  Macroscopic-scale nanostructures, situated at the interface of nanostructures
and bulk materials, hold significant promise in the realm of thermoelectric
materials. Nanostructuring presents a compelling avenue for enhancing material
thermoelectric performance as well as unlocking intriguing nanoscale phenomena,
including spin-dependent thermoelectric effects. This is achieved while
preserving high power output capabilities and ease of measurements related to
the overall macroscopic dimensions. Within this framework, the recently
developed three-dimensional interconnected nanowire and nanotube networks,
integrated into a flexible polymer membrane, emerge as promising candidates for
macroscopic nanostructures. The flexibility of these composites also paves the
way for advances in the burgeoning field of flexible thermoelectrics. In this
study, we demonstrate that the three-dimensional nanowire networks made of
ferromagnetic metals maintain the intrinsic bulk thermoelectric power of their
bulk constituent even for a diameter reduced to approximately 23 nm.
Furthermore, we showcase the pioneering magneto-thermoelectric measurements of
three-dimensional interconnected nickel nanotube networks. These macroscopic
materials, comprising interconnected nanotubes, enable the development of
large-area devices that exhibit efficient thermoelectric performance, while
their nanoscale tubular structures provide distinctive magneto-transport
properties. This research represents a significant step toward harnessing the
potential of macroscopic nanostructured materials in the field of
thermoelectrics.
