Influence of hot pressure on the magnetoresistance of CrO_2

摘要

In this paper, we investigate the influence of high temperature and high pressure (hot pressure) on the magnetic and transport properties of polycrystalline CrO_2 samples compacted under high pressure and high temperature of up to 5 GPa and 600℃, respectively. The magnetic moment increases with compacting temperature, and a metal-semiconductor transition is observed in hot-pressed samples, different from the cold-pressed samples. These results indicate that the formation of Cr_2O_3 at the grain boundaries of CrO_2 is suppressed by hot pressure. The magnitude of low field magnetoresistance of up to 1 T at 5 K is enhanced first with the increase of compacting temperature and then decreased under higher compacting temperature. This result can be well explained by the change of spin-dependent tunneling at the modulated grain boundaries of CrO_2 due to the transformation from Cr_2O_3 to CrO_2 under hot pressure.