Abstract
Track-etched polymer membranes with crossed nanochannels have been revealed to be most suitable as templates to produce large surface area and mechanically stable 3D interconnected nanowire (NW) networks by electrodeposition. Geometrically controlled NW superstructures made of NiCo ferromagnetic alloys exhibit appealing magnetoresistive properties. The combination of exact alloy compositions with the spatial arrangement of NWs in the 3D network is decisive to obtain specific magnetic and magneto-transport behavior. A proposed simple model based on topological aspects of the 3D NW networks is used to accurately determine the anisotropic magnetoresistance ratios. Despite of their complex topology, the microstructure of Co-rich NiCo NW networks display mixed fcc-hcp phases with the c-axis of the hcp phase oriented perpendicular to their axis. These interconnected NW networks have high potential as reliable and stable magnetic field sensors.
Highlights
The particular architectures and high degree of nanowire (NW) interconnectivity of three-dimensional (3D) NW networks make them attractive nanodevice components for a wide range of applications in energy harvesting/storage systems [1,2,3], electronic sensing devices and actuators [4,5,6], catalysts [7], electrochromic elements [8], solar cells [9], biosensors [10], and bio-analytical devices [11, 12]
As seen from the comparison between the hysteresis loops in the IP and OOP directions shown in Fig. 2a, the easy axis of magnetization for the Ni crossed nanowires (CNWs) network lies in the OOP direction; the magnetic behavior of the 3D networks in Fig. 2b–d become more isotropic as the Co content in the alloy progressively increases to the full Co CNW network
For Ni32Co68 CNWs, two peaks related to the hcp (100) and hcp (101) planes are found (JCPDS 05-0727), as shown in Fig. 3a, indicating that a mixture of the fcc and hcp phases are present in Co-rich NiCo CNWs, in agreement with the binary phase diagram of Co-Ni alloys showing a mixed hcp and fcc region between about 65 and 100 % Co, as previously observed in electrodeposited thin films [25,26,27] and nanowires [28, 29]
Summary
The particular architectures and high degree of nanowire (NW) interconnectivity of three-dimensional (3D) NW networks make them attractive nanodevice components for a wide range of applications in energy harvesting/storage systems [1,2,3], electronic sensing devices and actuators [4,5,6], catalysts [7], electrochromic elements [8], solar cells [9], biosensors [10], and bio-analytical devices [11, 12]. Template-assisted synthesis has proven to be a versatile bottom-up approach for low-cost, reliable, and largescale fabrication of 3D NW networks with controlled size, geometry, composition, and surface morphology These 3D NW networks are obtained by simple electrochemical deposition within the hierarchical nanopores of a suitable template. Among the various 3D nanoporous templates used for this purpose, track-etched polymeric membranes [7, 13] is the most promising as dense networks of crossed cylindrical nanopores can be obtained through sequential polycarbonate (PC) film irradiation with energetic heavy ions at different incidence angles, followed by selective chemical etching of the ion tracks within the polymer film [15] This template-assisted synthesis enables excellent control over the geometry, chemical composition, and nanoarchitectures that can be the framework for nanoscale devices and systems. In order to precisely determine the anisotropic magnetoresistance ratio of NiCo CNW networks from simple magneto-transport measurements, we propose a model that considers the spatial arrangement of NWs in the 3D network
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