Effect of Nd3+ Substitution on the Structural, Magnetic, Magnetocaloric, and Dielectric Performance of M-Type Hexaferrites
Résumé
Nd3+-doped Ba-Ca M-type hexaferrites Ba0.5Ca0.5NdxFe12-xO19 (x = 0.0, 0.1), hereafter referred to as BCNFO, were synthesized via a sol-gel auto-combustion route to investigate the influence of Nd incorporation on their structural, magnetic, magnetocaloric, and dielectric properties. Rietveld-refined XRD patterns combined with TEM observations confirm the formation of a single-phase magnetoplumbite structure with well-defined hexagonal grains and a slight lattice expansion attributed to the larger ionic radius of Nd3+. Raman spectra further support the structural stability and reveal phonon mode shifts associated with local distortions induced by doping.Magnetic characterization shows that Nd3+ substitution weakens the Fe-O-Fe superexchange network, leading to a decrease in saturation magnetization (98.87 → 86.62 emu.g -1 ) and Curie temperature (729 → 722 K), while maintaining high magnetic anisotropy. Although the maximum magnetic entropy change slightly decreases, the relative cooling power notably increases (up to 158 J.kg⁻¹), owing to the broadening of the magnetic transition and improved heat-transfer capability. Dielectric analyses reveal enhanced permittivity and pronounced Maxwell-Wagner relaxation, linked to strengthened interfacial polarization and increased Fe2+/Fe3+ electron hopping. The combined enhancement in magnetocaloric efficiency, dielectric behavior, and magnetic hardness highlights Nd-doped Ba-Ca hexaferrites as promising multifunctional materials for magnetic refrigeration, high-frequency electronics, and microwave device applications.
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