Issue 58, 2015

Unexpected surface superparamagnetism in antiferromagnetic Cr2O3 nanoparticles

Abstract

We report an unexpected superparamagnetic behavior of antiferromagnetic Cr2O3 nanoparticles. The Cr2O3 particle cores retain their original antiferromagnetic phase, while the surfaces of the particles become superparamagnetic. The X-ray diffraction results confirm that the sample has a corundum structure without any other phases. Through X-ray photoelectron spectroscopy characterization, the particle surfaces present three different oxidation states: Cr3+ (antiferromagnetic), Cr4+ (ferromagnetic), and Cr6+ (nonferromagnetic). A bimagnetic particle model with Cr3+ cores and higher Cr oxidation surface states is used to explain the experimental results. In addition, we observe that spin-flop transitions occur in the antiferromagnetic cores below the NĂ©el temperature (292 K). The spin-flop transition field is uncommon compared with other research, this novel behavior is attributed to the presence of superparamagnetism in the surfaces through the exchange field. These findings reveal the significance of surface states in mediating the magnetic properties in antiferromagnetic materials.

Graphical abstract: Unexpected surface superparamagnetism in antiferromagnetic Cr2O3 nanoparticles

Supplementary files

Article information

Article type
Paper
Submitted
06 Mar 2015
Accepted
08 May 2015
First published
11 May 2015

RSC Adv., 2015,5, 46705-46710

Author version available

Unexpected surface superparamagnetism in antiferromagnetic Cr2O3 nanoparticles

Z. Yang, J. Zhang, D. Gao, Z. Zhu, G. Yang and D. Xue, RSC Adv., 2015, 5, 46705 DOI: 10.1039/C5RA04009D

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