Compositional Control and Millimeter-Wave Properties of Micro-/Nano-Sized -Type Barium Hexaferrite Synthesized by Hydrothermal Method

Micro-/nano-sized BaFe₁₂O₁₉ particles were synthesized by the hydrothermal method, and the effects of Ba/Fe ratio, OH-/Cl- ratio, reaction time, and reaction temperature on the phase composition, static, and millimeter (mm)-wave magnetic properties of BaFe₁₂O₁₉ were studied. Phase composition analysis shows that non-stoichiometric and iron-deficient precursor is necessary to form M-type BaFe₁₂O₁₉ (BaM) of high purity under the optimized synthesis condition. Otherwise, the products should contain the trace of either α-Fe₂O₃ impurity phase or Fe₃O₄ transitional phase. It is found that the saturation magnetization (30-50 emu/g) and the coercivity values (300-600 Oe) of all the samples lie in the range of bulk BaM hexaferrite. The frequency dependence of the complex permeability of BaM composites has been studied in the Ka-band (26.5-40 GHz). With ferromagnetic resonance efficiently controlled by phase composition, the proposed BaM composites show potential application at mm waves.