Structural and Magnetic Studies of Thermally Treated NiFe 2 O 4 Nanoparticles
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IN recent times, magnetization of the ferromagnetic materials has evolved as a fundamental quantity resulting in significant growth in the synthesis and study of magnetic nanoparticles, as they show interesting properties that are different from their bulk counterparts due to their surface effect and quantum confinement effects.[1] Among the magnetic nanoparticle spinel, ferrites have gained much attention due to their interesting electrical, magnetic, optical, and catalytic properties, which make them a potential candidate[2] to be applied in various fields, such as magnetic storage systems,[3] magnetic resonance imaging,[4] photomagnetic devices,[5] ferrofluids, radar absorbing coating,[6] drug delivery,[7] and gas sensors.[8] NiFe2O4 is widely known for its high electromagnetic performance, high coercivity, moderate saturation magnetization,[1,8] good mechanical hardness, and excellent chemical stability,[9] which makes it a promising material for the foresaid
SURAJIT GHOSH, PRAYAS CHANDRA PATEL, DEBRAJ GANGOPADHYAY, POORNIMA SHARMA, RANJAN K. SINGH, and P.C. SRIVASTAVA are with the Department of Physics, Institute of Science, Banaras Hindu University, Varanasi, U.P. 221005, India. Contact e-mail: [email protected] Manuscript submitted May 1, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
applications. Like most ferrites, NiFe2O4 also has an inverse spinel structure[8] in which there exists face-centered-cubic (fcc) lattice of O2 ions and Fe3+ ions distributed over tetrahedral (A) and octahedral (B) sites equally and Ni2+ ions located in octahedral sites only. In the case of inverse spinel, magnetic moments of the A and B sites are aligned antiparallel to each other, resulting in the cancellation of the moment for Fe3+; thus, it forms a collinear ferromagnetic ordering with Curie temperature ~870 K (~597 C).[8] Depending on the cation distribution between octahedral and tetrahedral sites, spinel structure can be of ‘‘normal,’’ ‘‘inverse,’’ or ‘‘mixed’’ form and any changes in cation distribution can lead to switching among them.[8] Thus, the synthesis route that influences the cation distribution as well as composition, purity, and microstructure of the nanoparticles plays an important role in controlling the properties of the synthesized nanoparticles. Various synthesis techniques have been applied so far to synthesize nanoparticles of NiFe2O4 of desired properties, such as microemulsion synthesis,[1] hydrothermal synthesis,[10] sol-gel,[11] coprecipitation,[12] and combustion method.[13] The coprecipitation method, being a simple and low-cost technique, can be significant in preparing ferrite nanoparticles, as it provides easy control on various synthesis parameters. Moreover, many properties, such as particle size, stoichiometry, and structural phase of the nanoparticles, can also be controlled by sintering synthesized samples at elevated temperatures.[12]
In this context, we have employed a coprecipitation method followed by sintering the as-prepared samples at different elevated temperatures t
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