Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas (UNICAMP) Campinas, SP, Brazil.
Nanotechnology. 2010 Jan 22;21(3):035602. doi: 10.1088/0957-4484/21/3/035602.
We report an alternative synthesis method and novel magnetic properties of Ni-oxide nanoparticles (NPs). The NPs were prepared by thermal decomposition of nickel phosphine complexes in a high-boiling-point organic solvent. These particles exhibit an interesting morphology constituted by a crystalline core and a broad disordered superficial shell. Our results suggest that the magnetic behavior is mainly dominated by strong surface effects at low temperature, which become evident through the observation of shifted hysteresis loops (approximately 2.2 kOe), coercivity enhancement (approximately 10.2 kOe) and high field irreversibility (>or=50 kOe). Both an exchange bias and a vertical shift in magnetization can be observed in this system below 35 K after field cooling. Additionally, the exchange bias field shows a linear dependence on the magnetization shift values, which elucidate the role of pinned spins on the exchange fields. The experimental data are analyzed in terms of the interplay between the interface exchange coupling and the antiferromagnetically ordered structure of the core.
我们报告了一种镍氧化物纳米粒子（NPs）的替代合成方法和新颖的磁性。这些 NPs 是通过在高沸点有机溶剂中热分解镍膦配合物制备的。这些颗粒表现出由结晶核和宽无序表面壳组成的有趣形态。我们的结果表明，在低温下，磁性行为主要由强表面效应主导，这通过观察到的滞后回线移动（约 2.2 千奥斯特）、矫顽力增强（约 10.2 千奥斯特）和高场不可逆性（≥50 千奥斯特）得到证实。在磁场冷却后，该系统在 35 K 以下可以观察到交换偏置和磁化的垂直移动。此外，交换偏置场与磁化移动值呈线性关系，这阐明了固定自旋对交换场的作用。实验数据根据界面交换耦合和核的反铁磁有序结构之间的相互作用进行分析。
