Structural, Magnetic, Electric and Dielectric Properties of Cr-Ga Substituted BaM Hexaferrites synthesized by sol–gel auto-combustion route for High-Frequency Applications

I. Ali, M.U. Islam, M.S. Awan, M. Ahmad
Govt. Graduate College,
Pakistan

Keywords: Hexaferrites, Sol-gel auto-combustion, X-ray diffraction. Magnetic measurements AC conductivity, DC resistivity, dielectric constant, hexaferrites

Summary:

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 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 2.078-103 to 2.385-103 Gauss and 1.286-103 to 1.677-103 Gauss, respectively. The coercivity (iHc and bHc) 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. Room-temperature DC resistivity enhances with the substitution of Cr-Ga contents. The temperature dependence of the DC resistivity shows the semiconducting nature. The dielectric constant and dielectric tangent loss decrease, while AC conductivity increases with the increasing applied field frequency in the range of 1 MHz-3 GHz consistent with Koop-s theory and Maxwell-Wagner-s bi-layer model. The magnetic loss enhances, while the reflection coefficient decreases with the increase of frequency as well as with the increase of Cr-Ga contents. Owing to improved properties, these materials are potential candidates for high-frequency applications in GHz range.