“…In addition to spinel ferrites, the hexagonal ferrites—including M-type, W-type, X-type, Y-type, Z-type, and U-type—are also of great interest as high-frequency MAMs because of their planar magnetic anisotropy and natural resonance in the gigahertz range [90,91,92]. M-type barium ferrites (BaFe 12 O 19 ) and strontium ferrites (SrFe 12 O 19 ) are two typical examples of the hexagonal group that possess very strong uniaxial anisotropy, high saturation magnetization, and significant permeability [93,94], and thus the integration of BaFe 12 O 19 /SrFe 12 O 19 and CPs took a considerable share in the field of high-performance MAMs in the past decade [42,95,96,97,98,99,100,101,102]. However, high-temperature sintering (>800 °C) is always necessary for the formation of hexagonal ferrites [103], which results in serious agglomeration of ferrite particles and consequent difficulty in controlling the microstructure of the corresponding composites.…”