Magnetooptical and magnetic studies of Co and Cr doped CdMnTe

We investigate the magnetooptical and magnetic properties of two new CdMnTe-based diluted magnetic semiconductors. The first system consists of a series of Cd$_{1-x-y}$Mn$_ {x}$Cr$_{y}$Te alloys with Mn concentration x fixed at $\sim$0.37 and controlled Cr concentration y in the range $0 < y < 0.07$. The second system is the quaternary Cd$_{1-x-y}$Mn$_{x}$Co$_{y}$Te alloy, with the same Mn concentration (x = 0.37) and the Co concentration y in the range $0 < y < 0.009$. These systems are of interest in that they are expected to involve interactions of the minority magnetic ions (Cr and Co, respectively) with the surrounding majority Mn ions. Indeed, optical absorption and MCD spectra observed on these alloys reveal a series of new ``impurity'' peaks that are not present in the Cd$_{0.63}$Mn$_{0.37}$Te control samples. It is interesting that the magnetic field dependence of the MCD spectra as well as SQUID measurements reveal a ferromagnetic-like hysteresis loop in Cd$_{1-x-y}$Mn$_ {x}$Cr$_{y}$Te samples with Cr concentration y in the range of $0 < y < 0.03$. Surprisingly, the FM loop survives up to 295 K. But this ferromagnetic behavior is not observed in samples with $y > 0.05$. One should note that FM loops were not observed in Cd$_{1-x-y}$Mn$_{x}$Co$_{y}$Te samples.