Effects of Ga-Cr substitution on structural and magnetic properties of hexaferrite (BaFe12O19) synthesized by sol-gel auto-combustion route

A series of single phase and nanostructured Cr-Ga substituted M-type hexaferrites BaCrxGaxFe12-2xO19 (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 degrees C for 2 h and characterized by different experimental techniques such as differential scanning calorimetry (DSC), thermogravimetry (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 x 10(3) to 2.385 x 10(3) Gauss and 1.286 x 10(3) to 1.677 x 10(3) Gauss, respectively. The coercivity (iH(c) and bH(c)) enhanced which is attributed to increase in the magnetocrystalline anisotropy. The high values of retentivity and coercivity make these materials best candidate for high density recording media and permanent magnets. (C) 2012 Elsevier B.V. All rights reserved.