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<p>Holmium-doped nickel–cobalt ferrites with the chemical formula Ni<sub>0.5</sub>Co<sub>0.5</sub>Fe<sub>2</sub>O<sub>4</sub> where (x = 0 to 0.02 with the step of 0.005) were prepared by conventional solid-state method. X-ray diffraction has revealed that all compositions have single phase cubic spinel structure, with a decline in crystallite size from 56 to 52&#xa0;nm and with the lattice parameter shortening from 8.371 to 8.358&#xa0;Å upon substitution with Ho<sup>3+</sup>. The FTIR spectra displayed two distinct absorption peaks at around 600&#xa0;cm⁻<sup>1</sup> and 400&#xa0;cm⁻<sup>1</sup>, respectively, reflecting tetrahedral and octahedral metal–oxygen vibrations. Raman spectra revealed six typical modes, in agreement with the cubic spinel structure, and were also utilized along with XRD to conclude the cation distribution. UV–Vis spectroscopy disclosed a reduction in optical band gap ranging from 1.84 to 1.55&#xa0;eV with an increase in Ho<sup>3</sup>⁺ content. Magnetic analysis indicated an increase in magnetization (from 57 to 72&#xa0;emu/g) &amp; coercivity (from 144 to 170 Oe), attributed to cation redistribution and the incorporation of Ho<sup>3</sup>⁺ ions. Unlike conventional Ni–Co ferrites or other rare-earth substitutions, Ho<sup>3</sup>⁺ incorporation induces significant lattice distortion, enhances magneto crystalline anisotropy, and suppresses electron hopping conduction, thereby enabling simultaneous tuning of coercivity and resistivity. This distinctive combination of high magnetic performance with improved electrical resistivity makes Ho-doped Ni–Co ferrites particularly novel for high-frequency, microwave, and multifunctional device applications.</p> Graphical abstract <p></p>

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Effect of holmium doping on structural, cation distribution,optical and magnetic properties of Ni0.5Co0.5Fe2O4 ferrites

  • 期刊论文

  • 发表日期：

    2026年3月23日

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  • Radha Maddi,
  • Suresh Sripada

摘要

Holmium-doped nickel–cobalt ferrites with the chemical formula Ni0.5Co0.5Fe2O4 where (x = 0 to 0.02 with the step of 0.005) were prepared by conventional solid-state method. X-ray diffraction has revealed that all compositions have single phase cubic spinel structure, with a decline in crystallite size from 56 to 52 nm and with the lattice parameter shortening from 8.371 to 8.358 Å upon substitution with Ho3+. The FTIR spectra displayed two distinct absorption peaks at around 600 cm⁻1 and 400 cm⁻1, respectively, reflecting tetrahedral and octahedral metal–oxygen vibrations. Raman spectra revealed six typical modes, in agreement with the cubic spinel structure, and were also utilized along with XRD to conclude the cation distribution. UV–Vis spectroscopy disclosed a reduction in optical band gap ranging from 1.84 to 1.55 eV with an increase in Ho3⁺ content. Magnetic analysis indicated an increase in magnetization (from 57 to 72 emu/g) & coercivity (from 144 to 170 Oe), attributed to cation redistribution and the incorporation of Ho3⁺ ions. Unlike conventional Ni–Co ferrites or other rare-earth substitutions, Ho3⁺ incorporation induces significant lattice distortion, enhances magneto crystalline anisotropy, and suppresses electron hopping conduction, thereby enabling simultaneous tuning of coercivity and resistivity. This distinctive combination of high magnetic performance with improved electrical resistivity makes Ho-doped Ni–Co ferrites particularly novel for high-frequency, microwave, and multifunctional device applications.

Graphical abstract