Investigation on structure, thermodynamic and multifunctional properties of Ni-Zn-Co ferrite for Gd3+ substitution

Abstract

This study presents a modification of structure-dependent elastic, thermodynamic, magnetic, transport and magneto-dielectric properties of a Ni-Zn-Co ferrite tailored by Gd³⁺ substitution at the B-site replacing Fe³⁺ ions. The synthesized composition of Ni_0.7Zn_0.2Co_0.1Fe_2-x Gd _x O₄ (0 ≤ x ≤ 0.12) crystallized with a single-phase cubic spinel structure that belongs to the Fd3̄m space group. The average particle size decreases due to Gd³⁺ substitution at Fe³⁺. Raman and IR spectroscopy studies illustrate phase purity, lattice dynamics with cation disorders and thermodynamic conditions inside the studied samples at room temperature (RT = 300 K). Ferromagnetic to paramagnetic phase transition was observed in all samples where Curie temperature (T _C) decreases from 731 to 711 K for Gd³⁺ substitution in Ni-Zn-Co ferrite. In addition, Gd³⁺ substitution reinforces to decrease the A-B exchange interaction. Temperature-dependent DC electrical resistivity (ρ _DC) and temperature coefficient of resistance (TCR) have been surveyed with the variation of the grain size. The frequency-dependent dielectric properties and electric modulus at RT for all samples were observed from 20 Hz to 100 MHz and the conduction relaxation processes were found to spread over an extensive range of frequencies with the increase in the amount of Gd³⁺ in the Ni-Zn-Co ferrite. The RLC behavior separates the zone of frequencies ranging from resistive to capacitive regions in all the studied samples. Finally, the matching impedance (Z/η ₀) for all samples was evaluated over an extensive range of frequencies for the possible miniaturizing application.

Fig. 1. Structural analysis for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) using (a) Rietveld refinement of X-ray diffraction patterns (b) variations of lattice constants and crystallite size with the Gd content substitution and (c) variations of Hopping lengths with Gd content (x).

Fig. 2. (a–f) TEM micrographs obtained for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) nanoparticles along with selected area electron diffraction (SAED) pattern and the diffraction rings well-matched with the spinel structure.

Fig. 3. (a) Raman spectra of Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) scanned from 200 cm⁻¹ to 1600 cm⁻¹ (b) the effective force constants of tetrahedral (F_T) and octahedral (F_O) positions sites estimated from Raman spectra.

Fig. 4. (a) IR spectroscopy for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) samples scanned from 350 cm⁻¹ to 1600 cm⁻¹. (b) Forces constants of Fe–O at the octahedral site (k^Fe–O_O) and tetrahedral site (k^Fe–O_T), (c) Fe–O bond length octahedral site (L^Fe–O_O) and tetrahedral site (L^Fe–O_T) (d) overall force constant of ions at the octahedral site (K_O) and tetrahedral site (K_T) (e) cation–anion bond length at the octahedral site (L_O) and tetrahedral site (L_T).

Fig. 5. (a) Deviation of Young's modulus (E) and rigidity modulus (G) due to Gd³⁺ substitution in Ni–Zn–Co ferrite and (b) variation of the mean elastic wave velocity (V_m) and Debye temperature (θ_D) due to Gd³⁺ substitution for in Ni–Zn–Co spinel ferrite.

Fig. 6. (a) Temperature-dependent real permeability (μ′) for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) (b) thermo-magnetization under 1 kOe magnetic field with (b) First order derivative of magnetization with the variation of temperature.

Fig. 7. The variation Curie temperature (T_C) and exchange interaction (J) due to Gd³⁺ substitution in Ni–Zn–Co ferrite.

Fig. 8. (a) Temperature-dependent DC resistivity (ρ_DC) for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) samples and (b) The inset showing lnσ_DCvs. 1000/T plot and (c) variations of TCR with temperature for Gd³⁺ substitution in Ni–Zn–Co ferrite.

Fig. 9. Linear fitting of Arrhenius plot in between lnσ_DC and 1000/T for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ at two temperature regions where (a) x = 0.00, (b) x = 0.02, (c) x = 0.05, (d) x = 0.07, (e) x = 0.10 and (f) x = 0.12.

Fig. 10. Frequency-dependent dielectric properties of Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) where (a) absolute value of dielectric constant (|ε|) and (b) absolute electric modulus (|M|) estimated in the range of 20 Hz to 100 MHz at room temperature.

Fig. 11. Complex modulus plane plots for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) ferrites.

Fig. 12. The frequency-dependent impedance (Z) and RLC behavior of Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) samples at RT (300 K) where, (a) absolute value of impedance (|Z|) (b) phase angle for x = 0.00 and 0.02, (c) for x = 0.05 and 0.07 and (d) for x = 0.10 and 0.12.

Fig. 13. (a) Frequency-dependent Z/η₀ values and (b) Transmission wavelength (λ) for Ni_0.7Zn_0.2Co_0.1Fe_2−xGd_xO₄ (0 ≤ x ≤ 0.12) samples at RT (300 K).