Abstract
The ferrimagnetic spinel oxide combines high Curie temperature and spin polarization with tunable electrical and magnetic properties, making it a promising functional material for spintronic devices. We have grown epitaxial thin films on MgO(001) substrates with excellent structural properties both in pure Ar atmosphere and an mixture by laser molecular beam epitaxy and systematically studied their structural, magnetotransport, and magnetic properties. We find that the electrical conductivity and the saturation magnetization can be tuned over a wide range ( and at room temperature) by Zn substitution and/or finite oxygen partial pressure during growth. Our extensive characterization of the films provides a clear picture of the underlying physics of the spinel ferrimagnet with antiparallel Fe moments on the and sublattices: (i) Zn substitution removes both moments from the sublattice and itinerant charge carriers from the sublattice; (ii) growth in finite oxygen partial pressure generates Fe vacancies on the sublattice also removing itinerant charge carriers; and (iii) application of both Zn substitution and excess oxygen results in a compensation effect as Zn substitution partially removes the Fe vacancies. Both electrical conduction and magnetism are determined by the density and hopping amplitude of the itinerant charge carriers on the sublattice, providing electrical conduction and ferromagnetic double exchange between the mixed-valent ions on the sublattice. A decrease (increase) in charge carrier density results in a weakening (strengthening) of double exchange and thereby a decrease (increase) in the conductivity and the saturation magnetization. This scenario is confirmed by the observation that the saturation magnetization scales with the longitudinal conductivity. The combination of tailored films with semiconductor materials such as ZnO in multifunctional heterostructures seems to be particularly appealing.
1 More- Received 26 August 2008
DOI:https://doi.org/10.1103/PhysRevB.79.134405
©2009 American Physical Society