Abstract

In recent years, my work has focused on the study of magnetic nanostructures, ranging from the synthesis process, morphological and magnetic characterization, and even performing micromagnetic simulations. The systems I have investigated so far include ordered arrays of nanowires and nanotubes, thin films with controlled defects such as antidots and nano-domes, asymmetric nano-rings and hexagonal cobalt plates. Also, my work has focused on the study of complex nanostructures such as wire-tube nanostructures, nanostructures with wire-ring morphology and multi-segmented nanowires with different concentrations of nickel and cobalt for each segment [1-12]. Nanoparticle systems are interesting because particles with sizes below the mesoscopic scale confer new properties to the structures that are constructed with them. This occurs because the particle size is smaller than the characteristic length of a given phenomenon, thus exhibiting the particle a new behavior that is associated with its size and shape. The properties can also be adjusted by choosing a specific material, and even varying the magnetocrystalline anisotropy of the particle. Ferromagnetic materials exhibit magnetic domains which are regions where the magnetic moments point in the same direction. In general, the characteristic size of these domains is in the range of micrometers. However, it is possible to confine these domains at the nanoscale (usually with sizes smaller than 100 nm), where interesting effects occur. Particles with sizes less than 100 nanometers exhibit generally a monodomain. The magnetic behavior of these particles is very sensitive to changes in their size and geometry, thereby allowing control magnetization reversal mechanisms of these particles. In order to increase shape anisotropy in magnetic nanowires, we propose to increase the aspect ratio of nanowires decreasing their diameter. This may be possible by partially closing the nanopores of membrane (decreasing the diameter of the pores) by depositing insulators (specifically Al2O3) via atomic layer deposition. In this context, we propose to study multisegmented nanowires, with segments of different magnetic materials and/or alloys (the latter in order to control the magnetic anisotropy of each segment). In this project, we suggest using a combination of experimental techniques for growing wire-tube nanostructures within porous alumina membranes. First, it is possible to electrochemical deposition of magnetic materials within porous alumina membrane to create nanowires, followed by deposition of the same or other different material by ALD to create nanotubes of magnetic oxides into the no filled porous of the alumina membrane. Concerning nanotubes, we propose to consider the synthesis of various multilayer nanostructures, composed of metals and insulators, in order to find new phenomena, and to investigate the strong dipolar coupling between concentric nanotubes of different materials. We propose to study nano-hills synthesized ALD for thin films and multilayers (the idea is to mix magnetic with nonmagnetic films), from ultra-thin to thin films. ALD depends on the substrate that will be used, so it is important to mention that we will use metallic nanohills [78]. For this, we have synthesized a nanostructured non-magnetic metallic film replicating the hexagonal symmetry ordering of an anodized aluminum template. Moreover, magnetic measurements in a NanoMOKE system will be implemented, and it is necessary to use a non-polymeric substrate in order to take care of the sample by the laser temperature. In magnetic antidots, we propose to synthesize nanometric scale antidot arrays using focused ion beam (FIB) nanopatterning [108]. Thin films will be obtained by ALD deposition, using different magnetic materials and multilayered thin films, in order to study the magnetostatic coupling. In order to study the influence of the shape of the antidots, I propose to investigate antidots with stadium shape [109]. In this context, I expect that by varying the geometric parameters of the anti-stadia arrays, new axes of anisotropy appear that strongly influence the magnetic properties and mechanisms of magnetization reversal of these systems.