Electromagnetic wave absorption properties of La-Ca-Co-Al substituted M-type Sr-hexaferrite-rubber sheets in 50–75 GHz range

Abstract

This study reports on the electromagnetic (EM) wave absorption characteristics of M-type hexaferrite-rubber sheets, where Al was additionally substituted into high-performance permanent magnet compositions, Sr0.2La0.4Ca0.4Co0.25Fe9.75-xAlxO19-d (LCCA-SrM, x = 0, 0.2, 0.4). While non-substituted SrFe12O19 powder-rubber sheet had a ferromagnetic resonance frequency (fFMR) of 48.5 GHz, the LCCA-SrM (x = 0, 0.2, 0.4) rubber sheets showed increased fFMR values of 63.3, 66.2, and 68.5 GHz, respectively, with the increasing x values. The frequency of minimum reflection loss (fRLmin) also increased correspondingly with the change in fFMR. This significant increase in fFMR and fRLmin is attributed to the greatly enhanced magnetocrystalline anisotropy from the La-Ca-Co substitution in SrM and the incremental increase in magnetic anisotropy field (Hani) due to Al substitution. The absorption band (Δf) satisfying RL < −10 dB, was 45.0–53.4 GHz for SrM, and 52.9–75, 50–75, and 59–74.2 GHz for the x = 0, 0.2, and 0.4 samples, respectively. The x = 0.2 sheets demonstrated the widest absorption, covering 50–75 GHz. This study is highly promising as it is the first to demonstrate the feasibility of developing an EM wave absorber sheet for frequencies above 50 GHz using hexaferrite powder synthesized via the solid-state method, which offers scalability and cost-efficiency for mass production.