Eur. Phys. J. Plus (2020) 135: 413
https://doi.org/10.1140/epjp/s13360-020-00430-8

Regular Article

Interfacial spin coupling and exchange anisotropy in core–shell MnFe₂O₄/α-Fe₂O₃ nanocomposites

¹ 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

^* e-mail: samrat.udc@gmail.com

Received: 1 December 2019
Accepted: 30 April 2020
Published online: 19 May 2020

Abstract

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.