Abstract
Controlling functional properties of matter and combining them for engineering a functional device is, nowadays, a common direction of the scientific community. For instance, heterogeneous magnetic nanostructures can make use of different types of geometrical and compositional modulations to achieve the control of the magnetization reversal along with the nano-entities and, thus, enable the fabrication of spintronic, magnetic data storage, and sensing devices, among others. In this work, diameter-modulated FeNi nanowires are fabricated paying special effort to obtain sharp transition regions between two segments of different diameters (from about 450 nm to 120 nm), enabling precise control over the magnetic behavior of the sample. Micromagnetic simulations performed on single bi-segmented nanowires predict a double step magnetization reversal where the wide segment magnetization switches near 16 kA/m through a vortex domain wall, while at 40 kA/m the magnetization of the narrow segment is reversed through a corkscrew-like mechanism. Finally, these results are confirmed with magneto-optic Kerr effect measurements at the transition of isolated bi-segmented nanowires. Furthermore, macroscopic vibrating sample magnetometry is used to demonstrate that the magnetic decoupling of nanowire segments is the main phenomenon occurring over the entire fabricated nanowires.
Highlights
Nanoporous anodic alumina templates electrochemically engineered by anodization [1], allow the obtaining of elaborated and reproducible 3D arrangements of self-ordered nanopores with precise control on their lattice parameters, such as the pore diameter, interpore distance, pore length, and geometry
Nanowire-based thermoelectric structures have been investigated in order to achieve improved thermoelectric performance of the future generation of efficient thermoelectric devices, because the downsizing to nanoscale dimensions of these materials allows for increasing their surface to volume ratio in a controlled way and, increase the diffusive phonon scattering, which should revert into an increase of the figure of merit [22]
We report on the synthesis, morphology, and microstructure of bi-segmented FeNi alloyed nanowires geometrically modulated in diameter, together with the analysis of their magnetic properties by the vibrating sample magnetometry (VSM) technique for the bulk nanowires array, or well in the isolated nanowires by the magneto-optical Kerr effect, after releasing them from the patterned alumina substrate
Summary
Nanoporous anodic alumina templates electrochemically engineered by anodization [1], allow the obtaining of elaborated and reproducible 3D arrangements of self-ordered nanopores with precise control on their lattice parameters, such as the pore diameter, interpore distance, pore length, and geometry. Multisegmented magnetic nanowires produced by varying both the chemical composition of each segment [27,28,29,30,31,32], or more recently by properly tuning the geometrical modulation in the diameter of each nanowire segment [33,34], have been proposed as novel 3D systems of magnetic multibit memories and logical devices This peculiar assembling of building blocks made of consecutive segments with modulated composition and/or diameter for each nanowire, allows for the magnetization confinement in each nanowire segment, giving rise to arrays of nanowires with a magnetic multi-domain structure along the wire length, where the interface layer at the modulation can act as a pinning center for magnetic domain wall displacement [35]. A comparison between experimental measurements and micromagnetic simulations demonstrate the good agreement achieved among the obtained results These geometrically diameter-modulated ferromagnetic nanowires studied here can be considered as novel magnetic multidomain systems for ultrahigh-density data storage applications, in a similar way to racetrack memory devices
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