Sintering temperature dependence of room temperature magnetic and dielectric properties of Co 0.5 Zn 0.5 Fe 2 O 4 prepared using mechanically alloyed nanoparticles Samaila Bawa Waje a,n , Mansor Hashim a,b , Wan Daud Wan Yusoff b , Zulkifly Abbas b a Advanced Materials and Nanotechnology Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia b Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia article info Article history: Received 14 June 2009 Received in revised form 14 September 2009 Available online 30 October 2009 Keywords: Mechanical alloying Sintering temperature Permeability Permittivity Nanoparticles abstract Co 0.5 Zn 0.5 Fe 2 O 4 nanoparticles were prepared using mechanical alloying (MA) and sintering. The crystallite size, coercivity, retentivity and saturation magnetization were also measured. The frequency dependence of dielectric and the magnetic parameters, namely, real permittivity e 0 , loss tanget tan d, real permeability m 0 and loss factor m 00 were measured at room temperature for samples sintered from 600 to 1000 1C, in the frequency range 10 MHz to 1.0 GHz. The results show that the crystallite size of the resulting products ranges between 16 and 67 nm for as-milled sample and the sample sintered at 1000 1C, respectively. The sample sintered at 1000 1C, measured at room temperature exhibited a saturation magnetization of 37 emu g 1 . The values of permittivity remain constant within the measured frequency, but vary with sintering temperature. The permeability values, on the other hand however vary with both the sintering temperature and the frequency, thus, the absolute value of the permeability decreased after the natural resonance frequency. & 2009 Elsevier B.V. All rights reserved. 1. Introduction Magnetic nanoparticles have generated great interest due to their importance in fundamental understanding of physical processes and technological applications [1]. Due to the very small sizes of the particles involved, which are of the order of the magnetic domain sizes in the corresponding bulk materials, novel magnetic behaviors are observed for the nanosized magnetic particles when compared to that of the bulk counterparts [2]. The interesting magnetic properties of ferromagnetic spinel ferrites originate mainly from the magnetic interactions between cations with magnetic moments that are situated in the tetrahedral (A) and the octahedral (B) sites [3]. ZnFe 2 O 4 is a normal spinel with all the Fe 3+ ions in the B sites and all the Zn 2+ ions in the A sites, whereas CoFe 2 O 4 has an inverse spinel structure with the Co 2+ ions mainly in the B sites and Fe 3+ ions distributed almost equally between the A and the B sites [4]. Therefore, Co 0.5 Zn 0.5 Fe 2 O 4 has a mixed spinel type of structure. Although the preparation of cobalt–zinc ferrites have been reported elsewhere [6–8], our literature search shows that there is no report on the permittivity and permeability within 10 MHz to 1.0 GHz reported, despite the materials potential use as a wave absorber for electromagnetic interference (EMI). In this paper, we sintered mechanically alloyed (MA) nanoparticles to produce Co 0.5 Zn 0.5 Fe 2 O 4 ferrite at a relatively low temperature, compared to conventional solid-state technique. The nanoparticles were firstly prepared by mechanical alloying and then sintered at various temperatures from 600 to 1000 1C in order to fabricate polycrystalline materials. Their microstructure properties are reported as a function of frequency and the sintering temperatures. 2. Materials and method All reagents used were of analytical grade from Alfar Aesar without any further purification. The starting powders of Co 3 O 4 (99.7%), Fe 2 O 3 (99.5%) and ZnO (99.0%) were weighed according to the targeted proportion and milled using a SPEX8000D in order to produce Co 0.5 Zn 0.5 Fe 2 O 4 nanoparticles. Mechanical alloying was carried out at room temperature in a planetary ball mill equipped with a hardened steel vial and balls. In order to avoid an increase in the vial temperature, the milling procedure was interrupted for 5 min after every 15 min of milling. The milling media consisted of ten 12 mm diameter balls confined in a 120 ml volume container. A total of 8 g powder with no process control agent was used in all MA runs. The resulting particles were granulated using 2% PVA and lubricated using zinc stearate and then molded into samples of toroidal and disc shapes. The samples was ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials 0304-8853/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2009.10.041 n Corresponding author. Tel.: + 60 389467546; fax: + 60 38656 6061. E-mail address: samaila@hotmail.com (S.B. Waje). Journal of Magnetism and Magnetic Materials 322 (2010) 686–691