Core–shell Fe₃O₄@C magnetic nanoparticles which are of great interest for research have a widely applied prospect. However, people know little about the optical and magnetic properties of the small-size Fe₃O₄@C nanoparticles due to the difficulty of uniformly coating small size Fe₃O₄ nanoparticles. In this paper, the influence of carbon shell coating on the optical and magnetic properties of small size Fe₃O₄ nanoparticles was presented. Carbon coating can strengthen the absorption intensity in the UV–visible light region through the introduction of oxygen defects on the surface of the nanoparticles by nitric acid treatment. Fe₃O₄ and Fe₃O₄@C nanoparticles both display typical superparamagnetic behavior in the high-temperature regime and a blocked state at low temperature from hysteresis loop, zero-field cooled and field cooled curves. Carbon coating reduce the surface uniaxial anisotropy, thus the average blocking temperature <T_B> decreases from 59 K of Fe₃O₄ nanoparticles to 50 K of Fe₃O₄@C nanoparticles.

核壳Fe ₃ O ₄ @C磁性纳米粒子是研究热点，具有广泛的应用前景。然而，由于难以均匀涂覆小尺寸Fe ₃ O ₄纳米颗粒，人们对小尺寸Fe ₃ O ₄ @C纳米颗粒的光学和磁学性质知之甚少。在本文中，介绍了碳壳涂层对小尺寸Fe ₃ O ₄纳米粒子的光学和磁性能的影响。碳涂层可以通过硝酸处理在纳米粒子表面引入氧缺陷来增强紫外可见光区域的吸收强度。铁₃ O ₄和Fe ₃ O ₄ @C 纳米粒子在高温状态下都表现出典型的超顺磁性行为，在低温下从磁滞回线、零场冷却和场冷却曲线中都表现出阻塞状态。碳涂层降低了表面单轴各向异性，因此平均阻塞温度<T _B > 从 Fe ₃ O ₄纳米颗粒的59 K 降低到 Fe ₃ O ₄ @C 纳米颗粒的50 K。