Spin-dependent Seebeck Effect Research Articles

Thickness dependence on dynamical spin injection driven by thermal effects in CoFeB/Pt bilayer

In ferromagnetic metal (FM)/non-magnetic metal (NM) bilayer structures, dynamical spin injection is primarily attributed to spin pumping at the interface. However, thermal effects, such as the spin (dependent) Seebeck effect (S(d)SE) caused by FMR heating effect, are also expected to contribute, particularly farther from the interface within the FM layer. In this study, the detailed mechanism of dynamical spin injection in CoFeB/Pt bilayer films has been investigated. We demonstrate the proper evaluation of the CoFeB thickness dependence of inverse spin Hall voltage by subtracting the signal from single CoFeB system. The dynamical spin injection and FMR heating effect were observed to significantly depend on thickness. Additionally, we separated the contributions of SSE and SdSE by focusing on their diffusion properties and found that SSE is larger than SdSE in the CoFeB/Pt bilayer film.

Excellent spin diode and spin-dependent Seebeck effects in hetero-junctions based on ferromagnetic Cr3M4 (M = Se, Te)

Ferromagnetic (FM) half-metals have been regarded as the most promising candidates for spin injection into semiconductors due to their completely spin-polarized electronic states around the Fermi level. To explore the potential application of Cr3M4 (M = Se, Te) in spintronic devices, which are experimentally synthesized FM bulks as well as half-metallic monolayers with high Curie temperature, we propose to design a Bi2Se3/Cr3Se4 van der Waals hetero-junction and a 2D Cr3S4/Cr3Te4 hetero-junction motivated by the recent report on controlling synthesis of Cr x M y based heterostructures. First-principles calculations combined with non-equilibrium Green’s function uncover the perfect spin filtering and spin diode effect in Bi2Se3/Cr3Se4 van der Waals hetero-junction. More interestingly, the Cr3S4/Cr3Te4 hetero-junction shows an excellent spin-dependent Seebeck effect, in which spin-dependent currents with opposite spin orientation can be driven by a temperature gradient to flow in the opposite transport direction. These effects can be understood from the calculated spin-dependent band structures and transmission spectrum. Our results put forward a promising designing and application of spintronic devices based on Cr3M4 (M = Se, Te) FM materials.

Magnetoresistance and spin-dependent Seebeck effects in phthalocyanine-based molecular junctions with borophene electrodes

Magnetoresistance and spin-dependent Seebeck effects in phthalocyanine-based molecular junctions with borophene electrodes

Ab initio calculation of thermoelectric properties in 3d ferromagnets based on spin-dependent electron–phonon coupling

Crossed magneto-thermo-electric coefficients are central to novel sensors and spin(calori)tronic devices. Within the framework of Boltzmann’s transport theory, we calculate the resistivity and Seebeck coefficients of the most common 3d ferromagnetic metals: Fe, Co, and Ni. We use a fully first-principles variational approach, explicitly taking electron-phonon scattering into account. The electronic band structures, phonon dispersion curves, phonon linewidths, and transport spectral functions are reported, comparing with experimental data. Successive levels of approximation are discussed: constant relaxation time approximation, scattering for a non-magnetic configuration, then spin polarized calculations with and without spin–orbit coupling (enabling spin-flips). Spin polarization and explicit electron–phonon coupling are found to be necessary to reach a correct qualitative picture: the effect of spin flipping is substantial for resistivity and very delicate for the Seebeck coefficient. The spin-dependent Seebeck effect is also predicted.

Giant spin-dependent Seebeck effect from fully spin-polarized carriers in n-doped EuTiO3: a prototype material for spin-caloritronic applications

Left: up-spin μ↑ and down-spin μ↓ chemical potentials generated by a T gradient across a magnetic metal. Right: spin voltage Vs = (μ↑ − μ↓)/e at the two sides of the sample. Blue, green and red curves are for T = 10 K, 100 K, and 300 K.

Inducing magnetism in thermoelectric half-Heusler alloy NbCoSb through doping of Co/Mn metal for spin-caloritronics applications

Recent progress in spin caloritronics has boosted exploration of materials for their application in this novel field. Heusler alloys which were being hailed as thermoelectric and magnetic materials have seen uprise for their suitable properties however lack of studies featuring good coupling between magnetic and thermoelectric properties have seen little impact in the field of spin-caloritronics. Present work explored doping of transition metal in a thermoelectric half-Heusler alloys NbCoSb on Nb site to induce spin-polarization and spin-dependent transport properties. Co (Mn) doping results in 98.09% (19.38%) negative spin polarization and 0.51 μB/f.u. (1.98 μB/f.u.) magnetic moment. Magnetic exchange parameter shows presence of long range RKKY-type interaction in Co and Mn doped NbCoSb. On one-hand, doping of Co and Mn in NbCoSb suppressed the electronic transport properties whereas, on the other hand spin dependent Seebeck effect is introduced. The synergistic effect of magnetic and thermoelectric properties in non-magnetic NbCoSb via doping of Mn and Co shows large variation in the value of Seebeck coefficient, electrical conductivity and electronic thermal conductivity with flipping of spin-directions suggests Co rich NbCoSb as a promising candidate for spin-caloritronics application.

Magnetic and Thermospin Transport Properties of Triangular Graphene-Flake-Doped Boron Nitride Nanotubes

Magnetic nanotubes are a new material platform to realize the spin-dependent Seebeck effect (SDSE) and thermal spin-filtering effect (TSFE) in spin caloritronics. Here, we designed several magnetic nanotubes using triangular graphene-flake-doped boron nitride nanotubes (GFBNNTs) and found that the band structure of these GFBNNTs can be effectively engineered by embedding graphene flakes (GFs) of different sizes. The magnetic boron nitride nanotubes (BNNTs) ((5, 5)-6N) generate a good SDSE with nearly symmetric spin-up and spin-down currents, while the magnetic BNNTs ((10, 0)-6N) generate a good TSFE. These theoretical results about the SDSE and TSFE in nanotubes enrich the spin caloritronics and suggest material candidates to realize the SDSE and other inspiring thermospin phenomena.

Computational Study of Metal-Free Magnetism and Spin-Dependent Seebeck Effect in Silicene Nanoribbons with Zigzag and Klein Edges

Nanoribbons based on low-dimensional materials are potential candidates for nanoscale spintronics devices. Here, some ferromagnetic silicene nanoribbons with zigzag and Klein edges (N-ZKSiNRs) are constructed. It is demonstrated that the N-ZKSiNRs with various widths (N) are placed in various spin-resolved electronic situations. With the increase of the width parameter N from 4 to 19, the N-ZKSiNRs pass from the indirect-gap bipolar magnetic semiconducting state (BMS) to the bipolar spin-gapless semiconductor (BSGS) and eventually to half-metallicity (HM). Moreover, applying a temperature gradient through the nanoribbons leads to spin-dependent current with the opposite flowing and spin orientations, demonstrating the spin-dependent Seebeck effect (SDSE). Besides, it was found that the BSGS phase is superior to the BMS and HM for generating SDSE. These findings confirm that the ZKSiNRs are promising choices for 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.

Magnetoresistance and Spin-Dependent Seebeck Effects in Phthalocyanine-Based Molecular Junctions with Borophene Electrodes

Magnetoresistance and Spin-Dependent Seebeck Effects in Phthalocyanine-Based Molecular Junctions with Borophene Electrodes

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.

Perfect spin filtering effect, tunnel magnetoresistance and thermoelectric effect in metals-adsorbed blue phosphorene nanoribbons

The thermoelectric transport properties of Fe- and Ti-adsorbed blue phosphorene nanoribbons are studied using the first principles approach. The research indicates that Fe- and Ti-adsorbed blue phosphorene nanoribbons exhibit spin-dependent Seebeck effect. The devices based on the Fe-adsorbed blue phosphorene nanoribbons show perfect spin filtering effect caused by 100% spin polarization and 106% tunnel magnetoresistance. The spin-up current and the spin-down current are reversed in Ti-adsorbed blue phosphorene nanoribbons, indicating that a large spin current and a small charge current can be generated. These systems also exhibit negative differential resistance induced by the current-voltage curve. The band structures and transport spectrums are utilized to explain the physical mechanism of spin current generation. Metals-adsorbed blue phosphorene nanoribbons can be considered novel thermoelectric materials and used to make multifunctional thermal spintronic devices.

Temperature profile of nanospintronic device analyzed by spin-dependent Seebeck effect

The heat transport in a laterally configured nano-spintronic device, including a magnetic multi-layered nanowire has been investigated by detecting the second harmonic voltages. We show that the magnetic-field dependence of the second harmonic voltage in the multi-layered wire shows a clear spin-valve-like effect with the magnitude larger than the electrical spin valve effect. The second harmonic signal with its probe configuration dependence is found to be quantitatively explained by the spin-dependent Seebeck effect with a significant heat flow from the substrate. This demonstration paves the way for the precise analysis of the heat flow in nano-structured electronic devices.

Thermal Spin Torque in Double-Barrier Tunnel Junctions with Magnetic Insulators

The thermal spin torque induced by the spin-dependent Seebeck effect in double-barrier tunnel junctions is derived considering free-electron and tight-binding calculations. We show that in systems comprising ferromagnetic electrodes and nonmagnetic barriers, the in-plane component of the thermal spin torque is the dominant term, whereas in junctions comprising nonmagnetic electrodes and ferromagnetic barriers, both components, the in-plane and the out-of-plane, are comparable in magnitude. Moreover, larger torque amplitudes up to 3 orders of magnitude are obtained in the second system as a result of the spin-filtering effect; consequently, double-barrier tunnel junctions in the presence of magnetic insulators offer an enhanced thermal spin-torque mechanism for reliable applications. We propose taking advantage of quantum resonant tunneling through resonance states below the Fermi level in these structures that can pave a route toward achieving larger spin-torque efficiencies, even when considering smaller values of the exchange splitting. Furthermore, we identify the parameters needed to tune efficiently these resonant states.

Electrical and thermal generation of spin currents by magnetic bilayer graphene.

Ultracompact spintronic devices greatly benefit from the implementation of two-dimensional materials that provide large spin polarization of charge current together with long-distance transfer of spin information. Here spin-transport measurements in bilayer graphene evidence a strong spin-charge coupling due to a large induced exchange interaction by the proximity of an interlayer antiferromagnet (CrSBr). This results in the direct detection of the spin polarization of conductivity (up to 14%) and a spin-dependent Seebeck effect in the magnetic graphene. The efficient electrical and thermal spin-current generation is the most technologically relevant aspect of magnetism in graphene, controlled here by the antiferromagnetic dynamics of CrSBr. The high sensitivity of spin transport in graphene to the magnetization of the outermost layer of the adjacent antiferromagnet, furthermore, enables the read-out of a single magnetic sublattice. The combination of gate-tunable spin-dependent conductivity and Seebeck coefficient with long-distance spin transport in a single two-dimensional material promises ultrathin magnetic memory and sensory devices based on magnetic graphene.

Generic Seebeck effect from spin entropy

How magnetism affects the Seebeck effect is an important issue of wide concern in the thermoelectric community but remains elusive. Based on a thermodynamic analysis of spin degrees of freedom on varied d-electron-based ferromagnets and antiferromagnets, we demonstrate that in itinerant or partially itinerant magnetic compounds there exists a generic spin contribution to the Seebeck effect over an extended temperature range from slightly below to well above the magnetic transition temperature. This contribution is interpreted as resulting from transport spin entropy of (partially) delocalized conducting d electrons with strong thermal spin fluctuations, even semiquantitatively in a single-band case, in addition to the conventional diffusion part arising from their kinetic degrees of freedom. As a highly generic effect, the spin-dependent Seebeck effect might pave a feasible way toward efficient “magnetic thermoelectrics.”

Pure thermal spin current and perfect spin-filtering with negative differential thermoelectric resistance induced by proximity effect in graphene/silicene junctions

The spin-dependent Seebeck effect (SDSE) and thermal spin-filtering effect (SFE) are now considered as the essential aspects of the spin caloritronics, which can efficiently explore the relationships between the spin and heat transport in the materials. However, there is still a challenge to get a thermally-induced spin current with no thermal electron current. This paper aims to numerically investigate the spin-dependent transport properties in hybrid graphene/silicene nanoribbons (GSNRs), using the nonequilibrium Green’s function method. The effects of temperature gradient between the left and right leads, the ferromagnetic exchange field, and the local external electric fields are also included. The results showed that the spin-up and spin-down currents are produced and flow in opposite directions with almost equal magnitudes. This evidently shows that the carrier transport is dominated by the thermal spin current, whereas the thermal electron current is almost disappeared. A pure thermal spin current with the finite threshold temperatures can be obtained by modulating the temperature, and a negative differential thermoelectric resistance is obtained for the thermal electron current. A nearly zero charge thermopower is also obtained, which further demonstrates the emergence of the SDSE. The response of the hybrid system is then varied by changing the magnitudes of the ferromagnetic exchange field and local external electric fields. Thus, a nearly perfect SFE can be observed at room temperature, whereas the spin polarization efficiency is reached up to 99%. It is believed that the results obtained from this study can be useful to well understand the inspiring thermospin phenomena, and to enhance the spin caloritronics material with lower energy consumption.

Generation of pure spin current in graphene nanoribbons with continous antidots

Spin caloritronics, which combines the characteristics of thermoelectronics with the characteristics of spintronics, has a wide range of promising applications in high-speed and low-dissipation devices. In this paper, according to the density functional theory combined with nonequilibrium Green’s function method, we propose a scheme for generating pure spin current with spin dependent Seebeck effect in the zigzag-edged graphene nanoribbons by introducing continuous antidots (hexagonal defects). Specifically, by creating an antidot at one edge of the nanoribbon, an X-shape transmission spectrum around the Fermi level is formed, which results from the disrupted edge of the nanoribbon. The mechanism is well explained by the cooperation between the varying localization features of the eigenstates around the Fermi level for the unit cell and the scattering states at the Fermi level for the device. Therefore, the electrons of the two spin channels flow in the opposite directions under a temperature gradient, generating the spin current and charge current. By slightly tuning the chemical potential of the device, the charge current can be zero, while the spin current is not equal to zero. With the increase of adjacent antidot number along the width of the nanoribbons, the structures are more disrupted, thus promoting the pure spin current due to the increase of the spin Seebeck coefficient. However, for zigzag graphene nanoribbons with <i>W</i> zigzag carbon chains, the pure spin current decreases when the number of the antidots are more than (<i>W</i>/2–1), which results from the decrease of the spin conductance. So, the maximum pure spin current can be obtained when the number of the continuous antidots introduced along the width of nanoribbons reaches (<i>W</i>/2–1). These findings indicate a novel strategy for thermally generating the spin current by introducing continuous antidots along the nanoribbon bandwidth in zigzag graphene nanoribbons and will be greatly instructive in designing the graphene spintronic devices.

Bipolar Magnetic and Thermospin Transport Properties of Graphene Nanoribbons with Zigzag and Klein Edges

Magnetic nanoribbons based on one‐dimensional materials are potential candidates for spin caloritronics devices. Here, we constructed ferromagnetic graphene nanoribbons with zigzag and Klein edges (N‐ZKGNRs, N = 4–21) and found that the N‐ZKGNRs are in the indirect‐gap bipolar magnetic semiconducting state (BMS). Moreover, when a temperature difference is applied through the nanoribbons, spin‐dependent currents with opposite flow directions and opposite spin directions are generated, indicating the occurrence of the spin‐dependent Seebeck effect (SDSE). In addition, the spin‐dependent Seebeck diode effect (SDSD) also appeared in these devices. More importantly, we found that the BMS with a larger bandgap is promising for generating the SDSD, while the BMS with a smaller bandgap is promising for generating the SDSE. These findings show that ZKGNRs are promising candidates for spin caloritronics devices.

Spin-dependent seebeck effect and pure spin current in ferromagnetic fluorinated boron nitride nanotubes

Based on the density functional theory combined with non-equilibrium Green's function formalism, we investigate the electronic structure and spin caloritronic transport properties of ferromagnetic fluorinated boron nitride nanotubes (F-BNNTs). The results show that these systems exhibit robust half-metallic feature and obvious spin-dependent Seebeck effect . Especially, pure spin current without charge current can be realized by tuning the temperature and temperature difference or by tuning the chirality of F-BNNT. The underlying mechanism is analyzed by the Fermi-Dirac distribution function, spin-resolved transmission spectra, band structures and current spectra. These results demonstrate that the ferromagnetic F-BNNTs hold great potential for spin caloritronics and ultra-low-energy-consumption nanoelectronic devices. • Electronic structure and spin caloritronic transport properties of F-BNNTs are investigated. • F-BNNTs exhibit robust half-metallic feature and obvious Spin-dependent Seebeck effect. • Pure spin current is realized by tuning the temperature and temperature difference. • Pure spin current is realized by tuning the chirality of F-BNNT.