnetic resonance was acoustically excited. Based on a theoretical model, we ascribe the microscopic origin of this phenomenon to the resonant scattering involving ferromagnetic resonance excitations. The novel property may pave an avenue to further development of SAW devices for various purposes including microwave communications and quantum engineering applications.

論文

Surface structure of the 3$$times$$3-Si phase on Al(111), studied by the multiple usages of positron diffraction and core-level photoemission spectroscopy

佐藤 祐輔*; 深谷 有喜; 他14名*

Physical Review Materials (Internet), 9(1), p.014002_1 - 014002_11, 2025/01

本研究では、陽電子回折と内殻光電子分光の複合利用により、Al(111)3$$times$$3-Si表面の構造を明らかにした。ロッキング曲線の解析では、3$$times$$3-Si相が平坦なハニカム構造から構成されること、また、第一原理計算に基づくSi内殻スペクトルの解析では、単位胞内のSi原子の一つがAl原子と置換されていることがわかった。すなわち、3$$times$$3-Si相の表面超構造はAl原子を内包したSi二次元層である。

論文

Possible field-induced quantum state in a rhombic lattice antiferromagnet KCoPO$$_{4}$$$$cdot$$H$$_{2}$$O

藤原 理賀; 萩原 雅人; 幸田 章宏*; 中村 惇平*; 松尾 晶*; 金道 浩一*; 石角 元志*

Physical Review Materials (Internet), 9(1), p.014406_1 - 014406_9, 2025/01

We reported the magnetic behavior of a rhombic lattice quantum antiferromagnet KCoPO$$_{4}$$$$cdot$$H$$_{2}$$O. The rhombic lattice model is equivalent to a model of a square lattice with two different diagonal components, and competing exchange interactions potentially produce exotic quantum states. This compound is well characterized by the $$J$$$$_{rm{eff}}$$ = 1/2 state. The magnetic structure of KCoPO$$_{4}$$$$cdot$$H$$_{2}$$O is identified as an incommensurate helical structure, characterized by a magnetic modulation propagation vector $$bold{k}$$ = (0.1747(1) 0 0) with an in-plane moment rotating along the $$a$$ axis. Moreover, a magnetic field-induced phase transition is observed at approximately 1 T. The application of a magnetic field suppresses spin ordering and enhance spin fluctuations. Our experimental results suggest the presence of a quantum phase in the magnetic phase diagram of the spin-1/2 Heisenberg rhombic lattice antiferromagnet with easy-plane anisotropy.

論文

Vicinage effect on the yield of convoy electrons emitted from thin carbon foil induced by the penetration of 3.5 MeV/atom C$$_{n}$$$$^{+}$$ ions

椎名 陽子*; 木下 亮*; 舟田 周平*; 松田 誠; 今井 誠*; 川面 澄*; 左高 正雄*; 笹 公和*; 金子 敏明*; 冨田 成夫*

Physical Review A, 110(6), p.062826_1 - 062826_7, 2024/12

 被引用回数:0

We investigated the target thickness dependence of convoy electron yields resulting from bombardments with 3.5 MeV/atom C$$_{n}$$$$^{+}$$ (n = 1 - 3) cluster ions. We observed that for bombardments with C$$_{2}$$$$^{+}$$ and C$$_{3}$$$$^{+}$$ ions, the convoy electron yield per atom, Y$$_{n}$$/n, reaches a maximum around 3-5 $$mu$$g/cm$$^{2}$$ and decreases with increasing target thickness from 3.1 to 10.5 $$mu$$g/cm$$^{2}$$, and ultimately reaches an asymptotic value. This asymptotic value of the convoy electron yield was nearly proportional to the size of the cluster n, that is, Y$$_{n}$$ $$propto$$ n$$^{2}$$, consistent with previous observations. We found that the escape length of the convoy electrons for C$$_{3}$$$$^{+}$$ and C$$_{2}$$$$^{+}$$ is much longer than that of C$$^{+}$$ bombardment. The present result suggests that the enhancement of the escape length could be the origin of this vicinage effect (i.e., Y$$_{n}$$ $$>$$ nY$$_{1}$$) on the convoy electron yield.

論文

Large spontaneous Hall effect with flexible domain control in the antiferromagnetic material TaMnP

小手川 恒*; 中村 彰良*; Huyen, V. T. N.*; 新井 祐樹*; 藤 秀樹*; 菅原 仁*; 林 純一*; 武田 圭生*; 田端 千紘; 金子 耕士; et al.

Physical Review B, 110(21), p.214417_1 - 214417_8, 2024/12

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

In this study, we show that the orthorhombic system TaMnP exhibits a large anomalous Hall conductivity (AHC) in spite of the small net magnetization. Neutron scattering experiment and the observation of the AH effect comprehensively suggest a dominant AF structure in TaMnP is represented by $$B_{3g}$$. The AHC is one of the largest among those observed in AF materials at zero fields. First-principles calculations suggest that the spin-orbit interaction originating in nonmagnetic Ta-5$$d$$ electrons significantly contributes to the enhancement of Berry curvatures in the momentum space. We found that the AF domain switching is triggered by the magnetic fields along all the crystal axes. This indicates that the AF domain determining the sign of the Hall response can be controlled even through the small net magnetization symmetrically different.

論文

$$alpha$$-induced total reaction cross sections based on the intranuclear cascade model

中野 正博*; 山口 雄司; 古田 稔将*; 魚住 祐介*

Physical Review C, 110(6), p.064620_1 - 064620_5, 2024/12

 被引用回数:0

先行研究において核子及び重陽子誘起反応に対して拡張してきた核内カスケード(INC)模型に基づき、アルファ誘起全反応断面積を記述する。先行研究と矛盾しないパラメータを用いることで、INC模型の計算は$$^{12}$$C、$$^{28}$$Si、$$^{40}$$Ca、$$^{208}$$Pb標的の実験データをよく再現する。本研究では、離散準位制約とクーロン効果がアルファ誘起全反応断面積の記述において重要であり、それらの寄与が入射エネルギーと標的に依存することを示す。離散準位制約は軽い標的に対して特に重要であり、クーロン効果は$$^{208}$$Pbにおいて支配的である。このような傾向は、陽子及び重陽子誘起全反応断面積の記述と矛盾しない。

論文

Orbital moir$'e$ and quadrupolar triple-q physics in a triangular lattice

服部 一匡*; 石飛 尊之; 常次 宏一*

Physical Review Research (Internet), 6(4), p.L042068_1 - L042068_7, 2024/12

We numerically study orders of planer type $$(xy,x^2 -y^2)$$ quadrupoles on a triangular lattice with nearest-neighbor isotropic $$J$$ and anisotropic $$K$$ interactions. This type of quadrupoles possesses unique single-ion anisotropy proportional to a third order of the quadrupole moments. This provides an unconventional mechanism of triple-$$q$$ orders which does not exist for the degrees of freedom with odd parity under time-reversal operation such as magnetic dipoles. In addition to several single-$$q$$ orders, we find various orders including incommensurate triple-$$q$$ quasi-long-range orders with orbital moire and a four-sublattice triple-$$q$$ partial order. Our Monte-Carlo simulations demonstrate that the phase transition to the latter triple-$$q$$ state belongs to the universality class of the critical line of the Ashkin-Teller model in two dimensions close to the four-state Potts class. These results indicate a possibility of realizing unique quadrupole textures in simple triangular systems.

論文

Nonferroelectric phase with loss of cycloidal magnetic structure in Tb$$_{0.515}$$Gd$$_{0.485}$$Mn$$_{2}$$O$$_{5}$$

石井 裕太*; 坂倉 輝俊*; 石川 喜久*; 鬼柳 亮嗣; Lustikova, J.*; 青山 拓也*; 大串 研也*; 若林 裕助*; 木村 宏之*; 野田 幸男*

Physical Review B, 110(18), p.184404_1 - 184404_7, 2024/11

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

Neutron-scattering measurements were employed to investigate the magnetic ordering in Tb$$_{1-x}$$Gd$$_{x}$$Mn$$_{2}$$O$$_{5}$$ (x = 0.485) enriched with the $$^{160}$$Gd isotope, a member of multiferroic RMn$$_{2}$$O$$_{5}$$ (R = rare-earth element) compounds. This material, at low temperatures, exhibits commensurate magnetic (CM) ordering, which drives electric polarization. Notably, electric polarization diminishes as the temperature decreases further, while the CM ordering persists. Magnetic structure analyses revealed that a cycloidal magnetic structure along the c axis transforms into a sinusoidal-like structure, resulting in the nonferroelectric phase, whereas a collinear magnetic structure in the ab plane exhibits no significant change. The findings suggest that the cycloidal magnetic structure plays a key role in inducing electric polarization in the CM ordering of the present material.

論文

Relationship between orbital moment anisotropy, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya interaction in W/Co/Pt trilayers

Chi, Z.*; 芝田 悟朗; 藤森 淳; 他15名*

Physical Review B, 110, p.184401_1 - 184401_8, 2024/11

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

We have studied the Co layer thickness dependences of magnetocrystalline anisotropy (MCA), Dzyaloshinskii-Moriya interaction (DMI), and orbital moment anisotropy (OMA) in W/Co/Pt trilayers, in order to clarify their correlations with each other. We find that the MCA favors magnetization along the film normal and monotonically increases with decreasing effective magnetic layer thickness ($$t_{rm eff}$$). The magnitude of the Dzyaloshinskii-Moriya exchange constant ($$|D|$$) increases with decreasing $$t_{rm eff}$$ until $$T_{rm eff}$$ $$sim$$ 1 nm, below which $$|D|$$ decreases. The MCA and $$|D|$$ scale with 1/$$T_{rm eff}$$ for $$t_{rm eff}$$ larger than $$sim 1$$ nm, indicating an interfacial origin. Using X-ray magnetic circular dichroism (XMCD), we find non-zero OMA when $$t_{rm eff}$$ is smaller than $$sim 0.8$$ nm. The OMA increases with decreasing $$t_{rm eff}$$ more rapidly than what is expected from the MCA, indicating that factors other than OMA contribute to the MCA at small $$t_{rm eff}$$.

論文

Fission fragment yields of $$^{235}$$U($$n_{th}, f$$) evaluated with the CCONE code system

湊 太志*; 岩本 修

Physical Review C, 110(5), p.054311_1 - 054311_14, 2024/11

 被引用回数:0 パーセンタイル:0.00(Physics, Nuclear)

A calculation system with CCONE code is newly developed to estimate not only independent and cumulative fission fragment yields but also prompt fission neutron, prompt fission gamma, decay heats, and delayed neutrons simultaneously. This system enables us to study a correlation between various fission observables. To determine lots of parameters in this system efficiently, a Gaussian process and a least square fitting are adopted We tested the calculation system through a thermal neutron-induced fission on $$^{235}$$U. In this paper, we demonstrate the performance of the parameter search method and show that experimental fission fragment yield data and other observables resulting from fission are reproduced well by the new calculation system.

論文

Gravitational form factors of pion from top-down holographic QCD

藤井 大輔; 岩中 章紘*; 田中 満*

Physical Review D, 110(9), p.L091501_1 - L091501_8, 2024/11

 被引用回数:0 パーセンタイル:0.00(Astronomy & Astrophysics)

トップダウンのホログラフィック量子色力学(QCD)アプローチから、パイ中間子の重力形状因子(GFF)を運動量移動依存性を含めて初めて計算した。ハドロンのGFFは内部応力分布に関する情報を持っており、QCDがハドロンを形成するメカニズムの解明につながる可能性があるため重要である。このGFFsの前方極限値、すなわちD項も得られた。さらに、このアプローチでは、パイ中間子が無限個のグルーボールスペクトルを介して重力相互作用をする、いわゆるグルーボールドミナンスを観測した。

論文

Novel first-order phase transition and critical points in SU(3) Yang-Mills theory with spatial compactification

藤井 大輔; 岩中 章紘*; 北澤 正清*; 末永 大輝*

Physical Review D, 110(9), p.094016_1 - 094016_16, 2024/11

 被引用回数:0 パーセンタイル:0.00(Astronomy & Astrophysics)

ユークリッド時空の$$mathbb{T}^2timesmathbb{R}^2$$上の$$SU(3)$$ヤンミルズ理論の熱力学と相構造を有効模型によるアプローチで調べる。このモデルは、コンパクト化された2方向に沿った2つのポリアコフ・ループを力学変数として取り入れ、格子上で測定された$$mathbb{T}^2timesmathbb{R}^2$$上の熱力学を再現するように構成されている。モデル解析の結果、非閉じ込め相において$$mathbb{T}^2timesmathbb{R}^2$$上の新しい一次相転移が存在することが示され、この相転移は二次元$$Z_2$$普遍クラスに属するべき臨界点で終端する。この一次転移は、ポリアコフ・ループ・ポテンシャルにおける交差項によって誘起されるポリアコフ・ループの相互作用が原因であることを議論する。

論文

Likely existence of bound states and the Efimov effect in the triple-$$J/Psi$$ system

Pan, Y.-W.*; Liu, Z.-W.*; Geng, L.-S.*; 保坂 淳; Liu, X.*

Physical Review D, 110(9), p.094004_1 - 094004_8, 2024/11

 被引用回数:0 パーセンタイル:0.00(Astronomy & Astrophysics)

3つの$$J/Psi$$粒子からなる系が浅い束縛状態を作る可能性を指摘した。これはエフィモフ効果が関わっていると解釈される。

論文

Continuum excitations in a spin supersolid on a triangular lattice

Zhu, M.*; Romerio, V.*; Steiger, N.*; Nabi, S. D.*; 村井 直樹; 河村 聖子; Povarov, K. Y.*; Skourski, Y.*; Sibille, R.*; Keller, L.*; et al.

Physical Review Letters, 133(18), p.186704_1 - 186704_6, 2024/11

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

Magnetic, thermodynamic, neutron diffraction and inelastic neutron scattering are used to study spin correlations in the easy-axis XXZ triangular lattice magnet K$$_{2}$$Co(SeO$$_{3}$$)$$_{2}$$. Despite the presence of quasi-2D supersolid magnetic order, the low-energy excitation spectrum contains no sharp modes and is instead a broad and structured multiparticle continuum. Applying a weak magnetic field drives the system into an m = 1/3 fractional magnetization plateau phase and restores sharp spin wave modes. To some extent, the behavior at zero field can be understood in terms of spin wave decay. However, the presence of clear excitation minima at the M points of the Brillouin zone suggest that the spinon language may provide a more adequate description, and signals a possible proximity to a Dirac spin liquid state.

論文

Ca-induced phonon softening in BaTiO$$_{3}$$ revealed by inelastic X-ray and neutron scattering

木村 耕治*; 筒井 智嗣*; 山本 裕太*; 中埜 彰俊*; 川村 啓介*; 梶本 亮一; 蒲沢 和也*; Martin, A.*; Webber, K. G.*; 柿本 健一*; et al.

Physical Review B, 110(13), p.134314_1 - 134314_10, 2024/10

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

We performed inelastic X-ray and neutron scattering (IXS and INS) experiments for (Ba,Ca)TiO$$_{3}$$ single crystals to elucidate the effect of Ca doing on the atomic dynamics. Dispersion relations of transverse phonons in BaTiO$$_{3}$$, (Ba$$_{0.9}$$Ca$$_{0.1}$$)TiO$$_{3}$$, and (Ba$$_{0.8}$$Ca$$_{0.2}$$)TiO$$_{3}$$ were determined. The $textit{A}$-site-O vibrational mode as well as the acoustic mode were observed both by IXS and INS, whereas the Ti-O soft mode was detected only by INS. It was found that the $textit{A}$-site-O vibration exhibits significant softening with increasing Ca concentration, while the Ti-O soft mode is almost unaffected by the Ca doping. This finding is discussed in comparison with the polarization hysteresis loops and piezoelectric coefficients of (Ba,Ca)TiO$$_{3}$$. It is indicated that the softening of the $textit{A}$-site-O vibration contributes to the enhancement of the piezoelectricity of Ca-doped BaTiO$$_{3}$$-based materials.

論文

Tunable sigmoid behavior of a magnon-based parametron using a Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt bilayer disk

Emdi, G.*; 日置 友智*; 巻内 崇彦*; 齊藤 英治

Physical Review Applied (Internet), 22(3), p.L031002_1 - L031002_6, 2024/09

 被引用回数:0 パーセンタイル:0.00(Physics, Applied)

Sigmoidal curve behavior of 0 and n state probability in a magnon parametron, using yttrium iron garnet (Y$$_3$$Fe$$_5$$O$$_{12}$$) thin disk, is systematically investigated. We demonstrate that the probability distribution can be tuned by bias and pump microwave power. Our numerical calculation that considers increasing damping due to four-magnon scattering processes reproduces the results well.

論文

Ferrimagnetic structure in the high-pressure phase of $$alpha$$-Mn

荒木 新吾*; 岩本 凱成*; 秋葉 和人*; 小林 達生*; 宗像 孝司*; 金子 耕士; 長壁 豊隆

Physical Review B, 110(9), p.094420_1 - 094420_7, 2024/09

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

$$alpha$$-Mn相は、自発磁化が0.02$${mu}_{rm B}$$/Mnと比較的小さいにもかかわらず、圧力誘起弱強磁性(WFM)状態で大きな異常ホール効果(AHE)を示す。このAHEの背後にある根本的な機構を理解するために、2.0GPaの圧力下で単結晶中性子回折測定を行い、WFM相の磁気構造を決定した。I、II、III-1、IV-1位置のMnは、ほぼコリニアーな磁気モーメントが[001]方向に揃ったフェリ磁性構造を持つことを見出した。一方で、III-2とIV-2位置のMnの微小な磁気モーメントは(001)面内を向いている。この磁気構造で計算したネットの磁気モーメントの大きさ(-0.020$${pm}$$0.005)$${mu}_{rm B}$$/Mn原子)は、実験で決定された自発磁化と非常によく一致する。$$q$$ = (0, 0, 0)での磁気反射の観測は、AHEの出現の重要な条件を満たしている。

論文

Antiferromagnetism and phase stability of CrMnFeCoNi high-entropy alloy

Zhu, L.*; He, H.*; Naeem, M.*; Sun, X.*; Qi, J.*; Liu, P.*; Harjo, S.; 中島 健次; Li, B.*; Wang, X.-L.*

Physical Review Letters, 133(12), p.126701_1 - 126701_6, 2024/09

 被引用回数:1

It has long been suspected that magnetism could play a vital role in the phase stability of multi- component high-entropy alloys. However, the nature of the magnetic order, if any, has remained elusive. Here, by using elastic and inelastic neutron scattering, we demonstrate evidence of antiferromagnetic order below $$sim$$80 K and strong spin fluctuations persisting to room temperature in a single-phase face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy. Despite the chemical complexity, the magnetic structure in CrMnFeCoNi can be described as $$gamma$$-Mn-like, with the magnetic moments confined in alternating (001) planes and pointing toward the $$langle$$111$$rangle$$ direction. Combined with first-principles calculation results, it is shown that the antiferromagnetic order and spin fluctuations help stabilized the fcc phase in CrMnFeCoNi high-entropy alloy.

論文

Singular continuous and nonreciprocal phonons in quasicrystal AlPdMn

松浦 直人*; Zhang, J.*; 上村 祥史*; 古府 麻衣子; 枝川 圭一*

Physical Review Letters, 133(13), p.136101_1 - 136101_5, 2024/09

 被引用回数:1 パーセンタイル:66.04(Physics, Multidisciplinary)

In quasicrystals lacking translational symmetry but having highly ordered structures, understanding how phonons propagate in their aperiodic lattices remains an unsolved issue. We present an inelastic neutron scattering study on acoustic phonon modes of icosahedral quasicrystal AlPdMn, revealing hierarchical pseudo-gap structure in low-energy acoustic modes. Additionally, phonon intensities are asymmetric in energy and wave vectors with respect to the Bragg peak, indicating characteristic nonreciprocal phonon propagation in quasicrystals.

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