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

摘要

We have made magnetic susceptibility measurements of the diluted magnetic semiconductors Zn{dollar}sb{lcub}1-x{rcub}{dollar}Co{dollar}sb{lcub}x{rcub}{dollar}S, Cd{dollar}sb{lcub}1-x{rcub}{dollar}Co{dollar}sb{lcub}x{rcub}{dollar}S, Cd{dollar}sb{lcub}1-x{rcub}{dollar}Co{dollar}sb{lcub}x{rcub}{dollar}Se, and (CuIn){dollar}sb{lcub}1-x{rcub}{dollar}Mn{dollar}sb{lcub}2x{rcub}{dollar}Te{dollar}sb{lcub}2{rcub}{dollar}. For the Co-based alloys, measurements were done for temperatures 33 mK {dollar}le Tle{dollar} 4.2 K and for concentrations {dollar}0.03le xle0.103.{dollar} Transitions from paramagnetism were observed in all samples. The low temperature phase was attributed to spin-freezing. The spin-freezing temperature {dollar}Tsb{lcub}f{rcub}{dollar} was found to be a universal function of x. From a log-log plot of {dollar}Tsb{lcub}f{rcub}{dollar} versus x, a power law spatial dependence of the long-range exchange interaction was found, with an exponent {dollar}n=6.3pm1.2.{dollar} 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){dollar}sb{lcub}1-x{rcub}{dollar}Mn{dollar}sb{lcub}2x{rcub}{dollar}Te{dollar}sb2{dollar} materials, samples with {dollar}0.0034le xle0.101{dollar} were measured in the temperature range 33 mK {dollar}le Tle300{dollar} K. The samples all exhibited Curie-Weiss behavior. An antiferromagnetic effective nearest-neighbor exchange parameter {dollar}Jsb{lcub}eff{rcub}{dollar} was extracted from the Curie-Weiss temperature and plotted as a function of x. At the highest concentrations, {dollar}Jsb{lcub}eff{rcub}{dollar} was virtually constant, having a value {dollar}approx -18.5{dollar} K. As x was lowered, {dollar}Jsb{lcub}eff{rcub}/ksb{lcub}B{rcub}{dollar} fell sharply to the value {dollar}-{dollar}0.36 K. The sample with the lowest x had a large {dollar}Jsb{lcub}eff{rcub}/ksb{lcub}B{rcub}{dollar} value of {dollar}-{dollar}88.5 K. Spin-freezing transitions were also seen in samples with {dollar}x>0.01.{dollar} Hall effect measurements were done which established that the samples all had p type conductivity. The samples having the smallest {dollar}Jsb{lcub}eff{rcub}{dollar} values were the best conductors. We speculate that the behavior of {dollar}Jsb{lcub}eff{rcub}{dollar} could be the result of several different effects, including vacancies, ordering of the Mn ions on the lattice, and the RKKY interaction.