Structural and magnetic properties of CoFe₂O₄ ferrite nanoparticles doped by gadolinium

Abstract

This work’s main purpose is to investigate the effect of Gd3+ substitution on the structural, cation distribution, morphological, and magnetic characteristics of cobalt ferrite nanostructures. The nanostructures were synthesized through the sol-gel auto combustion technique. X-ray diffraction (XRD) analysis with the Rietveld refinement through the Material Analysis Using Diffraction (MAUD) program confirmed a single-phase spinel structure for lower contents of Gd3+. However, for higher concentrations, a trace of second phase GdFeO3 was evident. The crystallite size reduction from 17 to 11 nm with Gd3+ doping confirmed the formation of nanocrystalline Co–Gd ferrite. Cation distribution was another parameter inferred from the experimental data of XRD analyzed by the MAUD program. Fourier-transform infrared spectra confirmed the formation of spinel structure through two prominent vibrational modes observed at the desired wavelength range. FESEM analysis confirmed the data obtained from the XRD about the structure and morphology of the nano samples. Saturation magnetization (M S) of the nano samples evaluated at 10 K showed a decreasing behavior from 94 to 86 emu g−1 by Gd3+ doping, while a fluctuating trend of M S was observed at room temperature. Coercive field (H C) evaluated at 10 K reached a maximum value of about 1145 kA m−1 for the sample CoFe1.96Gd0.04O4, and then it decreased. At the same time, H C experienced no considerable change at 300 K. The possible concepts attributed to such a trend of H C were also investigated. Overall, the significant impact of Gd3+ doping on the cobalt ferrite nanoparticles causes Gd–Co ferrite to have a desirable capacity of permanent magnet materials and storage of information with high density. As a result, this ferrite may be a proper candidate to be utilized, especially at lower temperatures.

Effect of praseodymium in cation distribution, and temperature-dependent magnetic response of cobalt spinel ferrite nanoparticles

“…In the nano scale region, rotation of domains instead of domain wall movement, is the main responsible for magnetization demagnetization occurrence, since the small particles just contain few domain walls. As a result, much energy should be supplemented to rotate the domains which enhances the coercive field [18]. Considering the figures 4 and 11, as an expected phenomenon, improvement of crystallite size makes the coercive field values declined and vice versa for all the Pr contents.…”

“…In addition, the anisotropy constant improvement from 2.34 erg cm −3 for pure cobalt ferrite to 3.25 erg cm −3 for the sample x = 0.02, estimated by the LAS equation (table 4), may cause the H C to be enhanced. Far from that, the existence of the secondary phase confirmed by XRD analysis in the CoFe 1.94 Pr 0.06 O 4 ferrite nanoparticles is expected to improve H C due to the second phase residency in grain boundaries, and hindering the domain walls' movement [18]. However, the dramatic drop of coercive field when Pr content increases from x = 0.04 to x = 0.06 may be attributed to the remarkable fall of anisotropy constant.…”

“…The final observed increase in the crystallite size from 24 nm for x = 0.04 to 26 nm for x = 0.06 is attributed to the formation of secondary PrFeO 3 phase. It can be inferred that the energy spent on the Pr incorporation into the cobalt ferrite sub-lattices is now being spent on the crystallites' growth [18].…”

“…), and EDTA as a substance for complexion were used as starting chemical materials. After preparation of the sol during the same way just like our previous work [18], we increased the sol's temperature up to 60 °C while the heating process continued for 6 h to remain the system's temperature unchanged. Such heat treatment increased the viscosity of the solution until forming a massive fluffy powder after the time that the gel was entirely burnt in an auto combustion manner.…”

Sm Doped Cu–Ni Spinel Ferrite Nanoparticles for Hyperthermia and Photocatalytic Applications

“…It is well-known that the broadening in the peaks is a property of nanosized samples due to the loss of long-range ordering of atoms in the crystals. Observed broadening in all the recorded diffracted peaks certified that the prepared ferrite samples lie in the nanometric domain. − Normally, three fundamental parameters are responsible for the overall peak broadening in the XRD patterns in the nanometric range; they are the size effect of nanocrystallites, the generated microstrain in the nanocrystals, and the instrumental effect. − The effect of instrumental broadening was removed by recording a diffraction profile of the bulk LaB 6 powder under identical conditions and substituting it for the overall broadening. After eliminating the instrumental broadening, the overall line-width β (FWHM) of diffracted X-ray peaks contains only the nanocrystallite size (β size ) and microstrain (β strain ) broadening effects and it can be written as , β = false( β size + β strain ) = K λ D ⁡ cos ⁡ θ + 4 ε ⁡ tan ⁡ θ where K denotes the sphericity factor (≈0.89 for the particles owing spherical shape), λ is the wavelength of Cu–K α X-ray radiation (≈1.5406 Å), D specifies the mean crystallite size, ε signifies the microstrain existed inside the crystals and θ represents Bragg’s angle.…”