Thermoelectric Power Factor Enhancement by Spin‐Polarized Currents—A Nanowire Case Study

Abstract

Thermoelectric (TE) measurements have been performed on the workhorses of today's data storage devices, exhibiting either the giant or the anisotropic magnetoresistance effect (GMR and AMR). The temperature‐dependent (50–300 K) and magnetic field‐dependent (up to 1 T) TE power factor (PF) has been determined for several CoNi alloy nanowires with varying Co:Ni ratios as well as for CoNi/Cu multilayered nanowires with various Cu layer thicknesses, which are all synthesized via a template‐assisted electrodeposition process. A systematic investigation of the resistivity, as well as the Seebeck coefficient, is performed for CoNi alloy nanowires and CoNi/Cu multilayered nanowires. At room temperature, measured values of TE PFs up to 3.6 mW K−2 m−1 for AMR samples and 2.0 mW K−2 m−1 for GMR nanowires are obtained. Furthermore, the TE PF is found to increase by up to 13.1% for AMR CoNi alloy nanowires and by up to 52% for GMR CoNi/Cu samples in an external applied magnetic field. The magnetic nanowires exhibit TE PFs that are of the same order of magnitude as TE PFs of BiSbSeTe based thermoelectric materials and, additionally, give the opportunity to adjust the TE power output to changing loads and hotspots through external magnetic fields.

Spin Caloritronics in 3D Interconnected Nanowire Networks

“…Similar amplitudes have been obtained for the Co, Co Ni and NiFe alloys networks. The slightly larger MTP ratio amplitude compared to the MR ratio amplitude observed in Co Ni is also consistent with previous studies performed on NiCo alloy NWs [ 27 , 28 ]. In contrast, Figure 3 g,h reveals an enhancement of the MTP ratio up to three times larger than the corresponding MR ratio amplitude for the Ni NW network, in spite of similar field dependencies.…”

“…In contrast, the Ni NW network exhibits a MTP effect of −6% much larger than the MR ratio of ∼1.6%. This result is in good agreement with previous measurements performed on single Ni NWs and parallel arrays of Ni NWs, where MTP ratios were found up to 2.5-3 times larger than the corresponding MR ratios [27,28,45] and may be related to the spin-dependent Seebeck coefficients, S ↑ and S ↓ , of opposite sign [46]. It is interesting to note that for Ni thin films, the observed anisotropic MTP has approximately the same magnitude than the anisotropic MR (∼1.5%) [44].…”

“…The results are consistent with reported bulk Seebeck coefficients [23][24][25][26]. Moreover, the value reported for the Co 50 Ni 50 NW network is also consistent with the ones reported for parallel arrays of NiCo NWs [27,28]. The resistivity of the homogeneous NW networks were estimated assuming that the Matthiesen's rule holds for the different metallic NW networks.…”

Pseudo-monocrystalline properties of cylindrical nanowires confinedly grown by electrodeposition in nanoporous alumina templates

“…Moreover, nanostructured magnetic materials with tailored anisotropies have recently attracted the attention of many researchers due to their different magnetic, magnetomechanical, electro-optical, magneto-transport, magnetocaloric, and magnetothermopower properties. [9][10][11] In fact, under strong competition between shape and magnetocrystalline anisotropies, cylindrical nanowires can exhibit magnetic vortex domains at remanence, with promising potential for several technological applications. [12][13][14] A large variety of techniques for the synthesis of nanomaterials have been reported to date; [15][16][17][18][19] however, since most of these materials tend to crystallize with isotropic growth habits, few of these techniques allow the preparation of nanostructures with controlled anisotropic shapes.…”

Ni-Co Alloy and Multisegmented Ni/Co Nanowire Arrays Modulated in Composition: Structural Characterization and Magnetic Properties

“…This kind of 1D nanomaterial offers particular advantages due to its intrinsic high aspect ratio, peculiar microstructural characteristics, together with outstanding mechanical, electrical, magnetic, and optical properties, which enable their integration in novel energy conversion devices and data storage media, future stretchable electronic systems, sensors, and micro-nanodevices [10][11][12].…”