Interfacial spin coupling and exchange anisotropy in core–shell MnFe2O4/α-Fe2O3 nanocomposites
Department of Physics, National Institute of Technology Patna, Patna, Bihar, 800005, India
2 Department of Physics and Astronomy and Nebraska Center for Materials and Nanostructures, University of Nebraska, Lincoln, NE, 68588, USA
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Accepted: 30 April 2020
Published online: 19 May 2020
Core–shell MnFe2O4/α-Fe2O3 nanoparticles having core diameters from 5 nm to 28 nm are synthesized by chemical co-precipitation route and investigated structurally and magnetically. The existence of the cubic spinel phase of MnFe2O4 (FiM) core together with the rhombohedral phase of α-Fe2O3 (AFM) shell was confirmed by X-ray diffraction. The field-cooled hysteresis loop at 5 K reveals a strong exchange bias of 1.1 kOe along with a high coercivity of 4.81 kOe and vertical shift of 1.83% for the particles with the smallest core diameters. The exchange-bias (H E) and coercive (H C) fields decrease with increasing core diameter. Exchange-spring behavior was also observed in the hysteresis loops in all nanocomposite systems at 5 K due to the presence of the magnetically hard (α-Fe2O3) and soft (MnFe2O4) phases. The superparamagnetic limit shifted above room temperature even for the sample having core diameter of 5 nm due to the presence of strong interfacial spins coupling, and this coupling was also seen in the hysteresis loops obtained at room temperature.
© Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature, 2020