Magnetic and Electric Characterization of Different NI Systems Comprising Cylindrical Nanowires

F. MENESES; P. G. BERCOFF

Advances in Nanotechnology

Nova Science Publishers

Lugar: Nueva York; Año: 2020; p. 219 - 278

CylindricalNi nanowires (NWs) were synthesized by template-assisted electrodeposition usingporous alumina membranes made through a two-step anodization process. Differentmorphologies of the NWs were obtained by varying the templates and electrodepositionparameters. In this chapter we review the results on the magnetic and electricproperties of different systems made up of the so-obtained Ni NWs.Themagnetic anisotropy as a function of temperature was studied in a set of three NWsarrays with different diameters and surface topographies. We found thatcoercivity HC increaseswith temperature in arrays of NWs with rough surfaces and small diameters (_ 65 nm). For thicker wires (200 nm in diameter) andrelatively smooth surfaces, HC decreases as temperature rises. The experimentallydetermined coercive fields were compared with results of micromagneticcalculations and the value of the effective magnetic anisotropy was estimatedfrom the hysteresis loops measured at different temperatures, in goodagreement. We show that the observed temperature dependence of HC does not arise from an intrinsicproperty of pure Ni alone, but also from the NWs arrays microsctructure.Aninhomogeneous Ni nanostructure (nano-brush) composed of a NWs array and a toplayer attached to it was synthesized, having each component the same Ni mass. Themagnetic properties were investigated, comparing the results of the wholestructure with those obtained for the separate parts, a single layer and a NWsarray alone. We show that it is possible to control the nano-brush magneticbehavior through the coupling of the layer and the NWs array. The nano-brushmagnetic properties are dominated by the layer, except when the applied fieldis parallel to the NWs axis, in which case the wires shape anisotropy plays adeterminant role. Magnetoelectric measurements were performed on a single NWwith diameter of 110 nm, released from the alumina template. For differentapplied magnetic fields, anon-linearbehavior of current vs. voltage was measured, suggesting the presence of conductor/semiconductorinterfaces. There is a threshold value between 100 mT and 500 mT for theapplied field, above which the system?s breakdown voltage is reduced. Asimplified model of two Schottky barriers is proposed in order to account forthe results, which agrees with the formation of a thin NiO layer on the NWsurface.