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Crystalline ZnFe2O4 (zinc ferrite) material was prepared using the sol–gel technique and converted in the forms of 3 pellets, out of which 2 pellets were irradiated at room temperature by pulsed Nd:YAG laser with 1.5 W, λ = 532 nm named ZF1 and continuous AlGaAs diode laser of 4 W, λ = 808 nm called ZF2, respectively, while the 3rd pellet was kept as control and named ZF. Synchrotron X-ray Diffraction (S-XRD) reveals the marginal variation in the structure having the lattice parameters of 8.4364 Å for ZF, 8.4176 Å for ZF1 and 8.4187 Å for ZF2. The porosity after laser irradiation has been increased to 10.87% for ZF1 and 10.84%, for ZF2 from 10.28% for ZF. The blocking temperature (TB) has been ∼15 K for all samples. There had been a slight variation in the magnetization of irradiated pellets at 5 and 300 K compared to ZF. The separation between ZFC and FC curves, the measure of interaction between Fe ions has increased for irradiated pellets when compared with the separation for ZF. Moreover, magnetization (M) versus applied magnetic field (H) at 5 K in the range of ±1 T shows the ferrimagnetic behaviour and this ordering has been seen up to TB as visible from M-T curves, whereas the material becomes superparamagnetic above TB as observed from M-T & M-H measurements. [ABSTRACT FROM AUTHOR]

Zinc ferrite (ZF) nanomaterials were synthesised by the sol–gel auto-combustion method. Synchrotron-XRD confirms the formation of the pure F-d3m spinel structure whereas EDX reveals the composition of synthesised nano ZF. We investigated and compared the dielectric properties of un-irradiated pellet ZF-UI and irradiated pellets ZF-I1 (pulsed Nd:YAG laser dose of 1.2 W, λ = 1064 nm), ZF-I2 (pulsed Nd:YAG laser dose of 1.5 W, λ = 532 nm) and ZF-I3 (continuous AlGaAs diode laser of 4 W, λ = 808 nm) at room temperature. Dielectric constant (ε′) decreased prominently for ZF-UI while it decreased gradually for ZF-I1 and its decrement for ZF-I2 and ZF-I3 is very slow whereas dielectric constant (ε″) decreased prominently for ZF-UI and ZF-I1while reduced slowly for ZF-I2 and ZF-I3 in the low-frequency region. ε′ becomes ∼69% for ZF-I1 and ∼9% for ZF-I2 and ZF-I3 at a higher frequency of 2 MHz whereas ε″ for radiated samples becomes steady and nearly equitable at higher frequencies in comparison to that of ZF-UI in the measured frequency range of 10 kHz to 2 MHz. Dielectric loss (tan δ) of all irradiated samples has decreased and become ∼33% for ZF-I3, 43% for ZF-I2, nearly equal for ZF-I1 at 104 Hz and then decreased continuously up to 2 MHz when compared to tan δ for ZF-UI. The Jonscher power law has been fitted in measured ac conductivity (σac) with angular frequency (ω) graphs. DC conductivity (σdc), temperature-dependent parameter B(T) and frequency exponent (n) have been extracted. σdc for all irradiated samples has decreased and become nearly 51% for ZF-I1, 3% for ZF-I2 and 2% for ZF-I3 in comparison to that of ZF-UI whereas B(T) increased to 1.6 times for ZF-I3 and decreased to 0.7 times for ZF-I1 and 0.2 times for ZF-I2 while n shows slight decrement for ZF-I2 and ZF-I3. Interpretation from Cole–Cole plots for un-irradiated and irradiated pellets is in agreement with our investigations. These results suggest that the dielectric properties of ZF can be controlled and tuned by laser irradiation. [ABSTRACT FROM AUTHOR]

• A theoretical model has been augmented to predict Curie temperature and Neel temperature of Ni and Fe 3 O 4 nanoparticles. • Model has incorporated size, shape and relaxation factor of nanoparticles ranging from cubic, spherical, wire and film. • Curie temperature and Neel temperature both have decreased with the decrement in particle size. • The effect has been found prominent as shape is changed from film to cubic. • Predicated results are closer to experimental/simulation data particularly up to 20 nm particle size. A simple and unified model, based on size, shape, and surface effect is reported to estimate the magnetic properties of Ni and Fe 3 O 4 nanomaterials. The relaxation factor, which is the ratio of dangling bonds to an atom's total bonds, is reported in the theory to estimate the properties of magnetic nanomaterials. The Curie temperature is projected to decrease with the decrement in particle size. The particle shape influences the Curie temperature of Ni and Fe 3 O 4 nanoparticles and this effect becomes prominent with the reduction in particle size. The model is extended on the same ground to analyze the Neel temperature of Ni and Fe 3 O 4 nanomaterials. Neel temperature also decreases as particle size decreases. The variation of Curie temperature and Neel temperature is projected for spherical, cubic, wire, and film shaped nanoparticles. It is also observed that the effect of size is more appreciable when the shape changes from cubic to the film of nanoparticles. Although, model predictions are valid throughout the size range of nanoparticles, but more noticeable up to the size of 20 nm. Moreover, the reported model is valid for all conducting and semiconducting crystalline nanostructured materials. Our theoretical calculations are in agreement with the standing experimental data and the simulation results for nanoparticles in varying shapes and sizes. [ABSTRACT FROM AUTHOR]