Transport and magnetic properties of encapsulated Ni-NiO/ZrO/sub 2/ nanostructures

Nanoparticles of Ni encapsulated with either NiO or ZrO/sub 2/ are prepared by aqueous solution and their transport and magnetic properties are studied in detail. The encapsulated Ni particles are prepared by the simultaneous reduction of Ni-chloride and Zr-oxychloride using sodium borohydride as the reducing agent. The precursor solution has the following composition: 1M NiCl/sub 2/: x M ZrOCl/sub 2/ where x varies from 0 to 0.5 and M is the molar concentration. Results from X-ray diffraction pattern show that addition of ZrO/sub 2/ makes the Ni crystalline peaks strong and the amorphous NiO peak becomes weak indicating that ZrO/sub 2/ stabilizes Ni formation and also protects Ni from getting oxidized. XRD patterns and TEM reveal that Ni crystallites are /spl ap/ 20-40 nm in size. The electrical resistivity decreases first and then increases with the addition of ZrO/sub 2/. Also, addition of ZrO/sub 2/ promotes Ni formation by reducing the NiO shell initially leading to better interparticle connectivity while for x /spl ges/ 0.10 M the interparticle connectivity is reduced due to ZrO/sub 2/ encapsulation. Room temperature saturation magnetization increases with addition of ZrO/sub 2/ up to /spl ap/0.05 M and then decreases. The temperature dependent magnetization however shows a superparamagnetic behavior with the blocking temperature T/sub B/ being close to room temperature. The encapsulated Ni particles exhibit remanence and the coercivity field is found to be /spl ap/ 480 Oe.