Electron paramagnetic resonance in magnetic semiconductor epitaxial layers and superlattices

This thesis presents results of research on the paramagnetic resonance absorption of diluted magnetic semiconductors (DMSs) in layered form, i.e. compounds of the form {dollar}rm Asp{lcub}II{rcub}sb{lcub}1-x{rcub}Msb{lcub}x{rcub}Bsp{lcub}VI{rcub}{dollar}, where {dollar}rm Asp{lcub}II{rcub}{dollar} and {dollar}rm Bsp{lcub}VI{rcub}{dollar} are group II and VI elements, and M is a magnetic transition metal ion.; We have explored the possibility of using electron paramagnetic resonance (EPR) of Mn{dollar}sp{lcub}++{rcub}{dollar} for measuring uniaxial strain in II-VI superlattices. This work is motivated by the fact that the EPR of Mn{dollar}sp{lcub}++{rcub}{dollar} is strongly affected by crystalline fields. Changes in a crystalline field which arise from strain are thus automatically expected to have a profound effect on the EPR spectrum.; The EPR has exhibited a variety of new phenomena. We have observed giant crystal field splittings of Mn{dollar}sp{lcub}++{rcub}{dollar} in ZnTe/MnTe and CdTe/MnTe superlattices{dollar}sp{lcub}1,2{rcub}{dollar}. The EPR spectra are ascribed to isolated Mn{dollar}sp{lcub}++{rcub}{dollar} ions diffused into the ZnTe or CdTe layers from the MnTe layers. Furthermore, we have shown that these shifts can be used as a strain gauge in such superlattices, yielding the magnitude, sign, and uniformity of strain. Comparisons of results using neutron scattering agree well with results from EPR.; We have also measured the EPR of a series of {dollar}rm Znsb{lcub}1-x{rcub}Mnsb{lcub}x{rcub}Se{dollar} epilayer systems. The room temperature EPR linewidth versus x result in a simply varying quadratic relationship which offers an easy and precise method of determining the Mn{dollar}sp{lcub}++{rcub}{dollar} concentration in epilayers for {dollar}x>0.05{dollar}. The temperature dependence of the EPR linewidth was analyzed in terms of exchange-narrowing theory and the Dzyaloshinski-Moriya (D-M) exchange constant D{dollar}sb1{dollar} determined, with an average value of D{dollar}sb1=0.30{dollar} K, in reasonable agreement with Larson's calculated value.; Finally, we have investigated spin-spin interactions in very dilute systems by studying the {dollar}-{lcub}1over2{rcub}to{lcub}1over2{rcub}{dollar} transitions in a ZnTe/MnTe and CdTe/MnTe strained superlattice. The temperature dependence of the EPR linewidth has characteristics similar to those observed in high-x DMS systems (except in magnitude): a dramatic broadening with decreasing temperature. Analysis of the linewidths in terms of exchange-narrowing theory yields the surprising result that the D-M interaction is still the dominant magnetic interaction, even at very dilute Mn{dollar}sp{lcub}++{rcub}{dollar} concentrations, where the D-M interaction is expected to be small.