微观结构对FeCo/TiO_2纳米复合材料微波共振的影响

Influence of microstructure on waves resonance of FeCo/TiO_2 nanocomposites

采用机械化学法合成了FeCo/TiO_2纳米复合材料,该材料与石蜡的复合物在13.5GHz处复介电常数的实部ε′值具有较大的波动,复介电常数的虚部ε″产生强烈的介电共振峰,ε′-ε″的复平面上Cole-Cole图呈现一个全圆。制备态样品经500℃退火后,退火样品中FeCo纳米粒子的衍射峰明显变窄,表明晶粒尺寸增加,晶格缺陷减少,微观应力得到释放;同时,退火导致饱和磁化强度增加,矫顽力减小,介电共振行为消失。制备态样品的厚度为8.15mm时,反射损耗在12.6GHz处取得最大值-38.3dB,且当厚度为7.5mm时,超过-10dB的频宽为12~16.5GHz,几乎覆盖了整个Ku波段（12~18GHz）。该体系良好的电磁波吸收性能归功于FeCo/TiO_2纳米复合物特殊的微结构带来的非线性介电共振、强烈的自然共振和良好的电磁匹配。

FeCo/TiO2 nanocomposites,prepared by the mechanochemical synthesis,exhibit fluctuation ofε′and an intense dielectric resonance peak ofε″at 13.5 GHz.Real and imaginary part of the complex permittivityε′-ε″on the complex plane Cole-Cole plot show a full circle.Diffraction peak of FeCo nano particle is observed nar-rowed down can be attributed to increase of grain size,decrease of lattice imperfection and release of internal strain.And meanwhile,dielectric resonance is greatly weakened after annealing at 500 ℃,as a result of which the clear Cole-Cole full circle disappeared.Annealing also led to increase of saturation magnetization and de-crease of coercivity.For the as-milled sample,a maximum of reflection loss （RL）as large as -38.3 dB at 12.6 GHz for a layer of 8.15 mm thickness.However,for the annealed sample,a RL value exceeding -10 dB was obtained in 12-16.5 GHz for an absorber thickness of 7.5 mm,almost covering the entire Ku-band （12-18 GHz）.The great improvement of microwave-absorption properties for as-milled sample can be ascribed to a dielectric resonance and an excellent match of magnetic and dielectric loss.