Abstract
The paper presents an approach to enhance a magnetoresistance (MR) effect in CrO 2 powder compact by an oxidization reaction process. An aqueous potassium permanganate (KMnO 4) was used to react with the CrO 2 particles coated naturally with Cr 2O 3 layer. The experiment indicates that the strong oxidant can effectively adjust thickness of the natural Cr 2O 3 layer, and thereby change the surface state of the CrO 2 particles. Structural and magnetic properties for the improved CrO 2 particles have been characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and SQUID magnetometer. The results exhibit that the magnetotransport behavior of CrO 2 particles depends sensitively on the chemical reaction time. An optimal reaction process yields an obvious increase up to −33% in magnetoresistance at a temperature of 5 K for the chemical treated CrO 2 powder, compared to MR=-27% for the original CrO 2 powder. The mechanism of magnetotransport is assumed to originate from the spin-dependent tunneling in the granular system, which is consistent with our experimental results. The simple chemical approach has a potential to achieve an enhanced magnetoresistance in a metallic particle system by adjusting the surface state of the magnetic nanoparticle.
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