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Mg3(Bi,Sb)2 single crystals towards high thermoelectric performance
2020, Pan, Yu, Yao, Mengyu, Hong, Xiaochen, Zhu, Yifan, Fan, Fengren, Imasato, Kazuki, He, Yangkun, Hess, Christian, Fink, Jörg, Yang, Jiong, Büchner, Bernd, Fu, Chenguang, Snyder, G. Jeffrey, Felser, Claudia
The rapid growth of the thermoelectric cooler market makes the development of novel room temperature thermoelectric materials of great importance. Ternary n-type Mg3(Bi,Sb)2 alloys are promising alternatives to the state-of-the-art Bi2(Te,Se)3 alloys but grain boundary resistance is the most important limitation. n-type Mg3(Bi,Sb)2 single crystals with negligible grain boundaries are expected to have particularly high zT but have rarely been realized due to the demanding Mg-rich growth conditions required. Here, we report, for the first time, the thermoelectric properties of n-type Mg3(Bi,Sb)2 alloyed single crystals grown by a one-step Mg-flux method using sealed tantalum tubes. High weighted mobility ∼140 cm2 V−1 s−1 and a high zT of 0.82 at 315 K are achieved in Y-doped Mg3Bi1.25Sb0.75 single crystals. Through both experimental angle-resolved photoemission spectroscopy and theoretical calculations, we denote the origin of the high thermoelectric performance from a point of view of band widening effect and electronegativity, as well as the necessity to form high Bi/Sb ratio ternary Mg3(Bi,Sb)2 alloys. The present work paves the way for further development of Mg3(Bi,Sb)2 for near room temperature thermoelectric applications.
A New Highly Anisotropic Rh-Based Heusler Compound for Magnetic Recording
2020, He, Yangkun, Fecher, Gerhard H., Fu, Chenguang, Pan, Yu, Manna, Kaustuv, Kroder, Johannes, Jha, Ajay, Wang, Xiao, Hu, Zhiwei, Agrestini, Stefano, Herrero-Martín, Javier, Valvidares, Manuel, Skourski, Yurii, Schnelle, Walter, Stamenov, Plamen, Borrmann, Horst, Tjeng, Liu Hao, Schaefer, Rudolf, Parkin, Stuart S.P., Coey, John Michael D., Felser, Claudia
The development of high-density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat-assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin-film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m−3 is combined with a saturation magnetization of μ0Ms = 0.52 T at 2 K (2.2 MJ m−3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare-earth-free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m−1 K−1, make Rh2CoSb a candidate for the development of heat-assisted writing with a recording density in excess of 10 Tb in.−2. © 2020 The Authors. Published by Wiley-VCH GmbH
Thermoelectric Properties of Novel Semimetals: A Case Study of YbMnSb2
2020, Pan, Yu, Fan, Feng-Ren, Hong, Xiaochen, He, Bin, Le, Congcong, Schnelle, Walter, He, Yangkun, Imasato, Kazuki, Borrmann, Horst, Hess, Christian, Büchner, Bernd, Sun, Yan, Fu, Chenguang, Snyder, G. Jeffrey, Felser, Claudia
The emerging class of topological materials provides a platform to engineer exotic electronic structures for a variety of applications. As complex band structures and Fermi surfaces can directly benefit thermoelectric performance it is important to identify the role of featured topological bands in thermoelectrics particularly when there are coexisting classic regular bands. In this work, the contribution of Dirac bands to thermoelectric performance and their ability to concurrently achieve large thermopower and low resistivity in novel semimetals is investigated. By examining the YbMnSb2 nodal line semimetal as an example, the Dirac bands appear to provide a low resistivity along the direction in which they are highly dispersive. Moreover, because of the regular-band-provided density of states, a large Seebeck coefficient over 160 µV K−1 at 300 K is achieved in both directions, which is very high for a semimetal with high carrier concentration. The combined highly dispersive Dirac and regular bands lead to ten times increase in power factor, reaching a value of 2.1 mW m−1 K−2 at 300 K. The present work highlights the potential of such novel semimetals for unusual electronic transport properties and guides strategies towards high thermoelectric performance. © 2020 The Authors. Advanced Materials published by Wiley-VCH GmbH