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中国物理学会期刊

Co3Sn2S2单晶的磁性和电-热输运性能

CSTR: 32037.14.aps.72.20230621

Magnetic and electrical-thermal transport properties of Co3Sn2S2 single crystal

CSTR: 32037.14.aps.72.20230621
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  • Co3Sn2S2是一种磁性外尔半金属, 具有特殊的磁性和电子结构, 其独特的能带结构使其拥有反常霍尔效应、负磁阻效应和反常能斯特效应等多种物理性质. 本文采用自熔剂法合成了高质量的Co3Sn2S2单晶, 并研究了Co3Sn2S2低温下的电输运行为(磁阻效应与霍尔效应等)和热输运行为(塞贝克效应). 热磁曲线表明, 在居里温度点(TC = 178 K)以下140 K(TA)处存在特殊的磁结构, 为铁磁态与反铁磁态共存的磁性过渡态. 研究发现, 在100—160 K出现负的反常“凸形”磁阻, 且在TA附近出现最大临界磁场B0, 为1.41 T, 同时霍尔电阻率ρyx也在TA处取得最大值约20 μΩ·cm. 这可能是由于铁磁态与反铁磁态之间会相互竞争形成非平凡的自旋织构, 导致TA附近独特的电输运行为. Co3Sn2S2在低温下的散射机制为声学波散射和电子-声子散射的共同作用, 在60—140 K时, 自旋无序的增强会引起电子-声子散射增强, 使得的塞贝克系数S出现平台特征. 研究表明, Co3Sn2S2在低温下的特殊磁结构和电子自旋对其电-热输运行为有着重要影响.

     

    Co3Sn2S2 is a magnetic Weyl semimetal with special magnetic and electronic structure. Its unique band structure makes it have many interesting physical properties such as abnormal Hall effect, negative magnetoresistance effect, and abnormal Nernst effect. In this work, high quality Co3Sn2S2 single crystal with a dimension of 8 mm×7 mm×0.5 mm is synthesized by self-flux method. We measure its electrical transport properties (magnetoresistance effect, Hall effect, etc.) and thermal transport properties (Seebeck effect) at low temperature. The free surface of the single crystal exhibits obvious layered growth characteristics, indicating that the Co3Sn2S2 crystal grows along the c-axis direction. The value of the normalized resistivity ρ3 K/ρ300 K for the single crystal sample at 3 K is only 0.08, indicating that the crystal quality of the sample is at a relatively high level. The thermomagnetic (M-T) curves show that a special magnetic structure near 140 K (TA) below the Curie temperature point (TC = 178 K). This special magnetic structure is a magnetic transition state in which ferromagnetic state and antiferromagnetic state coexist, making them appear as a local minimum point in the M-T curve. The Co3Sn2S2 shows a negative anomalous “convex” magnetoresistance in a large range of 100—160 K, and there exists a maximum critical magnetic field B0 (1.41 T), near TA. The coercivity HC drops to almost zero at TA and the Hall resistivity ρyx also reaches a maximum value of about 20 μΩ·cm. This may be due to the competition between ferromagnetic state and antiferromagnetic state to form non-trivial spin texture, resulting in the unique electrical transport behavior near TA. When the temperature rises to TC, the Co3Sn2S2 undergoes a ferromagnetic phase transition, with a saturation magnetization of MS, anomalous Hall conductivity \sigma _yx^\rm A , and Hall resistivity ρyx sharply decreasing. Large anomalous Hall conductance \sigma _yx^A and anomalous Hall angle \sigma _yx^\rm A/\sigma are also present in Co3Sn2S2, with these values reaching 1.4×103 Ω−1·cm−1 and 18%, respectively. The magnetoresistance measurements reveal that the variation of the magnetoresistance with the magnetic field is due to the combination of linear and parabolic contributions. The change in magnetoresistance with the angle θ between the magnetic field B and the current I has a reversal symmetry with C2x symmetry, and the change in θ does not affect the contribution of its magnetoresistance source. In addition, positive magnetoresistance and negative magnetoresistance are found to be shifted at about 60 K. the shift in positive magnetoresistance and negative magnetoresistance are mainly attributed to the competing positive contribution of the Lorentz force to the magnetoresistance and the negative contribution of the spin disorder. The scattering mechanism of Co3Sn2S2 at low temperature is a combination of acoustic wave scattering and electron– phonon scattering. At 60–140 K, the enhancement of spin disorder causes enhanced electron–phonon scattering, resulting in a plateau characteristic of the Seebeck coefficient S. The research shows that the special magnetic structure and electron spin of Co3Sn2S2 at low temperatures have an important influence on its electrothermal transport behavior.

     

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