Synthesis and Study of Magnetic Nanostructures
Stoll, Sarah L
Nanostructures of magnetic semiconductors have widespread applications in the field of nanoscale device fabrication. Intrinsic magnetic semiconductors of the europium chalcogenide family (EuO, EuS, EuSe, EuTe) are of particular interest due to the wide range of magnetic properties exhibited in the family itself (from ferromagnetism to metamagnetism). Although there are nanostructures of different dimensions, one-dimensional magnetic nanostructures of single crystalline nature are highly sought after due to their domain structures, which make them ideal candidates for spintronic applications.The most common approach for preparing one-dimensional nanostructures is via template synthesis. However, template synthesis in general yields nanostructures of a polycrystalline nature. In this work we have synthesized one-dimensional nanostructures of Eu(OH)3, converted them to Eu2O3 and finally to EuO by means of simple chemical transformations, and followed the changes in morphology and crystallinity during the entire process.Indirect f-d exchange or RKKY-type coupling of conduction electrons is responsible for the ferromagnetism exhibited by the magnetic semiconductors of the europium chalcogenide family, which is completely different from the direct overlap or superexchange mechanism observed in the common magnetic materials. The magnetic properties of bulk EuO, EuSe and EuTe have been studied in the past by means of electron doping and the effect in case of EuS has been described as being “qualitatively similar”. However, very little experimental data is available on the system and none at all is available on nanostructured EuS. Here we have probed the magnetic properties of nanostructured EuS by doping with Gd, and studied the changes in θ and Tc as function of doping level.Chemical doping however, has certain problems associated with it particularly due to the introduction of foreign ions into the lattice. Photo-injection, which involves injection of an electron directly into the conduction band of the semiconductor without the involvement of foreign ions, has often been thought of as an alternative to chemical doping. The most well known example is the Grätzel cell. In this work we have investigated photo-injection by attaching dye molecules onto the surface of EuS nanoparticles and studied the effect of dye attachment on the optical properties of the semiconductor.
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