Magnetic and electrical-thermal transport properties of Co₃Sn₂S₂ single crystal

Abstract

Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub> 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, abnormal Nernst effect and so on. In this paper, high quality Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub> single crystal with dimension of 8×7×0.5 mm was synthesized by self-flux method. We measured 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 Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub> crystal grows along the c-axis direction. The value of the normalized resistivity <i>ρ</i><sub>3K</sub>/<i>ρ</i><sub>300K</sub> 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(<i>M</i>-<i>T</i>) curves show that a special magnetic structure near 140 K (<i>T</i><sub>A</sub>) below the Curie temperature point (<i>T</i><sub>C</sub>=178 K).This special magnetic structure is a magnetic transition state in which ferromagnetic and antiferromagnetic states coexist, making it appear as a local minimum point in the <i>M</i>-<i>T</i> curve. Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub>shows a negative anomalous "convex" magnetoresistance in the large range of 100-160 K, and there exist a maximum critical magnetic field <i>B</i><sub>0</sub> (1.41 T), near <i>T</i><sub>A</sub>. The coercivity <i>H</i><sub>C</sub> drops to almost zero at <i>T</i><sub>A</sub> and the Hall resistivity <i>ρ</i><sub>yx</sub> also reaches a maximum value of about 20 μΩ cm. This may be due to the competition between ferromagnetic and antiferromagnetic states to form non-trivial spin texture, resulting in the unique electrical transport behavior near <i>T</i><sub>A</sub>. When the temperature rises to <i>T</i><sub>C</sub>, Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub> undergoes a ferromagnetic phase transition, with a saturation magnetization of <i>M</i><sub>S</sub> and anomalous Hall conductivity <img > and Hall resistivity <i>ρ</i><sub>yx</sub> sharply decreased. Large anomalous Hall conductance <img >and anomalous Hall angle <img > are also present in Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub>, with values reaching 1.4*10<sup>3</sup> Ω<sup>−1</sup>cm<sup>−1</sup> and 18%, respectively. The magnetoresistance measurements revealed that the variation of the magnetoresistance with the magnetic field consists of a combination of linear and parabolic contributions. The change in magnetoresistance with the angle <i>θ</i> between the magnetic field <i>B</i> and the current <i>I</i> has a reversal symmetry with C<sub>2<i>x</i></sub> symmetry, and the change in <i>θ</i> does not affect the contribution of its magnetoresistance source. In addition, a shift in positive and negative magnetoresistance is found at about 60 K. This shift in positive and negative magnetoresistance is 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 Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub> at low temperatures 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 <i>S</i>. The research shows that the special magnetic structure and electron spin of Co<sub>3</sub>Sn<sub>2</sub>S<sub>2</sub> at low temperatures have an important impact on its electrothermal transport behavior.