Analytical magnetostatic model for 2D arrays of interacting magnetic nanowires and nanotubes.

A fully analytical model to describe the magnetostatic properties of these 2D nanocylinder arrays (tubes and wires) is presented. The model allows calculating the components of the effective demagnetizing field as a function of the cylinder height, inner and outer diameters, and the center-to-center distance. From these components, it is possible to calculate the shape anisotropy of the cylinder, the dipolar interaction between them, and the total magnetostatic energy. The model allows performing calculations very simply, using a simple spreadsheet or open-access software such as Geogebra. This allows analyzing the effect of each geometrical parameter in the different contributions to the magnetostatic energy. Amongst the most interesting findings is that the model describes naturally the magnetization easy-axis reorientation transition induced by the dipolar interaction, for which a general phase diagram has been calculated for both tubes and wires. For the case of nanowires, our results show a very good agreement with previously published results. While for nanotubes, the model predicts that the magnetization easy-axis reorientation transition is frustrated as the tube wall thickness decreases and reaches a critical value even when the distance between tubes is reduced to its lowest possible value.

Large-scale 3-D interconnected Ni nanotube networks with controlled structural and magnetic properties.

Large-scale, electrically interconnected three-dimensional (3-D) Ni crossed nanotube networks have been fabricated using an electrochemical dealloying method within the crossed nanopores of polymer host membranes. This method paves the way for the easy and cost-effective fabrication of 3-D magnetic NT networks with precise spatial arrangement and diameter and wall thickness of 10-100 nm controlled individually. The excellent control over geometrical parameters and morphological features of the Ni crossed nanotube networks leads to tunable magnetic and magneto-transport properties. Particularly, the low field magneto-transport behavior is consistent with the expected vortex-like states formed in different segments of the nanotube scaffold, whereas nucleation of domain walls at the intersection of the nanowire segments play a dominant role in the solid crossed nanowire networks counterpart. The present 3-D networks of nanomagnets are of special interest due to their potential for memory devices, computing architectures, sensing and biomedical applications.

Artificially modified magnetic anisotropy in interconnected nanowire networks.

Interconnected or crossed magnetic nanowire networks have been fabricated by electrodeposition into a polycarbonate template with crossed cylindrical nanopores oriented ±30° with respect to the surface normal. Tailor-made nanoporous polymer membranes have been designed by performing a double energetic heavy ion irradiation with fixed incidence angles. The Ni and Ni/NiFe nanowire networks have been characterized by magnetometry as well as ferromagnetic resonance and compared with parallel nanowire arrays of the same diameter and density. The most interesting feature of these nanostructured materials is a significant reduction of the magnetic anisotropy when the external field is applied perpendicular and parallel to the plane of the sample. This effect is attributed to the relative orientation of the nanowire axes with the applied field. Moreover, the microwave transmission spectra of these nanowire networks display an asymmetric linewidth broadening, which may be interesting for the development of low-pass filters. Nanoporous templates made of well-defined nanochannel network constitute an interesting approach to fabricate materials with controlled anisotropy and microwave absorption properties that can be easily modified by adjusting the relative orientation of the nanochannels, pore sizes and material composition along the length of the nanowire.