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Open AccessArticle

Investigating Exchange Bias and Coercivity in Fe3O4–γ-Fe2O3 Core–Shell Nanoparticles of Fixed Core Diameter and Variable Shell Thicknesses

1
Department of Physics, United Arab Emirates University, Al-Ain 15551, UAE
2
Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Straße-40, 01187 Dresden, Germany
3
Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata 700064, India
4
Department of Physics, Sultan Qaboos University, P.O. Box 36, Muscat PC 123, Sultanate of Oman
*
Author to whom correspondence should be addressed.
Nanomaterials 2017, 7(12), 415; https://doi.org/10.3390/nano7120415
Received: 15 October 2017 / Revised: 22 November 2017 / Accepted: 23 November 2017 / Published: 26 November 2017
We have carried out extensive measurements on novel Fe3O4–γ-Fe2O3 core–shell nanoparticles of nearly similar core diameter (8 nm) and of various shell thicknesses of 1 nm (sample S1), 3 nm (sample S2), and 5 nm (sample S3). The structure and morphology of the samples were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The direct current (DC) magnetic measurements were carried out using a superconducting quantum interference device (SQUID). Exchange bias and coercivity were investigated at several temperatures where the applied field was varied between 3 and −3 T. Several key results are obtained, such as: (a) the complete absence of exchange bias effect in sample S3; (b) the occurrence of nonconventional exchange bias effect in samples S2 and S1; (c) the sign-change of exchange bias field in sample S2; (d) the monotonic increase of coercivity with temperature above 100 K in all samples; (e) the existence of a critical temperature (100 K) at which the coercivity is minimum; (f) the surprising suppression of coercivity upon field-cooling; and (g) the observation of coercivity at all temperatures, even at 300 K. The results are discussed and attributed to the existence of spin glass clusters at the core–shell interface. View Full-Text
Keywords: nanoparticles; shell thickness; field cooling; exchange bias; coercivity nanoparticles; shell thickness; field cooling; exchange bias; coercivity
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MDPI and ACS Style

Obaidat, I.M.; Nayek, C.; Manna, K.; Bhattacharjee, G.; Al-Omari, I.A.; Gismelseed, A. Investigating Exchange Bias and Coercivity in Fe3O4–γ-Fe2O3 Core–Shell Nanoparticles of Fixed Core Diameter and Variable Shell Thicknesses. Nanomaterials 2017, 7, 415.

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