crystals Article Structural and Magnetic Properties Study of Fe 2 O 3 /NiO/Ni 2 FeO 4 Nanocomposites Zakia Alhashem 1, *, Chawki Awada 1, * , Faheem Ahmed 1 and Ashraf H. Farha 1,2   Citation: Alhashem, Z.; Awada, C.; Ahmed, F.; Farha, A.H. Structural and Magnetic Properties Study of Fe 2 O 3 /NiO/Ni 2 FeO 4 Nanocomposites. Crystals 2021, 11, 613. https://doi.org/10.3390/ cryst11060613 Academic Editors: Assem Barakat and Alexander S. Novikov Received: 1 April 2021 Accepted: 26 May 2021 Published: 29 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Physics, College of Science, King Faisal University, P.O. Box 400, Al-Ahsa 31982, Saudi Arabia; fahmed@kfu.edu.sa (F.A.); afarha@kfu.edu.sa (A.H.F.) 2 Semiconductors Technology Lab, Physics Department, Faculty of Science, Ain Shams University, Cairo 11566, Egypt * Correspondence: zalhashim@kfu.edu.sa (Z.A.); cawada@kfu.edu.sa (C.A.) Abstract: In the current work, the nanocomposites that consist chiefly of three components—α-Fe 2 O 3 , NiO and Ni 2 FeO 4 , in two different ratios 2:2:1 (FNN-221) and 2:1:1 (FNN-211), respectively—were produced. The synthesis was done in two steps by following the chemical co-precipitation and mechanical ball-milling route. The presence of individual phase was identified from the XRD data without the detection of any additional impurities. The phase fraction of each component estimated from the profile fitting of XRD patterns were found to be 41.2%, 39.7%, 19.1% in FNN-221 sample and 49.5%, 26.4%, 24.1% for FNN-211 sample, respectively, which were consistent with the experimental values. The total magnetization at 300 K was obtained to be 13.41 emu/g and 10.95 emu/g for FNN-221 and FNN-211 samples, respectively. In FNN-211 compound the zero field coercivity (H C ) expanded towards the higher field values thereby signifying the exchange bias behavior. Furthermore, the exchange bias field (H ex ) for FNN-211 was obtained as 35.1 Oe. Keywords: nanocomposites; co-precipitation; ball-milling; crystal growth; magnetometry; exchange bias 1. Introduction Recently, the multi-component magnetic nanoparticles captivated an enormous deal of research and technological interests among scientific communities. An important ad- vantage of such materials over single phased magnetic nanostructures is that the magnetic properties of the former are deeply correlated to the interfacial interactions and contact be- tween the components. Thus, their physical properties can be drastically tailored/induced simply by adjusting the chemical compositions, geometrical shapes and ratios of different components [1–5]. Because of these characteristics, the magnetic nanocomposites can be directly exploited in several new technological fields like spintronic devices, hyperthermia treatment, permanent magnets, photocatalysts and high-density magnetic storage me- dia [6–9]. Nanocomposites involving the ferrites (oxides of iron) are the most extensively investigated materials in this context. Lately, the methods for the production of ferrite nanocomposites have been centered around the fabrication of metal doped ferrites into a non-magnetic and/or matrix with weak magnetic polarity (SiO 2 , ZnO, titanates) [2,10–12]. The contrast in the magnetic polarity between the host matrix and the foreign particle facilitates a variation in the degree interactions among the charge carriers. Thereby the magnetic transition and anisotropic nature can be affected. The ferrites of Cobalt (Co) and Nickel (Ni) have shown synergistic improvement in their chemical and thermal sta- bility upon dispersion in a porous silica matrix [13–15]. Moreover, the low temperatures anomalies in the magnetic hysteresis and modification in the internal coercive field in the case of binary ferrites-ZnO nanocomposites, have also been mentioned in the litera- ture [10,16,17]. Not long ago Galizia et al. investigated a “wasp waist” hysteresis loop in spinel ferrites-composites. It has been noticed that the wasp-waist shape of hysteresis in the spinel ferrites composites is sensitive toward the phase fraction/ratios and particle size Crystals 2021, 11, 613. https://doi.org/10.3390/cryst11060613 https://www.mdpi.com/journal/crystals