The ability to control both spin and charge degrees of freedom in semiconductor nanostructrures is at heart of spintronic and quantum information technologies. Magnetically-doped semiconductor nanowires have emerged as a promising platform for spintronics, which warrants the exploration of their synthesis, electronic structure, and magnetic properties. Here we demonstrate the preparation of manganese-doped GaN and SnO2 nanowires by chemical vapor deposition and solvothermal methods, respectively. The investigation of both systems by electron microscopy and x-ray absorption spectroscopy at ensemble and single nanowire levels indicates that manganese dopants exist in a dual oxidation state, Mn2+ and Mn3+, with Mn2+ being the majority species. X-ray magnetic circular dichroism studies of individual nanowires suggest ferromagnetic interactions of manganese dopants, and the nanowire orientation-dependent magnetization owing to the magnetocrystalline anisotropy. The results of these studies demonstrate quantitative determination of the dopant electronic structure at the molecular level, and allow for a prediction of the magnetic properties of diluted magnetic semiconductor nanowires based on their orientation and geometry.
The synthesis of colloidal Cr3+-doped In2O3 NCs with the body-centered cubic bixbyte-type crystal structure, and Cr3+-doped SnO2 NCs with the rutile crystal structure was described. Ligand-field electronic absorption spectroscopy suggests
that Cr3+ dopants have quasi-octahedral coordination in both In2O3 and SnO2 NC host lattices. Unlike free-standing nanocrystals, the nanocrystalline films fabricated from colloidal Cr3+-doped In2O3 and SnO2 nanocrystals exhibit room
temperature ferromagnetism. Analogous magnetic behavior suggests the same origin of ferromagnetic ordering in both
materials. The observed ferromagnetism has been related to the existence of extended structural defects, formed at the
interfaces between nanocrystals in nanocrystalline films. These structural defects are likely responsible for the formation
of charge carriers which mediate the dopant magnetic moment ordering.
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