Abstract
We report here the investigations on the size dependent variation of magnetic properties of nickel ferrite nanoparticles. Nickel ferrite nanoparticles of different sizes (14 to 22 nm) were prepared by the sol-gel route at different annealing temperatures. They are characterized by TGA-DTA, XRD, SEM, TEM and Raman spectroscopy techniques for the confirmation of the temperature of phase formation, thermal stability, crystallinity, morphology and structural status of the nickel ferrite nanoparticles. The magnetization studies revealed that the saturation magnetization (Ms), retentivity (Mr) increase, while coercivity (Hc) and anisotropy (Keff) decrease as the particle size increases. The observed value of Ms is found to be relatively higher for a particle size of 22 nm. In addition, we have estimated the magnetic domain size using magnetic data and correlated to the average particle size. The calculated magnetic domain size is closely matching with the particle size estimated from XRD. Impedance spectroscopy was employed to study the samples in an equivalent circuit to understand their transport phenomena. It shows that nickel ferrite nanoparticles exhibit a non-Debye behavior with increasing particle size due to the influence of increasing disorders, surface effects, grain size and grain boundaries, etc.
Highlights
Ferrite nanoparticles have been studied extensively during the past few years because of their large number of applications
The X-ray diffraction (XRD) patterns were analyzed for the phase identification which showed that the observed d values are in good agreement with those in JCPDS (Card No10-325) data reported for nickel ferrite.[11,12]
The particle size dependent magnetic studies show a strong correlation between the particle size and magnetic properties such as Ms, Mr, Hc, and magnetic domain size, etc
Summary
Ferrite nanoparticles have been studied extensively during the past few years because of their large number of applications. These particles can be used for different recent applications as mentioned above This has motivated us to study and correlate the size dependent magnetization of nanoparticles to their single domain size. The disordered and canted surface spins affect the magnetic, electrical, and dielectric properties due to the smaller grains and grain boundaries.[7,8] In case of magnetic nanoparticles, the canted surface spins impede the alignment of magnetic moments along the direction of applied magnetic field and reduces Ms Nickel ferrite being a relatively soft ferrite, has a low value of Ms and Hc with high electrical resistivity. The frequency dependent imaginary part (M ′′) of the electric modulus shows that the electric modulus increases with the increase in particle size as a result of decrease in grain boundary effects.[9,10]
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