Octupole-driven magnetoresistance in an antiferromagnetic tunnel junction.

The tunnelling electric current passing through a magnetic tunnel junction (MTJ) is strongly dependent on the relative orientation of magnetizations in ferromagnetic electrodes sandwiching an insulating barrier, rendering efficient readout of spintronics devices1-5. Thus, tunnelling magnetoresistance (TMR) is considered to be proportional to spin polarization at the interface1 and, to date, has been studied primarily in ferromagnets. Here we report observation of TMR in an all-antiferromagnetic tunnel junction consisting of Mn3Sn/MgO/Mn3Sn (ref. 6). We measured a TMR ratio of around 2% at room temperature, which arises between the parallel and antiparallel configurations of the cluster magnetic octupoles in the chiral antiferromagnetic state. Moreover, we carried out measurements using a Fe/MgO/Mn3Sn MTJ and show that the sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet7 can be controlled by octupole direction. Strikingly, the TMR ratio (about 2%) of the all-antiferromagnetic MTJ is much larger than that estimated using the observed spin polarization. Theoretically, we found that the chiral antiferromagnetic MTJ may produce a substantially large TMR ratio as a result of the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles. Our work lays the foundation for the development of ultrafast and efficient spintronic devices using antiferromagnets8-10.

Phase Diagrams of Anthracene Derivatives in Pyridinium Ionic Liquids.

Crystal engineering for single crystallization of π-conjugated molecules has attracted much attention because of their electronic, photonic, and mechanical properties. However, reproducibility is a problem in conventional printing techniques because control of solvent evaporation is difficult. We investigated the phase diagrams of two anthracene derivatives in synthesized ionic liquids for non-volatile crystal engineering to determine the critical points for nucleation and crystal growth. Anthracene and 9,10-dibromoanthracene were used as representative π-conjugated molecules that form crystal structures with different packing types. Ionic liquids with an alkylpyridinium cation and bis(fluorosulfonyl)amide were good solvents for the anthracene derivatives from ca. 0 °C to 200 °C. The solubilities (critical points for crystal growth) of the anthracene derivatives in the ionic liquids reached the 100 mM level, which is similar to those in organic solvents. Ionic liquids with phenyl and octyl groups tended to show high-temperature dependence (a high dissolution entropy) with 9,10-dibromoanthracene. The precipitation temperature (critical point for crystal nucleation) at each 9,10-dibromoanthracene concentration was lower than the dissolution temperature. The differences between the dissolution and precipitation temperatures (supersaturated region) in the ionic liquids were greater than those in an organic solvent.

Ultrafast Dynamics of Intrinsic Anomalous Hall Effect in the Topological Antiferromagnet Mn_{3}Sn.

We investigate ultrafast dynamics of the anomalous Hall effect (AHE) in the topological antiferromagnet Mn_{3}Sn with sub-100 fs time resolution. Optical pulse excitations largely elevate the electron temperature up to 700 K, and terahertz probe pulses clearly resolve ultrafast suppression of the AHE before demagnetization. The result is well reproduced by microscopic calculation of the intrinsic Berry-curvature mechanism while the extrinsic contribution is clearly excluded. Our work opens a new avenue for the study of nonequilibrium AHE to identify the microscopic origin by drastic control of the electron temperature by light.

Non-Covalent Supramolecular 1D Alternating Copolymer in Crystal toward 2D Anisotropic Photon Transport.

To realize organic integrated optoelectronic circuits, there is a need for anisotropic optical waveguides at the micro/nanoscale. Anisotropic alignment of one-dimensional-ordered supramolecular structures composed of light-emissive π-conjugated molecules in a crystal may meet the requirements of such waveguides. Here, a bipyridyl-appended acrylonitrile-based π-conjugated molecule was designed, which produced a one-dimensional supramolecular polymer constructed through non-covalent bonding between a lone pair in bipyridyl and a σ-hole in 1,4-diiodo-2,3,5,6-tetrafluorobenzene. The one-dimensional copolymer of bipyridyl and 1,4-diiodo-2,3,5,6-tetrafluorobenzene is aligned horizontally with the two-dimensional crystal surface because of the angle-controlled supramolecular synthons. As a result of control over the non-covalent bonding direction, anisotropic photoluminescence and photon transport (optical waveguiding) characteristics are realized by orienting the transition dipole moment horizontally with respect to the two-dimensional surface. Compared with the loss coefficient αL =52 dB cm-1 for the long-axis direction of the two-dimensional platelet cocrystal, a very large difference of αS =2111 dB cm-1 is present in the crystal short-axis direction. The anisotropic waveguiding ability, αL /αS , is estimated to be 41, which is more than an order of magnitude greater than previously reported two-dimensional platelet crystal waveguides. This supramolecular synthon provides an approach to designing anisotropic photon transporters and highly regulated optical logic circuits.

Lasing in Low-Dimensional Crystals of a Fumaronitrile-Based Luminogen.

Low-dimensional structures are ideal for organic laser media because of their efficient waveguide, photon confinement, and stimulated emission. Control of the structure and alignment of luminescent molecules is very important for realizing laser media. Here, we fabricate low-dimensional crystals of bis(biphenyl)fumaronitrile (BPFN), which is an aggregation-induced emission luminogen. The BPFN molecule contains fumaronitrile, which displays solid-state luminescence, and biphenyl, which forms low-dimensional structures through dipole-dipole interactions. Solvent diffusion yielded two-dimensional platelet crystals of BPFN with strong dipole-dipole CH-π interactions. The high photoluminescence quantum efficiency of 0.46 and uniaxially aligned molecular π-electronic transition dipole moment in the two-dimensional crystals of BPFN resulted in optically pumped lasing even when using an optical excitation source with a long pulse duration (∼5 ns). One-dimensional BPFN crystals obtained via epitaxial growth on the cleaved surface of a KBr single crystal also displayed lasing behavior.

Observation of Omnidirectional Exchange Bias at All-Antiferromagnetic Polycrystalline Heterointerface.

Due to promising functionalities that may dramatically enhance spintronics performance, antiferromagnets are the subject of intensive research for developing the next-generation active elements to replace ferromagnets. In particular, the recent experimental demonstration of tunneling magnetoresistance and electrical switching using chiral antiferromagnets has sparked expectations for the practical integration of antiferromagnetic materials into device architectures. To further develop the technology to manipulate the magnetic anisotropies in all-antiferromagnetic devices, it is essential to realize exchange bias through the interface between antiferromagnetic multilayers. Here, the first observation on the omnidirectional exchange bias at an all-antiferromagnetic polycrystalline heterointerface is reported. This experiment demonstrates that the interfacial energy causing the exchange bias between the chiral-antiferromagnet Mn3Sn/collinear-antiferromagnet MnN layers is comparable to those found at the conventional ferromagnet/antiferromagnet interface at room temperature. In sharp contrast with previous reports using ferromagnets, the magnetic field control of the unidirectional anisotropy is found to be omnidirectional due to the absence of the shape anisotropy in the antiferromagnetic multilayer. The realization of the omnidirectional exchange bias at the interface between polycrystalline antiferromagnets on amorphous templates, highly compatible with existing Si-based devices, paves the way for developing ultra-low power and ultra-high speed memory devices based on antiferromagnets.

Flexible and Red-Emissive Organic Single-Crystal Microresonator for Efficient Active Waveguides.

We fabricated a flexible and red-emissive microcrystal resonator for highly efficient optical waveguiding. The microfiber crystals of diketopyrrolopyrrole (DPP) used in this work possess a high photoluminescence (PL) quantum efficiency (ΦPL = 0.45) and exhibit a micromechanical deformation shape in the curved state. The crystals show optical fringes in their PL spectra, suggesting the existence of a naturally formed Fabry-Pérot crystal resonator owing to its flat crystal surface. The group refractive index (ng) and Rabi splitting energy (ℏΩ) indicating the coupling strength between excitons and resonator photons are large (ng = 3.7-6.0, â„Ω = 1.38 eV), suggesting the strong confinement of waveguiding photons. Spatially resolved PL measurements revealed that the PL in a crystal fiber is efficiently waveguided, even in a curved crystal with a very small curvature radius of 11 µm. Strong photon confinement inside a crystal resonator is a plausible origin of efficient optical waveguiding.

Structural Phase Transitions in Anthracene Crystals.

Anthracene (C14 H10 ) and its derivatives, π-conjugated molecules in acenes, have been widely researched in terms of their reactions, physical properties, and self-assembly (or crystal engineering). These molecules can be functionalized to tune reactivities, optoelectronic properties, and self-assembling abilities. Structural changes in the molecular assemblies, solid states, and crystals have recently been discovered. Therefore, a systematic discussion of anthracene's molecular structure, packing, and optical properties based on its intermolecular structure and phase transitions is important for future chemical and structural design. In the present review, we discuss anthracene's molecular design, dimer packing, and crystal structure, focusing on the structural phase transitions of its crystals. We also provide examples of the phase transitions of anthracene crystals. Changes to edge-to-face of CH-π interaction and face-to-face packing of π-π interaction affect the thermodynamic stabilities of various crystal structures. These structures can inform the prediction of structural and physical properties.

Structural Phase Transitions in Anthracene Crystals.

Invited for this month's cover is the collaborating group of Prof. Shotaro Hayashi at Kochi University of Technology. The cover picture shows anthracene molecules depicted among sakura blossoms at Kochi University of Technology (KUT). Anthracenes are arranged with falling petals, giving a beautiful image of the molecular crystal engineering field. The cover was designed by Yuto Hino. More information can be found in the Review by S. Hayashi and co-workers.

A New Species of the Genus Ophiomonas Djakonov (Echinodermata: Ophiuroidea: Amphilepididae) from the Deep-Sea of Japan.

A new species, Ophiomonas shinseimaruae, is described based on five specimens collected from deep water settings, southeast of Cape Erimo, Hokkaido, Japan. Ophiomonas shinseimaruae sp. n. is distinguished from other congeners based on the following characters: elongate semi-circular and separated radial shields; triangular oral shields; flat and broad tentacle scales on the second tentacle pore; octagonal dorsal arm plates, approximately three times wider than long on proximal portion of the arm; and three arm spines present proximally on the arm. This is the first record of the genus Ophiomonas from Japanese waters. The COI nucleotide sequence for Ophiomonas shinseimaruae sp. n. is provided.

Synthesis and characterization of methoxy- or cyano-substituted thiophene/phenylene co-oligomers for lasing application.

As new candidates of thiophene/phenylene co-oligomer (TPCO) species, 5,5''-bis(4'-methoxy-[1,1'-biphenyl]-4-yl)-2,2':5',2''-terthiophene (BP3T-OMe) and 4',4'''-([2,2':5',2''-terthiophene]-5,5''-diyl)bis(([1,1'-biphenyl]-4-carbonitrile)) (BP3T-CN) were synthesized for lasing applications. Although most unsubstituted TPCO species crystallize in monoclinic form, BP3T-OMe and BP3T-CN crystallized in orthorhombic and triclinic forms, respectively. Since the unsubstituted species, 5,5''-bis(4-biphenylyl)-2,2':5',2''-terthiophene (BP3T), shows unique and superior lasing performance in single crystals, the newly synthesized BP3T-OMe and BP3T-CN have possibilities to show different or improved optoelectronic characteristics. Amplified spontaneous emission (ASE) and optically pumped lasing were observed from both of the single crystals based on their well-shaped crystalline cavity and high group refractive index values of 3.7-5.3 for excellent light confinement. The lasing threshold for the BP3T-OMe crystal was lower than that for the BP3T-CN crystal, which was attributed to their different molecular orientation, standing in the former and inclining in the latter.

Prediction of fracture lines of the calcaneus using a three-dimensional finite element model.

The various lines of calcaneal fractures indicate their complex nature and make their treatment challenging. There is still much debate regarding the position and direction of these fracture lines, even for the primary fracture line. The computed tomography-based finite element model is known to provide accurate predictions of fracture loads and virtual fracture locations for the femur and distal radius. This study aimed to establish how to predict the calcaneus fracture lines using the computed tomography-based finite element model for patients with contralateral calcaneal fractures and to investigate whether the predicted lines were similar to those of the fractured calcaneus. The calcanei of five men and two women aged 44-77 years (average age, 60 years) with contralateral calcaneal fractures were analyzed. To assess the precision of the predicted fracture lines of the contralateral calcanei, they were compared with the fracture locations found by three-dimensional models of the calcanei. The fracture lines of the finite element model simulated the actual fracture lines and diagnosed joint depression types of fractures (five cases) and tongue types (two cases), but only under certain conditions for each case. This trial simulated calcaneal fractures using a patient-specific computed tomography-based nonlinear finite element model. Therefore, we suggest that it is possible to reproduce calcaneal fractures using the finite element model. It was possible to predict with precision the actual calcaneal fracture for each patient and to reproduce fracture conditions. Therefore, this method is valuable because it can provide an understanding of the pathomechanism of calcaneal fractures. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:483-489, 2019.