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In this study, ferrimagnetic (SrFe12O19, SrFe12O19/NiFe2O4, and NiFe2O4) nanostructure particles were synthesized by the co-precipitation of chloride salts using the sodium hydroxide solution. The resulting precursors were heat-treated at 1100 °C for 4 h. After cooling in the furnace, the ferrite powders were pressed at 10 bars and then sintered at 1200 °C for 4 h. The saturation magnetization was increased and the coercivity was decreased by sintering (because of morphology changing) and alternating of the ferrite kind. For example, at SrFe12O19, the saturation magnetization was increased from 291 G to 300 G and the coercivity was decreased from 2.8 kOe to 1.8 kOe by sintering. The microwave absorption properties of the nanostructure particles were studied by ferromagnetic resonance and transmit-line theories, as well as Reflection Loss plots. Before sintering, the RL spectra of SrFe12O19 and the composite were below −3 dB, but they reached −6 dB at 11.1 GHz for NiFe2O4. The RL spectra of the samples were increased by sintering due to reduction of porosity and damping factor. The maximum microwave absorption reached −35 dB (at resonance frequency) for the NiFe2O4 state.

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nanostructure composite particles were synthesized by co-precipitation of chloride salts, in different stoichiometric ratios, by addition of sodium hydroxide solution. The resulting precursors were heat treated at temperatures in the range 800-1200°C for 4 h. Exchange interactions of the nanostructure composite particles were studied by use of exchange-coupling theory and plots of magnetic hysteresis. On the basis of exchange-coupling theory, the exchange interaction can be improved by increasing the soft phase content within the hard matrix. As temperature and soft phase ratio increase, the exchange interaction increases because of exchange length enhancement. The modified Brown's equation was also used to analyze the effects of exchange coupling on coercivity.