Effects of Mn-doping on the magnetic and microwave absorption properties of Co2W hexaferrite

BaCo₂Mn_xFe_16-xO₂₇ (x = 0,0.4, 0.8, 1.2, 1.6, 2.0, 2.4) hexaferrites were synthesized via solid-phase sintering to investigate Mn doping effects on the crystal structure, electromagnetic properties, and microwave absorption performance. X-ray diffraction (XRD) analysis reveals a pure W-phase for x ≤ 1.6, while secondary phases emerge when x ≥ 2.0. Magnetic measurements show a systematic decrease in coercivity (from 125.4 Oe at x = 0 to 53.4 Oe at x = 1.6) due to combined effects of grain size variation and changes in the magneto-crystalline anisotropy field induced by Mn doping. Saturation magnetization (M_s) exhibits a “V-shaped” trend, attributed to the smaller magnetic moment of Mn³⁺ ions compared to Fe³⁺ ions and their selective occupation of lattice sites with different magnetic moment directions. At x = 0.4, Mn ions occupy the Fe7 sites (with spin up Fe³⁺), reducing the M_s. At x = 0.8, additional Mn ions preferentially occupy Fe3 and Fe6 sites, causing a further decrease in M_s. However, at x = 1.2, extra Mn ions occupy the Fe4 and Fe5 sites (with spin down Fe³⁺), leading to an increase in M_s. Moreover, Mn doping effectively broadens the effective absorption bandwidth (EAB) of the samples. Notably, at x = 1.2, the sample demonstrates remarkable microwave absorption performance, achieving a reflection loss of -54.94 dB at a thickness of merely 1.58 mm, with an EAB exceeding 7.63 GHz, covering the Ku-band. This work demonstrates that Mn doping is an effective strategy to tailor both magnetic properties and microwave absorption in Co₂W hexaferrites, offering promising materials for Ku-band absorbers.