Cd-113 NMR study of transferred hyperfine interactions in the dilute magnetic semiconductors Cd1-xCoxS and Cd1-xFexS and impurity distribution in Cd0.994Co0.006S

Diluted magnetic semiconductor samples Cd0.99Fe0.01S and Cd0.994Co0.006S we re investigated by Cd-113 magic angle spinning NMR spectroscopy in the temp erature range of 180-400 K. These alloys were prepared by mixing Cd0.97M0.0 3S (M = Co, Fe) and the binary compound CdS in the appropriate molar ratios and maintaining the mixtures at about 1000 degrees C for seven-days. The m acroscopic homogeneity of the samples was determined by energy dispersive s pectroscopy. The microscopic homogeneity of the paramagnetic ion distributi on in these samples can be studied by analyzing their Cd-113 NMR spectra. T hese spectra contain a set of Cd* bands (the * sign indicates the observed cadmium atoms) that are shifted by the transferred hyperfine (THF) interact ion between the cadmium nuclei and their neighboring paramagnetic ions. Usi ng the temperature dependence of the positions, the relaxation times, and a nisotropies of these bands, we assigned each band to a well-defined next-ne arest neighbor M(2)-S-Cd(1)-S-Cd* conformation, and correlated the THF inte raction constants of all conformations to the M(2)-Cd* distances. All cadmi um bands in the spectra comprise a set of lines that correspond to Cd* atom s in conformations of the type M(3)-S-Cd(2)-S-Cd(1)-Cd*-S-Cd(1)-S-M(2). The relative intensities of the lines can be calculated for given x values, wh en we assume a random magnetic ion impurity distribution. For the Cd0.994C0 .006S sample, we found that the calculated line intensities were not consis tent with the experimental intensities. To explain this deviation and to si mulate a spectrum that fits the experimental data, we assumed that this sam ple consists of clusters with different concentrations of the impurity. Goo d agreement was obtained when about half of the cadmium atoms do not intera ct with the paramagnetic ions, and the other half interacts with ions that are randomly distributed in an alloy composed of Cd0.987Co0.013S. [S0163-18 29(99)14335-2].