Influence of Nd-Co Substitution on Structural, Electrical, and Dielectric Properties of X-Type Hexagonal Nanoferrites Imran Sadiq, Irshad Ali, Evgeny V. Rebrov, Shahzad Naseem, M.Naeem Ashiq, and M.U. Rana (Submitted April 26, 2013; in revised form September 20, 2013; published online October 24, 2013) A series of single phase X-type hexagonal ferrites with concentration Sr 22x Nd x Ni 2 Fe 282y Co y O 46 (x = 0.02, 0.04, 0.06, 0.08, 0.10 and y = 0.1, 0.2, 0.3, 0.4, 0.5) has been prepared by sol-gel method sintered at 1250 °C for 6 h. The x-ray diffraction analysis reveals the single phase of X-type hexagonal ferrites. The particle size was calculated by using SEM and TEM. The ferrite substituted with Nd 3+ and Co 2+ has average particle size in the range of 40-50 nm. The room temperature electrical resistivity experiences the significant enhancement from a value of 1.1 3 10 7 to 2.03 3 10 8 Xcm with the increase in Nd 3+ and Co 2+ concentration. The dielectric constant exhibits high value at low frequencies and decreases with the increase of frequency. The tangent dielectric loss shows the abnormal behavior which can be explained on the basis of hopping between the Fe 2+ and Fe 3+ ions on octahedral sites. The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices (MF). Keywords dielectric properties, electrical properties, ferrites, soft magnets, sol-gel processing, x-ray methods 1. Introduction Increasing attention has been devoted to hexagonal ferrites, the well-known ferrimagnetic materials, due to the high resistivity and permeability suitable for various applications, such as magnetic recording media, absorbers, and microwave and mm-wave devices (Ref 1). The hexagonal structure of these ferrimagnetic materials allows extremely high magnetocrystal- line anisotropy and gives them distinctive combination of dielectric and magnetic properties (Ref 2). Due to high uni- axial magnetic anisotropy, these materials are quite suitable for microwave absorption properties (Ref 3, 4). For the hexagonal structure, there are six possible different types designated M, W, X, Y, Z and U. It is well known that the structural, electrical, dielectric and magnetic properties can be tuned by substitution for Fe 3+ and Ba/Sr with other ions (Ref 5). Rare earth elements with typical relaxation properties can affect drastically the structural, electrical and magnetic properties (Ref 6-8). For electrical and dielectric properties, the nanosized forms of such materials are much interesting because of their excellent insulating performance. So, the methods which are capable of synthesizing nanosized substituted hexagonal ferrites become noteworthy (Ref 9). Various methods such as mechanical milling, inert gas consideration, hydrothermal reaction and standard ceramic method have been employed for the prepa- ration of nanosized hexagonal ferrites (Ref 10-12). Sol-gel method is an appropriate method with relatively low sintering temperature for the preparation of fine particles (Ref 13). Many researchers synthesized the rare earth substituted hexaferrites and reported their affect on structural and dielectric properties (Ref 7, 8, 14). Ashiq et al (Ref 15) adopted the sol- gel method to synthesize the Er-Ni substituted M-type hexa- ferrites. The results indicated high potential for being used in microwave and high density magnetic recording media tech- nology. However, the electrical and dielectric properties of Nd-substituted x-type hexagonal ferrites have seldom been reported, so we selected Nd-Co substituted x-type hexagonal ferrites for investigation. The main aim of this work is to synthesize nanoferrites and study the influence of rare earth element Nd 3+ and divalent Co 2+ substitution on structural, electrical and dielectric prop- erties of x-type hexagonal ferrites. 2. Experimental Procedure The polycrystalline samples with composition Sr 2x Nd x Ni 2 Fe 28y Co y O 46 (x = 0.02, 0.04, 0.06, 0.08, 0.10 and y = 0.1, 0.2, 0.3, 0.4, 0.5) were prepared by sol-gel method. The stoichiometric ratios of raw materials (Sr(No 3 ) 2 , Co(No 3 ) 2 , NiCl 2 . 6H 2 O, Nd 2 O 3 , Iron nitrate, Citric Acid) were mixed in deionized water. Nd 2 O 3 was converted in the Neodymium Nitrate using nitric acid. The gel was attained by stirring the solution at 80 °C. The gel was burnt at 400 °C for 1 h and then sintered at 1250 °C for 6 h to attain the required phase. Polyvinyl alcohol was used as a binder for making pellets. The Imran Sadiq, Irshad Ali, and M.U. Rana, Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan; Evgeny V. Rebrov , School of Chemistry and Chemical Engineering, QueenÕs University Belfast, Belfast, UK; Shahzad Naseem, Centre for Solid State Physics, University of Punjab, Lahore, Pakistan; and M. Naseem Ashiq, Institute of Chemical Sciences, Bahauddin Zakariya University, Multan 60800, Pakistan. Contact e-mails: khanphysics@yahoo.com and mazharrana@bzu.edu.pk. JMEPEG (2014) 23:622–627 ÓASM International DOI: 10.1007/s11665-013-0758-x 1059-9495/$19.00 622—Volume 23(2) February 2014 Journal of Materials Engineering and Performance