Ferromagnetic Bismuth-Substituted CeO 2 Nanostructures and Prevalence of Antiferromagnetic Clusters
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ORIGINAL PAPER
Ferromagnetic Bismuth-Substituted CeO2 Nanostructures and Prevalence of Antiferromagnetic Clusters S. K. Alla 1,2 & Sher Singh Meena 3 & Nidhi Gupta 4 & R. K. Mandal 1 & N. K. Prasad 1 Received: 19 July 2020 / Accepted: 25 August 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Bismuth-substituted CeO2 (Bi0.05Ce0.95O2) nanostructured material have displayed room temperature ferromagnetic behavior. The substitution of Ce ions with Bi3+ ions decreased the saturation magnetization (MS) value of CeO2. UV-Vis and photoluminescence spectroscopic analyses revealed the occurrence of defect states i.e. surface oxygen vacancies in the sample, which facilitated ferromagnetic interactions in the Bi-substituted CeO2 nanostructures. Further, the clusters in the sample could provide antiferromagnetic interaction amongst ions, which reduced the MS value of CeO2. The clusters in the annealed sample was substantiated from its ZFC/FC curve. X-ray photoelectron spectroscopy analysis revealed the presence of Bi3+, Ce3+, and Ce4+ ions in the sample. High-resolution transmission electron microscopy (HRTEM) images suggested the spherical and rodshaped morphology for the particles. Keywords Spherical morphology . Surface oxygen vacancies . Antiferromagnetic interactions . Clusters
1 Introduction The prevalence of defect states, specifically oxygen vacancies, in various nanocrystalline oxide materials, led to open up new ways for designing various functional materials [1–3]. The missing oxygen atoms in the crystalline materials result in charge imbalance in the system, which allows redistribution of charges [4]. Consequently, the defect states are induced in the materials, which have an influence on their structural and optical properties. The defects at the surface such as surface oxygen vacancies demonstrated improved electrochemical, catalytic, electric, and magnetic properties [5–7]. Because of surface oxygen vacancies, CeO2 nanostructures have shown many intrinsic advantages like redox property, oxygen storage
* N. K. Prasad [email protected] 1
Department of Metallurgical Engineering, Indian Institute of Technology (BHU), Varanasi 221005, India
2
Department of Physics, Vignan’s Institute of Information Technology, Visakhapatnam 530049, India
3
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
4
Technical Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
capacity (OSC), photocatalysis, and room temperature ferromagnetic behavior (RTFM) [8–10]. It is articulated that the long-range ferromagnetic ordering occurs in several materials such as ZnO, TiO2, CeO2, Al2O3, HfO2, and SnO2 when their size reduces to nanodimension [11]. This has been accomplished to the prevalence of surface oxygen vacancies. In contrast, they exhibit dia- or paramagnetic behavior when their particle size lies in the micrometer range. CeO2 is an n-type semiconductor and can retain its fluorite structure even after the loss of its lattice oxygen atoms
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