Tri-valent (Nd³? &Cr³?) Substituted Pb-M Hexaferrite for Structural, Magnetic, Electric & Photoluminescence Investigations

Abstract

Tri-valent (Nd³? & Cr³?) Substituted Pb-M Hexaferrite(Pb0.8Nd0.2Fe12O19&Pb0.8Cr0.2Fe12O19) Solid Solution has been synthesized using Auto-Combustion synthesis approach and reported for tailored Crystalline Signature, Magnetic Investigations, enhanced Photoluminescence and Electric (?\', ?\" & ?ac vs. Frequency at Room Temperature) properties. Hexagonal structural phase with space group P63/mmc No. 194 has been identified from Bragg reflection positioned at 2? ~ 34.12 & 34.36 in Pb0.8Cr0.2Fe12O19&Pb0.8Pb0.2Fe12O19.Decreased Porosity with enlarged grain size and grain growth demonstrate densification and compactness of grain due to high temperature sintering identified from Micrographs recorded using Scanning Electron Microscope. Other crystalline signatures such as calculated crystallite size calculated using Debye Scherrer formula, Macro strain, Dislocation density have been stamped for successful synthesis of Nano sized hexagonal ceramic oxide. Least value of Macrostrain, Dislocation densitysignature for well-ordered crystalline lattice arrangement after substitution of with different ionic radii of substituent (Nd³? & Cr³?) compared with Parent Metal ion (Pb2+) in PbFe12O19 M type hexaferrite. S- shaped M (Magnetization) vs. H (Applied External Magnetic Field) identified enhanced magnetic signature after substitution of (Nd³? & Cr³?) with Parent Metal ion (Pb2+) in PbFe12O19 M type hexaferrite where at least coercive behavior confined soft ferrite nature (suitable for Temporary Magnet) suggests that prepared solid solutions crucial for storage devices based on (0 & 1) memory as well as for in transformers used in electrical devices whereas multi domain structural arrangement along with ferromagnetic behavior evident for < 1 square-ness ratio. Spin up and down coupling of Fe3+at octahedral and tetrahedral sites has been confirmed from variation in value of magnetic moment (?B) as substituent varied from Nd³? to Cr³?. Shift in emission peak in luminescence spectra shows change in rate of recombination after emission whereas capacitive response studied using dielectric and conductivity spectroscopy shows that prepared Nano-Ceramic hexaferrite can be useful in Capacitive Applications

Introduction

The text discusses the development and characterization of Nd³?- and Cr³?-substituted PbFe??O?? M-type hexaferrite nanoceramics for multifunctional applications, particularly in magnetic, dielectric, optical, luminescent, microwave, and high-frequency electronic devices.

Background

Ceramic oxides are important advanced materials because of their chemical and thermal stability, high electrical resistivity, mechanical strength, magnetic properties, dielectric behavior, and resistance to wear. Their properties can be modified by changing their composition, crystal structure, particle size, and defect concentration.

M-type hexaferrites, with a general formula such as MFe??O??, are especially attractive because they possess:

• High magnetocrystalline anisotropy

• Good chemical and thermal stability

• Moderate saturation magnetization

• High electrical resistivity

• Low eddy-current losses

• Useful dielectric properties

• Good resistance to demagnetization

These characteristics make them suitable for permanent magnets, magnetic recording, data storage, microwave devices, electromagnetic interference (EMI) shielding, high-frequency electronics, communication systems, and magnetodielectric applications.

Research Focus

The study focuses on PbFe??O??, a lead-based M-type hexaferrite, and investigates the effects of replacing Pb²? with trivalent Nd³? (neodymium) and Cr³? (chromium).

The two compositions studied are:

• Pb?.?Nd?.?Fe??O??

• Pb?.?Cr?.?Fe??O??

The substitution of ions with different valence states and ionic radii creates charge imbalance and oxygen vacancies, which can modify the crystal structure, magnetic exchange interactions, electrical conduction, dielectric response, and magnetocrystalline anisotropy.

Research Gap

Although the individual effects of rare-earth and transition-metal substitutions in hexaferrites have been widely studied, the text identifies a need for a or Cr³?, then study how this chemical change alters the material's crystal structure and functional properties. The XRD results confirm that the better understanding of how Nd³? and Cr³? substitutions affect the structural, magnetic, dielectric, optical, and luminescent properties of PbFe??O??.

In particular, the research seeks to understand:

• Changes in lattice structure caused by different ionic radii

• Oxygen-vacancy formation

• Changes in cation distribution

• Modification of Fe–O–Fe super-exchange interactions

• Changes in magnetocrystalline anisotropy

• Frequency-dependent dielectric behavior

• Charge-hopping and polarization mechanisms

• Relationships between structural changes and functional properties

Experimental Method

The nanoceramics were synthesized using the auto-combustion method.

The major steps were:

1. Metal nitrates were mixed in the required stoichiometric proportions.

2. De-ionized water was added and the solutions were continuously stirred.

3. Citric acid was used as a fuel during combustion.

4. The resulting powder was calcined at 900°C for 8 hours.

5. The powder was mixed with 2 wt% PVA as a binder.

6. Pellets were prepared and sintered at 1100°C for 2 hours.

7. The resulting materials were characterized using several techniques.

Characterization Techniques

The study uses:

• X-ray diffraction (XRD): To determine crystal structure, phase formation, lattice parameters, crystallite size, strain, and dislocation density.

• Scanning Electron Microscopy (SEM): To examine surface morphology and microstructure.

• Vibrating Sample Magnetometry (VSM): To study magnetic properties.

• Impedance analysis: To investigate dielectric and electrical behavior.

• Photoluminescence spectroscopy: To investigate luminescence properties.

• Optical analysis: To study band-gap-related characteristics.

Initial Results

XRD analysis shows that the synthesized materials exhibit a well-crystallized hexagonal M-type ferrite structure. The diffraction peaks are sharp and narrow, indicating good crystallinity.

The materials were identified as belonging to the hexagonal P6?/mmc crystal structure (space group No. 194), consistent with M-type hexaferrite.

The diffraction peaks for the substituted samples show slight shifts compared with the standard PbFe??O?? structure. These shifts indicate that substitution of Pb²? by Nd³? and Cr³? produces changes in:

• Lattice parameters

• Interplanar spacing

• Crystallite size

• Microstrain

• Dislocation density

• Overall crystal arrangement

These structural changes are attributed mainly to the different ionic radii and valence states of Nd³? and Cr³? compared with Pb²?, along with structural defects and densification during high-temperature sintering.

Conclusion

In the present investigation, influence of partial substitution of Nd³? and Cr³? at the Pb²? site in PbFe12O19 on the structural, morphological, luminescence, magnetic and dielectric have been studied and reported with stoichiometric proportion of Pb0.8Nd0.2Fe12O19 and Pb0.8Cr0.2Fe12O19 synthesized using Auto combustion approach. X-ray diffraction data shows that increase in crystallite size, crystallite cell volume, strain reveals influence of substituent with larger ionic radii as comparison with lower ionic radii. Irregular shaped with inter-granular regions with increased grain growth along with dense polycrystalline morphology with substitution of Nd³? & Cr³? resulted with discernible differences in grain morphology and packing. Magnetic measurements confirmed ferromagnetic behaviour for both compositions. Pb0.8Nd0.2Fe12O19 exhibited higher remanent magnetization ~7.049 emu g?¹, saturation magnetization ~96.1 emu g?¹, effective Bohr magneton 20.149& anisotropy constant ~6939.01 as compare with Pb0.8Cr0.2Fe12O19, for which the corresponding values were 6.582 emu g?¹, 92.3 emu g?¹, 19.052 and 6552.33, respectively. Conversely, the Cr-substituted composition exhibited slightly higher coercivity 68.15Oe than the Nd-containing composition 67.32 Oe. The squareness ratio decreased marginally from 0.073 to 0.071 with Cr substitution. The dielectric measurements demonstrated strong frequency dispersion of both the real and imaginary components of dielectric permittivity, particularly in the low-frequency region, followed by reduced frequency dependence at higher frequencies. The AC conductivity remained comparatively low at lower frequencies but increased markedly in the higher-frequency region, indicating enhanced localized charge-carrier hopping. The Nd-substituted composition exhibited higher high-frequency AC conductivity than the Cr-substituted composition. The results demonstrate that substitution of Nd³? and Cr³? provides an effective route for tailoring the coupled magnetic, dielectric and electrical properties of Pb-based hexaferrites for potential high-frequency electronic and magneto-dielectric applications.

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Copyright © 2026 Mr. Ashwani, Mrs. Priyanka Sharma, Dr. Narendra Jakhar, Dr. Krishna Kumar Singh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.