Abstract
Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich films with different stoichiometry ( and ) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/FeO bilayers deposited before on Nb-doped SrTiO(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of cations in the low-spin state on octahedral sites for the film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements.
Highlights
Ferrites such as CoFe2 O4 (CFO) have intriguing electronic and magnetic properties that are increasingly attracting attention, for advancing the fields of spintronics and spin caloritronics
We demonstrated that thin cobalt ferrite films can be prepared by reactive solid phase epitaxy (RSPE) due to the intermixing of epitaxial Fe3 O4 /CoO and CoO/Fe3 O4 bilayers [18,21]
Since the cation distribution of cobalt ferrite can be changed by thermal treatment [26,27], we report here on a case study concerning mainly the cation distribution and the resulting magnetic behavior of two cobalt ferrite films prepared by RSPE
Summary
Ferrites such as CoFe2 O4 (CFO) have intriguing electronic and magnetic properties that are increasingly attracting attention, for advancing the fields of spintronics and spin caloritronics. In these fields magnetic insulators (MI) can be used as spin-filters for the generation of highly spin-polarized electron currents due to their spin-dependent band gaps [1,2,3,4,5,6], thereby creating the possibility of faster and less energy consuming spintronic devices. Thin CFO films are useful as supports for Pt films to create thermally generated spin currents [7,8] via the spin Seebeck effect (SSE) [9]. Owing to the absence of a magnetic proximity effect in Pt/CoFe2 O4 bilayers [10], no parasitic effects, such as the anomalous Nernst effect [11], are induced, simplifying the evaluation of the SSE signal and making CFO films quite interesting for spin caloritronic applications.
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