The Peltier effect modulates the temperature of a junction comprising two different conductors in response to charge currents across the junction, which is used in solid-state heat pumps and temperature controllers in electronics. Recently, in spintronics, a spin counterpart of the Peltier effect was observed. The ‘spin Peltier effect' modulates the temperature of a magnetic junction in response to spin currents. Here we report thermal imaging of the spin Peltier effect; using active thermography technique, we visualize the temperature modulation induced by spin currents injected into a magnetic insulator from an adjacent metal. The thermal images reveal characteristic distribution of spin-current-induced heat sources, resulting in the temperature change confined only in the vicinity of the metal/insulator interface. This finding allows us to estimate the actual magnitude of the temperature modulation induced by the spin Peltier effect, which is more than one order of magnitude greater than previously believed.

The Peltier effect, discovered in 1834, converts a charge current into a heat current in a conductor, and its performance is described by the Peltier coefficient, which is defined as the ratio of the generated heat current to the applied charge current. To exploit the Peltier effect for thermoelectric cooling or heating, junctions of two conductors with different Peltier coefficients have been believed to be indispensable. Here we challenge this conventional wisdom by demonstrating Peltier cooling and heating in a single material without junctions. This is realized through an anisotropic magneto-Peltier effect in which the Peltier coefficient depends on the angle between the directions of a charge current and magnetization in a ferromagnet. By using active thermography techniques, we observe the temperature change induced by this effect in a plain nickel slab. We find that the thermoelectric properties of the ferromagnet can be redesigned simply by changing the configurations of the charge current and magnetization, for instance, by shaping the ferromagnet so that the current must flow around a curve. Our experimental results demonstrate the suitability of nickel for the anisotropic magneto-Peltier effect and the importance of spin-orbit interaction in its mechanism. The anisotropic magneto-Peltier effect observed here is the missing thermoelectric phenomenon in ferromagnetic materials-the Onsager reciprocal of the anisotropic magneto-Seebeck effect previously observed in ferromagnets-and its simplicity might prove useful in developing thermal management technologies for electronic and spintronic devices.

We demonstrate the generation of alternating spin current (SC) via spin-rotation coupling (SRC) using a surface acoustic wave (SAW) in a Cu film. Ferromagnetic resonance caused by injecting SAWs was observed in a Ni-Fe film attached to a Cu film, with the resonance further found to be suppressed through the insertion of a SiO_{2} film into the interface. The intensity of the resonance depended on the angle between the wave vector of the SAW and the magnetization of the Ni-Fe film. This angular dependence is explicable in terms of the presence of spin transfer torque from a SC generated via SRC.

1Spin liquid is a state of electron spins where quantum fluctuation breaks magnetic ordering with keeping spin correlation [1]. It has been one of central topics of magnetism because of its relevance to fascinating phenomena such as high-T c superconductivity [2, 3] and topological states [4]. In spite of the profound physics, on the other hand, spin liquid itself has been quite difficult to utilize.Typical spin liquid states are realized in one-dimensional spin systems, called quantum spin chains [5, 6]. Here we show that a spin liquid in a spin-1/2 quantum chain generates and carries spin current via its long-range spin fluctuation. This is demonstrated by observing an anisotropic negative spin Seebeck effect [7][8][9][10][11][12] along the spin chains in Sr 2 CuO 3 . The result shows that spin current can flow even in an atomic channel owing to the spin liquid state, which can be used for atomic spin-current wiring.A flow of electrons spin angular momentum is called spin current [13]. In condensed matter science, transport properties of spin current have attracted considerable interest since the discovery of various spin-current phenomena [14, 15]. In spintronics [16], on the other hand, it is of critical importance to find materials which can carry spin angular momentum efficiently in integrated microscopic devices.Two types of spin current have experimentally been explored so far. The first one is conduction-electron spin current, which is mediated by an electron motion in metals and semiconductors. Its velocity and propagation length are thus limited by electron diffusion [17]. The other type is spin-wave spin current [18,19], where spin waves, wavelike propagation of spin motions in magnets, carry spin angular momentum. Its excitation gap is equal to a spin-wave gap, proportional to magnetic anisotropy. Importantly, spin-wave spin current can exist even in insulators in which spin relaxation via conduction electrons is absent, an advantage which may realize fast and long-range spin current transmission, opening a new field of insulator-based spintronics. However, spin-wave spin current in classical magnets may not be suitable for microscopic devices, since handling spin waves becomes difficult when devices are miniaturized toward atomic scale; in ferromagnets, spontaneous magnetization brings about significant stray fields, causing crosstalk. In an antiferromagnetic system, on the other hand, spin ordering patterns should be broken or interfered when a device is in atomic scale; in both cases, spin waves become vulnerable. Therefore, to realize spin-current transport in microscopic devices, spin ordering is expected to vanish with 2 keeping strong interaction among spins.Here, we would like to make a new type of spin current debut: spinon spin current, which may provide a channel for atomic spin transmission to satisfy the requirements. A spinon generally refers to magnetic elementary excitation in quantum spin liquid states [1]. When system size of a magnet is reduced to atomic scale, quantum spin fluct...

To know the properties of a particle or a wave, one should measure how its energy changes with its momentum. The relation between them is called the dispersion relation, which encodes essential information of the kinetics. In a magnet, the wave motion of atomic spins serves as an elementary excitation, called a spin wave, and behaves like a fictitious particle. Although the dispersion relation of spin waves governs many of the magnetic properties, observation of their entire dispersion is one of the challenges today. Spin waves whose dispersion is dominated by magnetostatic interaction are called pure-magnetostatic waves, which are still missing despite of their practical importance. Here, we report observation of the band dispersion relation of pure-magnetostatic waves by developing a table-top all-optical spectroscopy named spin-wave tomography. The result unmasks characteristics of pure-magnetostatic waves. We also demonstrate time-resolved measurements, which reveal coherent energy transfer between spin waves and lattice vibrations.

The spin Peltier effect (SPE), heat-current generation due to spin-current injection, in various metal (Pt, W, and Au single layers and Pt/Cu bilayer)/ferrimagnetic insulator (yttrium iron garnet: YIG) junction systems has been investigated by means of a lock-in thermography (LIT) method. The SPE is excited by a spin current across the metal/YIG interface, which is generated by applying a charge current to the metallic layer via the spin Hall effect. The LIT method enables the thermal imaging of the SPE free from the Joule-heating contribution. Importantly, we observed spin-current-induced temperature modulation not only in the Pt/YIG and W/YIG systems but also in the Au/YIG and Pt/Cu/YIG systems, excluding the possible contamination by anomalous Ettingshausen effects due to proximity-induced ferromagnetism near the metal/YIG interface. As demonstrated in our previous study, the SPE signals are confined only in the vicinity of the metal/YIG interface; we buttress this conclusion by reducing a spatial blur due to thermal diffusion in an infrared emission layer on the sample surface used for the LIT measurements. We also found that the YIG-thickness dependence of the SPE is similar to that of the spin Seebeck effect measured in the same Pt/YIG sample, implying the reciprocal relation between them.PACS numbers: 72.20. Pa,

Spatial distribution of temperature modulation due to anomalous Ettingshausen effect (AEE) is visualized in a ferromagnetic FePt thin film with in-plane and out-of-plane magnetizations using the lock-in thermography technique. Comparing the AEE of FePt with the spin Peltier effect (SPE) of a Pt / yttrium iron garnet junction provides direct evidence of different symmetries of AEE and SPE. Our experiments and numerical calculations reveal that the distribution of heat sources induced by AEE strongly depends on the direction of magnetization, leading to the remarkable different temperature profiles in the FePt thin film between the in-plane and perpendicularly magnetized configurations. (99 words) * Spin-current (J s )-mediated interconversion between electric charge current (J c ) and heat current (J q ), research field of which is frequently called "spin caloritronics" [1], has largely fascinated us from the viewpoint of not only fundamental physics but also potential applications. Spin Seebeck effect (SSE) [2-4] and spin Peltier effect (SPE) [5,6] are representative phenomena of spin caloritronics. SSE enables us to convert a temperature gradient (∇T) to pure J s owing to the collective magnetization dynamics activated by ∇T [7,8]. On the other hand, SPE is the reverse process of SSE, in which the flow of J s produces J q due to the transfer of spin angular momentum and energy from conduction electron spins to local spins, and vice versa, and the resultant non-equilibrium states of the magnon and electron systems [5]. Eventually, the SPE induces ∇T along J s . In both cases of SSE and SPE, junctions consisting of ferromagnetic and paramagnetic materials are often studied [2,3,5,6,9], e.g. a ferrimagnetic insulator yttrium iron garnet (YIG) and a paramagnetic metal Pt. For SSE, the J s due to the non-equilibrium spin state at the ferromagnet / paramagnet interface is observed as electric voltage in the paramagnet via the spin-orbit interaction, i.e. a spin Hall effect (SHE) [10]. The SPE has recently been observed in junctions with YIG and Pt by using microfabricated thermopiles [5] and active infrared emission microscopy called lock-in thermography (LIT) [6,11,12]. J s was generated via the SHE of Pt by the J c flow, and the interaction of J s and spontaneous magnetization (M) of YIG modulated the temperature of the junction.In addition to the SSE and SPE, anomalous Nernst effect (ANE) and anomalous Ettingshausen effect (AEE) are famous thermoelectric phenomena in ferromagnets that have been known for a long time [13], in

An unconventional approach to enhance the transverse thermopower by combining magnetic and thermoelectric materials, namely the Seebeck-driven transverse thermoelectric generation (STTG), has been proposed and demonstrated recently. Here, we improve on the previously used sample structure and achieve large transverse thermopower over 40 μV K −1 due to STTG in on-chip devices. We deposited polycrystalline Fe-Ga alloy films directly on n-type Si substrates, where Fe-Ga and Si serve as the magnetic and thermoelectric materials, respectively. Using microfabrication, contact holes were created through the SiOx layer at the top of Si to electrically connect the Fe-Ga film with the Si substrate. These thin devices with simple structure clearly exhibited enhancement of transverse thermopower due to STTG, and the obtained values agreed well with the estimation over a wide range of the size ratio between the Fe-Ga film and the Si substrate.