Materials Chemistry and Physics 111 (2008) 225–231 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Microstructure, hysteresis and microwave absorption analysis of Ba (1 - x) Sr x Fe 12 O 19 ferrite S. Bindra Narang a,∗ , Charanjeet Singh b , Yang Bai c , I.S. Hudiara d a Department of Electronics Technology, Guru Nanak Dev University, Amritsar, Punjab, India b Department of Electronics and Communication Engineering, Amritsar College of Engineering and Technology, Mananwala, Amritsar, Punjab, India c School of Materials Science and Engineering, University of Science and Technology Beijing, China d KC College of Engg. and IT, Nawanshahar, Punjab.India article info Article history: Received 4 August 2007 Received in revised form 20 March 2008 Accepted 23 March 2008 Keywords: Ceramics X-ray diffraction topography Magnetic properties Microstructure abstract M-type hexagonal ferrite series, Ba (1-x) Sr x Fe 12 O 19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0), has been synthesized by conventional ceramic method. Hysteresis parameters have been investigated at an applied field of 10kOe and absorption has been studied at X-band as a function of thickness, substitution and frequency. Microstructure and X-ray diffraction confirmed hexagonal structure of ferrite. The substitution causes profound increase in absorption, coercivity and magnetization. The magnetic parameters have been characterized by taking into account microstructure and preferential site occupancy. Curie temperature decreases with substitution due to the formation of spin canting structure. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Ferroxdure MFe 12 O 19 , hexagonal ferrites are known for their uniaxial magnetocrystalline anisotropy with ease of magnetization along c-axis [1]. In the past 50 years, various synthesis techniques with different substitutions have been adopted to produce mate- rials suitable for magnetic recording and microwave applications. Barium ferrite can be used as microwave absorber owing to high saturation magnetization, coercivity and anisotropy field [2]. The application of hexagonal ferrites in the area of magnetic recording demands proper control of homogeneity and morphology. Magnetic properties of BaM or SrM hexagonal ferrite can be tailormade by substitution of Ba 2+ and/or Fe 3+ ions. Reports are available in the literature for various properties of Ba–Sr ferrite. Huanosta-Tera et al. [3] studied ac and dc electrical properties of Ba (1-x) Sr x Fe 12 O 19 ferrite using ceramic method. An et al. [4] have reported magnetic properties of Ba–Sr ferrite synthesized by sol–gel method while Parkin et al. [5] have rationalized magnetic properties of same ferrite synthesized by self-propagating high temperature synthesis. Unfortunately, there is not yet a consistent relationship between microstructure and magnetic and microwave absorption properties in Sr-substituted BaM ferrite. The present work just provides the expected contribution to this subject. ∗ Corresponding author. Tel.: +91 183 2256203; fax: +91 183 2258820. E-mail address: sukhleen2@yahoo.com (S.B. Narang). 2. Experimental Polycrystalline M-type hexagonal ferrites of composition Ba (1-x) SrxFe12O19 (x =0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared using two route standard ceramic methods with calcination carried out at 1250 ◦ C for 20 h. Magnetic properties were measured by vibrating sample magnetometer (Lake Shore VSM 7307) at an applied external field of 10kOe. The phase structure was characterized using X-ray diffrac- tion (Philips Expert Diffractometer) with Cu K radiation ( = 1.54 ˚ A) and microstruc- ture was studied with SEM instrument (Hitachi S-4700 FESEM). Curie temperature was measured by gravity method. Microwave absorption was studied as a function of thickness, frequency and substitution at X-band using power meter (Agilent 321) and frequency synthesizer (HP 83751A) by absorber testing device method (ATD) [6]. 3. Results and discussion 3.1. XRD X-ray diffraction patterns of samples (Fig. 1) show that mag- netoplumbite structure has been formed. The change in relative intensities may be related to occupation of crystallographic sites by substituted ions. From structural parameters characterized by lattice constants ‘a’ and ‘c’(Table 1), it becomes clear that lattice constant ‘a’ shows less variation and lattice constant ‘c’ follows fast reduction with Sr 2+ ions substitution. This follows the fact that all hexagonal ferrites exhibit constant lattice parameter ‘a’ and vari- able parameter ‘c’ [7]. It also indicates that Sr 2+ ions substitution causes considerable change in easy magnetized c-axis than in a- axis. This is attributed to small ionic radii of Sr 2+ ions (1.12 ˚ A) than Ba 2+ ions (1.34 ˚ A) [4]. 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.03.025