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<p>Fe<sub>x</sub>Co<sub>3-x</sub>O<sub>4</sub> nanoparticles (NPs) with <i>x</i> varied from 0.55 to 1.0 were synthesized by the auto-combustion method and subjected to the thermal treatment at different temperatures, T<sub>treat</sub>, (400–900&#xa0;°C) and durations (1,&#xa0;12,&#xa0;24&#xa0;h). An exceptionally strong impact of T<sub>treat</sub> on size, morphology and magnetic properties of NPs was revealed. The NPs average size increased by one to two orders of magnitude at T<sub>treat</sub> = 800–900&#xa0;°C, which was associated mainly with the sintering process. Room temperature magnetization dependences on an external magnetic field were described by narrow hysteresis loops with the saturation magnetization M<sub>s</sub> increasing strongly with an increase of <i>x</i> and T<sub>treat</sub> and low room temperature coercivity H<sub>c</sub> increasing strongly with a decrease of the measurement temperature. The magnetic ions distribution over the crystal positions was probed with Mössbauer spectroscopy. To explain the peculiarities of the magnetic properties of the studied NPs and to correlate them with the distribution of magnetic ions over the crystal positions, we assumed the possibility of a transition of Co<sup>3+</sup> ions from a low-spin to a high-spin state due to the distortion of the crystal field when replacing Co<sup>3+</sup> ions with Fe<sup>3+</sup> ions in octahedral positions. The intense MCD peak, centered near 1.85&#xa0;eV, coincides in energy with the radiation of solid-state red lasers widely used in the NPs medical applications.</p>

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Impact of the thermal treatment and the Fe concentration in FexCo3-xO4 nanoparticles on their size, morphology, magnetic properties and the Co3+ ion’s spin-state

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Irina S. Edelman,
  • Dmitriy A. Petrov,
  • Chun-Rong Lin,
  • Sergey M. Zharkov,
  • Tatyana A. Andryushchenko,
  • Maxim S. Molokeev,
  • Yuriy V. Knyazev,
  • Alexander L. Sukhachev,
  • Bing-Yi Chen

摘要

FexCo3-xO4 nanoparticles (NPs) with x varied from 0.55 to 1.0 were synthesized by the auto-combustion method and subjected to the thermal treatment at different temperatures, Ttreat, (400–900 °C) and durations (1, 12, 24 h). An exceptionally strong impact of Ttreat on size, morphology and magnetic properties of NPs was revealed. The NPs average size increased by one to two orders of magnitude at Ttreat = 800–900 °C, which was associated mainly with the sintering process. Room temperature magnetization dependences on an external magnetic field were described by narrow hysteresis loops with the saturation magnetization Ms increasing strongly with an increase of x and Ttreat and low room temperature coercivity Hc increasing strongly with a decrease of the measurement temperature. The magnetic ions distribution over the crystal positions was probed with Mössbauer spectroscopy. To explain the peculiarities of the magnetic properties of the studied NPs and to correlate them with the distribution of magnetic ions over the crystal positions, we assumed the possibility of a transition of Co3+ ions from a low-spin to a high-spin state due to the distortion of the crystal field when replacing Co3+ ions with Fe3+ ions in octahedral positions. The intense MCD peak, centered near 1.85 eV, coincides in energy with the radiation of solid-state red lasers widely used in the NPs medical applications.