Large Spin-Dependent Thermoelectric Effects in NiFe-based Interconnected Nanowire Networks

Abstract

NiFe alloy and NiFe/Cu multilayered nanowire (NW) networks were grown using a template-assisted electrochemical synthesis method. The NiFe alloy NW networks exhibit large thermopower, which is largely preserved in the current perpendicular-to-plane geometry of the multilayered NW structure. Giant magneto-thermopower (MTP) effects have been demonstrated in multilayered NiFe/Cu NWs with a value of 25% at 300 K and reaching 60% around 100 K. A large spin-dependent Seebeck coefficient of –12.3 μV/K was obtained at room temperature. The large MTP effects demonstrate a magnetic approach to control thermoelectric properties of flexible devices based on NW networks.

Magnetic Nanowires

“…Despite their complex nano-architecture, interconnected NW networks made of Co/Cu, CoNi/Cu and Py/Cu multilayers were found to exhibit very large CPP-GMR responses reaching values of 40% at RT and 86% at T = 15 K for CoNi/Cu [64]. The same features were observed on the Co/Cu and Py/Cu CNW samples [65,67], as shown in Figure 10a-c.…”

“…Next, the template-assisted electrodeposition method was used for the synthesis of well-defined 3D architecture consisting of crossed nanowire (CNW) and nanotube (CNT) networks [60][61][62][63]66]. In addition, magnetic and non-magnetic layers were electrochemically stacked to make interconnected multilayered nanowires [64,65,67]. Figure 4 illustrates the various 3D nanofiber architectures which have so far been investigated.…”

“…In addition, since the geometrical features of the crossed core(Cu)/shell(Ni) nanocables can be carefully modified via the control over the reduction or deposition potential, Ni CNT networks with different wall thickness in the range 10-50 nm were obtained after carrying out the dealloying step of the Cu core [63]. In addition, CNWs with multilayer structure of FM/Cu, with FM = Co, CoNi and NiFe alloys were fabricated in the host 3D porous templates [64,65,67]. Interestingly, this fabrication method appears as a very convenient approach for large scale production of current-perpendicular to-plane (CPP) giant magnetoresistance (GMR) films based on CNW networks, as shown in Sections 3.3 and 3.5.…”

“…The research activity at UCLouvain on magnetic NWs were also motivated by related applications in microwave devices [46][47][48][49][50][51][52][53][54] and multiferroic nanocomposites [55][56][57][58][59]. Recently, we demonstrated the suitability of three-dimensional (3D) nanoporous polymer templates to form dense interconnected magnetic NW networks with tunable geometrical parameters in terms of nanowire size, density, and orientation opens up the possibility for a controlled synthesis of a large variety of complex 3D networks of high aspect-ratio nanostructures with different geometries and materials [60][61][62][63][64][65][66][67]. Their unique architectures and high degree of nanowire interconnectivity facilitate the ability to perform magneto-transport measurements and to investigate the interplay between electronic and thermoelectric transport and magnetic properties.…”

“…(a) CPP-GMR versus magnetic field applied in the plane of the crossed NW networks at T = 15 K and T = 300 K for (a) Co/Cu, (b) CoNi/Cu and (c) Py/Cu multilayered nanowires (adapted from[64,65,67]). Figure adapted from ref [65].…”