Magnetic Semiconductor Solid Solutions

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NON-TECHNICAL DESCRIPTION: The goal of this project is to synthesize materials of the type Eu(S,Se) and (Eu, Sm)Se. The host material, EuSe is a special semiconductor that can exhibit one type of magnetism (ferromagnetism) under high magnetic fields and a second type (antiferromagnetism) at low fields. In the first system, incorporation of sulfur, should shift the magnetic ordering from antiferro- to ferromagnetic, which will allow a study of the relationship between the electronic structure and magnetic ordering in order to understand the mechanism behind magnetic refrigeration (magnetocaloric effect). In the second system, substitution of samarium for europium will enable the understanding of the relationship between the electronic structure and the charge on the rare earth element. The research will target these materials in both the bulk and as nanoparticles, providing a synergistic understanding of the role of morphology and size on the magnetic and electronic properties. TECHNICAL DESCRIPTION: The project involves the synthesis of both bulk and nanoparticles of lanthanide monochalcogenides, which are intrinsically semiconducting and magnetic. The role of anion solid solutions of Eu(S,Se) will be investigated to determine the consequences of the anion changes to the electronic structure and how this changes the magneto-caloric effect. In addition, magnetic circular dichroism will be used to probe the excited states of these alloys. The second project involves probing the role of the lanthanide in solid solutions of (Eu,Sm)Se, to understand the lanthanide oxidation state as a function of the electronic structure. Although EuSe has been found to contain divalent europium and SmSe has divalent samarium, low doping levels of samarium inject samarium in the trivalent state. These variations will be investigated through use of L-edge X-ray absorption spectroscopy.