Electrical Conductivity Percolation Effects in CrO$_{2}$-MgB$_{2}$ Nanocomposites

Cold-pressed half-metals/insulators are known to show an enhanced extrinsic powder magnetoresistance (MR) due to intergranular and intergrain spin-dependent tunneling. In this work we use a mixture of metal/superconductor (CrO$_{2})_{x}$(MgB$_{2})_{1-x}$ nanocomposites to study conduction percolation effects. The samples were cold pressed in the form of pellets from the mixture of pure CrO$_{2}$ and MgB$_{2}$ powders. Transport and magneto-transport properties of various composition compacts measured as a function of temperature. Magneto-transport measurements performed over a temperature range of 2-100K show a hysteretic behavior with the peak values of MR coinciding with the CrO$_{2}$ coercive fields, with a maximum MR value for the composition near the percolation threshold of $\sim $ 42{\%} at 2 K. The electrical resistivity displayed a sharp maximum near the percolation threshold, a feature that is likely to be unique for such type of systems. We will discuss the implications of our results for the analysis of conduction percolation within the framework of a simple percolation model and a possible connection to Andreev reflection effect in this system at low temperatures.