Spin-dependent Transport Properties of CrO₂ Micro Rod

The CrO₂ micro rod powder was synthesized by decomposing the CrO₃ flakes at a specific temperature to yield precursor and annealing such a precursor in a sealed glass tube. The magneto-transport properties have been measured by a direct current four-probe method using a Cu/CrO₂ rods/colloidal silver liquid electrode sandwich device. The largest magnetoresistance (MR) around ~72 % was observed at 77 K with applied current of 0.05 μA. The non-linear I-V curve indicates a tunneling type transport properties and the tunneling barrier height is around 2.2 ± 0.04 eV at 77 K, which is obtained with fitting the non-linear I-V curves using Simmons' equation. A mixing of Cr oxides on the surface of CrO₂ rod observed by X-ray photoemission spectroscopy provides a tunneling barrier rather than a single phase of Cr₂O₃ insulating barrier. The MR shows strong bias voltage dependence and is ascribed to the two-step tunneling process.