Vacuum xxx (xxxx) xxx Please cite this article as: Shalendra Kumar, Vacuum, https://doi.org/10.1016/j.vacuum.2020.109717 Available online 31 August 2020 0042-207X/© 2020 Elsevier Ltd. All rights reserved. Investigations of TM (Ni, Co) doping on structural, optical and magnetic properties of CeO 2 nanoparticles Shalendra Kumar a, * , Kavita Kumari b, ** , Fahad A. Alharthi c , Faheem Ahmed a , Rezq Naji Aljawf d , P.A. Alvi e , Rajesh Kumar f , Mohd Hashim g , Saurabh Dalela h a Department of Physics, College of Science, King Faisal University, P.O Box 400, Hofuf, Al-Ahsa, 31982, Saudi Arabia b Department of Physics, DPG Degree College, Gurugram, 122001, India c Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh, 11451, Saudi Arabia d Department of Physics, Ibb University, Ibb, Yemen e Department of Physics, Banasthali Vidyapith, Banasthali, 304022, Rajasthan, India f University School of Basic and Applied Sciences, Guru Gobind Singh Indraprastha University, New Delhi, 110078, India g Department of Physics, Aligarh Muslim University, Aligarh, 202002, India h Department of Pure & Applied Physics, University of Kota, Kota, 324005, Rajasthan, India A R T I C L E INFO Keywords: CeO 2 XRD Magnetic properties TEM DC Magnetization DMS ABSTRACT The undoped and Ce 0.95 TM 0.05 O 2 (TM: Ni, Co) nanoparticles (NPs), synthesized by co-precipitation method, have been investigated. The structural, morphological, and magnetic properties of the synthesized NPs were char- acterized through X-ray diffraction (XRD), Transmission electron microscopy (TEM), UV–vis absorption spec- troscopy, and dc-magnetization. The particle size as obtained through XRD analysis was found in the range of 7.0–13.0 nm. The Rietveld refnement of the XRD pattern confrms the single-phase nature of NPs. The lattice parameters determined using the Rietveld refnement process was found to have minimum value (5.407 Å) for Co doping as compared to pure CeO 2 . The value of strain is maximum for Co-doped CeO 2 . The particle sizes obtained by TEM show dissimilarity with the XRD outcomes. However, the defects obtained using dislocation density is larger (2.0 × 10 2 ) in Co-doped CeO 2 NPs. The lowest value of the bandgap has been observed (~1.6 eV) for Co- doped CeO 2 NPs. The highest value of saturation magnetization was found to be 8.1 × 10 3 emu/g for Co-doped CeO 2 NPs with a small coercivity of 61.5 Oe. The magnetization measurements infer that the pure and TM doped CeO 2 nanoparticles show weak ferromagnetic behavior at room temperature. 1. Introduction The potential of CeO 2 (ceria) as a foremost candidate for the manufacturing of dilute magnetic semiconductors (DMS) mount due to many reasons. The frst reason being that the cubic fuorite structure of CeO 2 , having a lattice parameter of 0.541 nm, is quite similar to that of silicon. Secondly, it exhibits considerable transparency in the visible range of the spectrum [1–8]. Such properties of ceria make it functional for spintronic applications [9]. The signifcant magnetic moment has been observed in transition metal (TM) doped CeO 2 . This magnetic moment comes from intrinsic origins. While seeking that origin, many factors have been debated like synthesis procedures, magnetic impu- rities, metallic phases, and clusters, etc. But the ferromagnetism induced due to the inaccuracies or miscalculations in the synthesis procedures, impurities, or the unintended metallic phases is accidental. Hence, we cannot rely on the accidently induced ferromagnetism for the manufacturing of robust technological devices. Likewise, magnetic im- purities like transition elements cannot be considered as the sole cause of ferromagnetism because there are many reports which convey that even the doping of CeO 2 with non-3d elements also gives rise to ferro- magnetic signals [10]. Therefore, it becomes essential to determine the actual cause of the intrinsic ferromagnetism in the initially non-magnetic metal oxide systems. Further, it has been observed that ferromagnetic response appears when CeO 2 is transformed from bulk to nano form or doped with any alien element like transition metal ions, light elements, or rare-earth metals [10–13]. However, the trivial * Corresponding author. ** Corresponding author. E-mail addresses: sjagdish@kfu.edu.sa, shaliuphy@gmail.com (S. Kumar), kkmalhan@gmail.com (K. Kumari). Contents lists available at ScienceDirect Vacuum journal homepage: http://www.elsevier.com/locate/vacuum https://doi.org/10.1016/j.vacuum.2020.109717 Received 30 April 2020; Received in revised form 12 August 2020; Accepted 17 August 2020