Magnetic susceptibility studies of cobalt-based II-VI and manganese-based chalcopyrite diluted magnetic semiconductors

Paul Michael Eugene Shand, Purdue University


We have made magnetic susceptibility measurements of the diluted magnetic semiconductors Zn$\sb{1-x}$Co$\sb{x}$S, Cd$\sb{1-x}$Co$\sb{x}$S, Cd$\sb{1-x}$Co$\sb{x}$Se, and (CuIn)$\sb{1-x}$Mn$\sb{2x}$Te$\sb{2}$. For the Co-based alloys, measurements were done for temperatures 33 mK $\le T\le$ 4.2 K and for concentrations $0.03\le x\le0.103.$ Transitions from paramagnetism were observed in all samples. The low temperature phase was attributed to spin-freezing. The spin-freezing temperature $T\sb{f}$ was found to be a universal function of x. From a log-log plot of $T\sb{f}$ versus x, a power law spatial dependence of the long-range exchange interaction was found, with an exponent $n=6.3\pm1.2.$ This value is very close to the value n = 6.8 obtained for the equivalent Mn-based materials. We give a detailed comparison of our results for the Co-based alloys with the Mn-based data and discuss the properties of the long-range interaction which leads to spin freezing in both alloy systems. For the (CuIn)$\sb{1-x}$Mn$\sb{2x}$Te$\sb2$ materials, samples with $0.0034\le x\le0.101$ were measured in the temperature range 33 mK $\le T\le300$ K. The samples all exhibited Curie-Weiss behavior. An antiferromagnetic effective nearest-neighbor exchange parameter $J\sb{eff}$ was extracted from the Curie-Weiss temperature and plotted as a function of x. At the highest concentrations, $J\sb{eff}$ was virtually constant, having a value $\approx -18.5$ K. As x was lowered, $J\sb{eff}/k\sb{B}$ fell sharply to the value $-$0.36 K. The sample with the lowest x had a large $J\sb{eff}/k\sb{B}$ value of $-$88.5 K. Spin-freezing transitions were also seen in samples with $x>0.01.$ Hall effect measurements were done which established that the samples all had p type conductivity. The samples having the smallest $J\sb{eff}$ values were the best conductors. We speculate that the behavior of $J\sb{eff}$ could be the result of several different effects, including vacancies, ordering of the Mn ions on the lattice, and the RKKY interaction.




Crooker, Purdue University.

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