Comprehensive structural and magnetic properties of iron oxide nanoparticles synthesized through chemical routes Anamika Ghosh a, b , Veeturi Srinivas b , Ramaprabhu Sundara a, * a Alternative Energy Nanotechnology Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai, 600036, India b Department of Physics, Indian Institute of Technology Madras, Chennai, 600036, India article info Article history: Received 6 August 2019 Received in revised form 5 November 2019 Accepted 5 November 2019 Available online xxx Keywords: Superparamagnetic Size effect Exchange interaction High temperature magnetization Anisotropy constant ISP model abstract Magnetite (Fe 3 O 4 ) is one of the most widely explored ceramic materials for the applications in various industrial and biomedical levels. Applications towards specific field require tuning of its properties, which can be modulated by controlling particle size as well as different synthesis parameters and conditions. In present work, we have chosen six different chemical synthesis routes and performed a comparative study on variations in structural and physical properties. Present results show that all the synthesis methods provide particles of nanometer range, but the average size of the particle and particle size distribution is different for each method. Present analyses of room temperature and low tempera- ture magnetic data confirm the possibility of presence of superparamagnetic state in 6e8 nm particles. Moreover, the interaction effects are dominant above blocking temperature. From the magnetization data it is also shown how the exchange term evolves as the particle size increases. Additionally, high temperature magnetic measurements are also carried out to compare size dependent magnetic response towards increasing temperature. Since the finite size effects dominate in this range of particles, we believe present study can provide a guideline to choose particular synthesis method for specific application. © 2019 Elsevier B.V. All rights reserved. 1. Introduction Spinel ferrites nanoparticles (NPs) have been the subject of in- terest for the past few decades because of their remarkable mag- netic properties particularly in the high-frequency region. Spinel ferrites with structural formula AB 2 O 4 , where A represents divalent cation (Fe þ2 ) distributed in tetrahedral site and B represents trivalent cation (Fe þ3 ) in octahedral site coordinated by oxygen [1 ,2]. Properties of ferrites are solely dependent on the cationic distribution among tetrahedral and octahedral sites. However, size effects play an important role in modifying the physical and mag- netic properties that enables us to use them for a wide range of potential applications, such as, electronic circuits, power delivering devices, electromagnetic interference suppression, and in biomedicine [1 ,3e7]. Among various magnetic nanoparticles (MNP), typically iron oxides nanoparticles (IONPs) which form in three natural types, such as, hematite (a-Fe 2 O 3 ), maghemite (g- Fe 2 O 3 ), and magnetite (Fe 3 O 4 ) are physically and chemically stable, biocompatible and environmentally safe [8], thus presenting unique characteristics for clinical applications. As the particle size is reduced it undergoes multidomain state to a stable single domain state below a critical diameter, D c , and then it undergoes stable to unstable single domain called superparamagnetic (SPM) particles [8]. Stable single domain particles show high coercivity and remanence which is highly desirable for memory storage applica- tion while SPM particles show zero coercivity and remanence suitable for various biomedical applications. In fact, IONPs reach smaller sizes (about 10e20 nm for iron oxide), superparamagnetic properties become evident, so that the particles reach a better performance for most of the aforementioned applications [8]. Despite the growing body of evidence attesting their biomedical usefulness, superparamagnetic IONPs are still in early stage of clinical investigation, with studies pointing out to the need for their improvement prior to their commercialization. As mentioned earlier the functions of IONPs directly related to size, shape, coating and stability which in turn depend on synthesis methods. Surface effect of nanoparticles arises from the uncompensated surface spin or canted spin that lead reduction in magnetization compared to its * Corresponding author. E-mail addresses: nmkghosh04@gmail.com (A. Ghosh), veeturi@iitm.ac.in (V. Srinivas), ramp@iitm.ac.in (R. Sundara). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2019.152931 0925-8388/© 2019 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds xxx (xxxx) xxx Please cite this article as: A. Ghosh et al., Comprehensive structural and magnetic properties of iron oxide nanoparticles synthesized through chemical routes, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152931