Core–shell MnFe₂O₄/α-Fe₂O₃ nanoparticles having core diameters from 5 nm to 28 nm are synthesized by chemical co-precipitation route and investigated structurally and magnetically. The existence of the cubic spinel phase of MnFe₂O₄ (FiM) core together with the rhombohedral phase of α-Fe₂O₃ (AFM) shell was confirmed by X-ray diffraction. The field-cooled hysteresis loop at 5 K reveals a strong exchange bias of 1.1 kOe along with a high coercivity of 4.81 kOe and vertical shift of 1.83% for the particles with the smallest core diameters. The exchange-bias (H_E) and coercive (H_C) fields decrease with increasing core diameter. Exchange-spring behavior was also observed in the hysteresis loops in all nanocomposite systems at 5 K due to the presence of the magnetically hard (α-Fe₂O₃) and soft (MnFe₂O₄) phases. The superparamagnetic limit shifted above room temperature even for the sample having core diameter of 5 nm due to the presence of strong interfacial spins coupling, and this coupling was also seen in the hysteresis loops obtained at room temperature.

核-壳锰铁₂ ö ₄ /的α-Fe _2层ö ₃具有纤芯直径为5纳米至28纳米的纳米颗粒通过化学共沉淀合成路线合成和结构上和磁的影响。锰铁的立方尖晶石相的存在₂ ö ₄与α-Fe的菱形相（FIM）芯一起₂ ö ₃（AFM）壳是由X-射线衍射证实。磁芯直径s最小的颗粒在5 K时的场冷磁滞回线显示出1.1 kOe的强交换偏置以及4.81 kOe的高矫顽力和1.83％的垂直位移。交换偏置（^ h _Ë）和矫顽（H _C）场随铁心直径的增加而减小。交换弹簧行为也被用在磁滞回线以5K观察到所有的纳米复合材料的系统由于硬磁（α-Fe的存在₂ ö ₃）和软（锰铁₂ ö ₄）相位。由于存在强的界面自旋耦合，即使对于具有5nm核心直径的样品，超顺磁极限也移至室温以上，并且在室温下获得的磁滞回线中也可以看到这种耦合。