Optical and magneto-optical study of nickel and cobalt ferrite epitaxial thin films and submicron structures

Abstract

Epitaxial films and ordered arrays of submicron structures of nickel and cobalt ferrites were deposited on Nb doped SrTiO 3 by pulsed laser deposition. X-Ray diffraction and atomic force microscopy showed that the films have a good crystalline quality and smooth surfaces. A larger number of phonon bands was observed in the polarization dependent Raman spectra of the ferrite films than expected for the cubic spinel structures. This is explained by short range ordering of the Ni 2þ (or Co 2þ) and Fe 3þ cations at the octahedral sites inducing a lowering of the symmetry. The same behavior was also observed in the Raman spectra measured for the submicron structures, suggesting the same cation distribution as in the films. The diagonal components of the dielectric function for nickel and cobalt ferrites are determined from ellipsometry in the 0.73-5 eV photon energy range. The absorption edge was analyzed using a bandgap model and the energies for the indirect and direct optical transitions were calculated. It was found that both nickel and cobalt ferrites are indirect bandgap materials with bandgaps of 1.65 eV and 1.42 eV, respectively, while the first direct transitions lie at 2.69 eV and 1.95 eV, respectively. Magneto-optical Kerr effect spectroscopy in combination with spectroscopic ellipsometry allowed the off-diagonal elements of the dielectric tensor to be determined in the energy range from 1.7 eV to 5 eV. V

Enhanced photocatalytic activity of degrading short chain chlorinated paraffins over reduced graphene oxide/CoFe2O4/Ag nanocomposite

“…7b. The band gap of CoFe 2 O 4 is about 1.6 eV, which is consistent with those values reported in literature [46,47]. …”

Microwave combustion synthesis of zinc substituted nanocrystalline spinel cobalt ferrite: Structural and magnetic studies

“…The estimated band gap values of Co 1 À x Zn x Fe 2 O 4 (x¼ 0, 0.1, 0.2, 0.3, 0.4 and 0.5 fractions) are 1.88 eV, 1.89 eV, 1.90 eV, 2.03 eV, 2.05 eV and 2.10 eV respectively. The value of direct band gap obtained for pure cobalt ferrite in the present study is lower than the bulk, which is around 1.95 eV [28]. Further, on doping with zinc, the band gap goes on increasing with increase in Zn (x ¼0.1 to x¼0.5) mole percentage in cobalt ferrite matrices [29].…”

“…The lattice parameters of the ferrite spinels were calculated from the Xray diffraction patterns using Eq. (4) as follows [28]:…”

Wide-Range Structural and Chemical Stability of the Magnetic Oxide NiFe₂O₄ Grown by O₂-Assisted Pulsed Laser Deposition

“…While the Eu compounds are limited to low Curie temperatures, magnetic oxides with sizeable magnetic properties at and above room temperature give perspective for application. One representative of such high-T C magnetic oxides is the spinel NiFe 2 O 4 , which has a large bandgap of 1.65 eV [5] and a high Curie temperature of T C = 865 K [6]. Due to the complex crystalline structure of the spinel lattice, the growth of epitaxial and well-ordered NiFe 2 O 4 thin films is a challenging task [7]- [9].…”