Intrinsic exchange bias is known as the unidirectional exchange anisotropy that emerges in a nominally single-component ferro-(ferri-)magnetic system. In this work, with magnetic and structural characterizations, we demonstrate that intrinsic exchange bias is a general phenomenon in (Ni, Co, Fe)-based spinel oxide films deposited on α-Al2O3(0001) substrates, due to the emergence of a rock-salt interfacial layer consisting of antiferromagnetic CoO from interfacial reconstruction. We show that in NixCoyFe3-x-yO4(111)/α-Al2O3(0001) films, intrinsic exchange bias and interfacial reconstruction have consistent dependences on Co concentration y, while the Ni and Fe concentration appears to be less important. This work establishes a family of intrinsic exchange bias materials with great tunability by stoichiometry and highlights the strategy of interface engineering in controlling material functionalities.
Phase‐pure [NiO]0.5[Al2O3]0.5spinel nanoparticles (NPs) with limited aggregation were obtained via liquid‐feed flame spray pyrolysis (LF‐FSP) by combusting metalloorganic precursor solutions. Thereafter “chocolate chip‐like” Nix[NiO0.5‐x][Al2O3]0.5nanoparticles consisting of primary [NiO0.5‐x][Al2O3]0.5particles with average particle sizes of 40‐60 nm decorated with Ni metal particles (<10 nm in diameter) dispersed on the surface were synthesized by heat treating the spinel NPs at 800°C/7 h in flowing 5% H2:N2100 mL/min in a fluidized bed reactor. The synthesized materials were characterized using TEM, XRD, FTIR, and TGA/DTA. The Ni depleted areas consist primarily of γ‐Al2O3. The Ni content (800°C) was determined by TGA to be ≈11.3 wt.% based on TGA oxidation behavior. The successful synthesis of such nanocomposites with limited aggregation on a high temperature support provides a facile route to synthesize well‐defined NP catalysts. This work serves as a baseline study for an accompanying paper, wherein thin, flexible, dense films made from these same NPs are used as regenerable catalysts for carbon nanotube syntheses.
more » « less- NSF-PAR ID:
- 10447412
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 102
- Issue:
- 12
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 7145-7153
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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