纯Co2C纳米粒子的交换偏置效应
The Exchange Bias effect in pure Co2C nanoparticles
摘要：
我们研究了纯过渡金属碳化物纳米颗粒的低温磁性，Co2 C，平均粒径为$40 \pm 10$ nm。这些Co 2C纳米颗粒在室温下是铁磁性的（FM），阻断温度高于室温。在50 K以下，矫顽场突然偏离Kneller定律.在这个低温制度的磁化磁滞回线显示由于交换偏置（EB）的效果，与交换场的~ 250 Oe的移位。EB效应和交流和直流磁测量的训练分析表明，EB出现在纳米粒子由于核-壳结构与FM核心和集群玻璃壳。壳层包含未补偿的自旋，其中一些是自由旋转的，而另一些是冻结的。用密度泛函理论（DFT）计算了Co2 C团簇的结构和磁性，证实了Co2 C团簇具有核壳结构，其中有序的核具有均匀的磁矩分布，无序的壳具有不均匀的磁矩分布.
英文摘要：
We study the low temperature magnetic properties of nanoparticles of pure transition metal carbide, viz., Co2C, with an average particle diameter of $40 \pm 10$ nm. These Co2C nanoparticles are ferromagnetic (FM) up to room temperature with blocking temperatures above room temperature. The coercive field shows abrupt deviation from the Kneller law below 50 K. In this low temperature regime the magnetization hysteresis loop shows shifts due to exchange bias (EB) effect, with an exchange field of ~ 250 Oe. Analysis of training of the EB effect and ac and dc magnetic measurements suggest that EB arises in the nanoparticles due to a core-shell structure with a FM core and a cluster glass shell. The shell contains uncompensated spins, some of which are freely rotatable while some are frozen. DFT calculations of structural and magnetic properties of small Co2C clusters of diameter of few Angstroms confirm a core-shell structure, where the structurally ordered core has uniform magnetic moment distribution and the structurally disordered shell has non-uniform moment distribution.
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