Electronic Structure and Field Effects of an Organic-Based Room Temperature Magnetic Semiconductor; Doctoral theses

摘要

The future of spin-electronics or 'spintronics' lies in the development of viable magnetic semiconductors that can effectively operate at room temperature Vanadium tetracyanoethylene (V TCNE) approximately (2) is a magnetic semiconductor with an ordering temperature well above that of room. Its highly disordered structure has hampered a comprehensive description of the interactions between the V and TCNE sublattices that give rise to its magnetic and electrical properties. We report the results of high-resolution x-ray absorption (XAS) and magnetic circular dichrosim (MCD) studies probing the electronic structure of V TCNE approximately 2 in an effort to elucidate the nature of these interactions. Included in this study are the first reports of gas phase neutral TCNE XAS spectra as well as the first reports of MCD spectra of the carbon and nitrogen absorption edges for the V TCNE approximately 2 system. The vanadium spectrum reveals a spin split L3 and L2 spectrum that is qualitatively modeled for V(II) using crystal field multiplet (CFM) theory calculations except for a region of excess intensity on the high energy side of both the L3 and L2 absorption edges. We speculate that the origin of this excess intensity is vanadium present in valence states higher than V(II) and antibonding states from the hybridization of the V centers and TCNE. Despite the localized nature of the x-ray absorption process the C and N spectra of the TCNE suggest that we are probing molecular final states of TCNE from different sites rather atomically isolated states. In addition, the carbon and nitrogen absorption spectra reveal that this molecular orbital structure remains largely intact in going from the gas phase to the condensed phase in V TCNE approximately 2.