Superparamagnetic nickel particles in yttria-stabilized zirconia prepared by reduction of Pechini-derived solution.

The magnetic behavior of very fine metallic Ni (Ni) particles dispersed in a matrix of 10 % by mol (m/o) YO-stabilized ZrO (10YSZ) was examined. Specimens that nominally contained 0.1, 0.5, and 1 m/o Ni were prepared by a high-purity chemical synthesis method followed by a reduction treatment in H. A 0.5 m/o Ni specimen was also made by heating in vacuum, within a carbon environment. dc and ac susceptibility measurements revealed the presence of superparamagnetic Ni as well as Ni. A Stoner-Wohlfarth formulation was applied to determine that the average Ni particle size was between 4 and 7 nm, and this was confirmed by transmission electron microscopy. The activation energy for single-domain particle spin reversal and K, the effective anisotropy constant, were determined. K was higher for the vacuum heat treatment specimen because it contained less residual organic material, and therefore a higher density of Ni particles. It is shown that it is possible to make very fine Ni particles in YSZ via a direct conversion from Ni nitrates. [ABSTRACT FROM AUTHOR]