Cation distribution and enhanced surface effects on the temperature-dependent magnetization of as-prepared NiFe2O4 nanoparticles

Abstract

Nickel ferrite, i.e., NiFe 2 O 4 , nanoparticles are synthesized by sol-gel method using urea as a neutralizing agent. The formation of spinel phase and crystal structure of the as-prepared sample is analyzed by X-ray diffraction and transmission electron microscope. In order to confirm phase formation and cation arrangement, room temperature 57 Fe Mössbauer spectroscopy is employed. The degree of inversion (i) estimated from the relative peak area is found to be 0.6, which confirms a mixed spinel structure of the asprepared sample. Zero-field-cooled/field-cooled measurements showed evidence of superparamagnetic behavior associated with the nanosized particles. Hysteresis loop measurements revealed temperature-dependent magnetic properties: The coercive field (H C ) decreases with increasing temperature and deviates from the Kneller's law for ferromagnetic nanostructures; and the saturation magnetization (M s ) follows modified Bloch's law in the temperature range between 25 and 400 K. However, below 25 K, an abrupt increase in magnetization of nanoparticles is observed. In order to understand this behavior, an additional contribution has to be added to the core magnetization to properly fit the data. Hence, a surface correction term to the Bloch's law is found to describe the temperature dependence of magnetization in the core-shell NiFe 2 O 4 nanoparticles.

Spinel Ferrite Nanoparticles: Correlation of Structure and Magnetism

“…However, the degree of inversion in the NPs is often close to 0.5 and the mixed spinel structure is the most common. For example, the NiFe 2 O 4 is a typical inverse spinel, while in NPs obtained by the sol-gel method, the δ value of 0.6 was reported [143]. A very similar values were observed for sol-gel-prepared NPs of CoFe 2 O 4 [69] (inverse spinel in bulk) and of ZnFe 2 O 4 with normal spinel bulk structure [144].…”

Bioactivity evaluation of nanosized ZnFe2O4 fabricated by hydrothermal method

“…The cation inversion allows the ferromagnetic A-B superexchange interaction between iron ions to occur, which improves the magnetization of ZnFe 2 O 4 . The weakening of the magnetization at higher temperatures results from spin canting effects [47], which dominates over cation inversion in the sample, as observed in Fig. 3.…”

“…In Fig. 7b, we also observed the positive control group, where the cells were treated with a cytotoxic solvent, dimethyl sulfoxide (DMSO) [47]. The positive control group shows the cells when the added solvent influences their behaviour; in this case, killing them.…”

Hydrothermal synthesis of NiFe2O4 nano-particles: structural, morphological, optical, electrical and magnetic properties

“…For the temperature greater than blocking temperature (T > T B , i.e., > 260 K) the magnetic moment of single-domain particles is progressively unblocked and the magnetization in the presence of magnetic field attains its thermal equilibrium value, like an atomic paramagnet. However, since the magnetic moment of a single-domain particle is larger than that of an atom, the magnetic state for T > T B is called super-paramagnetic, which exhibits almost zero values of coercivity and remanence of the material [41]. In this study, it happened at T > 260 K. The super-paramagnetic nature of nano-NF particles is very much clear from the M-H loop behaviour recorded at 270 K, wherein the coercivity and remanence are almost equal to zero (figure 14b).…”

“…Nano-ferrites are promising materials for microwave devices, magnetic resonance imaging (MRI), catalysis, magnetic recording, microwave absorbers, biosensors, biomedical drug delivery, power transformers and telecommunication applications, due to their high thermal stability and enhanced electrical, optical and magnetic properties when compared with bulk materials [1][2][3][4]. Nano-nickel-ferrite is a mixed spinel ferrite having cation distribution of [Ni 2+ Fe 3+ ] A [Ni 2+ Fe 3+ ] B [5]. Many researchers have successfully synthesized NiFe 2 O 4 nano-particles by various techniques such as co-precipitation [6], green nano-technology [7], sol-gel [8], reactive milling [9], solvothermal [10] and egg-white precursor [11] methods in order to investigate the structural, optical, morphological, electrical and magnetic properties.…”