本文以磁控溅射制备的Co
2MnSn薄膜为研究对象,研究了薄膜沉积温度对其反常能斯特效应和自旋塞贝克效应相关特性的影响及其物理机制。研究表明,通过调节沉积温度可以得到B2结构的Co
2MnSn薄膜;随着沉积温度的升高,薄膜的磁性和金属性也将得到增强。本文以B2相的Co
2MnSn薄膜为对象,重点研究了其在温度梯度下的反常能斯特效应和自旋塞贝克效应。实验发现,常温下,500℃沉积的Co
2MnSn薄膜的反常能斯特系数为0.7 μV/K,比常温下Fe,Co,Ni等传统金属(约0.03 μV/K)大20倍。本文研究还进一步表明,通过调节Co
2MnSn薄膜的制备温度,可以在一定程度上调控其反常能斯特效应和自旋塞贝克效应,这将有益于热电材料以及热电效应相关设备的研发。
In this paper, Co
2MnSn thin films prepared by magnetron sputtering were taken as the research object, and the effect of films deposition temperature on the characteristics of the anomalous Nernst effect and spin Seebeck effect and its physical mechanism were investigated. The research results show that Co
2MnSn thin films with B2 structure can be obtained by adjusting the deposition temperature. As the deposition temperature increases, the magnetic and metallic properties of the thin film were enhanced. Taking the B2 phase Co
2MnSn thin films as the object, this paper focuses on the anomalous Nernst effect and the spin Seebeck effect under the temperature gradient. The experiment results show that the anomalous Nernst coefficient of Co
2MnSn thin film deposited at 500˚C is 0.7 μV/K, which is 20 times larger than that of 3 d metals, such as Fe, Co, and Ni. The research in this paper further shows that by controlling the preparation temperature of Co
2MnSn thin films, the anomalous Nernst effect and spin Seebeck effect can be adjusted to a certain extent, which will be beneficial to the research and development of thermoelectric materials and thermoelectric effect related equipment.
根据所施加温度梯度的不同,自旋塞贝克效应和反常能斯特效应均有两种不同构型,其中温度梯度垂直于薄膜平面的为纵向构型,温度梯度平行于薄膜平面的为横向构型。对于反常能斯特效应,其由于温度梯度所导致的电信号是可以直接测量的,以本文所研究的Co2MnSn薄膜为例,一种典型的反常能斯特效应信号测量结构如图1(a)所示。当向Co2MnSn施加一个纵向的温度梯度 ∇ T ,并沿垂直 ∇ T 的方向施加外磁场M时,会在与 ∇ T 和M正交的方向产生一个电场E,根据反常能斯特效应相关理论,其产生的电场可以描述为 [8]:
薄膜制备方法如下:用于反常能斯特效应研究的样品,通过直流磁控溅射方法在10 mm × 10 mm × 0.5 mm的MgO(100)基片上沉积了厚度为50 nm的Co2MnSn薄膜,横向尺寸6.0 mm × 2.5 mm。沉积温度分别为室温,300℃,400℃和500℃,溅射腔真空度2 × 10−4 Pa。用于自旋塞贝克效应研究的样品,考虑到A.Sola [24] 等人提到的电信号的稳定性问题,采用直流磁控溅射的方式,在MgO的基片上制备了Co2MnSn(50nm)/Pt(4nm)/Au(5nm)的薄膜,集成了测量单元的薄膜样品结构如图2(a)所示。样品整体为铁磁金属/重金属异质结结构,横向尺寸6.0 mm × 2.5 mm,Au电极的横向尺寸均为1 mm × 2.5 mm。当向样品施加一个纵向的温度梯度 ∇ T ,并沿垂直 ∇ T 的方向施加外磁场M时,会在重金属层产生一个与 ∇ T 和M正交的电场E。样品的晶体结构和磁性通过X射线衍射仪和振动样品磁强计进行表征。
式中 V T , V F M , V S S E , R T , R F M 和 R N M 分别表示总的热电压、反常能斯特电压、自旋塞贝克电压,样品总电阻,铁磁层电阻和普通金属电阻。其中 V T / R T , V F M / R F M 和 V S S E / R N M 分别表示归一化总热电信号,单纯铁磁层的热电信号,纵向自旋塞贝克效应引起的热电信号。
何晓刚,杨栋超,黄秀峰,许云丽,易立志. Co2MnSn薄膜结构调控与自旋热输运性质研究Structure Regulation and Thermal Spin Transport Properties of Co2MnSn Films[J]. 凝聚态物理学进展, 2020, 09(03): 33-41. https://doi.org/10.12677/CMP.2020.93005
参考文献ReferencesZutic, I., Fabian, J. and DasSarma, S. (2004) Spintronics: Fundamentals and Applications. Review of Modern Physics, 76, 323-410. <br>https://doi.org/10.1103/RevModPhys.76.323Jungwirth, T., Wunderlich, J.R. and Oleinik, K. (2012) Spin Hall Effect Devices. Nature Materials, 11, 382-390.
<br>https://doi.org/10.1038/nmat3279Ando, K., Takahashi, S. and Ieda, J. (2011) Inverse Spin-Hall Effect In-duced by Spin Pumping in Metallic System. Journal of Applied Physics, 109, Article ID: 103913. <br>https://doi.org/10.1063/1.3587173Bauer, G., Saitoh, E. and Wees, B. (2012) Spin Caloritronics. Nature Materials, 11, 391-399.
<br>https://doi.org/10.1038/nmat3301Ikhlas, M., Tomita, T. and Koretsune, T. (2017) Large Anomalous Nernst Effect at Room Temperature in a Chiral Antiferromagnet. Nature Physics, 13, 1085-1090. <br>https://doi.org/10.1038/nphys4181Kannan, H., Fan, X. and Celik, H. (2017) Thickness Dependence of Anomalous Nernst Coefficient and Longitudinal Spin Seebeck Effect in Ferromagnetic Ni<sub>x</sub>Fe<sub>100−x</sub> Films. Scientific Re-ports, 7, Article No. 6175.
<br>https://doi.org/10.1038/s41598-017-05946-1Uchida, K., Takahashi, S. and Harii, K. (2008) Observation of the Spin Seebeck Effect. Nature, 455, 778-781.
<br>https://doi.org/10.1038/nature07321Holanda, J., Alves, S.O. and Cunha, R.O. (2017) Longitudinal Spin Seebeck Effect in Permalloy Separated from the Anomalous Nernst Effect: Theory and Experiment. Physical Review B, 95, Article ID: 214421.
<br>https://doi.org/10.1103/PhysRevB.95.214421Chuang, T.C., Su. P.L. and Po-Hsun, W. (2017) Enhancement of the Anomalous Nernst Effect in Ferromagnetic Thin Films. Physical Review B, 96, Article ID: 174406. <br>https://doi.org/10.1103/PhysRevB.96.174406Ando, Y. (2015) Spintronics Technology and Device Devel-opment. Japanese Journal of Applied Physics, 54, Article ID: 10101. <br>https://doi.org/10.7567/JJAP.54.070101Mizuguchi, M. and Nakatsuji, S. (2019) Energy-Harvesting Materials Based on the Anomalous Nernst Effect. Science and Technology of Advanced Materials, 20, 262-275. <br>https://doi.org/10.1080/14686996.2019.1585143Uchida, K.I., Adachi, H. and Kikkawa, T. (2016) Thermo-electric Generation Based on Spin Seebeck Effects. Proceedings of the IEEE, 104, 1946-1973. <br>https://doi.org/10.1109/JPROC.2016.2535167Sakuraba, Y. (2016) Potential of Thermoelectric Power Gen-eration Using Anomalous Nernst Effect in Magnetic Materials. Scripta Materialia, 111, 29-32. <br>https://doi.org/10.1016/j.scriptamat.2015.04.034Rezende, S.M., Rodríguez-Suárez, R.L. and Cunha, R.O. (2016) Bulk Magnon Spin Current Theory for the Longitudinal Spin Seebeck Effect. Journal of Magnetism and Mag-netic Materials, 400, 171-177.
<br>https://doi.org/10.1016/j.jmmm.2015.07.102Reichlova, H., Schlitz, R. and Beckert, S. (2018) Large Anom-alous Nernst Effect in Thin Films of the Weyl Semimetal Co<sub>2</sub>MnGa. Applied Physics Letters, 113, 212405.1-212405.5. <br>https://doi.org/10.1063/1.5048690Sakai, A., Mizuta, Y.P. and Nugroho, A.A. (2018) Giant Anomalous Nernst Effect and Quantum-Critical Scaling in a Ferromagnetic Semimetal. Nature Physics, 14, 1119-1124. <br>https://doi.org/10.1038/s41567-018-0225-6Sakuraba, Y., Hyodo, K. and Sakuma, A. (2018) Strategic En-hancement of Anomalous Nernst Effect in Co<sub>2</sub>MnAl<sub>1−x</sub>Si<sub>x</sub> Heusler Compounds. https://arxiv.org/abs/1807.02209Graf, T., Claudia, F. and Stuart, S.P.P. (2011) Simple Rules for the Under-standing of Heusler Compounds. Progress in Solid State Chemistry, 39, 1-50. <br>https://doi.org/10.1016/j.progsolidstchem.2011.02.001Geiersbach, U., Bergmann, A. and Westerholt, K. (2002) Structural, Magnetic and Magnetotransport Properties of Thin Films of the Heusler Alloys Cu<sub>2</sub>MnAl, Co<sub>2</sub>MnSi, Co<sub>2</sub>MnGe and Co<sub>2</sub>MnSn. Journal of Magnetism and Magnetic Materials, 240, 546-549. <br>https://doi.org/10.1016/S0304-8853(01)00866-6Rai, D. and Thapa, R. (2013) Electronic Structure and Magnetic Properties of X<sub>2</sub>YZ (X = Co, Y = Mn, Z = Ge, Sn) Type Heusler Compounds: A First Principle Study. Phase Transitions, 85, 1-11.
<br>https://doi.org/10.1080/01411594.2012.661860Wang, Z., Vergniory, M.G. and Kushwaha, S. (2016) Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys. Physical Review Letters, 117, Article ID: 236401. <br>https://doi.org/10.1103/PhysRevLett.117.236401Manna, K., Sun, Y. and Muechler, L. (2018) Heusler, Weyl and Berry. Nature Reviews Materials, 3, 244-256.
<br>https://doi.org/10.1038/s41578-018-0036-5Balke, B., Ouardi, S. and Graf, T. (2010) Seebeck Coefficients of Half-Metallic Ferromagnets. Solid State Communications, 150, 529-532. <br>https://doi.org/10.1016/j.ssc.2009.10.044Sola, A., Basso, V. and Kuepferling, M. (2019) Spincaloritronic Measurements: A Round Robin Comparison of the Longitudinal Spin Seebeck Effect. IEEE Transactions on Instru-mentation and Measurement, 68, 1765-1773.
<br>https://doi.org/10.1109/TIM.2018.2882930Zhang, W., Jiko, N. and Okuno, T. (2007) Structural and Mag-netic Properties of Co<sub>2</sub>MnSn Films and Co<sub>2</sub>MnSn/Cr Multilayers. Journal of Magnetism and Magnetic Materials, 309, 132-138.
<br>https://doi.org/10.1016/j.jmmm.2006.06.023