CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International ] (]]]]) ]]]–]]] Influence of cobalt substitution on the magnetic properties of zinc nanocrystals synthesized via micro-emulsion route Huma Malik a , Azhar Mahmood b , Khalid Mahmood a , Maria Yousaf Lodhi a , Muhammad Farooq Warsi b,n , Imran Shakir c,d , Hassan Wahab e , M. Asghar a , Muhammad Azhar Khan a,nn a Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan b Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan c Deanship of Scientific Research, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia d Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS Institute of Information Technology (CIIT), Lahore, Pakistan e Physics Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan Received 21 January 2014; received in revised form 5 February 2014; accepted 6 February 2014 Abstract A series of nanocrystalline spinel ferrites with chemical formula Co x Zn 1 x Fe 2 O 4 (x ¼ 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were synthesized by the micro-emulsion technique. The samples were annealed at 700 1C for 7 h at the rate of 15 1C/min. The cubic spinel structure was systematically examined by X-ray diffraction and Fourier transform infrared spectroscopy. The lattice constant decreased from 8.39 to 8.34 Å as the Co concentration increased from x ¼ 0 to x ¼ 1 because of the smaller ionic radii of Co as compared to Zn. The dielectric properties of the synthesized nanomaterials were studied in the frequency range 1–3 GHz. The dielectric properties were influenced by Co substitution and were explained by the electron hopping mechanism between Fe 2 þ and Fe 3 þ ions. Vibrating sample magnetometry was used to study the magnetic parameters of these nanoferrites. M–H loops of the materials show Co x Zn 1 x Fe 2 O 4 nanocrystals to exhibit ferrimagnetic behavior at room temperature. The magnetic properties are explained in terms of cation distribution and grain size effect. Thus high M s (21.29 emu/g) and H c (1382.4 Oe) exhibited by the CoFe 2 O 4 nanocrystals are favorable for their potential use in high density recording media applications. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Nanocrystalline ferrites; Co-substitution; Micro-emulsion; XRD; M–H loops 1. Introduction Since last two decades, the nanomaterials have been extensively studied worldwide because of their unique proper- ties that are not exhibited by the corresponding bulk materials. Among various nanomaterials, the spinel ferrite (MFe 2 O 4 , M ¼ Ni, Co, Mn, Zn, etc.) nanocrystals have become immen- sely popular magnetic materials due to some unique properties exhibited by these materials. These properties include large magnatocrystalline anisotropy, high coericivity, mechanical harness and chemical stability [1–3]. These specific properties make them useful in various technical applications such as magnetic recording devices, magnetic storage devices, mag- netic resonance imaging enhancement, catalysis, drug targeting and gas sensors [4–7]. Furthermore, nanoferrites are gaining substaintial interest among the research community as they exhibit a relationship between magnetic properties and their crystal structure. It is reported in literature that small crystalline size significantly improved the electrical and magnetic proper- ties of ferrites [8]. Therefore different synthesis techniques like hydrothermal treatment [9], emulsion method [10], co-precipitation [11], mechano-chemical method [12], micro-wave sintering [13], electrochemical synthesis [14], sol –gel synthesis [14] and chemical micro-emulsion method [15] are frequently used for the synthesis www.elsevier.com/locate/ceramint http://dx.doi.org/10.1016/j.ceramint.2014.02.015 0272-8842 & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. n Corresponding author. nn Corresponding author. Tel.: þ 92 62 9255461. E-mail address: azhar_manais@yahoo.com (M.A. Khan). Please cite this article as: H. Malik, et al., Influence of cobalt substitution on the magnetic properties of zinc nanocrystals synthesized via micro-emulsion route, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.02.015