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In materials showing a linear magnetoelectric (ME) effect, unconventional functionalities can be anticipated such as electric control of magnetism and nonreciprocal optical responses. Thus, the search for new linear ME materials is of interest in materials science. Here, using a recently proposed design principle of linear ME materials, which is based on the combination of local structural asymmetry and collinear antiferromagnetism, we demonstrate that an anion-deficient fluorite derivative, Mn3Ta2O8, is a new linear ME material. This is evidenced by the onset of magnetic-field-induced electric polarization in its collinear antiferromagnetic phase below TN = 24 K. Furthermore, we also find an antiferroelectric-like phase transition at TS = 55 K, which is attributable to an off-center displacement of magnetic Mn2+ ions. The present study shows that Mn3Ta2O8 is a rare material that exhibits both ME and antiferroelectric-like transitions. Thus, Mn3Ta2O8 may provide an opportunity to investigate the physics associated with complicated interactions between magnetic (spin) and electric dipole degrees of freedom.

Spin-orbit coupled honeycomb magnets with the Kitaev interaction have received a lot of attention due to their potential of hosting exotic quantum states including quantum spin liquids. Thus far, the most studied Kitaev systems are 4d/5d-based honeycomb magnets. Recent theoretical studies predicted that 3d-based honeycomb magnets, including Na2Co2TeO6 (NCTO), could also be a potential Kitaev system. Here, we have used a combination of heat capacity, magnetization, electron spin resonance measurements alongside inelastic neutron scattering (INS) to study NCTO's quantum magnetism, and we have found a field-induced spin disordered state in an applied magnetic field range of 7.5 T < B (vertical to b-axis) < 10.5 T. The INS spectra were also simulated to tentatively extract the exchange interactions. As a 3d-magnet with a field-induced disordered state on an effective spin-1/2 honeycomb lattice, NCTO expands the Kitaev model to 3d compounds, promoting further interests on the spin-orbital effect in quantum magnets., 19 pages and 5 figures for main text. 16 pages and 6 figures for Supplemental Material

A triplon refers to a fictitious particle that carries angular momentum S=1 corresponding to the elementary excitation in a broad class of quantum dimerized spin systems. Such systems without magnetic order have long been studied as a testing ground for quantum properties of spins. Although triplons have been found to play a central role in thermal and magnetic properties in dimerized magnets with singlet correlation, a spin angular momentum flow carried by triplons, a triplon current, has not been detected yet. Here we report spin Seebeck effects induced by a triplon current: triplon spin Seebeck effect, using a spin-Peierls system CuGeO3. The result shows that the heating-driven triplon transport induces spin current whose sign is positive, opposite to the spin-wave cases in magnets. The triplon spin Seebeck effect persists far below the spin-Peierls transition temperature, being consistent with a theoretical calculation for triplon spin Seebeck effects., Triplons are elementary spin excitations characteristic of dimerized magnets, carrying a spin angular momentum one. Here, the authors report evidence for spin current of triplons via thermal transport measurements in a spin-dimer compound CuGeO3.

The kagome lattice is a fertile platform to explore topological excitations with both Fermi-Dirac and Bose-Einstein statistics. While relativistic Dirac Fermions and flat-bands have been discovered in the electronic structure of kagome metals, the spin excitations have received less attention. Here we report inelastic neutron scattering studies of the prototypical kagome magnetic metal FeSn. The spectra display well-defined spin waves extending up to 120 meV. Above this energy, the spin waves become progressively broadened, reflecting interactions with the Stoner continuum. Using linear spin wave theory, we determine an effective spin Hamiltonian that reproduces the measured dispersion. This analysis indicates that the Dirac magnon at the K-point remarkably occurs on the brink of a region where well-defined spin waves become unobservable. Our results emphasize the influential role of itinerant carriers on the topological spin excitations of metallic kagome magnets., 6 pages, 4 figures

Observation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state., There exist many theoretical models of frustrated quantum magnetism, most of which lack convincing experimental realisations. Here the authors combine several experimental methods to argue that KCu6AlBiO4(SO4)5Cl behaves as a square-kagome-lattice quantum Heisenberg antiferromagnet.

Chemical doping is one of the most important strategies for tuning electrical properties of semiconductors, particularly thermoelectric materials. Generally, the main role of chemical doping lies in optimizing the carrier concentration, but there can potentially be other important effects. Here, we show that chemical doping plays multiple roles for both electron and phonon transport properties in half-Heusler thermoelectric materials. With ZrNiSn-based half-Heusler materials as an example, we use high-quality single and polycrystalline crystals, various probes, including electrical transport measurements, inelastic neutron scattering measurement, and first-principles calculations, to investigate the underlying electron-phonon interaction. We find that chemical doping brings strong screening effects to ionized impurities, grain boundary, and polar optical phonon scattering, but has negligible influence on lattice thermal conductivity. Furthermore, it is possible to establish a carrier scattering phase diagram, which can be used to select reasonable strategies for optimization of the thermoelectric performance., Comment: 21 pages, 5 figures

In the field of magnetoelectric coupling, especially via the spin-dependent metal-ligand d-p hybridization mechanism found in multiferroic Ba2MGe2O7 (M = Mn, Co), detailed knowledge of the microscopic structural parameters is essential, also for the theoretical modeling. In this article, we report a systematic structural study of Ba2MnGe2O7 single crystal under varying temperatures between 110 and 673 K using non-destructive in situ single crystal synchrotron radiation diffraction. The maximum entropy method (MEM) was applied to the X-ray diffraction data for the determination of the deformation in the electron density and the orbital hybridization between the 3d of Mn and 2p of O in the Mn-O bond. Within this entire temperature range, the structure was described in a single crystallographic space group P (4) over bar2(1)m and no structural phase transition has been detected. Interestingly, the forbidden reflections, which arise from multiple diffractions so-called "Renninger effect," were observed at all temperatures without any symmetry lowering. The changes in the structural parameters [bond-lengths, bond-angles, anisotropic displacement parameters, and electron density distributions (EDDs) of the atoms] with temperature are revealed, helping to understand some aspects comprising orbital hybridization in multiferroic Ba2MnGe2O7.

CePdSi3 with H // [100] exhibits multiple metamagnetic transitions. Since there is no frustration in this system, it is suggested that the origin of the multiple metamagnetic transitions is the inf...

We have investigated the low-temperature magnetism of sodium superoxide (NaO2), in which spin, orbital, and lattice degrees of freedom are closely entangled. The magnetic susceptibility shows anomalies at T1 = 220 K and T2 = 190 K, which correspond well to the structural phase transition temperatures, and a sudden decrease below T3 = 34 K. At 4.2 K, the magnetization shows a clear stepwise anomaly around 30 T with a large hysteresis. In addition, the muon spin relaxation experiments indicate no magnetic phase transition down to T = 0.3 K. The inelastic neutron scattering spectrum exhibits magnetic excitation with a finite energy gap. These results confirm that the ground state of NaO2 is a spin-singlet state. To understand this ground state in NaO2, we performed Raman scattering experiments. All the Raman-active libration modes expected for the marcasite phase below T2 are observed. Furthermore, we find that several new peaks appear below T3. This directly evidences the low crystal symmetry, namely, the presence of the phase transition at T3.We conclude that the singlet ground state of NaO2 is due to the spin-Peierls instability.

In materials showing a linear magnetoelectric (ME) effect, unconventional functionalities can be anticipated such as electric control of magnetism and nonreciprocal optical responses. Thus, the search for new linear ME materials is of interest in materials science. Here, using a recently proposed design principle of linear ME materials, which is based on the combination of local structural asymmetry and collinear antiferromagnetism, we demonstrate that an anion-deficient fluorite derivative, Mn

This paper finds a cross correlation in Ba${}_{2}$MnGe${}_{2}$O${}_{7}$ where the magnetic anisotropy energy is scaled by electric polarization instead of magnetic moment.

Finding new materials with antiferromagnetic (AFM) Kitaev interaction is an urgent issue for quantum magnetism research. We conclude that Na

The High Resolution Chopper Spectrometer (HRC) is installed at the Japan Proton Accelerator Research Complex (J-PARC) and is utilized for a wide range of dynamical studies of materials over a wide energy-momentum space with high resolution. Neutron Brillouin scattering (NBS), i.e., inelastic neutron scattering close to the forward direction, can be performed with the HRC, because this instrument utilizes low angle detectors and high-energy neutrons which facilitates a high resolution. Since the solid angle of the detection area for NBS experiments is limited to very low scattering angles, improvements of the HRC are required to increase the neutron flux with reducing the background. Given the success of the HRC for NBS studies, the neutron intensities for NBS experiments have been improved by changing the detector layout, reducing deformation of the slit package during rotation of the Fermi chopper, and fabricating a longer collimator. At present, we have made further improvements. At around the incident neutron energy Ei = 100 meV, the neutron flux was significantly increased for an energy resolution of ΔE∕Ei = 2%, and the best energy resolution achieved was nearly 1% resolution with an acceptable neutron flux.

When a theoretical model is realized in nature, small perturbation terms play important roles in the selection of the ground state in geometrically frustrated magnets. In case of a triangular spin tube, the two-dimensional network of the inter-tube interaction forms characteristic lattices. Among them Kagome-Triangular (KT) lattice is known to exhibit an enriched phase diagram including various types of non-trivial structures: non-coplanar cuboc structure, coplanar 120° structure with the two-dimensional propagation vector of $${\boldsymbol{k}}_{2\mathrm{D}}$$ k 2 D = (0, 0), $$\sqrt 3 \times \sqrt 3$$ 3 × 3 structure with $${\boldsymbol{k}}_{2{\mathrm{D}}}$$ k 2 D = (1/3, 1/3), and incommensurate structure. We investigate the magnetic state in the model material CsCrF4 by using neutron diffraction technique. Combination of representation analysis and Rietveld refinement reveals that a very rare structure, i.e., a quasi-120° structure with $${\boldsymbol{k}}_{2{\mathrm{D}}}$$ k 2 D = (1/2, 0), is realized at the base temperature. The classical calculation of the phase diagram elucidates that CsCrF4 is the first experimental realization of the KT lattice having ferromagnetic Kagome bond. A single-ion anisotropy and Dzyaloshinskii-Moriya interaction play key roles in the selection of the ground state. Furthermore, a successive phase transition having an intermediate state represented by $${\boldsymbol{k}}_{2{\mathrm{D}}}$$ k 2 D = (1/3, 1/3) is observed. The intermediate state is a partially ordered 120° structure which is induced by thermal fluctuation.

The magnetic excitations in $\mathrm{CoP}{\mathrm{S}}_{3}$, a two-dimensional van der Waals (vdW) antiferromagnet with ${\mathrm{Co}}^{2+}$ ion on a honeycomb lattice, have been measured using powder inelastic neutron scattering. The absence of spin-orbit exciton around 30 meV indicates that ${\mathrm{Co}}^{2+}$ ions in $\mathrm{CoP}{\mathrm{S}}_{3}$ have an $S=3/2$ state rather than a spin-orbital entangled ${J}_{\mathrm{eff}}=1/2$ ground state. And, clear dispersive spin waves are observed with a large spin gap of \ensuremath{\sim}13 meV. The magnon spectra were fitted using an XXZ-type ${J}_{1}\text{\ensuremath{-}}{J}_{2}\text{\ensuremath{-}}{J}_{3}$ Heisenberg Hamiltonian with single-ion anisotropy assuming no magnetic exchange interaction between the honeycomb layers. The best-fit parameters show ferromagnetic exchange interactions ${J}_{1}=\ensuremath{-}2.08\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ and ${J}_{2}=\ensuremath{-}0.26\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ for the nearest- and second-nearest neighbors and a sizable antiferromagnetic exchange interaction ${J}_{3}=4.21\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ for the third-nearest neighbor with the strong easy-axis anisotropy $K=\ensuremath{-}2.06\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$. The anisotropic XXZ-type Hamiltonian could only achieve a suitable fitting. The exchange interaction for the out-of-plane spin component is smaller than that for the in-plane one by a ratio $\ensuremath{\alpha}={J}_{z}/{J}_{x}=0.6$. Our result directly shows that $\mathrm{CoP}{\mathrm{S}}_{3}$ is an experimental realization of the XXZ model with a honeycomb lattice in two-dimensional vdW magnets.

The effect of chemical substitution on the ground state of the geometrically frustrated antiferromagnet ${\mathrm{CsCrF}}_{4}$ has been investigated through a neutron powder diffraction experiment. Magnetic Fe-substituted ${\mathrm{CsCr}}_{0.94}{\mathrm{Fe}}_{0.06}{\mathrm{F}}_{4}$ and nonmagnetic Al-substituted ${\mathrm{CsCr}}_{0.98}{\mathrm{Al}}_{0.02}{\mathrm{F}}_{4}$ samples are measured, and magnetic Bragg peaks are clearly observed in both samples. Magnetic structure analysis revealed a ${120}^{\ensuremath{\circ}}$ structure having a magnetic propagation vector ${\mathbit{k}}_{\mathrm{mag}}=(0,0,1/2)$ in ${\mathrm{CsCr}}_{0.94}{\mathrm{Fe}}_{0.06}{\mathrm{F}}_{4}$. For ${\mathrm{CsCr}}_{0.98}{\mathrm{Al}}_{0.02}{\mathrm{F}}_{4}$, a quasi-${120}^{\ensuremath{\circ}}$ structure having ${\mathbit{k}}_{\mathrm{mag}}=(1/2,0,1/2)$ is formed. It is notable that the identified magnetic structure in ${\mathrm{CsCr}}_{0.94}{\mathrm{Fe}}_{0.06}{\mathrm{F}}_{4}$ belongs to a different phase of ground states from those in ${\mathrm{CsCr}}_{0.98}{\mathrm{Al}}_{0.02}{\mathrm{F}}_{4}$ and the parent ${\mathrm{CsCrF}}_{4}$. These results suggest that the Fe substitution strongly influences the ground state of ${\mathrm{CsCrF}}_{4}$.

Magnetic correlation in ${\mathrm{YBaCo}}_{4}{\mathrm{O}}_{7}$ with kagome and triangular lattices was studied through inelastic-neutron-scattering measurements on a single crystal sample. The broad magnetic excitation was observed below 45 meV and showed dispersions both within the $c$ plane and along the $c$ axis. The wave vector with the minimum energy of the magnetic excitation was totally different from the magnetic Bragg point. Our analysis with the first-moment-sum rule suggests that Co ions in ${\mathrm{YBaCo}}_{4}{\mathrm{O}}_{7}$ form a unique three-dimensional network with the geometrically frustration.

We performed inelastic neutron scattering measurements on a polycrystalline sample of a classical kagome antiferromagnet ${\mathrm{NaBa}}_{2}{\mathrm{Mn}}_{3}{\mathrm{F}}_{11}$ to investigate the possibility of a dispersionless zero-energy excitation associated with rotation of spins along the chains. The observed spectra indeed exhibit such an excitation with strong intensity at low energy, as well as dispersive excitations with weak intensity at high energy. Combining the measurements with calculations from linear spin-wave theory reveals that ${\mathrm{NaBa}}_{2}{\mathrm{Mn}}_{3}{\mathrm{F}}_{11}$ is a good realization of the classical kagome antiferromagnet which exhibits a dispersionless mode lifted by the magnetic dipole-dipole interaction.

We performed neutron diffraction experiments on a single crystal of an $S=\frac{1}{2}$ frustrated ferromagnetic chain compound ${\mathrm{NaCuMoO}}_{4}$(OH) at zero and finite magnetic fields. Three magnetic Bragg peaks with the propagation vector of $\mathbit{q}=(0,\ensuremath{\delta},0)$ $[\ensuremath{\delta}=0.481(1)]$ were observed at the zero field, which means that an incommensurate helical magnetic order was realized. Using the ratio of the intensities between these magnetic peaks, a proper-screw structure was suggested, where the spiral plane is the crystallographic $ac$ plane. While the $\ensuremath{\delta}$ is unchanged at lower fields, it decreases linearly with the field where ${\ensuremath{\mu}}_{0}H\ensuremath{\ge}2.5\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. The field dependence is consistent with that of the field-induced spin density wave state that originated from the formation of the bound state of two magnons in the $S=\frac{1}{2}$ frustrated ferromagnetic chain.

We report experimental and theoretical evidence that Rb$_2$Cu$_2$Mo$_3$O$_{12}$ has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled frustrated spin-$1/2$ chains and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya interaction are identified in inelastic neutron-scattering and electron spin resonance spectra. A tiny magnetic field generates ferroelectricity without closing the spin gap, indicating a novel class of ferroelectricity induced by a vector spin chirality order., Comment: main text (6 pages, 5 figures) + supplemental material (10 pages, 8 figures), to appear in Phys. Rev. B (R)

For a symmetry-consistent theoretical description of the ferroelectric phase of Ba2MnGe2O7 melilite compound, a precise knowledge of its crystal structure is a prerequisite. Here we report results of single-crystal neutron diffraction experiments on Ba2MnGe2O7 at room (300 K) and low (10 K) temperatures. The structural model based on the tetragonal space group P421m describes the Ba2MnGe2O7 symmetry both at room and low temperatures. We found reflections forbidden in the typical P421m melilite-type structure. A comparison of the experimental data collected by means of both thermal and cold neutrons with simulated multiple diffraction patterns allows us to unambiguously demonstrate that forbidden peaks originate from multiple diffraction (Renninger effect) rather than from real symmetry lowering. The precise structural parameters at 300 and 10 K are presented for the first time and compared with those of other magnetoelectric melilite-type germanates.

// Rina Nakakaji 1, 2, * , Masanari Umemura 1, * , Kenji Mitsudo 2 , Jeong-Hwan Kim 1 , Yujiro Hoshino 3 , Itaru Sato 1, 2 , Takatsugu Masuda 4 , Masahiro Yamamoto 5 , Mitomu Kioi 2 , Toshiyuki Koizumi 2 , Takayuki Fujita 1 , Utako Yokoyama 1 , Masaki Iida 2 , Motohiko Sato 6 , Hiroshi Sato 7 , Shoko Murofushi 7 , Sayaka Shibata 8 , Ichio Aoki 8 , Haruki Eguchi 7 , Iwai Tohnai 2 and Yoshihiro Ishikawa 1 1 Cardiovascular Research Institute, Yokohama City University Graduate School of Medicine, Yokohama, Japan 2 Department of Oral and Maxillofacial Surgery, Yokohama City University Graduate School of Medicine, Yokohama, Japan 3 Department of Environment and Natural Sciences, Yokohama National University Graduate School of Environment and Information Sciences, Yokohama, Japan 4 Tokyo Neutron Science Laboratory, Tokyo University Institute for Solid State Physics, Kashiwa, Japan 5 Department of Chemistry of Functional Molecules, Konan University Faculty of Science and Engineering, Kobe, Japan 6 Department of Physiology, Aichi Medical University, Nagakute, Japan 7 Advanced Applied Science Department, Research Laboratory, IHI Corporation, Yokohama, Japan 8 Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan * These authors contributed equally to this work Correspondence to: Masanari Umemura, email: umemurma@yokohama-cu.ac.jp Yoshihiro Ishikawa, email: yishikaw@med.yokohama-cu.ac.jp Keywords: iron-salen; taxol; oral cancer; paclitaxel; magnetism Received: July 14, 2017 Accepted: February 20, 2018 Epub: February 26, 2018 Published: March 20, 2018 ABSTRACT N,N’-Bis(salicylidene)ethylenediamine iron (Fe(Salen)) is an anti-cancer agent with intrinsic magnetic property. Here, we covalently linked Fe(Salen) to paclitaxel (PTX), a widely used anti-cancer drug, to obtain a magnetized paclitaxel conjugate (M-PTX), which exhibited magnetic characteristics for magnet-guided drug delivery and MRI visualization. M-PTX increased apoptosis and G2/M arrest of cultured human oral cancer cell lines in the same manner as PTX. Furthermore, marked contrast intensity was obtained in magnetic resonance imaging (MRI) of M-PTX. In a mouse oral cancer model, a permanent magnet placed on the body surface adjacent to the tumor resulted in distinct accumulation of M-PTX, and the anti-cancer effect was greater than that of M-PTX without the magnet. We believe that this strategy may improve future cancer chemotherapy by providing conventional anti-cancer drugs with novel functionalities such as magnet-guided drug delivery or MRI-based visualization/quantitation of drug distribution.

One of the consequences of antisymmetric spin–orbit interactions due to a lack of inversion symmetry are unusually large upper critical fields observed in heavy-electron superconductors. The upper ...

Dimensionality is a critical factor in determining the properties of solids and is an apparent built-in character of the crystal structure. However, it can be an emergent and tunable property in geometrically frustrated spin systems. Here, we study the spin dynamics of the tetrahedral cluster antiferromagnet, pharmacosiderite, via muon spin resonance and neutron scattering. We find that the spin correlation exhibits a two-dimensional characteristic despite the isotropic connectivity of tetrahedral clusters made of spin 5/2 Fe3+ ions in the three-dimensional cubic crystal, which we ascribe to two-dimensionalisation by geometrical frustration based on spin wave calculations. Moreover, we suggest that even one-dimensionalisation occurs in the decoupled layers, generating low-energy and one-dimensional excitation modes, causing large spin fluctuation in the classical spin system. Pharmacosiderite facilitates studying the emergence of low-dimensionality and manipulating anisotropic responses arising from the dimensionality using an external magnetic field., 22 pages, 22 figures

We reconstruct a magnetic phase diagram of the non-centrosymmetric CePtSi3 through magnetization measurements for H || [100]. The observed magnetization curves show four newly found anomalies in ad...

A new square-planar zinc oxyhalide, Sr2ZnO2Cl2, was successfully synthesized using a high-pressure method. Absorption spectroscopy revealed an indirect band gap of 3.66 eV. Electronic structure calculations indicated a strong hybridization between Zn 3dx2−y2 and O 2p orbitals, which is distinct from tetrahedrally coordinated ZnO.

Magnetization and neutron scattering measurements have been carried out on an antiferromagnet ${\mathrm{Ba}}_{2}{\mathrm{CoSi}}_{2}{\mathrm{O}}_{7}$. The observed magnetic excitation is almost dispersionless, and the neutron intensity is only modulated along the [101] direction. The dispersionless magnetic excitation suggest that the ${\mathrm{Ba}}_{2}{\mathrm{CoSi}}_{2}{\mathrm{O}}_{7}$ system is a quasi-one-dimensional antiferromagnet. Classical spin-wave theory for a one-dimensional antiferromagnet can explain the dispersionless spin excitation. The magnetic structure determined by the measurement of the neutron powder diffraction is consistent with no observation of the multiferroic property in this system.

Investigating exotic magnetic materials with spintronic techniques is effective at advancing magnetism as well as spintronics. In this work, we report unusual field-induced suppression of the spin-Seebeck effect (SSE) in a quasi one-dimensional frustrated spin-$\frac{1}{2}$ magnet LiCuVO$_4$, known to exhibit spin-nematic correlation in a wide range of external magnetic field $B$. The suppression takes place above $|B| > 2$ T in spite of the $B$-linear isothermal magnetization curves in the same $B$ range. The result can be attributed to the growth of the spin-nematic correlation while increasing $B$. The correlation stabilizes magnon pairs carrying spin-2, thereby suppressing the interfacial spin injection of SSE by preventing the spin-1 exchange between single magnons and conduction electrons at the interface. This interpretation is supported by integrating thermodynamic measurements and theoretical analysis on the SSE., accepted for publication in Phys. Rev. Lett