期刊
NANOSCALE
卷 5, 期 17, 页码 7872-7881出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c3nr02247a
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- U.S. Department of Energy (DOE) [DE-FC07-08ID14926]
- INL-LDRD under the DOE [DE-AC07-05ID14517]
- DOE by Battelle [DE-AC05-76RL01830]
Cr-doped core-shell iron/iron-oxide nanoparticles (NPs) containing 0, 2, 5, and 8 at.% of Cr dopant were synthesized via a nanocluster deposition system and their structural and magnetic properties were investigated. We observed the formation of a sigma-FeCr phase in 2 at.% of Cr doping in core-shell NPs. This is unique since it was reported in the past that the sigma-phase forms above 20 at.% of Cr. The large coercive field and exchange bias are ascribed to the antiferromagnetic Cr2O3 layer formed with the Fe-oxide shell, which also acts as a passivation layer to decrease the Fe-oxide shell thickness. The additional s-phase in the core and/or Cr2O3 in the shell cause the hysteresis loop to appear tight waisted near the zero-field axis. The exchange interaction competes with the dipolar interaction with the increase of sigma-FeCr grains in the Fe-core. The interaction reversal has been observed in 8 at.% of Cr. The observed reversal mechanism is confirmed from the Henkel plot and delta M value, and is supported by a theoretical watermelon model based on the core-shell nanostructure system.
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