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

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Manna,  Kaustuv
Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Citation

Obaidat, I. M., Nayek, C., Manna, K., Bhattacharjee, G., Al-Omari, I. A., & Gismelseed, A. (2017). Investigating Exchange Bias and Coercivity in Fe3O4-gamma-Fe2O3 Core-Shell Nanoparticles of Fixed Core Diameter and Variable Shell Thicknesses. Nanomaterials, 7(12): 415, pp. 1-17. doi:10.3390/nano7120415.


Cite as: http://hdl.handle.net/21.11116/0000-0000-2F30-6
Abstract
We have carried out extensive measurements on novel Fe3O4-gamma-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.