Review Effects of Ga–Cr substitution on structural and magnetic properties of hexaferrite (BaFe 12 O 19 ) synthesized by sol–gel auto-combustion route Ihsan Ali a,⇑ , M.U. Islam a , M.S. Awan b , Mukhtar Ahmad a a Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan b Center for Micro and Nano Devices, Department of Physics, COMATS Institute of Information Technology, Islamabad, Pakistan article info Article history: Received 16 July 2012 Received in revised form 18 August 2012 Accepted 28 August 2012 Available online 6 September 2012 Keywords: Hexaferrites Sol–gel auto-combustion X-ray diffraction Magnetic measurements abstract A series of single phase and nanostructured Cr–Ga substituted M-type hexaferrites BaCr x Ga x Fe 122x O 19 (x = 0.0–0.4) were synthesized by sol–gel auto-combustion route. The powder samples were pressed into pellets of diameter 12 mm using an excellent technique Cold Isostatic Pressing (CIP) at a pressure of 2000 bar for higher densification. The powdered samples were sintered at 1000 °C for 2 h and character- ized by different experimental techniques such as differential scanning calorimetry (DSC), thermogravi- metry (TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffractions (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS) and vibrating sample magnetometry (VSM) magnetometry analyses. DSC–TG analysis was carried out to observe the transformation of different phases during heat treatment. X-ray diffraction (XRD) confirmed the formation of single phase M-type hexagonal ferrites. The crystallite size calculated by the Scherer equation was found to be in the range of 30–48 nm, which is small enough to obtain a suitable signal-to-noise ratio in the high density recording media. The saturation magnetization and retentivity were observed to increase from 2.078  10 3 to 2.385  10 3 Gauss and 1.286  10 3 to 1.677  10 3 Gauss, respectively. The coercivity (iH c and bH c ) enhanced which is attributed to increase in the magnetocrystalline anisotropy. The high val- ues of retentivity and coercivity make these materials best candidate for high density recording media and permanent magnets. Ó 2012 Elsevier B.V. All rights reserved. Contents 1. Introduction ......................................................................................................... 118 2. Experimental procedure................................................................................................ 119 2.1. Synthesis of Ba-hexaferrite and its derivatives ........................................................................ 119 3. Results and discussion ................................................................................................. 119 3.1. Differential scanning calorimetry (DSC) analysis ...................................................................... 119 3.2. FTIR spectroscopy ............................................................................................... 119 3.3. X-ray diffraction analysis ......................................................................................... 120 4. Physical properties .................................................................................................... 120 5. Magnetic properties ................................................................................................... 121 6. Conclusions .......................................................................................................... 124 References .......................................................................................................... 125 1. Introduction The M-type hexaferrites (BaFe 12 O 19 ) are important ferromag- netic oxides. These materials can be used in bulk form in many electrical and electronic devices because of their superior magnetic properties. These materials are used in microwave devices, small motors, and, more recently, magnetic recording applications [1,2]. For improving the fundamental magnetic properties of hexa- ferrites, a number of studies were carried out on the synthesis methods and cationic substitutions of divalent or multivalent ions and of their mixture. The Fe 3+ ions in M-type hexaferrite structure are distributed on five different crystallographic sites such as three 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.08.122 ⇑ Corresponding author. Tel.: +92 61 9210343; fax: +92 61 9210068. E-mail addresses: ihsanali.ap@gmail.com (I. Ali), muislampk@yahoo.com (M.U. Islam). Journal of Alloys and Compounds 547 (2013) 118–125 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom