Because of the wide applications in magnetic ferrite nanoparticles in various areas like. biology, electronic, sensors and etc., there is a growing interest in this materials [1]. In this work, nanoparticles of (Ni0.98Co0.02Mn0.02Fe1.98O4) system were synthesized by sol–gel combustion method at different calcination temperatures and then investigated their physical properties. For preparation of this ferrite, metal nitrates and citric acid (molar ratio was 1:1) were used as the starting materials. And Ammonia was used to adjust the pH value. Figure 1 shows the XRD patterns at room temperature for the samples, (a), (b) and (c) which calcinated at 500 ºC, 700 ºC and 900 ºC. The Figure 1 illustrates that all diffraction peaks are correspond to cubic spinel structure at 700 ºC and thus the phase was completed at this temperature. By increasing the calcination temperature from 700 ºC to 900 ºC, the right phase of the ferrite is reduced. Also it is observed that with increasing the temperature, nanoparticle size increases (31.92 nm, 41.05 nm and 86.20 nm for (a), (b) and (c) samples respectively). The values of lattice constant of the samples are a little larger than that of for NiFe2O4. This indicates the incorporation of Co and Mn dopants in the spinel lattice of Ni ferrite, due to larger ionic radius of Co and Mn regarding to Ni. [2]-[3]. The result of TEM images confirms the XRD’s analysis.

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