Abstract Nanoparticles of Cr substituted Co-Mg ferrites with chemical composition Co 0.5 Mg 0.5 Cr x Fe 2−x O 4 (0 ≤ x ≤ 1) have been synthesized by sol-gel auto combustion route. Rietveld refined powder X-ray diffraction patterns confirmed nanocrystalline single phase formation of all the ferrite samples in the face centred cubic spinel structure in the space group of Fd 3 m (No. 192). Cr doping for Fe in the Co-Mg ferrite leads to monotonic decrease in the saturation magnetization at 300 K as well as at 5 K, which can be described due to the weakening of super exchange interaction because of the replacement of Fe 3+ ions by weak magnetic Cr 3+ ions at the octahedral site. Decrement observed in coercivity from 0.085T to 0.044 T at room temperature with increase in Cr concentration is indicative of the decrement in the isotropic field. Coercivity follows the Kneller's law for Co 0.5 Mg 0.5 Fe 2 O 4 ferrite within the temperature range 5–300 K. Interestingly the saturation magnetization was observed to increase whereas the coercivity decreases with increase in the annealing temperature in Co 0.5 Mg 0.5 Cr 0.6 Fe 1.4 O 4 ferrite.

中文翻译：

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纳米晶Cr掺杂Co-Mg铁氧体的结构和磁性行为

摘要 通过溶胶-凝胶自燃法合成了化学成分为Co 0.5 Mg 0.5 Cr x Fe 2-x O 4 (0 ≤ x ≤ 1) 的Cr 取代Co-Mg 铁氧体纳米颗粒。Rietveld 精制粉末 X 射线衍射图证实，所有铁氧体样品均在 Fd 3 m 空间群（编号 192）的面心立方尖晶石结构中形成纳米晶单相。在 Co-Mg 铁氧体中对 Fe 的 Cr 掺杂导致饱和磁化强度在 300 K 和 5 K 时单调下降，这可以描述为由于 Fe 3+ 离子被置换而导致超交换相互作用减弱八面体位置的弱磁性 Cr 3+ 离子。随着 Cr 浓度的增加，在室温下观察到的矫顽力从 0.085T 下降到 0.044T，这表明各向同性场中的下降。