Enhancement in physical properties of barium hexaferrite with substitution
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Sachin Kumar Department of Chemistry, Guru Nanak Dev University, Amritsar, Punjab 143005, India
Bilal H. Bhat Department of Physics, University of Kashmir, Kashmir 190006, India
Ajeet Kumar Srivastavaa) Department of Physics, Lovely Professional University, Phagwara, Punjab 144411, India (Received 11 February 2015; accepted 28 July 2015)
M-type barium hexaferrite powders were synthesized using modified Pechini sol gel auto combustion method. The powder samples were heat treated at 900 °C for 5 h and were subjected to the structural, thermal, dielectric, magnetic, and optical studies. X-ray powder diffraction patterns show the formation of pure phase of M-type hexaferrite. Thermal analysis reveals that the weight loss of precursor becomes constant after 680 °C. The presence of two prominent peaks near 430 and 580 cm1 in Fourier transform infrared spectroscopy spectra indicates the formation of M-type hexaferrites. The M–H curve has been used to study the magnetic behavior. The maximum value of coercivity is found for x 5 0.41, which is higher than that of the pure barium hexaferrite. The band gap dependency on composition was studied using UV–Vis NIR spectroscopy. It was found that the dielectric constant is high at low frequency and decreases with an increase in frequency. Hexagonal structure of hexaferrite is visualized in transmission electron images.
I. INTRODUCTION
M-type hexaferrites (Ba1Fe12O19, abbreviated as BaM), because of their magnetic, chemical, and dielectric properties, have attracted keen interest among researchers for its manifold applications. M-type barium hexaferrites have high coercivity (6700 Oe),1 high saturation magnetization (72 emu/g),2 and high Curie temperature (TC 5 502 °C).3 These materials can be used in magnetic hose (to transport magnetic field due to magnetic nature), perpendicular magnetic recording devices, super capacitors, self-biased and millimeter devices, microwave devices (mobile technology), electromagnetic wave absorber, sound devices, and fridge magnets.4–9 For recording media, storage must be in a high number of bits per unit area, known as areal density. It must have a low signal to noise ratio and thermal stability. Nanosized grain with uniform size distribution possesses the properties of recording media. The synthesis of appropriate uniform size particle is a challenging task. Contributing Editor: Michael E. McHenry a) Address all correspondence to this author. e-mail: [email protected] A previous error in this article has been corrected, see 10.1557/jmr. 2015.286. DOI: 10.1557/jmr.2015.244
The dual layered structure of BaM contains 2 molecules of BaM having SRS*R* stacks. The hexagonal structure of R and R*, having general formula (BaFe6O11) consists of three oxygen layers, whereas S and S* have a spinel structure with 2 oxygen layers having the formula (Fe6O8). The Asterisk in the stacks signifies their rotation at 180°. A unit cell of hexagonal ferrite contains 38O2, 2Ba21 ions, 24Fe31 ions of which all the Fe31 ions are situated in trigonal bipyram
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