# Magnetic Nanowires
## 4 Discussion
On the other hand, the 3D networks of magnetic nanowires and nanotubes are of special interest due to their potential for memory devices, computing architectures, sensing applications and spin caloritronics devices. Among the advantages of the interconnected nanowire architecture are its mechanically stable and self-supporting feature after chemical dissolution of the polymer membrane, as well as the ease of carrying out magneto-transport measurements. The close relationship between the magnetic and structural properties of homogeneous and multilayered nanowire networks has a direct impact on their magneto-transport behavior. The feasibility to obtain considerable magnetoresistance signals, being stable over time, in CNW networks made them very interesting structures for their use as magnetic sensors. In addition, embedded nanowire networks in porous polymer films are also perspective materials for spin caloritronics and heat management applications. So far, major experimental issues are the insufficient power generation capability in magnetic nanostructures (such as spin valve nanopillars and magnetic tunnel junctions) given the sub-micrometer lateral dimensions. The template synthesis method provides a simple and cost-effective pathway to fabricate flexible, macroscopic-scale interconnected network films made of multilayered nanowires showing giant magneto-resistance and giant magneto-thermoelectric effects. The 3D nanowire networks provide promise for flexible thermogenerators that cannot be considered with conducting polymers because of their relatively poor thermoelectric performance and with widely used inorganic thermoelectric semiconductors such as bismuth telluride-based alloys, as they are both brittle and expensive. In addition, our recent work has allowed us to demonstrate extremely large and magnetically  
Figure 17: **(a)** sketch of a microwave circulator based on an unbiased ferromagnetic nanowires array embedded in a porous anodic alumina membrane; **(b)** measured (red) and predicted (blue squares) results for a circulator based on a ferromagnetic NiFe NW array (adapted from [51]); **(c)** photograph of a substrate integrated waveguide (SIW) resonance isolator device using ferromagnetic NW grown in nanoporous alumina; **(d)** isolation, defined as the ratio expressed in dB between forward \(\mid\)S21\(\mid\)and reverse \(\mid\)S12\(\mid\) transmissions of signal (\(l=20\log_{10}(\left|S_{21}\right|/\left|S_{12}\right|)\)), predicted by Comsol simulator (dashed line) and observed experimentally (solid line) are shown; the positive value of isolation confirms that transmission is favored from port 1 to port 2 (adapted from [52]). Figure adapted from refs [51; 52] with permission of the author. modulated thermoelectric power factor up to 2-5 larger than that of (Bi2 Te3)-based alloys and at least one order of magnitude larger than those of optimized conducting polymers. Experiments performed on multilayered nanowire networks have enabled us to demonstrate the magnetic field control of Peltier cooling of macroscopic electronic components and to directly extract key material parameters for spin caloritronics such as spin-dependent Seebeck and Peltier coefficients. A practical thermoelectric cooler made of flexible and shapeable thermoelectric modules consisting of stacked nanowire network films that are connected electrically in series and thermally in parallel can be easily obtained. With this, we radically change the background of the burgeoning field of spin caloritronics and open an exciting and a promising pathway for the next generation of flexible and light weight thermoelectric devices exploiting the spin degree of freedom and the realization of magnetic thermal switch for heat management. In addition, our flexible thermoelectric films based on macroscopic 3D interconnected nanowire networks can also be used in applications for devices with low energy requirements when the supply of heat essentially is free as with waste heat. The author declares no conflict of interest.