Electric generation of spin current via spin Hall effect is of great interest as it allows an efficient manipulation of magnetization in spintronic devices. Theoretically, pure spin current can be also created by a temperature gradient, which is known as spin Nernst effect. Here, we report spin Nernst effect-induced transverse magnetoresistance in ferromagnet/non-magnetic heavy metal bilayers. We observe that the magnitude of transverse magnetoresistance in the bilayers is significantly modified by heavy metal and its thickness. This strong dependence of transverse magnetoresistance on heavy metal evidences the generation of thermally induced pure spin current in heavy metal. Our analysis shows that spin Nernst angles of W and Pt have the opposite sign to their spin Hall angles. Moreover, our estimate implies that the magnitude of spin Nernst angle would be comparable to that of spin Hall angle, suggesting an efficient generation of spin current by the spin Nernst effect.

Seebeck coefficient S, high electrical conductivity σ, and low thermal conductivity κ, which are normally expressed by the thermoelectric figure of merit, ZT = σS 2 T/κ, where T is the absolute temperature. [1][2][3][4][5] To improve ZT, research on various materials has been performed, where κ is minimized by phonon engineering, [3] and the power factor (σS 2 ) is enhanced by modification of the band structure. [4] As an alternative and novel route to improve the thermoelectric efficiency, several interesting approaches, such as the spin Seebeck, anisotropic Seebeck, electrolyte Seebeck, and photo Seebeck effects, have been proposed recently. [6][7][8][9] Among these approaches, the spin Seebeck effect [9] has especially attracted attention with regard to thermoelectrics in various magnetic systems (or spin thermoelectrics) as a new strategy for thermoelectric energy conversion [10][11][12][13][14] and as a spin current source in spintronic devices. [15][16][17][18][19][20] Although the spin Seebeck effect is fascinating as the spin counterpart of the Seebeck effect, practical thermoelectric power generation using spin Seebeck effect is yet to be developed. Therefore, obviously, the most critical aspect of spin thermoelectrics for practical applications is to increase the efficiency of energy conversion, which has been engineered with regard to thermal conductivity, [21,22] band gap of the semiconductor, [16,23,24] and the spin Hall angle (θ SH ), [13] among others. In addition to these attempts, a spin thermopile consisting of wire elements of a ferromagnetic (FM)/electrode bilayer can increase the overall voltage by alternating the polarity of each element in a zigzag structure, [13,[25][26][27] as magnetic materials certainly can gain benefits from tunability of the magnetic direction and a nanoscale modulating structure. [28][29][30] Previously, spin thermopiles utilizing the anomalous Nernst effect (ANE) alone showed enhanced signals with alternating signs of ANE coefficients (C ANE ) or with an alternating magnetic direction. [27] However, its operating magnetic field is somewhat large, on the order of kOe, and the signal shows hysteretic behavior when subjected to coercive-field modulation to control the magnetic direction. It has also been reported that thermopiles with the inverse spin Hall effect (ISHE) can be fabricated The thermoelectric effect in various magnetic systems, in which electric voltage is generated by a spin current, has attracted much interest owing to its potential applications in energy harvesting, but its power generation capability has to be improved further for actual applications. In this study, the first instance of the formation of a spin thermopile via a simplified and straightforward method which utilizes two distinct characteristics of antiferromagnetic IrMn is reported: the inverse spin Hall effect and the exchange bias. The former allows the IrMn efficiently to convert the thermally induced spin current into a measurable voltage, and the latter can be used to control the ...

A simple and robust platform, based on polymer-grafted nanoparticles to facilitate a controlled morphology of nano-fillers, provides a route for strategically designing nanostructured EM wave absorbers with a percolated MWCNT network as well as a controlled NP arrangement.

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Fe 3 O 4 nanoparticles dispersed on single-walled carbon nanotube (SWCNT) composites are synthesized through a simple in-situ co-arc discharge process followed by an annealing process. A well-integrated Fe 3 O 4 /SWCNT composite exhibiting the strong microwave absorption (MA, À36.9 dB at 10.5 GHz) and a wide effective bandwidth (5.5 GHz) is obtained by controlling the annealing conditions. The high effective MA performance of this composite was ascribed to the well integration of magnetic nanoparticles (Fe 3 O 4 ) on the SWCNT, creating a synergetic effect. This work demonstrates an economical approach to produce Fe 3 O 4 /SWCNT composites with good MA performance.

Porous magnetite (Fe 3 O 4 ) nanospheres are successfully prepared through a one-pot solvothermal method with a gas-bubble-assisted Ostwald ripening process. The formation mechanism is explored by studying the reaction parameters, including the concentration of the precipitating agent, capping agent, and urea gas source for a fixed reaction temperature and time. The authors' results show that the Fe 3 O 4 nanospheres are composed of many primary nanocrystals, the sizes of which are well regulated by urea concentration. As such, the size of the spherical primary nanocrystal determines the porosity of Fe 3 O 4 nanospheres. Strong reflection loss of À49.2 dB is observed at 11.9 GHz for highly porous Fe 3 O 4 nanospheres with a thickness of 2.7 mm due to multiple scatterings in void spaces and increased dielectric loss caused by higher interfacial polarization relaxation loss in the porous structure. The authors believe that the prepared porous Fe 3 O 4 nanospheres are good candidates for electromagnetic absorption applications.

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