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Preparation, Magnetic Studies and Band Structure Calculation of NiFe2O4 Nanoparticles

Nabiyouni G., Fesharaki M., Zolotovsky A.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

2011

Vol. 15, No 1

107-119

We have undertaken a comprehensive theoretical study of the band structure, density of states, dependence of the Curie point and saturation magnetization on the size of NiFe2O4 nanoparticles prepared by the conventional ceramic method. Commercially available NiFe2O4 powder was first annealed in an oxygen environment in a furnace at 1100oC for 3h. The X-ray diffraction pattern indicated that the sample was single-phase at this stage. The average grain size estimated by scanning electron microscopy (SEM) was in the range of 300 to 350nm. The magnetic behavior of the sample at room temperature was studied by means of a superconducting quantum interference device (SQUID). The Curie temperature of the nickel ferrite powder was measured using an LCR meter. The measurement of the Curie temperature and saturation magnetization indicated that a decrease in the grain size leads to a decrease in the Curie temperature and in the saturation magnetization. The small value of saturation magnetization was attributed to a spin-glass-like surface layer on the nanocrystalline nickel ferrite with a ferrimagnetically aligned core (H.Nathani and S.Gubbala 2004 J.Mater. Sci. and Engin. B 111 95). Good agreement was obtained between theory and experimental results.

Giant magnetoresiscance in spintronic Co/Pt nanowire structures

Nabiyouni G.

Metrology and Measurement Systems

2008

Vol. 15, nr 2

135-143

We used electrodeposition for growing of pure metallic, alloy and multilayer nanowires. Electrodeposition of cobalt/platinum nanowires was achieved in the cylindrical pores of a commercially available nuclear tracked polycarbonate membrane. In order to make an ohmic contact, prior to electrodeposition one side (the back one) of the membranes was coated with gold, using a simple evaporation technique. An assembly of nanowires with an average diameter of 80 nm and a length of 6 microns was achieved. Our multilayer nanowires were grown from an electrolyte containing Co2+ and Pt2+ ions. The samples were then characterized using scanning and transmission electron microscopy. The selected area diffraction patterns of the wires showed that the growth is polycrystalline, though the measured grain size was relatively large [1]. Magnetic properties of the nanowires were studied using vibrating sample magnetometry (VSM). Resistivity of the Co/Pt multilayer nanowires then was measured as a function of applied magnetic field in both parallel and perpendicular to the nanowire growth directions. The samples clearly exhibit a giant magnetoresistance (GMR) effect which can be explained in terms of spin-dependent scattering phenomena. The results are of particular interest since they promise potential devices for nano-magnetic sensors, especially devices based on spintronic materials [2, 3, 4].