CoNb3S6单晶中磁性及反常霍尔效应研究

MAGNETIC PROPERTIES AND ANOMALOUS HALL EFFECT OF SINGLE CRYSTAL CoNb3S6

袁培骞

11849413

硕士

物理学

吴留锁

2020-05-28

2020-07-07

哈尔滨工业大学

深圳

尽管反常霍尔效应现象已经被发现有一百多年，铁磁材料中的反常霍尔效应的来源问题仍然困扰着人们。通常情况下，在线性的反铁磁材料中不存在反常霍尔效应。然而在非共线性的反铁磁材料以及拓扑材料中，由于存在大的贝利相位而导致大的反常霍尔效应。本论文将主要围绕二维层状反铁磁材料CoNb3S6中存在的巨大的反常霍尔效应，从实验角度出发，研究其中反常霍尔效应的可能来源。我们通过化学气相传输的方法，生长了CoNb3S6的单晶样品。单晶X衍射结果表明生长出来的单晶样品的晶体结构空间群都为P6322 (No.182)，并且各个元素的比例都接近: Co:Nb:S≈1:3:6。然而，低温下磁化率，比热和霍尔效应的测量发现，即使同一批次生长的样品中也会存在着不同磁性。在论文中，我们一共分析了四个具有代表性的样品，并逐一详细分析了每个不同样品的磁性和反常霍尔效应的关联。其中有两种样品整体并未表现出反常霍尔效应，而另外两种样品在相变温度之下整体表现出大的反常霍尔效应，同时伴随着c轴铁磁分量的出现。但是前期的文献均没有报道这些现象。通过一系列的研究比较发现：CoNb3S6样品中反常霍尔效应与c轴的铁磁分量有明显的关联，但是材料中弱的铁磁分量并不能解释样品中大的反常霍尔效应。虽然粉末中子衍射实验发现CoNb3S6有着共线性的反铁磁结构，但是由于样品的依赖性，我们仍然不能排除某些有大的反常霍尔效应的样品存在着非共面螺旋的磁有序，也仍然不能排除非共面的磁有序对其中大反常霍尔效应的贡献。进一步的分析需要借助单晶中子衍射手段来分别研究各个不同样品的磁结构。

Although the phenomena of Anomalous Hall Effect has been discovered for more than one hundred of years, the intrinsic mechanism of the Anomalous Hall Effect is still unclear. In addition, the Anomalous Hall Effect is usually not expected in a collinear antiferromagnet, when the net magnetization is zero. However, recently, it has been shown that the Anomalous Hall Effect can exist in non-collinear antiferromagnetic materials due to the Berry phase curvature in momentum space caused by the special spin configuration. In this dissertation, we will focus on the Anomalous Hall Effect observed in the antiferromagnetic intercalated transition metal dichalcogenide CoNb3S6, where the conventional argument of the anomalous Hall effect in ferromagnet does not apply.Single crystals of intercalated transition metal dichalcogenide CoNb3S6 were synthesized by the chemical vapor transform method. Single crystal X-Ray diffraction has been performed at room temperature, and all the grown crystals of CoNb3S6 was refined to be of the same structure with the chiral space group P6322 (No.182), and the ratio of different elements was verified to be Co:Nb:S≈1:3:6. However, with lowering temperature, it was found that different crystals even grown from the same batch behave differently. Magnetic susceptibility, specific heat and transport measurements indicate distinct magnetic properties on different samples although they all show the same crystal structure at room temperature. We have select four representative samples, and all the thermal and related transport properties were presented. The Anomalous Hall Effect has been observed in two of the four samples, while it is absent in the other two samples. These observations have not been reported in the previous reports.Based on these detailed study, we found out that the Anomalous Hall Effect are related to the existence of the canted ferromagnetic components in CoNb3S6 samples, but on the other side, the weak ferromagnetic components can not explain such a giant Anomalous Hall Effect coefficient. Although the neutron scattering experiments suggested that the antiferromagnetic order is collinear, we still can not rule out the possibility that the non-collinear antiferromagnetic order persist in some of the samples with large Anomalous Hall Effect. Further study with single crystal neutron diffraction on different samples are needed to clarify the origin of the Anomalous Hall Effect in CoNb3S6.

反常霍尔效应 反铁磁 非共线性磁结构 中子散射

Anomalous Hall Effect antiferromagnet non-collinear magnetic structure neutron scatter

中文

联合培养

南方科技大学

袁培骞. CoNb3S6单晶中磁性及反常霍尔效应研究[D]. 深圳. 哈尔滨工业大学,2020.