Influence of ultrasonic treatment on magnetotransport of CrO2 granular compacts

The transport properties of ultrasonic-treated CrO2 particles are studied. The experimental results indicate that the ultrasonic treatment not only leads to an increase in the resistivity, but also reduces the saturation magnetization of CrO2 powders. These modifications are attributed to a change in the surface state of the CrO2 particles. Furthermore, a modified surface state can yield a decreasing magnetoresistance of CrO2 granular compacts. XPS analysis provides supports that the surface nature of CrO2 particles is altered after ultrasonic treatment. The reduced saturation magnetization is related to the existence of a magnetic dead layer, which is estimated to be of a few nanometers thick. This work reveals that our ultrasonic technique is a method to control magnetotransport of granular materials by altering the surface state of the particles.