Development of Novel Magnetic Metal Oxide Thin Films and Carbon Nanotube Materials for Potential Device Applications

Earlier we reported exchange coupling between bilayers of CoFe2O4/CoFe2, where CoFe2O4 and CoFe2 are the hard and soft magnetic layers, respectively. These results suggested that trilayers structures of CoFe2O4/CoFe2/CoFe2O4 are strong candidates for low hysteresisloss spin spring materials. To study this possibility, we extended our investigation to the synthesis of CoFe2O4/CoFe2/CoFe2O4 tri-layers under different sputtering deposition conditions, which included oxygen pressure in the case of the CoFe2O4 component and the application of a magnetic field during the deposition of the soft CoFe2. The most significant finding was the blocking field increased more than 30 by the application of an applied field during deposition of the soft CoFe2, resulting in a decrease in hysteretic losses by a similar percentage. The discussion of spin spring results is in terms of an increase in uniaxial anisotropy energy in the CoFe2 layers due to short range ordering of Fe-Fe and Co-Co pairs during deposition. We also report on the results of fabrication and measurement of uniaxial iron-filled multi-wall carbon nanotubes. These nanowires required four times higher applied magnetic field (1500 Oe) to reach saturation compared to planar nanometer thin films of Fe on MgO(100) that reached saturation at around 380 Oe. The results show that Fe nanowires exhibited a two-fold magnetic symmetry.