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The magnetoresistance ~MR! and microstructures of half-metallic CrO2 nanoparticle systems were studied. Using field alignment, the needle-shaped CrO2 single domain particles were aligned in the same orientation. The MR of this structure showed a magnetic junction-like behavior with two well-separated peaks in the MR at coercivity fields and the MR of the aligned CrO2 particles reached .41% at a relatively low field of about 1000 Oe. The magnetotransport mechanism was analyzed in terms of spin dependent tunneling between CrO2 nanoparticles. Using transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy techniques, the intergranular tunneling barrier was characterized to be a very thin Cr2O3 interface layer between the CrO2 particles. Temperature dependence of MR and conductivity in cold-pressed CrO2 nanopowders were studied. The MR significantly decreased with increasing temperature and the spin independent hopping conduction is suggested to be responsible for the suppression of MR at high temperature. © 2001 American Institute of Physics.




Copyright 2001 AIP (American Institute of Physics) Publishing LLC.