Abstract The microstructure of the CrO2 particles prepared by high temperature and high pressure (HTHP) method was studied by HRTEM. It is found that the CrO2 particles synthesized at 500 and 550 °C are covered by Cr2O3 surface layers of about 6 nm thick. However, the CrO2 particles synthesized at 400 and 450 °C do not have Cr2O3 surface layers. The saturation magnetization of the CrO2 particles synthesized at different temperatures is all very close to the theoretical value. The magnetoresistance (MR) of the CrO2 particles synthesized at 500 and 550 °C is much larger than that of the CrO2 particles synthesized at 400 and 450 °C, which should be due to the enhancement of tunneling magnetoresistance by insulating Cr2O3 surface layers. The tunneling MR of the CrO2 particles can be fitted well by expression of C1(M/Ms)2 + C2(M/Ms)4 + C3(M/Ms)6. The proportion of the higher-order terms of (M/Ms)2 in the expression is tightly related to the existence of the Cr2O3 surface layer.

中文翻译：

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高温高压下制备的CrO 2 的微观结构和磁传输性能研究

摘要 采用HRTEM研究了高温高压(HTHP)法制备的CrO2颗粒的微观结构。发现在 500 和 550 °C 合成的 CrO2 颗粒被约 6 nm 厚的 Cr2O3 表面层覆盖。然而，在 400 和 450 °C 合成的 CrO2 颗粒没有 Cr2O3 表面层。在不同温度下合成的CrO2颗粒的饱和磁化强度都非常接近理论值。在 500 和 550 °C 合成的 CrO2 颗粒的磁阻 (MR) 远大于在 400 和 450 °C 合成的 CrO2 颗粒的磁阻 (MR)，这应该是由于绝缘 Cr2O3 表面层增强了隧道磁阻。C1(M/Ms)2 + C2(M/Ms)4 + C3(M/Ms)6 的表达式可以很好地拟合CrO2 颗粒的隧道MR。