A comparative study of some manganese- and iron-based chalcopyrite semiconductor alloys: Basic properties and the effects of ordering.

Abstract

Dilute magnetic semiconductor alloys based on I-III-VI$\sb2$ chalcopyrite structure compounds and containing either iron or manganese as the magnetic component, were investigated in the context of a comparative study. The implications and effects of crystallographic ordering were of particular interest to this research. As a result of these experimental investigations, the phase diagram of the CuIn$\sb{\rm 1-x}$Fe$\sb{\rm x}$S$\sb2$ system was proposed, and certain modifications to the previously accepted phase diagrams of the systems containing manganese were given. For the iron containing system, the magnetic behaviour was interpreted in terms of a Curie-Weiss law, and the applicability of ligand field theory was investigated as a theoretical basis for understanding the results so obtained. It was determined that a transition similar to the $\sp6$A$\sb1$-$\sp4$T$\sb1$ crossover of crystal field theory may occur as a function of iron concentration in this material. Various computer fits and simulations were carried out in order to analyze the diffraction, and magnetic susceptibility measurements made on the alloys containing manganese. Besides displaying the usual non-magnetic-ion type of cationic ordering as in the transition from zincblende to chalcopyrite structure, these systems have been shown to exhibit behaviour characteristic of magnetic-ion crystallographic ordering (Mn-ordering). These ordering properties have been shown to be highly sensitive to sample heat treatment. The diffraction techniques were found to be insensitive to the types of Mn- ordering suspected to occur, however these alloys yielded direct evidence for the Mn-ordering in the form of their static, low field magnetic susceptibility behaviour. Of particular interest, some of the low temperature annealed, high concentration magnetic ion materials were found not to display the low temperature spin-glass cusp characteristic of the rapidly cooled samples, and this was interpreted to be the clearest signature of the Mn-ordering. The manganese systems may deviate from the chalcopyrite structure in the low temperature region of the phase diagram. The magnetic behaviour of these alloys was shown to be consistent with a long-range exchange, mean-field analysis of the planar ordering model. (Abstract shortened by UMI.)