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Peltier effects, which produce a heat flux at the junction of two different materials, have been an important technology for heating and cooling by electrical means. Whereas Peltier devices have advantages such as cleanliness, silence, compactness, flexibility, reliability, and efficiency, relatively complicated modular structures are unavoidable, leading to a higher cost than that of commonly used refrigeration technology. Here, we provide a concept of a Peltier device composed of a single magnetic material exhibiting a first-order magnetic transition. Our concept is based on a controllable junction structure consisting of two magnetic phases with opposite Peltier coefficients instead of a semiconductor junction. Using $${\mathrm{Mn}}_{1.96}{\mathrm{Cr}}_{0.04}\mathrm{Sb}$$ Mn 1.96 Cr 0.04 Sb samples with the first-order magnetic transition between ferrimagnetic (FI) and antiferromagnetic (AF) states, we successfully made a stable junction structure of AF/FI/AF by a pulse heating method and achieved a maximum Peltier coefficient of 0.58 mV. Our device concept was further verified by a numerical simulation based on a finite element method. The single-material Peltier effect reported here avoids a complex device design involving material junctions and is importantly reconfigurable.

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.

Magneto-piezoelectric effect (MPE) refers to generation of strain in response to electric currents in magnetic metals which lack both time-reversal and space-inversion symmetries. A recent experimental paper demonstrated the MPE in the antiferromagnetic metal EuMnBi2 at 77 K, but the limited temperature range of the MPE measurement hampered detailed discussion on the MPE. Here we extend the measurement temperature range down to liquid He temperature, and studied the dependences of the MPE on the laser position, frequency and amplitude of electric currents, and temperature in the very low temperature range. We show that the MPE signal is enhanced at low temperatures and reaches a maximum magnitude in the antiferromagnetically ordered states of both Eu and Mn ions. An effective piezoelectric coefficient for the MPE at 4.5 K is estimated to be as large as 3500 pC/N, which is much larger than piezoelectric coefficients of typical piezoelectric ceramics, although the magnitude of real MPE displacements should be limited due to strong Joule heating at high electric currents. The present results may open up a new strategy to realize new lead-free piezoelectric materials.

We have experimentally demonstrated a phase change control of Hall effects in ferromagnetic MnBi thin films at room temperature. Two distinct ferromagnetic phases, i.e., a low-temperature phase and a quenched high-temperature phase, were obtained by slow-cooling or quenching the sputtered MnBi films. The measurement of Hall effects showed that the anomalous Hall resistivity has different coercivity and remanence between the two phases. By optimizing the Mn/Bi ratio, it is even possible to repeatedly switch the sign of Hall resistivity, which could be utilized as a concept of phase-change memory based on ferromagnetic transport.

We have investigated thermoelectric properties of the antiferromagnetic semimetal $\mathrm{Fe}{\mathrm{Ge}}_{2}$. As temperature decreases from 340 K, the Seebeck coefficient takes a maximum around the N\'eel temperature and then decreases to show a sign change from positive to negative 50 K. When a strong magnetic field is applied perpendicular to the sample plane, the sign change disappears, and the positive Seebeck coefficient is observed in the whole temperature range. This large magneto-Seebeck effect is anisotropic since the Seebeck coefficient is insensitive to in-plane magnetic fields. Based on the Mott formula, we discuss the origins for this anisotropic magneto-Seebeck effect.

In superconductors, a topological configuration of the superconducting order parameter called a superconducting vortex carries magnetization. Such a magnetic topological object behaves like a minute particle generating a magnetic flux. Since the flux is localized with a nanometer scale, the vortex provides a nano-scale probe for local magnetic fields. Here we show that information of magnetic stripes in insulators can be read out by using vortices in an adjacent superconductor film as a probe. The orientation and width of magnetic micro stripes are both transcribed into resistance change of the superconductor through the modulation of vortex mobility affected by local magnetization. By changing the direction of external magnetic fields, zero-field resistance changes continuously according to the stripe orientation, and its modulation magnitude reaches up to 100%. The width of the stripes can also be estimated from the oscillatory magnetoresistance. Our results demonstrate a new possibility for non-volatile analog memory devices based on topological objects.

To explore recent advancements in the use of point-of-care ultrasound in the pediatric intensive care unit or during the perioperative period. Ultrasound is useful for selecting an appropriate endotracheal tube size, predicting postextubation stridor, assessing vocal cord paralysis, performing ultrasound-guided lung recruitment, assessing circulatory volume status, performing transcranial Doppler for assessment of cerebral perfusion, assessing intracranial hypertension, assessing central venous catheter tip position, and performing arterial line cannulation. There has been rapid progress in the use of point-of-care ultrasound in pediatric critical care, which can revolutionize daily clinical practice. However, further studies are required to verify that some of these areas of clinical application are translatable and scalable to widespread adoption.

Nonlinear effects of spin pumping have been investigated by numerically calculating the temporal evolution of the magnon number affected by three- and four-magnon interactions. We showed that the three-magnon interaction gives rise to the enhancement of spin-pumping spin current. We also found that the four-magnon interaction in combination with the three-magnon interaction can be responsible for the experimentally observed low-frequency oscillation of spin current.

Thermoelectric effects have been applied to power generators and temperature sensors that convert waste heat into electricity. The effects, however, have been limited to electrons to occur, and inevitably disappear at low temperatures due to electronic entropy quenching. Here, we report thermoelectric generation caused by nuclear spins in a solid: nuclear-spin Seebeck effect. The sample is a magnetically ordered material MnCO$_{3}$ having a large nuclear spin ($I = 5/2$) of $^{55}$Mn nuclei and strong hyperfine coupling, with a Pt contact. In the system, we observe low-temperature thermoelectric signals down to 100 mK due to nuclear-spin excitation. Our theoretical calculation in which interfacial Korringa process is taken into consideration quantitatively reproduces the results. The nuclear thermoelectric effect demonstrated here offers a way for exploring thermoelectric science and technologies at ultralow temperatures., Comment: This is a post-peer-review, pre-copyedit version of an article published in Nature Communications. The final authenticated version is available online at: http://dx.doi.org/10.1038/s41467-021-24623-6

We investigated the Dirac-cone state and its modulation when an ultrathin film of topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ was epitaxially grown on a van der Waals ferromagnet ${\mathrm{Cr}}_{2}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ (CST) by angle-resolved photoemission spectroscopy. We observed a gapless Dirac-cone surface state in six quintuple-layer (6QL) ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ on CST, whereas the Dirac cone exhibits a gap of 0.37 eV in its 2QL counterpart. Intriguingly, this gap is much larger than those for ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ films on Si(111). We also revealed no discernible change in the gap magnitude across the ferromagnetic transition of CST, suggesting the very small characteristic length and energy scale of the magnetic proximity effect. The present results suggest a crucial role of interfacial coupling for modulating Dirac electrons in topological-insulator hybrids.

We measure the mode-resolved direction of the precessional motion of the magnetic order, i.e., magnon polarization, via the chiral term of inelastic polarized neutron scattering spectra. The magnon polarization is a unique and unambiguous signature of magnets and is important in spintronics, affecting thermodynamic properties such as the magnitude and sign of the spin Seebeck effect. However, it has never been directly measured in any material until this work. The observation of both signs of magnon polarization in Y_{3}Fe_{5}O_{12} also gives direct proof of its ferrimagnetic nature. The experiments agree very well with atomistic simulations of the scattering cross section.

A rectenna, standing for a rectifying antenna, is an apparatus which generates d.c. electricity from electric fluctuations. It is expected to realize wireless power transmission as well as energy harvesting from environmental radio waves. To realize such rectification, devices that are made up of internal atomic asymmetry such as an asymmetric junction have been necessary so far. Here we report a material that spontaneously generates electricity by rectifying environmental fluctuations without using atomic asymmetry. The sample is a common superconductor without lowered crystalline symmetry, but, just by putting it in an asymmetric magnetic environment, it turns into a rectifier and starts generating electricity. Superconducting vortex strings only annihilate and nucleate at surfaces, and this allows the bulk electrons to feel surface fluctuations in an asymmetric environment: a vortex rectenna. The rectification and generation can be switched on and off with only a slight change in temperature or external magnetic fields., Devices that generate electricity from electric fluctuations are promising for wireless power transmission as well as energy harvesting from environmental radio waves. Here the authors report the electric power generation from environmental fluctuations by using superconducting vortex strings in MoGe/YIG bilayer system.

Various spintronic phenomena originate from the exchange of angular momentum between the spin of electrons and other degrees of freedom in crystalline materials. Many degrees of freedom, such as magnetization1 and mechanical motion2, have already been united into this exchange framework. However, the nuclear spin—a key angular momentum—has yet to be incorporated. Here we observe spin pumping from nuclear magnetic resonance (NMR), in which nuclear spin dynamics emits a spin current, a flow of spin angular momentum of electrons. By using the canted antiferromagnet MnCO3, in which typical nuclear spin-wave formation is established due to the reinforced hyperfine coupling, we find that a spin current is generated from an NMR. Nuclear spins are indispensable for quantum information technology3 and are also frequently used in various sensors, such as in magnetic resonance imaging4. The observed NMR spin pumping allows spin-current generation from nuclei and will enable spintronic detection of nuclear spin states. Spin current is generated by pumping from nuclear spin waves. The nuclear magnetic resonance is used to transfer angular momentum from the nuclei of an antiferromagnet to a propagating spin current that is subsequently collected in a distant electrode.

We have experimentally studied a magnetopiezoelectric effect (MPE), i.e., dynamic distortion caused by AC electric currents, in the antiferromagnetic conductor ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$ at low temperatures down to $77\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ using laser Doppler vibrometry. When AC electric currents are applied to ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$, dynamic displacement signals which increase in proportion to the current amplitude are clearly observed at $77\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, but their magnitude and temperature dependence strongly depend on Joule heating effects caused by the applied electric currents. Especially, poor thermal contact of ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$ samples to the sample holder produces second-harmonic displacement signals owing to thermal expansion due to the Joule heating, and tends to affect the temperature dependence of the MPE signals. In a measurement run without any heating effects, a sharp enhancement of the MPE signal is observed at the N\'eel temperature of ${\mathrm{CaMn}}_{2}{\mathrm{Bi}}_{2}$, which suggests that fluctuations of itinerant Mn moments near the N\'eel temperature play an important role in the MPE. We speculate that electric currents produce nonequilibrium antiferromagnetic moments via the antiferromagnetic Edelstein effect and the induced antiferromagnetic momemts enhance the MPE signal with the help of a large magnetovolume coupling near the N\'eel temperature. The MPE efficiency as a piezoelectric response reaches 300--$500\phantom{\rule{0.16em}{0ex}}\mathrm{pC}/\mathrm{N}$ at a maximum, which is comparable to high values of piezoelectric coefficients detected in the piezoelectric (ferroelectric) ceramics.

We have studied the longitudinal spin Seebeck effect (LSSE) in the layered ferromagnetic insulators ${\mathrm{CrSiTe}}_{3}$ and ${\mathrm{CrGeTe}}_{3}$ covered by Pt films in the measurement configuration where spin current traverses the ferromagnetic Cr layers. The LSSE response is clearly observed in the ferromagnetic phase and, in contrast to a standard LSSE magnet ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$, persists above the critical temperatures in both ${\mathrm{CrSiTe}}_{3}/\mathrm{Pt}$ and ${\mathrm{CrGeTe}}_{3}/\mathrm{Pt}$ samples. With the help of a numerical calculation, we attribute the LSSE signals observed in the paramagnetic regime to exchange-dominated interlayer transport of in-plane paramagnetic moments reinforced by short-range ferromagnetic correlations and strong Zeeman effects.

Spin currents can be carried by electrons and by magnons. Experiments now show that, in one-dimensional spin chains, spin currents can also be carried by particle-like excitations known as spinons. Quantum spin fluctuation in a low-dimensional or frustrated magnet breaks magnetic ordering while keeping spin correlation1. Such fluctuation has been a central topic in magnetism because of its relevance to high-Tc superconductivity2 and topological states3. However, utilizing such spin states has been quite difficult. In a one-dimensional spin-1/2 chain, a particle-like excitation called a spinon is known to be responsible for spin fluctuation in a paramagnetic state. Spinons behave as a Tomonaga–Luttinger liquid at low energy, and the spin system is often called a quantum spin chain4. Here we show that a quantum spin chain generates and carries spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect5,6,7,8,9,10 along the spin chains in Sr2CuO3. The results show that spin current can flow even in an atomic channel owing to long-range spin fluctuation.

Thermoelectric properties of chromium-modified Mn2Sb are systematically investigated to evaluate the power factors. Single-crystalline samples of Mn2−xCrxSb with 0 ≤ x ≤ 0.1 were successfully grown...

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

Coherence peak effects in a superconductor induced by a thermal spin current are reported. We measured inverse spin Hall effects induced by spin injection from a ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ into a superconductor NbN using longitudinal spin Seebeck effects. In the vicinity of the superconducting transition temperature of the NbN, a large enhancement of the spin Seebeck voltage is observed, whose sign is opposite to that for the vortex Nernst effect, but is consistent with a calculation for a coherence peak effect in the superconductor NbN., 5 pages, 4 figures

Spin currents in antiferromagnetic materials have recently attracted much interest in the field of spintronics. Although the thermal generation effect of spin currents, as in the spin Seebeck effect (SSE), is powerful for their study, the SSE in antiferromagnets has been experimentally studied only for Cr${}_{2}$O${}_{3}$ and MnF${}_{2}$. In this work, the authors experimentally observe the SSE in the polar antiferromagnet \ensuremath{\alpha}-Cu${}_{2}$V${}_{2}$O${}_{7}$. Comparison of the experimental results with calculations using magnetic parameters determined by neutron scattering studies reveals that the magnon scattering plays an important role in the antiferromagnetic SSE observed in \ensuremath{\alpha}-Cu${}_{2}$V${}_{2}$O${}_{7}$.

A magnon Nernst effect, an antiferromagnetic analog of the magnon Hall effect in ferromagnetic insulators, has been studied experimentally for the layered antiferromagnetic insulator ${\mathrm{MnPS}}_{3}$ in contact with two Pt strips. Thermoelectric voltage in the Pt strips grown on ${\mathrm{MnPS}}_{3}$ single crystals exhibits nonmonotonic temperature dependence at low temperatures, which is unlikely to be explained by electronic origins in Pt but can be ascribed to the inverse spin Hall voltage induced by a magnon Nernst effect. Control of antiferromagnetic domains in the ${\mathrm{MnPS}}_{3}$ crystal by magnetoelectric cooling is found to modulate the low-temperature thermoelectric voltage in Pt, which is evidence consistent with the emergence of the magnon Nernst effect in Pt-${\mathrm{MnPS}}_{3}$ hybrid structures.

Although magnetism and superconductivity hardly coexist in a single material, recent advances in nanotechnology and spintronics have brought to light their interplay in magnetotransport in thin-film heterostructures. Here, we found a periodic oscillation of Nernst voltage with respect to magnetic fields in Pt|LiFe5O8 (Pt|LFO) bilayers grown on a cuprate superconductor YBa2Cu3O7−x (YBCO). At high temperatures above the superconducting transition temperature (T C ) of YBCO, spin Seebeck voltages originating in Pt|LFO layers are observed. As temperature decreases well below T C , the spin Seebeck voltage is suppressed and unconventional periodic voltage oscillation as a function of magnetic fields appears; such an oscillation emerging along the Hall direction in the superconducting state has not been observed yet. Dynamics of superconducting vortices pinned by surface precipitates seems responsible for the oscillatory Nernst effect.

The Kitaev quantum spin liquid on a honeycomb lattice has received much interest in magnetism, mainly because of the possibility of emergence of novel excitations called Majorana quasiparticles. The quest is under way to realize this exotic state in actual materials. One of the promising materials is the layered honeycomb material RuCl${}_{3}$, for which the signatures of the Majorana quasiparticles have been reported. Here, the authors investigate the magnetic thermal conductivity of RuCl${}_{3}$ along with bulk thermodynamic measurements. They find that in the temperature range on the order of the Kitaev-coupling strength anomalous heat conduction takes place, which correlates with the growth of the magnetic specific heat. The result is consistent with the propagation of magnetic excitations, likely itinerant Majorana quasiparticles, driven by Kitaev coupling.

This study examined whether children understand that people selectively conceal or express emotion depending upon the context. We prepared two contexts for a verbal display task for 70 first-graders, 80 third-graders, 64 fifth-graders, and 71 adults. In both contexts, protagonists had negative feelings because of the behavior of the other character. In the prosocial context, children were instructed that the protagonist wished to spare the other character’s feelings. In contrast, in the real-emotion context, children were told that the protagonist was fed up with the other character’s behavior. Participants were asked to imagine what the protagonists would say. Adults selected utterances with positive or neutral emotion in the prosocial context but chose utterances with negative emotion in the real-emotion context, whereas first-graders selected utterances with negative emotion in both contexts. In the prosocial context, the proportion of utterances with negative emotion decreased from first-graders to adults, whereas in the real-emotion context the proportion was U-shaped, decreasing from first- to third-graders and increasing from fifth-graders to adults. Further, performance on both contexts was associated with second-order false beliefs as well as second-order intention understanding. These results indicate that children begin to understand that people selectively conceal or express emotion depending upon context after 8 to 9 years. This ability is also related to second-order theory of mind.

We have studied transport properties of composite oxides composed of ferrimagnetic conductor Fe 3O 4 (magnetite) and insulating α-Fe 2O 3 (hematite) at room temperature. High-density composite oxides with different Fe 3O 4/Fe 2O 3 ratios were successfully synthesized by melting Fe 2O 3 rods at high temperatures in ambient atmosphere. Transport properties of Fe 3O 4-Fe 2O 3 composites were measured and compared with that of Fe 3O 4 single crystals. As the ratio of the insulating Fe 2O 3 concentration to the conductive Fe 3O 4 one increases, the longitudinal resistivity increases exponentially, while the Seebeck coefficient decreases linearly. The contrasting dependences of electric and thermoelectric transports on the insulating Fe 2O 3 concentration indicate that the thermoelectric transport is less susceptible to disorder effects than electric ones. The measurement of the Hall effect shows that the anomalous Hall effect due to the ferrimagnetic Fe 3O 4 phase is clearly observed in the composite oxides. In line with the resistivity increase with the Fe 2O 3 concentration, the anomalous Hall resistivity increases, following the universal scaling relation established in the dirty limit. The anomalous Nernst effect due to the Fe 3O 4 phase is also observed in the composite oxides. The anomalous Nernst coefficient decreases with increasing Fe 2O 3 concentration, and the decrease is found to be related to the anomalous Hall effect through the Mott relation.

Ascorbate (AsA) is an important antioxidant and an enzyme cofactor involved in various metabolic pathways. In this study, we investigated the effects of estrogen (ES)-inducible transient expression of genes encoding enzymes involved in the d-mannose/l-galactose (d-Man/l-Gal) pathway for plant AsA biosynthesis on AsA levels under light and dark conditions. No significant difference was observed in AsA levels between Arabidopsis plants transiently expressing phosphomannose isomerase (PMI1), GDP-d-Man pyrophosphorylase (GMP/VTC1), GDP-Man-3′,5′-epimerase (GME), and l-Gal 1-phosphate phosphatase (GPP/VTC4), but AsA levels in the plants transiently expressing GDP-l-Gal phosphorylase (GGP/VTC2) were 2.5-fold higher than those in control plants 7 d after ES treatment. The increase in AsA levels under continuous light conditions and the decrease in AsA levels under dark conditions were enhanced and suppressed, respectively, in the ES-treated plants. These results suggest that GGP/VTC2 acts as a rate-limiting step regulating AsA biosynthesis in response to light and dark conditions.

The electron mobility is one of the key parameters that characterize the charge-carrier transport properties of materials, as exemplified by the quantum Hall effect as well as high-efficiency thermoelectric and solar energy conversions. For thermoelectric applications, introduction of chemical disorder is an important strategy for reducing the phonon-mediated thermal conduction, but is usually accompanied by mobility degradation. Here, we show a multilayered semimetal β-CuAgSe overcoming such a trade-off between disorder and mobility. The polycrystalline ingot shows a giant positive magnetoresistance and Shubnikov de Haas oscillations, indicative of a high-mobility small electron pocket derived from the Ag s-electron band. Ni doping, which introduces chemical and lattice disorder, further enhances the electron mobility up to 90,000 cm(2) V(-1) s(-1) at 10 K, leading not only to a larger magnetoresistance but also a better thermoelectric figure of merit. This Ag-based layered semimetal with a glassy lattice is a new type of promising thermoelectric material suitable for chemical engineering.

We have fabricated ultra-sensitive nanomechanical resonators with an integrated non-local spin valve structure. The obtained sensitivity is 1.42 × 10−17 N for the flexural mode and 1.68 × 10−18 N for the torsional mode, which indicates that the resonator is able to detect spin relaxation in terms of torque measurements.