Cu_1−xFe_xO nanoparticles were prepared using a freeze-drying process followed by heat treatment. The particles were then characterized using Mössbauer spectroscopy and magnetization techniques. The results revealed complex magnetic behavior, which can be attributed to the presence of two different magnetic regions: the particle core, which has antiferromagnetic fluctuations, and the particle shell, where uncompensated spins are responsible for their superparamagnetic characteristics. At low temperatures, the moments freeze, revealing a ferromagnetic order for the shells and a dipolar magnetic interaction among the nanoparticles. In addition, an exchange-bias field revealed magnetic interactions between the core and the shell of the nanoparticles. The ferromagnetism observed in this system suggests that antiferromagnetic oxide matrices can be used for diluted magnetic semiconductor applications, if suitably doped.

中文翻译：

---

掺杂Fe的CuO纳米粒子的核-壳行为和交换偏压

铜_1-x铁_x使用冷冻干燥过程随后进行热处理来制备O纳米颗粒。然后使用Mössbauer光谱学和磁化技术对颗粒进行表征。结果揭示了复杂的磁行为，这可以归因于两个不同的磁性区域的存在：具有反铁磁波动的粒子核和粒子壳，其中未补偿的自旋负责其超顺磁特性。在低温下，力矩冻结，揭示出壳的铁磁顺序和纳米粒子之间的偶极磁相互作用。另外，交换偏置场揭示了纳米颗粒的核与壳之间的磁性相互作用。