High‐temperature ferromagnetism in Fe‐doped wurtzite and zincblende CdS nanoparticles

Abstract

The evolution of Curie-Weiss temperature (Q) has been investigated in thiol-capped Fe-doped wurtzite (WZ) and zincblende (ZB) CdS nanoparticles. Fe doped CdS nanoparticles with different crystal structures namely WZ and ZB have been obtained by varying its synthesis temperature. It has been found that the magnetic impurity ions are distributed randomly in ZB samples, whereas it form clusters near the surface of WZ CdS nanoparticles. These distributions of magnetic impurities ions alter the density of charge carriers and hence have a significant effect on Q. An increase in Q by nearly an order of magnitude has been observed in WZ, as compared to the ZB CdS nanoparticles, which is explained well by considering a relative variation in inter-Fe separation in the two polymorphs of CdS within the framework of the Heisenberg model. Spatial distribution of Fe 3þ ions in ZB and WZ CdS nanoparticles.A blueshift in the UV-visible absorption spectra is observed due to etching, which removes more Fe 3þ ions in WZ CdS.