Magnetic and electrical properties of various 3d transition metal and rare earth chalcogenides.

摘要

Transition metal and rare earth chalcogenides display a great diversity of interesting physical properties ranging from superconductivity to ferromagnetism to magnetic frustration. Because of these properties, metal chalcogenides have the potential to be used in numerous solid state devices. This thesis investigates the magnetic and electrical properties of various 3d transition metal and lanthanide chalcogenides with a focus on tailoring their physical properties through chemical doping.; Ferromagnetic semiconductors are materials that display both ferromagnetism and semiconductivity and are of recent interest because of their potential application to spintronic devices. However, compounds that exhibit both of these properties are very rare. In this study, attempts were made to prepare ferromagnetic semiconductors by altering the electrical properties of known room-temperature magnets by chemical substitutions. Materials that were examined during this project include a myriad of compounds within the Fe-Se-S, Ni-Se-S, Co-Se-S systems as well as SbCrSe3. Although no new ferromagnetic semiconductors were discovered, many of the compounds were found to exhibit interesting physical properties.; The synthesis and physical properties of several rare earth chalcogenides with the Th3P4 structure type were also investigated because of the potential use of these materials in high temperature thermoelectric generators. This study focused on compounds within the Ln-X systems where Ln=Nd, Sm, Gd or Dy and X=Se or Te. These chalcogenides were also subjected to chemical modifications in an attempt to manipulate their thermoelectric properties. Several compounds were successfully synthesized and were found to have relatively large Seebeck coefficients at 1000°C, which makes them promising candidates for use in such applications. Chalcogenides that contain both a 3d transition metal and a rare earth element were also investigated in an attempt to locate novel compounds with interesting crystal structures and magnetic and electric properties.