A Facile Route to Synthesis of Ferromagnetic and Antiferromagnetic Phases of Iron Oxide Nanoparticles by Controlled Heat
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ORIGINAL PAPER
A Facile Route to Synthesis of Ferromagnetic and Antiferromagnetic Phases of Iron Oxide Nanoparticles by Controlled Heat Treatment of Ferritin Sunil Kumar 1 & Anjali Thakur 1 & Saral K. Gupta 2 & Parasmani Rajput 3 & Amarjeet Singh 1 Received: 4 July 2020 / Accepted: 13 August 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Magnetic nanoparticles of ferromagnetic and antiferromagnetic phases were synthesized from controlled heat treatment of dry ferritin powder in a bottom-up approach. Heat treatment paves the way for synthesis of Fe2O3 solid phase from iron molecular complexes stored in the cavity of ferritin; the strong increase (~ 150 times) in saturation magnetization is a sign of the presence of ferromagnetic exchange coupling which exists only in solid phase. In this experimental study, vibrating sample magnetometer (VSM) was used to study magnetic induction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed for analysis of structure and morphology of the samples. Differential scanning calorimetry (DSC) was used to search for indicators of structural phase transformation through scanning of temperature. The nanoparticle size with highly narrow distribution (mean size ~ 6 nm) was observed by SEM for sample annealed at 430 °C. As indicated by XRD measurements, the majority phase of Fe2O3 nanoparticles was amorphous up to 500 °C, whereas DSC demarcates the crystalline phase transition temperature at 545 °C. The annealing temperature range from 400 to 500 °C was found to be suitable for growing ferromagnetic nanoparticles endowed with high saturation magnetization and low coercivity. At higher range of annealing temperature (500– 700 °C), XRD confirms the presence of α-Fe2O3 (haematite) phase which is an antiferromagnetic crystalline system with weak magnetization. A systematic decline of magnetization on increasing the annealing temperature beyond 500 °C was attributed to finite size effects and increased purity of antiferromagnetic phase. Keywords Nanoparticles . Ferritin . Iron oxide . Magnetic ordering . Phase transition
1 Introduction Nanosize iron oxide is a fascinating material with richness of several polymorphs endowed with unique magnetic and optical properties [1]. Several polymorphs of iron oxide—αFe2O3 (haematite), β-Fe2O3, γ-Fe2O3 (maghemite) and εFe2O3—are available with different crystal structure symmetries [1]. Each crystalline phase is characterized with a distinctive magnetic ordering suitable for soft and hard magnetic * Amarjeet Singh [email protected] 1
Department of Physics, Himachal Pradesh University, Summer Hill, Shimla 171005, India
2
Department of Physics, Banasthali Vidyapith, Banasthali, Rajasthan 304022, India
3
Atomic & Molecular Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
applications. Magnetization and demagnetization is easy to achieve in former case and hard to achieve for later. Soft magnetic materials are ubiquitous in power electronics [2]. Recent
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