Effect of Cr3+–Al3+ co-substitution on structural, magnetic and microwave absorption properties of Sr-hexaferrites

The SrCrxAlxFe12−2xO19, (x = 0.0–1.0) are prepared by microwave-hydrothermal (M-H) method at 200 °C/60 min and the obtained powders were sintered at 1100 °C/4 h. With Cr–Al co-doping, the lattice constant ‘a’ is increased by 0.024% and c is decreased by 0.078%. The average grain size is decreased with doping and the grain shape is changed from hexagonal to more spherical with x. The saturation magnetization (Ms) is decreased from 59.00 emu/g (x = 0.0) to 47.44 emu/g (x = 1.0). The coercive field (Hc) is observed between 2147 and 2715 Oe. The real part of permittivity (ε′) increased from 4.70 (x = 0.0) to 5.18 (x = 0.6), and decreased to 5.00 (x = 1.0). The imaginary part of permittivity (ε″) increased from 0.965 (x = 0.0) to 1.220 (x = 1.0). The real (μ′) and imaginary part of permeability (μ″) decreased with doping concentration and explained using atomic site occupancy in the hexaferrite. The maximum reflection loss (RL) is observed for x = 0.8 i.e., − 21.15 dB at 10.90 GHz.