Magnetic effects on optical energy gap values of (CuIn)1−z Mn2z Te2 alloys

Abstract

Measurements of optical absorption were made as a function of temperature in the range 15–300 K to give optical energy gap E0 values for polycrystalline samples of (CuIn)1−z Mn2z Te2 alloys with z=0.4 and 0.5. Absorption edges were observed for both the ordered and disordered zinc-blende phases and also for a lower energy transition assumed to be an internal Mn2+ transition. As confirmed by magnetic susceptibility data, the dominant phase in these alloys was the ordered zinc blende. For this phase, the variation of E0 with temperature in the vicinity of the magnetic transition temperature Tg was analyzed to give the magnetic contribution ΔE, which increases the value of E0. ΔE was determined as the difference between the experimental values of E0 and an extrapolation from higher temperatures where the magnetic contribution is negligible. These values of ΔE were fitted to the relation d/dt(ΔE)=−Pt−μ, where t=‖T−Tg ‖/Tg , and good agreement was found with previous theoretical predictions for the effect on the band gap of a critical point such as Tg . As predicted, different behavior was observed close to Tg and at temperatures outside the critical range, μ having a value close to zero in the first range and close to 0.5 in the second.