Doped magnetite (Sn_xFe_3-2/3xO₄) nanoparticles (NPs) (12–50 nm) with different amount of Sn²⁺ ions (x) were synthesized using co-precipitation method. Sn²⁺ doping reduces the anticipated oxidation of Fe₃O₄ NPs to maghemite (γ-Fe₂O₃), making them attractive in several magnetic applications. Detailed characterizations during heating–cooling cycles revealed the possibility of tuning the unusual observed magnetization dipping temperature/amplitude, irreversibility, and Curie point of these NPs. We attribute this dip to the chemical reduction of γ-Fe₂O₃ at the NPs surfaces. Along with an increase in the dipping temperature, we found that doping with Sn²⁺ reduces the dipping amplitude, until it approximately disappears when x = 0.150. Based on the core-shell structure of these NPs, a phenomenological expression that combines both modified Bloch law (M = M₀[1 − γ(T/T_C)]^β) and a modified Curie–Weiss law (M = − α[1/(T − T_C)^δ]) is developed in order to explain the observed M-T behavior at different applied external magnetic fields and for different Sn²⁺ concentrations. By applying high enough magnetic field, the value of the parameters γ and δ ≈ 1 which are the same in modified Bloch and Curie–Weiss laws. They do not change with the magnetic field and depend only on the material structure and size. The power β for high magnetic field was 2.6 which is as expected for this size of nanoparticles with the core dominated magnetization. However, the β value fluctuates between 3 and 10 for small magnetic fields indicating an extra magnetic contribution from the shell structure presented by Curie–Weiss term. The parameter (α) has a very small value and it turns to negative values for high magnetic fields.

使用共沉淀法合成了不同数量的Sn ²⁺离子（x）的掺杂磁铁矿（Sn _x Fe _{3-2 / 3 x} O ₄）纳米颗粒（NPs）（12-50 nm）。的Sn ²⁺掺杂降低Fe的预期氧化₃ Ò ₄的NP到磁赤铁矿（γ-的Fe ₂ ö ₃），使得它们在几个磁应用中具有吸引力。在加热-冷却循环中进行的详细表征表明，有可能调整这些NP的异常观察到的磁化浸渍温度/幅度，不可逆性和居里点。我们认为这浸化学还原的γ -铁₂NP表面的O ₃。随着浸入温度的升高，我们发现掺杂Sn ²⁺会降低浸入幅度，直到x = 0.150时浸入幅度几乎消失。基于这些NP的核壳结构，结合了经修改的Bloch定律（M = M ₀ [1- γ（T / T _C）] ^β）和经过修改的居里-魏斯定律（M =  -α [1 /（T - T _C）^δ ]）的产生是为了解释观察到的M-在不同的外加磁场和不同的Sn ²⁺浓度下的T行为。通过施加足够高的磁场，参数γ和δ≈1的值与修改的布洛赫和居里-魏斯定律相同。它们不随磁场变化，而仅取决于材料的结构和尺寸。高磁场的功率β为2.6，这与具有核心主导的磁化强度的纳米颗粒的尺寸一样。但是，对于较小的磁场，β值在3到10之间波动，这表明居里·魏斯（Curie-Weiss）项表示的壳结构产生了额外的磁作用。参数（α）的值非常小，对于高磁场，它变为负值。