Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Magnetic and dielectric properties of Zn substituted cobalt oxide nanoparticles H. Bindu Duvuru a , S.K. Alla b,c , S.K. Shaw b , Sher Singh Meena d , Nidhi Gupta e , B.B.V.S. Vara Prasad f , M.M. Kothawale g , M.K. Kumar a , N.K. Prasad b,* a JNTUA College of Engineering, Ananta puramu, 515002, India b Department of Metallurgical Engineering, Indian Institute of Technology (BHU), Varanasi, 221005, India c Department of Basic Science and Humanities, Vignan's Institute of Information Technology, Visakhapatnam, 530049, India d Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085, India e Technical Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085, India f Department of Physics, MVGR College of Engineering, Vizianagaram, 535005, Andhra Pradesh, India g Department of Physics, Dnyanprassarak Mandal's College and Research Centre, Assagao, Bardez, Goa, 403 507, India ARTICLE INFO Keywords: Co 3 O 4 nanoparticles Zn substitution Microwave refluxing Magnetic Dielectric properties ABSTRACT Zinc-substituted cobalt oxide nanoparticles (Zn x Co 3-x O 4, 0 ≤ x ≤ 0.5) were produced by microwave refluxing technique. The structural, microstructural and magnetic properties of these samples were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and mag- netic property measurement system (MPMS) respectively. XRD and TEM analyses confirmed the single phase nature for all the samples. Rietveld analysis of the samples further confirmed the substitution of Zn-ions into the Co 3 O 4 lattice. The chemical states of the elements were studied using X-ray photoelectron spectroscopy (XPS), which suggest the presence of Zn 2+ , Co 2+ , and Co 3+ ions in the samples. The maximum saturation magneti- zation (M S ) values of 0.33 Am 2 /kg was obtained for x = 0.01 sample, and then it continuously reduced with increased Zn content. The dielectric property of the samples was studied in the frequency range of 40 Hz–110 MHz. The samples x = 0.05 and 0.5 displayed the lowest conductivity due to the narrow size dis- tribution of grains. 1. Introduction Currently, the researches on magnetic, optical, catalytic, and elec- trochemical properties of Co 3 O 4 created great interest due to its wide technological applications. The applications include gas sensors, elec- trochemical devices, solid-state sensors, heterogeneous catalysts, and lithium-ion batteries [1–7]. Co 3 O 4 possess cubic normal spinel crystal structure with tetrahedral sites occupied by Co 2+ (3 d 7 ) ions and oc- tahedral sites by Co 3+ (3 d 6 ) ions [8]. Predominantly, the magnetic moment of Co 3 O 4 arises due to Co 2+ ions. However, it also has a small contribution from spin-orbit coupling [8]. In contrast, Co 3+ ions at octahedral sites do not contribute to the permanent magnetic moment. Further, it is well documented that cubic bulk Co 3 O 4 is an anti- ferromagnetic material with Néel temperature (T N ) ≈ 40K [8]. The antiferromagnetic ordering for this oxide exists due to super-exchange interactions through two favorable paths such as Co 2+ –O–Co 2+ and Co 2+ –O–Co 3+ –O– Co 2+ . Interestingly, a weak ferromagnetic behavior is also noticed for cobalt oxide nanoparticles [9–11]. Besides, the magnetic properties of Co 3 O 4 are highly sensitive to shape, crystallinity, and magnetization direction. For example, Prabaharan et al. reported that the Co 3 O 4 na- noparticles produced by precipitation method, exhibit weak ferromag- netic behavior with an M S value of 0.34 Am 2 /kg [12]. The other re- searchers have also reported weak ferromagnetic behavior for Co 3 O 4 nanoplates [13]. As stated earlier, this cobalt oxide nanoparticles also display antiferromagnetic characteristic below 27 K, super- paramagnetic nature between 27 and 45 K but paramagnetic behavior above 45 K [14]. Further, Moro et al. produced cobalt oxide nanoparticles by the continuous-flow hydrothermal method [9]. They observed fascinating magnetic properties such as weak ferromagnetism, spin canting of ions at the surface, exchange bias effect at low temperatures and super- paramagnetism at room temperature. In contrast, Co 3 O 4 nanotubes have shown weak ferromagnetic behavior and the presence of strong https://doi.org/10.1016/j.ceramint.2019.05.185 Received 13 March 2019; Received in revised form 16 May 2019; Accepted 17 May 2019 * Corresponding author. E-mail address: nandkp.met@iitbhu.ac.in (N.K. Prasad). Ceramics International 45 (2019) 16512–16520 Available online 18 May 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved. T