Measurements of the Temperature Dependence of Energy Gaps in Magnetically-Ordered Cr-Rich Cr–Al Alloys

Abstract

The magnitude and temperature dependence of energy gaps in Cr-rich Cr–Al alloys are obtained by infrared reflectivity measurements at wavelengths from 1 to 40 micrometers. This alloy system is intriguing because it exhibits both incommensurate and commensurate itinerate electron antiferromagnetism (AFM) as well as semiconducting properties, depending on Al concentration. Single-crystal alloys with up to 6.4%Al are studied, and polycrystalline alloys of 19 to 38%Al. Alloys with up to 1 at%Al exhibit absorptions near 0.12 and 0.45 eV, similar to pure Cr. Alloys of 1.4 and 1.9%Al show no temperature-dependent structure which can be associated with itinerate AFM and corroborate the recent suggestion of an intermediate magnetic state between 1.1 and 3%Al. Alloys containing 3 to 6.4%Al have absorption near 0.35 eV which is attributed to commensurate AFM ordering. Alloys with 19 and 27%Al exhibit absorptions near 0.3 and 0.041 eV, corresponding to commensurate magnetic order and semiconductor-like structure, respectively.