Spin Caloritronic Devices Research Articles

Energy-efficient synthesis and thermoelectric properties of Ni1-xCrx (x = 0.08, 0.10, and 0.17) alloys

Ni1-xCrx alloys are predominantly used as the p-leg in type E and K thermocouples and have promising applications in energy harvesting, including powering low-power devices and deep space power production. Their high electrical conductivity, long-term stability, and cost-effectiveness also make them attractive for spin caloritronic devices due to the modification of the density of states at the Fermi level by Cr impurities. This study introduces an energy-efficient and sustainable approach for manufacturing Ni1-xCrx alloys (with x = 0.08, 0.10, and 0.17) by incorporating KOH as a mineralizer. Nanosized Ni powders, synthesized via hydrothermal methods, are alloyed with commercial Cr powders, promoting rapid diffusion and alloy formation, followed by consolidation at 1110ºC for 6 hours in a 20 % H2 and 80 % N2 atmosphere. Compared to the traditional melting process, which typically takes over 124 hours for alloy formation, our method offers significant time savings. The Ni1-xCrx alloy with x = 0.10 exhibits the highest thermopower, achieves a maximum power factor of 4.56 μW/cm-K2 at 330 K, and exhibits reduced thermal conductivity compared to alloys produced by powder metallurgy. The dimensionless figure of merit (zT) reaches 0.029 at 330 K and 0.022 at 693 K for the Ni0.90Cr0.10 alloy, surpassing values obtained through powder metallurgy.

Giant spin caloritronic properties in spin-semiconductor graphene nanoribbons via zigzag edge extensions

In this work, we theoretically studied the spin caloritronic properties of 7-width armchair graphene nanoribbons with isolated zigzag edge extension (D-system), cove-to-zigzag edge extensions (D1-system), cove-to-cove edge extensions (D2-system), and zigzag-to-zigzag edge extensions (D3-system), respectively, by combining first-principles calculations with a non-equilibrium Green's function method. The results illustrate that the D-system and D1-system with sublattice imbalance show spin-semiconductor properties and obtain thermally induced pure spin current devoid of charge current due to the symmetric spin-up and spin-down channels around the Fermi level. Additionally, it observes substantial spin-dependent Seebeck coefficients Ssp, approximately −2.5 mV/K for the D-system and −3.0 mV/K for the D1-system, near chemical potential ±0.5 eV. More than that, the D1-system showcases a remarkable spin-dependent thermoelectric figure of merit, ZspT, at room temperature, approximately approaching 8 near the Fermi level. In contrast, the D2-system and D3-system only achieved charge-dependent thermoelectric figure of merit of about 0.5 due to the preservation of sublattice balance. Our findings provide important suggestions for designing spin caloritronic devices with high efficiency.

Significant effects of magnetic electrodes on rhenium phthalocyanine molecules

The investigation focused on examining the spin polarization and thermal spin polarization transport characteristics of dual rhenium phthalocyanine (Re2PC2) molecular junctions. This analysis was conducted using first-principles density-functional theory and the non-equilibrium Green's function approach. Calculations were performed on molecular junctions in two configurations: one at a non-magnetic electrode (Au) and the other at a magnetic electrode (Ni). A comparison of the spin transport properties of the two electrodes shows significant differences. The magnetic electrode has a notable effect on the spin-polarization and thermal spin-polarization transport properties of the devices. In contrast, the nickel electrode bis-phthalocyanine rhenium molecular device exhibits perfect spin/thermal spin-filtering efficiencies in a parallel structure. The properties of the dual phthalocyanine rhenium molecular devices were significantly affected by the nature of the electrodes. This makes dual rhenium phthalocyanine molecular junctions have great potential for the development of high-performance multifunctional spintronic and spin caloritronic devices.

Temperature Evolution of Magnon Propagation Length in Tm3Fe5O12 Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping.

The magnon propagation length, ⟨ξ⟩, of a ferro-/ferrimagnet (FM) is one of the key factors that controls the generation and propagation of thermally driven magnonic spin current in FM/heavy metal (HM) bilayer based spincaloritronic devices. For the development of a complete physical picture of thermally driven magnon transport in FM/HM bilayers over a wide temperature range, it is of utmost importance to understand the respective roles of temperature-dependent Gilbert damping (α) and effective magnetic anisotropy (Keff) in controlling the temperature evolution of ⟨ξ⟩. Here, we report a comprehensive investigation of the temperature-dependent longitudinal spin Seebeck effect (LSSE), radio frequency transverse susceptibility, and broad-band ferromagnetic resonance measurements on Tm3Fe5O12 (TmIG)/Pt bilayers grown on different substrates. We observe a significant drop in the LSSE voltage below 200 K independent of TmIG film thickness and substrate choice. This is attributed to the noticeable increases in effective magnetic anisotropy field, HKeff (∝Keff) and α that occur within the same temperature range. From the TmIG thickness dependence of the LSSE voltage, we determined the temperature dependence of ⟨ξ⟩ and highlighted its correlation with the temperature-dependent HKeff and α in TmIG/Pt bilayers, which will be beneficial for the development of rare-earth iron garnet based efficient spincaloritronic nanodevices.

Magnon dynamics in a skyrmion-textured domain wall of antiferromagnets

We theoretically investigate the interaction between magnons and a Skyrmion-textured domain wall in a two-dimensional antiferromagnet and elucidate the resultant properties of magnon transport. Using supersymmetric quantum mechanics, we solve the scattering problem of magnons on top of the domain wall and obtain the exact solutions of propagating and bound magnon modes. Then, we find their properties of reflection and refraction in the Skyrmion-textured domain wall, where magnons experience an emergent magnetic field due to its non-trivial spin texture-induced effective gauge field. Based on the obtained scattering properties of magnons and the domain wall, we show that the thermal transport decreases as the domain wall's chirality increases. Our results suggest that the thermal transport of an antiferromagnet is tunable by modulating the Skyrmion charge density of the domain wall, which might be useful for realizing electrically tunable spin caloritronic devices.

Large magnetoresistance and temperature-driven spin filter effect in spin valve based on half Heusler alloy.

High spin-injection-efficiency (SIE) and thermal spin-filter-effect (SFE) from a magnetic material to a barrier material are crucial to the high performance of a spintronic device and a spin caloritronic device, respectively. By performing a nonequilibrium Green's function combined with first-principles calculations, we study the voltage-driven and temperature-driven spin transport properties of a half Heusler alloy RuCrAs based spin valve with different atom-terminated interfaces. The spin valve with a CrAs-top (or Ru-top) interface structure has an ultrahigh equilibrium magnetoresistance (MR) ratio of ∼1.56 × 109% (or ∼5.14 × 108%), ∼100% SIE, a large MR ratio, and high spin current intensity under bias voltage, suggesting that it has a great potential application in spintronic devices. The spin valve with the CrAs-top (or CrAs-bri) interface structure has a perfect SFE due to its very high spin polarization of temperature-driven currents, and it is useful in spin caloritronic devices.

Theoretical study on spin-dependent zigzag-direction thermoelectric transport properties of Mn-doped blue phosphorene

With the increasing demand for energy, it has become imperative to investigate the thermoelectric properties that can be beneficial to directly converting heat into electric energy. Here, we theoretically study the thermoelectric transport of the Mn-doped blue phosphorene (blue-P) along the zigzag direction. We show that the spin-polarized electronic transport in the blue-P can be produced by the Mn-doping induced half-metallic energy band structure, and the Seebeck coefficients can take positive and negative values, indicating that the main carriers may be holes and electrons. Thus, the spin-down, spin, and charge Seebeck coefficients show a high peak and a deep valley, while the spin and charge thermoelectric figures of merit show two wide peaks. Moreover, the spin and charge thermoelectric figures of merit are found to be so large that the Mn-doped blue-P along the zigzag direction can be used as good thermoelectric materials. In addition, we consider the effect of the doping concentration on the electronic structure and thermoelectric transport properties. This research should be an important reference for designing spin caloritronic and thermoelectric devices.

The spin caloritronic transport properties of newly designed devices consisting of a sawtooth graphene nanoribbon and its derived five-member ring structure.

Achieving high spin polarization transport and a pure spin current is particularly desired in spintronics. We use a sawtooth graphene nanoribbon (STGNR) and its derived five-member ring structure (5-STGNR) to design new spin caloritronic devices, since they have been successfully prepared experimentally and have an interface with no lattice distortion. By using first-principle calculations combined with the non-equilibrium Green's function approach, we have studied the spin caloritronic transport properties of several STGNR-based devices, including the structures with symmetrical and asymmetrical edges, and found some excellent spin caloritronic properties, such as spin polarization, magnetoresistance and the spin Seebeck effect. By introducing a temperature difference, giant magnetoresistance and spin Seebeck effects are achieved in a heterojunction with a symmetrical edge, whereas spin polarization is more effective in a heterojunction with an asymmetrical edge. Meanwhile, the metal-semiconductor-metal junction, which is composed of STGNRs with a symmetrical edge, exhibits approximately 100% spin polarization and produces a perfect thermally induced pure spin current at room temperature. Our results indicate that the devices consisting of a sawtooth graphene nanoribbon and its derived five-member ring structure are promising novel spin caloritronic devices.

Large magnetoresistance in phosphorus-sulfur compounds (TMPS4) based temperature regulated spin-caloritronic devices

Two-dimensional (2D) transition metal phosphorus-sulfur compounds (TMPS 4 ) have attracted great theoretical and experimental attention because of their broadband modulation and high hole mobility that can be used in nanodevices. Therefore, their Curie temperature and thermal properties deserve further study for applications in electronic devices. The electromagnetic properties and spin transport properties of 2D transition metal phosphorus-sulfur compounds are systematically investigated by density functional theory (DFT) and DFT combined with the nonequilibrium Green's function method. We find that TMPS 4 materials cover almost all spin electronic behaviors, including half-metals, magnetic and nonmagnetic semiconductors, and metals. The simulation results show that the magnetic tunnel junction constructed based on TMPS 4 has a perfect thermal spin filtering effect and a negative differential resistance effect. Especially, we obtain up to 10 10 % thermal colossal magnetoresistance and almost 100% spin polarization, as well as a high current on/off ratio of ∼10 7 . Based on these results, it is proved that TMPS 4 can be a substrate material for the development of high performance for spin-caloritronic and spintronic devices.

Tuning the Thermal Spin Transport Properties via Redox Reactions and Force

Spin caloritronic devices, multifunctional devices combining spintronics and caloritronic, are crucial for the sustainable development of humans. A novel spin caloritronic device is presented using anthraquinone-based molecular sandwiched among two semi-infinite zigzag graphene nanoribbons containing asymmetrical edge hydrogenation electrodes. We demonstrate that the temperature gradient between the right and the left electrodes can generate spin-up and spin-down currents flowing in opposite orientations. Besides, the mentioned currents possess approximately the same magnitudes, indicating a nearly nondissipative spin Seebeck effect. We also find that these currents are significantly dissimilar for the redox reactions and force at different temperature gradients, demonstrating that the developed system can provide acceptable switching action. The obtained results reflect that the redox reactions and force can control the spin Seebeck effect.

Helicity-tunable spin Hall and spin Nernst effects in unconventional chiral fermion semimetals XY ( X=Co,Rh ; Y=Si,Ge )

Transition metal monosilicides CoSi, CoGe, RhSi and RhGe in the chiral cubic B20 structure have recently been found to host unconventional chiral fermions beyond spin-1/2 WFs, and also exhibit exotic physical phenomena such as long Fermi arc surface states, GME and quantized CPGE. Thus, exploring novel spin-related transports in these unconventional chiral fermion semimetals may open a new door for spintronics and spin caloritronics. In this paper, we study the intrinsic SHE and SNE in the CoSi family based on ab initio relativistic band structure calculations. First, we find that unlike nonchiral cubic metals, the CoSi family have two independent nonzero SHC (SNC) tensor elements, namely, $\sigma_{xy}^z$ and $\sigma_{xz}^y$ ($\alpha_{xy}^z$ and $\alpha_{xz}^y$) instead of one element. Furthermore, the SHC ($\sigma_{xy}^z$ and $\sigma_{xz}^y$) and helicity of the chiral structure are found to be correlated, thus enabling SHE detection of structural helicity and also chiral fermion chirality. Second, the intrinsic SHE and SNE in some of the CoSi family are large. In particular, the calculated SHC of RhGe is as large as -140 ($\hbar$/e)(S/cm). The calculated SNC of CoGe is also large, being -1.3 ($\hbar$/e)(A/m K) at room temperature. Due to their semimetallic nature with low electrical conductivity, these topological semimetals may have large spin Hall and spin Nernst angles, being comparable to that of Pt metal. The SHC and SNC of these compounds can also be increased by raising or lowering $\mu$ to, e.g., the topological nodes, via either chemical doping or electrical gating. Our findings thus indicate that the CoSi family not only would provide a material platform for exploring novel spin-transports and exotic phenomena in unconventional chiral fermion semimetals but also could be promising materials for developing better spintronic and spin caloritronic devices.

Thermal Spin Transport Properties in Diarylethene-Based Molecule Devices

Spin caloritronic devices, as multifunctional devices, combining spintronics, and caloritronics, are essential for the sustainable development of humans. Here, a novel spin caloritronic device is presented using a diarylethene molecule photoswitch sandwiched among two semi-infinite zigzag graphene nanoribbons containing asymmetrical edge hydrogenation electrodes. We demonstrate that the temperature gradient between the right and the left electrodes can generate spin-up (SU) and spin-down (SD) currents moving in opposite orientations. Moreover, the mentioned currents possess approximately the same magnitudes, indicating a nearly nondissipative spin Seebeck effect. We also find that these currents are significantly dissimilar for the two photochromic isomers at different temperature gradients, demonstrating the excellent system’s switching nature. The obtained results reveal that the light can control the thermal spin transport properties.

Deposition temperature dependence of thermo-spin and magneto-thermoelectric conversion in Co2MnGa films on Y3Fe5O12 and Gd3Ga5O12

We have characterized Co2MnGa (CMG) Heusler alloy films grown on Y3Fe5O12 (YIG) and Gd3Ga5O12 (GGG) substrates at different deposition temperatures and investigated thermo-spin and magneto-thermoelectric conversion properties by means of a lock-in thermography technique. X-ray diffraction, magnetization, and electrical transport measurements show that the deposition at high substrate temperatures induces the crystallized structures of CMG, while the resistivity of the CMG films on YIG (GGG) prepared at and above 500 °C (550 °C) becomes too high to measure the thermo-spin and magneto-thermoelectric effects due to large roughness, highlighting the difficulty of fabricating highly ordered continuous CMG films on garnet structures. Our lock-in thermography measurements show that the deposition at high substrate temperatures results in an increase in the current-induced temperature change for CMG/GGG and a decrease in that for CMG/YIG. The former indicates the enhancement of the anomalous Ettingshausen effect in CMG through crystallization. The latter can be explained by the superposition of the anomalous Ettingshausen effect and the spin Peltier effect induced by the positive (negative) charge-to-spin conversion for the amorphous (crystallized) CMG films. These results provide a hint to construct spin-caloritronic devices based on Heusler alloys.

Giant anomalous Hall and anomalous Nernst conductivities in antiperovskites and their tunability via magnetic fields

The anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC) are two prominent transport phenomena in ferromagnetic materials of a topological nature. Based on first-principles calculations, we evaluate the AHC and ANC of 35 cubic ferromagnetic antiperovskites (APVs) and observe giant AHC and ANC as large as 1128 S/cm and 6.31 ${\mathrm{AK}}^{\ensuremath{-}1}{\mathrm{m}}^{\ensuremath{-}1}$ for ${\mathrm{Co}}_{3}\mathrm{LiN}$ and ${\mathrm{Co}}_{3}\mathrm{PtN}$, respectively. Detailed analysis reveals that the origin of giant ANC can be attributed to the occurrence of Weyl nodes near the Fermi energy, as demonstrated for ${\mathrm{Co}}_{3}\mathrm{PtN}$. Interestingly, both the magnitude and sign of AHC and ANC can be tuned by changing the magnetization $(\mathbf{M})$ directions, which could be applied to realize spin-caloritronics devices.

The Magnetic and Thermally-Induced Spin-Related Transport Features Using Germanene Nanoribbons With Zigzag and Klein Edges

The current work employs the first-principles computations and non-equilibrium Greens function to investigate the magnetic and thermally-induced spin-related transport features using germanene nanoribbons with zigzag and Klein edges (ZKGeNRs). It was demonstrated that the ZKGeNRs with various widths (N) are placed in various spin-resolved electronic states. By increasing the width parameter N from 4 to 9, the ZKGeNRs moves from an indirect-gap bipolar magnetic semiconducting state (BMS) to bipolar spin gapless semiconductor (BSGS), and finally to ferromagnetic metal (FM). Moreover, since the right and the left temperatures of the ZKGeNRs device are different, the spin-up and spin-down currents flow in reverse orientations, demonstrating the spin-dependent Seebeck effect (SDSE). Besides, the threshold temperature decreases as N increases and then disappears, while the spin currents increase as N increases. Simulation results indicated that the ZKGeNRs could be an appropriate choice for spin caloritronic devices and could be utilized in future low-power consumption applications.

Silicene Nanoribbon Based Spin-Field Effect Transistor With Spin Filtering and Spin Seebeck Effects

The present work reports the application of density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism based framework to investigate the voltage-dependent spin transport properties for a Z-shaped silicene nanoribbon (SiNR) based spin-field effect transistor (spin-FET). The structural and magnetic properties of transition metal passivated zigzag-SiNR with symmetric and asymmetric hydrogenation at other ends have been analyzed to identify the suitability of these materials as a potential source and drain electrodes for the proposed spin-FET model. The analysis reveals that the device displays an excellent spin filtering effect and oscillatory transfer characteristics in the parallel configuration (PC) mode. Also, a high drive current and I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ _{ON}$</tex-math></inline-formula> /I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ _{OFF}$</tex-math></inline-formula> ratio and both positive and negative transconductance are achieved. Additionally, the device generates a highly spin-polarized thermal current with the spin Seebeck effect and high spin filtration efficiency under the influence of temperature gradient. These findings defend that the proposed device model can be treated as multifunctional spintronic and spin caloritronic devices.

A robust spin-dependent Seebeck effect and remarkable spin thermoelectric performance in graphether nanoribbons.

The generation of spin currents is a significant issue in spintronics. A spin current can be induced by a temperature gradient in the spin-dependent Seebeck effect, which has attracted growing interest over recent years. Herein we propose spin caloritronic devices based on magnetic graphether nanoribbons and investigate the spin thermoelectric properties by first-principles calculations. Owing to the symmetrical spin-resolved transmission spectra, our devices exhibit a robust spin-dependent Seebeck effect and could generate a pure spin current. Moreover, they manifest a high spin Seebeck coefficient and a giant spin figure of merit. Our findings demonstrate that graphether-nanoribbon-based devices possess remarkable spin thermoelectric performance, and might be promising candidates for spin caloritronics.

Large Magnetoresistance in Phosphorus-Sulfur Compounds (Tmps4) Based Temperature Regulated Spin-Caloritronic Devices

Large Magnetoresistance in Phosphorus-Sulfur Compounds (Tmps4) Based Temperature Regulated Spin-Caloritronic Devices

Intrinsic magnon Nernst effect in pyrochlore iridate thin films

We theoretically study the magnon spin thermal transport using a strong coupling approach in pyrochlore iridate trilayer thin films grown along the [111] direction. As a result of the Dzyaloshinskii-Moriya interaction (DMI), the spin configuration of the ground state is an all-in/all-out ordering on neighboring tetrahedra of the pyrochlore lattice. In such a state, the system has an inversion symmetry and a Nernst-type thermal spin current response is well defined. We calculate the temperature dependence of the magnon Nernst response with respect to the magnon band topology controlled by the spin-orbit coupling parameters and observe topologically protected chiral edge modes over a range of parameters. Our study complements prior work on the magnon thermal Hall effect in thin-film pyrochlore iridates and suggests that the [111] grown thin-film pyrochlore iridates are a promising candidate for thermal spin transport and spin caloritronic devices.

Vacancy tuned thermoelectric properties and high spin filtering performance in graphene/silicene heterostructures

The main contribution of this paper is to study the spin caloritronic effects in defected graphene/silicene nanoribbon (GSNR) junctions. Each step-like GSNR is subjected to the ferromagnetic exchange and local external electric fields, and their responses are determined using the nonequilibrium Green’s function (NEGF) approach. To further study the thermoelectric (TE) properties of the GSNRs, three defect arrangements of divacancies (DVs) are also considered for a larger system, and their responses are re-evaluated. The results demonstrate that the defected GSNRs with the DVs can provide an almost perfect thermal spin filtering effect (SFE), and spin switching. A negative differential thermoelectric resistance (NDTR) effect and high spin polarization efficiency (SPE) larger than 99.99% are obtained. The system with the DV defects can show a large spin-dependent Seebeck coefficient, equal to Ss ⁓ 1.2 mV/K, which is relatively large and acceptable. Appropriate thermal and electronic properties of the GSNRs can also be obtained by tuning up the DV orientation in the device region. Accordingly, the step-like GSNRs can be employed to produce high efficiency spin caloritronic devices with various features in practical applications.