[Paper Review] Magnetic, Optoelectronic, and Rietveld refined structural properties of Al3+ substituted nanocrystalline Ni-Cu spinel ferrites: An experimental and DFT based study

N. Hasan, S. S. Nishat+5 more|arXiv (Cornell University)|Jan 26, 2023

Magnetic Properties and Synthesis of FerritesMaterials Science3 citations

TL;DR

This study investigates Al³⁺-doped nanocrystalline Ni₀.₇Cu₀.₃Fe₂₋ₓO₄ (x = 0.00–0.10) synthesized via sol-gel autocombustion, combining experimental XRD/Rietveld refinement, VSM magnetometry, and DFT calculations. It reveals a decrease in saturation magnetization and Bohr magneton with Al³⁺ doping, soft magnetic behavior (low coercivity and remanence), and a narrow bandgap of 2.99 eV with defect states, indicating optoelectronic tunability for spintronic and photonic applications.

ABSTRACT

The nanocrystalline Ni0.7Cu0.3AlxFe2-xO4 (x=0.00: 0.02: 0.10) is prepared through the sol-gel autocombustion route.Both XRD and Rietveld confirm the single-phase cubic spinel structure of the investigated materials.Other structural parameters refined by the Rietveld refinement analysis are corroborated to single-phase cubic spinel formation of the NPs.Leveraging a vibrating sample magnetometer (VSM) the consequence of Al3+ substitution on the magnetic parameters is studied.The saturation magnetization (MS) and Bohr magneton are found to decrease with Al3+ substitution.The Remanence ratio and coercivity (HC) are observed to be very low suggesting the materials are soft ferromagnetic.First-principle calculations were carried out using the density functional theory (DFT) to demonstrate the optoelectronic behavior of the materials.The electronic bandgap is found low as Eg=2.99eV for the explored materials with observing defect states at 0.62eV.The optoelectronic properties of Al3+ substituted Ni-Cu ferrite NPs have been characterized through the DFT simulation for the first time, demonstrating their potentiality for optoelectronic device applications.The materials' optical anisotropy is observed along the x-axis, which manifests their tunability through light-matter interaction.

Motivation & Objective

• To synthesize and characterize Al³⁺-substituted nanocrystalline Ni-Cu spinel ferrites with controlled doping levels.
• To investigate the structural evolution and phase purity using XRD and Rietveld refinement.
• To analyze the magnetic behavior and confirm soft ferrite characteristics via VSM measurements.
• To explore the optoelectronic properties using density functional theory (DFT) calculations.
• To evaluate the potential of these materials for optoelectronic and spintronic device applications.

Proposed method

• Sol-gel autocombustion synthesis was employed to produce nanocrystalline Ni₀.₇Cu₀.₃AlₓFe₂₋ₓO₄ (x = 0.00–0.10) ferrites.
• X-ray diffraction (XRD) with Rietveld refinement was used to confirm single-phase cubic spinel structure and refine lattice parameters.
• Vibrating sample magnetometry (VSM) was applied to measure saturation magnetization (Ms), remanence, and coercivity (Hc).
• Density functional theory (DFT) calculations were performed to analyze electronic band structure, bandgap, and defect states.
• Optoelectronic properties were evaluated through simulated optical absorption and electronic transitions.
• The influence of Al³⁺ substitution on structural and magnetic parameters was systematically analyzed across the doping range.

Experimental results

Research questions

• RQ1 How does Al³⁺ substitution affect the structural parameters and phase purity of Ni-Cu ferrites?
• RQ2 What is the impact of Al³⁺ doping on the magnetic properties, particularly saturation magnetization and coercivity?
• RQ3 What is the electronic bandgap and defect state distribution in Al³⁺-doped Ni-Cu ferrites as predicted by DFT?
• RQ4 How does the optical anisotropy of the material vary, and what does this imply for light-matter interaction?
• RQ5 To what extent do these materials exhibit tunable optoelectronic behavior suitable for device applications?

Key findings

• Rietveld refinement confirmed the formation of a single-phase cubic spinel structure across all Al³⁺ doping levels (x = 0.00–0.10).
• Saturation magnetization (Ms) and Bohr magneton values decreased with increasing Al³⁺ concentration, indicating reduced net magnetic moment.
• Coercivity (Hc) and remanence were found to be very low, confirming soft magnetic character of the doped ferrites.
• DFT calculations revealed a narrow bandgap of 2.99 eV, with the presence of defect states near the band edges.
• Optical anisotropy was observed along the x-axis, suggesting tunable response to light-matter interaction.
• The combination of experimental and DFT results demonstrates the potential of Al³⁺-doped Ni-Cu ferrites for optoelectronic and spintronic applications.