The magnetic and magnetotransport properties of field-aligned half-metallic ${\mathrm{CrO}}_2$ powders have been studied. Needle-shaped nanoparticles of ${\mathrm{CrO}}_2$ have been aligned in a strong magnetic field. The aligned powder sample shows a strong anisotropy along the alignment direction. The conduction mechanism of the aligned ${\mathrm{CrO}}_2$ powder sample has been examined and is consistent with the intergranular spin-dependent tunneling. Negative tunneling magnetoresistance of about 41% is achieved in a small field in the vicinity of the coercive field at 5 K. The magnetoresistance (MR) versus field curve shows two well-separated narrow peaks at the coercive fields and resembles that of a magnetic tunnel junction. This junctionlike MR results from the narrow switching field distribution of the aligned powders. Our results suggest that the aligned magnetic ${\mathrm{CrO}}_2$ particles may find novel applications in spin-transport structures and devices.

• Received 20 September 2000

DOI:https://doi.org/10.1103/PhysRevB.63.054434