| AVS 57th International Symposium & Exhibition | |
| Electronic Materials and Processing | Monday Sessions |
| Session EM+MI-MoA |
| Session: | Semiconducting and Highly Correlated Oxides |
| Presenter: | J.A. Moyer, Yale University |
| Authors: | J.A. Moyer, Yale University C.A.F. Vaz, Yale University D.A. Arena, Brookhaven National Laboratory V.E. Henrich, Yale University |
| Correspondent: | Click to Email |
Developing new materials with large spin polarizations, high Curie temperatures and resistivities similar to those of semiconductors would greatly benefit the field of spintronics. Cobalt ferrite (CoFe2O4), like its parent compound magnetite (Fe3O4), is a promising material for spintronic applications due to its high Curie temperature (Tc=793 K) and large predicted spin polarization; however, CoFe2O4 is an insulator. Cobalt ferrite becomes an n-type conductor when doped with excess iron – Co1-xFe2+xO4; the origin of the conduction is electron hopping between Fe2+ cations in octahedral sites. The strong localization of electrons on the Fe2+ cations in this highly correlated oxide keeps the conductivity in the semiconducting range. In this work, heteroepitaxial Co1-xFe2+xO4 thin films have been grown on MgO (100) and MgAl2O4 (100) and (110) with x ranging from 0 to 0.5. The electronic band structure near the Fermi energy is measured with ultraviolet photoelectron spectroscopy (UPS), and the results are correlated with resistivities determined from transport measurements. This range of doping allows for the resistivity to be tailored over two orders of magnitude. The cation valence states and occupation sites are determined with x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS). Bulk magnetic moments are obtained with SQUID magnetometry, while bulk and site specific orbital and spin magnetic moments are obtained using x-ray magnetic circular dichroism (XMCD). The XMCD measurements provide a view of the spin polarization of the Fe2+ octahedral cations responsible for conduction. The wide variety of measurements enables us to determine the electronic structure of Co1-xFe2+xO4, an important development for the goal of determining the viability of Co1-xFe2+xO4 as a spin-polarized source or detector in spintronic devices.
This research is primarily supported by NSF Grant MRSEC DMR-0520495.