Synthesis, Characterization, and Electromagnetic Wave Absorbing Properties of M12+-M24+ Substituted M-Type Sr-Hexaferrites

Mn-Ti, Zn-Ti, Zn-Zr substituted M-type Sr-hexaferrites (SrM), SrFe12-2xM1xM2xO19 (0 <= x <= 2.0, M-1 = Mn or Zn; M-2 = Ti or Zr) were synthesized, and their solubility, crystalline structure, and high-frequency properties were studied. Zn-Zr substitution caused a relatively large lattice parameter change and resulted in lower solubility (x <= 1.0) in the M-type phase compared with Mn-Ti and Zn-Ti substitutions. However, the ferromagnetic resonance frequency (f(FMR)) effectively decreased with increasing x in SrFe12-2xZnxZrxO19 (Zn-Zr:SrM) (0 <= x <= 1.0) and the electromagnetic wave (EM) absorption frequency also varied according to the shift in f(FMR) in the 7-18 GHz range. This is attributed to a gradual decrease in the magnetocrystalline anisotropy of Zn-Zr:SrM (0 <= x <= 1.0) with an increase in x. Zn-Zr:SrM (x = 0.9)-epoxy(10 wt%) composites exhibited a high EM absorption in the X-band (8-12 GHz) with the lowest reflection loss of x = 0.8 showed a broad Ku band (12-18 GHz) absorption performance satisfying RL f <= 18 GHz.