Hybrid carbon nanotube composites with two different types of fillers have attracted considerable attention for various advantages. The incorporation of micro-scale secondary fillers creates an excluded volume that leads to the increase in the electrical conductivity. By contrast, nano-scale secondary fillers shows a conflicting behavior of the decreased electrical conductivity with micro-scale secondary fillers. Although several attempts have been made in theoretical modeling of secondary-filler composites, the knowledge about how the electrical conductivity depends on the dimension of secondary fillers was not fully understood. This work aims at comprehensive understanding of the size effect of secondary particulate fillers on the electrical conductivity, via the combination of Voronoi geometry induced from Swiss cheese models and the underlying percolation theory. This indicates a transition in the impact of the excluded volume, i.e., the adjustment of the electrical conductivity was measured in cooperation with loading of second fillers with different sizes.

We report annealing time effects on the microstructural evolution and resultant magneto-transport property changes in Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta spin valves comprising PtMn layer thicknesses ranging from 10 to 30 nm. Postdeposition annealing was performed at 270 °C up to 35 h. The blocking temperatures of samples with 20 nm PtMn and 30 nm PtMn layers were found to be 350 °C and 400 °C, respectively. The magnetoresistance and interlayer coupling field changes became large as annealing time increased, in particular, for samples with relatively thicker PtMn layers. The main cause of microstructural changes and property degradation was due to interlayer diffusion of atomic constituents such as Mn, most likely through grain boundaries. Light B doping (1 at. %) in both free and pinned CoFe layers was proven effective in terms of blocking diffusion processes.