Physical and magnetic properties of highly aluminum doped strontium ferrite nanoparticles prepared by auto-combustion route

Microstructural Characteristics and Magnetic Properties of Al-Substituted Barium Hexaferrite Nanoparticles Synthesized by Auto-Combustion Sol–Gel Processing

“…These results could be due to a smaller ionic radius of substituted Al 3+ ions (0.535Å) in comparison to the ionic radius of Fe 3+ ions (0.645Å). It can be also concluded that the reduction of cell dimensions is due to the solubility of Al 3+ ions in the M-type hexaferrite lattice which is in agreement with the previous literature in this field [2,5,6]. On the other hand, with substituting of Al 3+ ions in the lattice of hexaferrite and according to the Bragg equation (λ = 2dsinθ), the diffraction peaks' positions are gradually shifted to the right as compared to pure barium ferrite (x = 0) as shown in Fig.…”

“…However, the amount of substituting of Al 3+ ions and also its placement in the hexagonal structure of barium ferrite can be significantly affected on magnetic properties. On the other hand, with substituting Al 3+ ions in the crystal structure of barium ferrite, because of decreasing particle size, H c can be improved [1,2,5]. In the current Fig.…”

“…Since the discovery of the M-type hexagonal ferrite ceramics (MFe 12 O 19 , M = Ba, Sr, and Pb) in the middle of the twentieth century, there has been much interest due to their specific magnetic properties such as their high magnetization, large magnetocrystalline anisotropy (high coercive field), high Curie temperature, and excellent chemical stability, mechanical strength, and corrosion resistivity [1][2][3]. Barium ferrite has been widely used as permanent magnets, perpendicular magnetic recording media, and electrical and microwave devices [1,4,5].…”

“…To achieve these applications, the coercive field (H c ) plays a crucial role. The coercive field can be remarkably increased with substitution of Fe 3+ by some ions such as Al 3+ [2,5,6], Ce 3+ [7], Cr 3+ [8,9], Ga 3+ [9], Ho 3+ [10], La 3+ [11], Nd 3+ [12,13], etc. As it is well known, in the structure of barium hexaferrite, Fe 3+ ions occupy five nonequivalent sites of which are three octahedral (2a, 4f 2 , and 12k), one trigonal bipyramidal (2b), and one tetrahedral (4f 1 ) [14].…”

“…These crystallographic sites are coupled by the Fe 3+ -O-Fe 3+ superexchange interaction leading to the ferromagnetic structure [5,13,15]. When Al 3+ ions are entered to the lattice of BaFe 12 O 19 and substitute instead of Fe 3+ ions, the coercive field will be changed with the changing of the magnetocrystalline anisotropy field [2,5]. However, the amount of substituting of Al 3+ ions and also its placement in the hexagonal structure of barium ferrite can be significantly affected on magnetic properties.…”