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Study of crystallite size on magnetic properties of nanocrystalline FeCo2O4
In the present work, the effect of crystallite size on the magnetic properties of nanocrystalline FeCo2O4, synthesized by co-precipitation technique, has been studied. The as synthesized sample has been annealed at 500 , 900 & 1000 to vary the crystallite size. The XRD results confirm the presence of single cubic phase in all the annealed samples and increase in the crystallite size with the increasing annealing temperature. FESEM images show the spherical morphology of prepared nanoparticles which become irregular in shape as temperature increases and particle size also increases with increasing annealing temperature. XPS analysis confirms the mixed oxidation states of Fe with Fe+2 and Fe+3, Co with Co+2 and Co+3. The temperature dependence magnetization (M-T curves) and field dependence magnetization (M-H curves) at different temperatures have been measured using Quantum design MPMS3 SQUID magnetometer. The low temperature M-H curves show the presence of metamagnetic phase transition in the samples annealed at 900 oC and 1000 oC. This possibly occurs due to the co-existence of ferromagnetic and antiferromagnetic phases in the synthesized samples. The coexistence of AFM and FM phases may be attributed to spin canting/surface spin disorder in nanocrystalline magnetic nanoparticles. Furthermore, the samples annealed at higher temperature show strong ferromagnetism, higher saturation magnetization, higher coercivity and remanence. Moreover, the M-H curves, measured below 100 K, of the samples annealed at 500 oC and 900 oC show jumps in the magnetization value at certain magnetic fields (see Fig. 1). The detail correlation between structural and observed magnetic properties will be described and discussed in this paper.
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