Magnetoresistance in granular CrO2 : influence of crystallographic and magnetic microstructure

TL;DR

This study investigates how the crystallographic and magnetic microstructure influence magnetoresistance in high-purity CrO2, revealing temperature-dependent behaviors and microstructure effects relevant for spintronic applications.

Contribution

It provides new insights into the role of microstructure on magnetoresistance in CrO2 across a wide temperature range, including unusual MR features near magnetic transition temperatures.

Findings

Unhysteretic negative MR up to 200 K.

Positive MR and pinning effects near 290 K.

Enhanced MR with increased grain boundary density.

Abstract

We report magnetotransport measurements on high purity sintered samples of spintronic CrO2 in an unexplored crystallographic regime between 5-300 K. The negative magnetoresistance (MR) as derived from RH isotherms is observed to be unhysteretic up to temperatures as high as 200 K. Between 240-290 K, RH isotherms exhibit some unusual features including a positive MR and strong pinning effects. These feature disappear above 290 K and is apparently related with the antiferromagnetic ordering of the insulating grain boundary. Qualitatively similar features with significantly enhanced MR are also observed when the GB density is increased. These results bring out the role played by the magnetic and crystallographic microstructure on the magnitude, sign and hysteresis of the magnetoresistance in this technologically important material.