Abstract
A comparative study of the magnetic properties of the arrays of Co nanowires and nanotubes with large external diameters (180 nm) has been carried out. The nanowires/nanotubes were grown by electrodeposition into the self-assembled pores of anodic alumina membranes. The experimental study of their magnetic behavior was focused on the angular dependence of hysteresis loops and their parameters. In both nanowire and nanotube arrays, from the analysis of experimental data, effective longitudinal magnetic anisotropy is concluded, which is stronger in the case of the nanotube array. In addition, the extremely small remanence observed for all loops indicates the important role played by magnetostatic interactions. Micromagnetic simulations were first performed considering intrinsic shape and magnetocrystalline anisotropy terms, together with an effective easy-plane anisotropy to account for those magnetostatic interactions. A qualitative agreement between experiments and simulations is found despite the complexity introduced by the intrinsic and extrinsic array properties (i.e., large diameters, grain structure, and array configuration). In addition, simulations were also carried out for individual nanowire/nanotube with a particular emphasis to understand their differences at the remanence, due to pure geometry contribution.
Highlights
Cylindrical magnetic nanowires (NWs) and nanotubes are technologically promising and important nanostructures that are relevant for several applications: 3D magnetic recording, optoelectronics, sensors, actuators, spintronics, logical devices, permanent magnets, barcode nanostructures catalysis, and bio and environmentally friendly applications [1,2,3,4,5,6,7,8,9,10,11,12,13]
Regarding the theoretical description on individual nanowires, the high uniaxial magnetocrystalline anisotropy of the hcp phase in competition with the shape anisotropy leads to a strong dependence of the coercive field and remanence on the easy axis orientation [21] and on the particular granular structure in Co based nanowires [22]
Hysteresis loops for all intermediate directions show that nanowire and nanotube arrays are harder to magnetize in those directions than in parallel-applied fields
Summary
Cylindrical magnetic nanowires (NWs) and nanotubes are technologically promising and important nanostructures that are relevant for several applications: 3D magnetic recording, optoelectronics, sensors, actuators, spintronics (i.e., spin valves, magnetic tunnel junctions), logical devices, permanent magnets, barcode nanostructures catalysis, and bio and environmentally friendly applications (such as water purification or hyperthermia) [1,2,3,4,5,6,7,8,9,10,11,12,13]. Regarding the theoretical description on individual nanowires, the high uniaxial magnetocrystalline anisotropy of the hcp phase in competition with the shape anisotropy leads to a strong dependence of the coercive field and remanence on the easy axis orientation [21] and on the particular granular structure in Co based nanowires [22].
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