论文标题
纯CO2C纳米颗粒中的交换偏差效应
The Exchange Bias effect in pure Co2C nanoparticles
论文作者
论文摘要
我们研究纯过渡金属碳化物的纳米颗粒的低温磁性特性，即CO2C，平均颗粒直径为$ 40 \ pm 10 $ nm。这些CO2C纳米颗粒是铁磁（FM），直至室温，温度高于室温。强制场显示出低于50 K的膝内勒定律的突然偏差。在这种低温状态下，磁化磁滞回路显示出由于交换偏差（EB）效应而导致的变化，交换场的交换场约为250 OE。对EB效应和AC和DC磁性测量的训练的分析表明，由于具有FM核心和簇玻璃壳的核心壳结构，纳米颗粒发生EB。壳包含无偿旋转，其中一些是可以自由旋转的，而有些则是冷冻的。 DFT计算的小二氧化碳簇的结构和磁性簇的直径很少，这证实了核心壳结构，其中结构有序的核心具有均匀的磁矩分布，并且结构无序的壳具有非均匀的力矩分布。
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.
