We have extensively studied the laser-induced Fano scattering, electron–phonon coupling, bond length and phonon lifetime of the α-Fe2O3 nanostructure prepared through a simple co-precipitation method.

The particle size-dependent surface optical (SO) phonon and magnon modes of NiO nanoparticles were extensively studied using room-temperature confocal Raman spectroscopy. The required nanoparticles were synthesized using a simple co-precipitation method, and the suitable particle sizes were obtained by varying the annealing temperature from 300 to 900 °C. The SO phonon modes of the prepared NiO nanoparticles were blue shifted and broadened as the nanoparticle size was reduced due to the lattice contraction and boundary relaxation, respectively. The presence of SO phonon modes was studied using the dielectric continuum (DC) model for a nearly spherical-like particle, and a violation of DC model was observed in the experimental SO mode frequency due to the presence of first order magnon background over the phonon modes. The magnon background and SO mode frequency differences were increased with the nanoparticle size. The absence of magnon and second-order phonon modes in smaller NiO nanoparticles indicates the reduced spin correlation between the next nearest neighbor Ni2+ ions in the crystal lattice and the presence of uncompensated surface spins. Moreover, the size-dependent magnetic properties were investigated using the M–H curve, and the NiO nanoparticle shows the mixed faces of antiferromagnetic (AFM) and ferromagnetic (FM) properties in the smaller size particle and correlates the Raman scattering results.

No abstract

In the present work, the influence of Ag induced plasmon on surface optical (SO) phonon modes of NiO nanoparticles were extensively studied using room temperature Raman spectroscopy. Remarkable intensity enhancements...

In the present study, the influence of laser intensity on phonon and magnon properties of nickel oxide (NiO) nanoparticles were extensively studied using room temperature Raman spectroscopy. The required NiO nanoparticles were synthesized using a simple sol–gel method. The structural and morphological properties were characterized using powder X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), and transmission electron microscopy (TEM) techniques. The rarely reported surface optical (SO) phonon modes of NiO nanoparticles were observed and well‐studied using the dielectric continuum (DC) model. A mismatch between the experimental and DC model SO phonon wavenumbers were observed and is attributed to one magnon‐induced first order phonon shift. The difference between the experimental and DC model SO phonon wavenumbers were reduced with increase in laser power, which indicates the diminishing behavior of magnon excitations. The laser power dependency of highly distinguishable two magnon (2 M) excitation of NiO nanoparticles were well studied. The 2 M modes were experienced a red shift and decrease in intensity with increase in laser power.

No abstract

We have extensively studied the phonon, magnon and magnetic properties of copper (Cu)‐doped nanocrystalline nickel(II) oxide (NiO) using room‐temperature Raman spectroscopy. The required nanomaterials were synthesized using a simple sol–gel method. The phonon modes of NiO nanoparticles have been observed in a large background of magnon excitations, and the wavenumbers of phonon modes were deviated from the theoretical predictions due to the phonon–magnon interaction. The variations of magnon excitations with the Cu doping concentrations were investigated based on reduced spin correlation length and superexchange interaction. The two‐magnon (2M) excitations were suppressed and blue shifted with Cu doping concentration indicating the variations in the magnetic behaviour. The modification of antiferromagnetic nature and the formation of multiphase magnetic properties of NiO nanoparticles were investigated using a vibrating sample magnetometer (VSM) and discussed in detail. The variations in the phonon and magnon excitations can be used to probe the magnetic nature and spintronic applications of NiO nanoparticles.

Non-degenerate pump–probe transmission spectroscopy is used to examine the ultrafast dynamics of photo-excited carriers in hematite nanoforms at various pump fluences. Using coupled rate equations, the kinetics of self-trapped exciton (STE) formation and its interaction with free excitons resulting in exciton annihilation were studied. It is shown from this model that the majority of the excitons were trapped by polaronic trap states to form self-trapped excitons within ∼3.5 ps. The findings indicate that free excitons and STEs interact non-linearly, similar to trap-assisted bi-molecular Auger recombination to annihilate one another. It is observed that there is substantial dependence of kinetics of STE formation and exciton decay on photo-excited exciton density, and the nature of this dependence indicates the reduced screening of electron–phonon interaction. Using the screening model applied to the rate constants of STE formation and decay, we estimate the saturation exciton density to be ∼3.3 × 1017 cm−3 and the average STE density to be ∼3.8 × 1018 cm−3 in the hematite nanoforms. We also noticed that doping K and Ni to hematite nanoforms up to 5% did not remarkably change the nature of the exciton dynamics.