Absorbing properties investigation of SrFe₁₂O₁₉ NiFe₂O₄ composite nanopowders with core shell structure

The nanoscale magnetic composite powders SrFe₁₂O₁₉-NiFe₂O₄ with core-shell structure were prepared by two-step citrate sol-gel, with Fe(NO₃)₃Ni(NO₃)₂ and Sr(NO₃)₂ as the main materials. The XRD, TEM, VSM and vector network analyzer were used to analyze the structure, feature and absorbing quality of the nano-powder. The results show that the phase structure of the powder is related to the content of NiFe₂O₄, when the mass ratio of SrFe₁₂O₁₉ to NiFe₂O₄ is 1∶2 and calcined temperature is 1050℃, the phase of the powder is similar than that of NiFe₂O₄, the magnetization(M_s)of SrFe₁₂O₁₉ and the coreshell nano-powde raises from 42.6 emu/g to 51.4 emu/g, and the coercivity(H_c) is 336 Oe, which is between that of SrFe₁₂O₁₉ (5395 Oe) and NiFe₂O₄ (160 Oe). The absorbing quality is enhanced when the frequency is from 8 GHz to 18 GHz. When the frequency is 12 GHz, the microwave absorption can reach maximum point which is -9.7 dB. The composite nano-powder is an excellent absorbing material.