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<p>The bulk magnets of Sr<sub>0.67</sub>Ca<sub>0.33</sub>Fe<sub>9</sub>Al<sub>3-<i>x</i></sub>Cr<sub><i>x</i></sub>O<sub>19</sub> (<i>x</i> = 0.0, 0.5, 1.0, 1.5) were synthesized via a solid-phase reaction method. The results demonstrate that the structural integrity of strontium ferrites is maintained through the co-substitution of Al and Cr for Fe. Hysteresis loops analysis reveals that, at <i>x</i> = 0, the coercivity (<i>H</i><sub>c</sub>) reaches a high value of 1.58&#xa0;T. As Cr content increases, the saturation magnetization (<i>M</i><sub>s</sub>) increases while <i>H</i><sub>c</sub> decreases. The average grain size ranges from 0.6 to 0.8&#xa0;μm. The addition of Al results in a high magnetocrystalline anisotropy field (<i>H</i><sub>a</sub>), which decreases with increasing Cr<sup>3+</sup> content. Detailed studies on low-temperature magnetic properties indicate excellent coercivity at low temperatures, for example, the Sr<sub>0.67</sub>Ca<sub>0.33</sub>Fe<sub>9</sub>Al<sub>2.5</sub>Cr<sub>0.5</sub>O<sub>19</sub> sample exhibits a <i>H</i><sub>c</sub> of 1.13&#xa0;T at 10&#xa0;K. To elucidate the influence of Al on magnetic properties, additional anisotropic magnets Sr<sub>0.67</sub>Ca<sub>0.33</sub>Fe<sub>12-<i>x</i></sub>Al<sub><i>x</i></sub>O<sub>19</sub> (<i>x</i> = 0, 1, 2, 3) were prepared. The study shows that Al significantly enhances coercivity, achieving a high coercivity and good squareness with Al content increasing from <i>x</i> = 0 to <i>x</i> = 1 and 2, despite a continuous decrease in saturation magnetization. However, at a higher Al content, such as at <i>x</i> = 3, the squareness of the demagnetization curve decreases significantly. Furthermore, the addition of Al improves low-temperature coercivity, with <i>H</i><sub>c</sub> reaching 1.11&#xa0;T at 50&#xa0;K when <i>x</i> = 3. First-principles calculations using density functional theory confirm that the substitution of Fe<sup>3+</sup> with non-magnetic Al<sup>3+</sup> at the 12<i>&#xa0;k</i> sites reduces saturation magnetization, consistent with the experimental results.</p>

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Preparation of strontium ferrite bulk magnets with high coercivity at low-temperature

  • 期刊论文

  • 发表日期：

    2025年6月3日

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  • Yunchuan Zhang,
  • Xiangru Ren,
  • Qin Wang,
  • Yilong Ma,
  • Xianfu Luo,
  • Donglin Guo

摘要

The bulk magnets of Sr0.67Ca0.33Fe9Al3-xCrxO19 (x = 0.0, 0.5, 1.0, 1.5) were synthesized via a solid-phase reaction method. The results demonstrate that the structural integrity of strontium ferrites is maintained through the co-substitution of Al and Cr for Fe. Hysteresis loops analysis reveals that, at x = 0, the coercivity (Hc) reaches a high value of 1.58 T. As Cr content increases, the saturation magnetization (Ms) increases while Hc decreases. The average grain size ranges from 0.6 to 0.8 μm. The addition of Al results in a high magnetocrystalline anisotropy field (Ha), which decreases with increasing Cr3+ content. Detailed studies on low-temperature magnetic properties indicate excellent coercivity at low temperatures, for example, the Sr0.67Ca0.33Fe9Al2.5Cr0.5O19 sample exhibits a Hc of 1.13 T at 10 K. To elucidate the influence of Al on magnetic properties, additional anisotropic magnets Sr0.67Ca0.33Fe12-xAlxO19 (x = 0, 1, 2, 3) were prepared. The study shows that Al significantly enhances coercivity, achieving a high coercivity and good squareness with Al content increasing from x = 0 to x = 1 and 2, despite a continuous decrease in saturation magnetization. However, at a higher Al content, such as at x = 3, the squareness of the demagnetization curve decreases significantly. Furthermore, the addition of Al improves low-temperature coercivity, with Hc reaching 1.11 T at 50 K when x = 3. First-principles calculations using density functional theory confirm that the substitution of Fe3+ with non-magnetic Al3+ at the 12 k sites reduces saturation magnetization, consistent with the experimental results.