Magnetic interactions and reversal mechanisms in Co nanowire and nanotube arrays

Abstract

Ordered hexagonal arrays of Co nanowires (NWs) and nanotubes (NTs), with diameters between 40 and 65 nm, were prepared by potentiostatic electrodeposition into suitably modified nanoporous alumina templates. The geometrical parameters of the NW/NT arrays were tuned by the pore etching process and deposition conditions. The magnetic interactions between NWs/NTs with different diameters were studied using first-order reversal curves (FORCs). From a quantitative analysis of the FORC measurements, we are able to obtain the profiles of the magnetic interactions and the coercive field distributions. In both NW and NT arrays, the magnetic interactions were found to increase with the diameter of the NWs/NTs, exhibiting higher values for NW arrays. A comparative study of the magnetization reversal processes was also performed by analyzing the angular dependence of the coercivity and correlating the experimental data with theoretical calculations based on a simple analytical model. The magnetization in the NW arrays is found to reverse by the nucleation and propagation of a transverse-like domain wall; on the other hand, for the NT arrays a non-monotonic behavior occurs above a diameter of $50 nm, revealing a transition between the vortex and transverse reversal modes. V C 2013 American Institute of Physics. [http://dx

Magnetic Force Microscopy Characterization of Magnetic Nanowires and Nanotubes

“…It was shown that, thanks to their hollow structure, NTs present lower magnetic interactions compared with the same diameter and same density NWs [9,45,49]. It was further indicated that the physical reason of low exchange energy in NTs was the absence of curling related vortices which are present in other magnetic structures.…”

“…Nevertheless, the structural, magnetic, and magnetization Switching field distribution of the medium before and after magnetostatic field correction. Reprinted with permission from [36] reversal properties of ferromagnetic NTs were investigated experimentally as a function of their geometrical parameters by other magnetometry techniques [9,15,25,45,46,50,65]. In multisegmented nanocylinders, with alternating magnetic wires and tubes segments, it was shown that the NT segments switch their magnetization before the NWs resulting in a trapped domain wall between the two segments [51].…”

“…Furthermore, there is an increasing demand for new types of materials with different structures and improved physical properties to be used in miniaturized devices. This has led, along with other conceivable candidates, to the production of magnetic NWs and NTs because of their unique magnetic properties and potential technological applications in, for instance, microwave devices [2][3][4], chemical sensors [5,6], high-density data storage [7][8][9], and light emitters [10][11][12]. Magnetic NWs and NTs are attractive in physics, but they also got an enormous attraction in biological and biomedical applications [13][14][15][16].…”

Electrochemical methods for template-assisted synthesis of nanostructured materials

“…Nanoporous anodic Al 2 O 3 films, obtained by the simple and inexpensive technique for two-step anodization of high-purity Al substrates (Masuda and Fukuda, 1995;Masuda and Satoh, 1996), have attracted huge interest and have been used as templates for the synthesis of a wide range of nanomaterials (Eftekhari, 2008;Lupu, 2010;Nalwa, 2011), including ordered arrays of magnetic nanowires Vázquez et al, 2005;Prida et al, 2007;Klammer et al, 2010), nanoparticles (Gultepe et al, 2007;Badini et al, 2011), nanotubes (Imai et al, 1999;Daub et al, 2007;Zierold et al, 2011;Proença et al, 2013) arrays of antidots (Masuda and Fukuda, 1995;Vázquez et al, 2008;López-Antón et al, 2009;Béron et al, 2011;Merazzo et al, 2012). Anodization of Al consists of the anodic oxidation of an Al electrode under wellcontrolled electrochemical conditions.…”

Temperature dependence of the training effect in electrodeposited Co/CoO nanotubes

“…The opening of the pores was performed by floating the sample in phosphoric acid, which led to a small enlargement of the final pore diameter to $40 nm. 28 For the subsequent potentiostatic electrodeposition of Co NTs inside the pores, an Au metallic contact of $50 nm was sputtered at the pores' opened ends to serve as the working electrode during deposition. 29 A Pt mesh and Ag/AgCl (in 4 M KCl) were used as counter and reference electrodes, respectively.…”