Andreev reflection spectroscopy of ferromagnetic Fe<sub>0.26</sub>TaS<sub>2</sub> with layered structure
Authors: Yu Xiao-Yang , Feng Hong-Lei , Gu Gang-Xu , Liu Yong-He , Li Zhi-Lin , Xu Tong-Shuai , Li Yong-Qing ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   School of Physics and Electrical Engineering, Anyang Normal University, Anyang 455000, China,   School of Physical Sciences, Peking University, Beijing 100871, China
Published: December 2020

<sec>An elementary mission of spintronics research is to prevent the interface reacting in spin device and extract spin polarization of ferromagnetic material reliably. Layered transition metal sulfide has very strong anisotropic magnetism, magnetoresistance, and unique Hall effect. It provides a good platform for studying the magnetic order related physical phenomena and may lay a foundation for spintronic applications. In this work, the magnetism, electronic transport and Andreev reflection spectrum of a novel ferromagnetic material Fe<sub>0.26</sub>TaS<sub>2</sub> with a layers-stacked structure are measured. Strong magnetic anisotropy, double-peak magnetoresistance and anomalous Hall effect are found. In the magnetic measurement, the strong magnetic anisotropy behavior in Fe<sub>0.26</sub>TaS<sub>2</sub> single crystal is observed. Curie temperature <i>T</i><sub>C</sub> of the Fe<sub>0.26</sub>TaS<sub>2</sub> single crystal is confirmed by zero field cooling, field cooling and Arrot plot. The electronic transport in the Fe<sub>0.26</sub>TaS<sub>2</sub> single crystal also reveals strong anisotropic behaviors, such as butterfly-like magnetoresistance and obvious anomalous hall effect below <i>T</i><sub>C</sub>.</sec><sec>To obtain the spin polarization of Fe<sub><i>x</i></sub>TaS<sub>2</sub>, we fabricate an Fe<sub><i>x</i></sub>TaS<sub>2</sub>/superconductor Andreev junction to measure the spin polarization that is fitted by the modified Blonder-Tinkham-Klapwijk (BTK) theory. Perhaps the diffusion of Pb can form an alloy structure, creating another superconductor behavior. The two-gap BTK theory confirms our hypothesis, and the result spin polarization can reach 26%. To avoid the interference from Pb alloy superconductor, we also fabricate an Fe<sub>0.26</sub>TaS<sub>2</sub>/Al/Pb superconductor junction by evaporating Al and then Pb film on the surface of Fe<sub>0.26</sub>TaS<sub>2</sub> in sequence. The results of BTK fit show that the spin polarization from the first technical route cannot be reliable due to the tunneling layer on the Al interface. In order to obtain a clean interface, Fe<sub>0.26</sub>TaS<sub>2</sub>/NbSe<sub>2</sub> junction is fabricated through mechanical-exfoliation and dry-transfer method. Through the Andreev reflection spectrum of this junction, the spin polarization of Fe<sub>0.26</sub>TaS<sub>2</sub> is extracted to be 47% ± 7%. For various two-dimensional ferromagnetic materials, our work suggests that the dry-transfer method is well applicable in spin polarization extraction. The results of spin polarization indicate that the Fe<sub>0.26</sub>TaS<sub>2</sub> is a promising candidate of next-generation material of spintronics.</sec>