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Abstract In an effort to reconcile the various interpretations for the cation components of the 2p3/2observed in x-ray photoelectron spectroscopy (XPS) of several spinel oxide materials, the XPS spectra of both spinel alloy nanoparticles and crystalline thin films are compared. We observed that different components of the 2p3/2core level XPS spectra, of these inverse spinel thin films, are distinctly surface and bulk weighted, indicating surface-to-bulk core level shifts in the binding energies. Surface-to-bulk core level shifts in binding energies of Ni and Fe 2p3/2core levels of NiFe2O4thin film are observed in angle-resolved XPS. The ratio between surface-weighted components and bulk-weighted components of the Ni and Fe core levels shows appreciable dependency on photoemission angle, with respect to surface normal. XPS showed that the ferrite nanoparticles NixCo1−xFe2O4(x= 0.2, 0.5, 0.8, 1) resemble the surface of the NiFe2O4thin film. Surface-to-bulk core level shifts are also observed in CoFe2O4and NiCo2O4thin films but not as significantly as in NiFe2O4thin film. Estimates of surface stoichiometry of some spinel oxide nanoparticles and thin films suggested that the apportionment between cationic species present could be farther from expectations for thin films as compared to what is seen with nanoparticles.
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Surface segregation in multicomponent magnetic Bismuth ferrite nanoparticles
Abstract Surface segregation is a ubiquitous phenomenon driven by minimization of the total free energy. In this paper we study surface segregation in multicomponent magnetic Bismuth ferrite nanoparticles alloyed with varying amounts of Dysprosium, Zinc and Titanium. We employ surface and bulk sensitive spectroscopic probes to unravel a significant surface segregation of Bismuth oxide and Titanium oxide. High coercive fields of BiFe0.95Ti0.05O3(BFTO) and BiFe0.96(Zn, Ti)0.02O3(BFZTO) at room temperature reveal that they have a strong exchange bias. This suggests that the Titanium oxide is magnetically active, and there is a Ti induceddoferromagnetism in action between these nanoparticles. We show, with the addition of Dy2O3, the Ti induceddoferromagnetism is suppressed making (BDFZTO) superparamagnetic. We observe that all three differently alloyed Bismuth ferrite nanoparticles show a non-saturating paramagnetic background.
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- PAR ID:
- 10621733
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- Physica Scripta
- Volume:
- 100
- Issue:
- 7
- ISSN:
- 0031-8949
- Page Range / eLocation ID:
- 075981
- Subject(s) / Keyword(s):
- surface segregation, nanoparticels, exchange interaction
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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