Effect of aluminum substitution on microwave absorption properties of barium hexaferrite

Abstract

Aluminum substituted barium hexaferrites were prepared by the self-propagating combustion method and subsequent calcination at 850 °C. The crystalline structure, complex permittivity, complex permeability, and hyperfine parameters of BaFe 12 − x Al x O 19 ( x varies from 1.5 to 2.3 in steps of 0.2) were measured with x-ray diffraction(XRD), vector network analyzer and Mössbauer spectroscopy. The XRD results show that all Al 3 + ions enter into the lattice of hexagonal bariumferrite. The substitution of Al 3 + ions can greatly affect the complex permittivity and permeability of bariumferrite. With increasing substitution, the real part of complex permittivity increases gradually, and the peaks of the imaginary part of complex permeability shift into higher frequency band. When the substitution amount x is 1.9, the largest movement of the peaks is 1.95 GHz, which indicates that the ferromagnetic resonant frequency of bariumferrite increases by 1.95 GHz. The Al 3 + ions preferentially occupy the 4 f 2 , 2 a , 4 f 1 , and 12 k sites in the subcrystalline structure up to x = 1.9 , and then the Al 3 + ions mainly occupy 12 k sites. This change also results in 2 b sites with a large quadrupole splitting. These occupations lead to a variable magnetocrystalline anisotropy field.