Magnetismo de nanofios de cobalto e níquel fabricados por eletrodeposição em alumina anódica porosa

Abstract

In this thesis were investigated the magnetic properties of magnetic nanowire arrays of Co and Ni electrodeposited in porous anodic alumina templates. The electrochemical method was employed in the manufacturing steps of templates and growth of nanowires. For the templates, the potentiostatic two step anodization process with gradual reduction of potential at the end of process was employed. The templates presented good regularity, and conductor channels at the pore bottom (dendritic region). The growth of Co and Ni nanowires in porous templates was performed by galvanostatic pulsed eletrodeposition. The samples were characterized morphologically and structurally by scanning electron microscopy and X-ray diffraction, respectivelly. For the sample with Co nanowires we obtained nanowires with 65 nm in diameter and 6 μm in length, with hcp hexagonal structure type. For Ni nanowires, samples with 65 nm and 80 nm of diameter and 6μm in length were obtained, presenting an fcc cubic structure type. The magnetic characterization was performed by vibrating sample magnetometry - SQUID, which were performed magnetic moment measurements as a function of magnetic field, temperature and the angle between the applied magnetic field and the main axis of the nanowires. The results showed the directions of easy magnetization axis, the contributions of different types of magnetic anisotropy and influences related to the morphology of the nanowires and the template. For Co nanowires, the shape anisotropy is the most relevant and the easy axis of magnetization is in the direction of the main axis of the nanowires. For the two samples with Ni nanowires, were determined 15º and 26º angles as the respective directions of magnetization easy axis. The effect of magnetoelastic anisotropy is more relevant in the case of Ni nanowires. For both systems (Co and Ni) was possible to verify the importance of morphological factors, in which the diameter and average separation of the nanowires play a key role, because they are directly related to inter-nanowire magnetostatic interaction.