层状铁磁体Fe0.26TaS2的Andreev反射谱

Andreev reflection spectroscopy of ferromagnetic Fe0.26TaS2 with layered structure

如何避免界面反应、可靠地提取材料的自旋极化率是自旋电子学的一个基本问题.本文选取了一种独特的铁磁性层状过渡族金属硫化物Fe0.26TaS2,研究了单晶材料的磁性、电子输运和Andreev反射谱.磁性和输运结果表明,低温下Fe0.26TaS2单晶存在强磁各向异性、双峰磁电阻和反常霍尔效应.通过干法转移方案制备的干净界面的Fe0.26TaS2超导异质结的Andreev反射谱,发现该材料的自旋极化率为47%±7%.本文展示的干法转移制备超导/磁性异质结的方法可广泛用于测量各种二维磁性材料的自旋极化率.

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 Fe0.26TaS2 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 Fe0.26TaS2 single crystal is observed.Curie temperature TC of the Fe0.26TaS2 single crystal is confirmed by zero field cooling,field cooling and Arrot plot.The electronic transport in the Fe0.26TaS2 single crystal also reveals strong anisotropic behaviors,such as butterfly-like magnetoresistance and obvious anomalous hall effect below TC.To obtain the spin polarization of Fex TaS2,we fabricate an Fex TaS2/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 Fe0.26TaS2/Al/Pb superconductor junction by evaporating Al and then Pb film on the surface of Fe0.26TaS2 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,Fe0.26TaS2/NbSe2 junction is fabricated through mechanical-exfoliation and dry-transfer method.Through the Andreev reflection spectrum of this junction,the spin polarization of Fe0.26TaS2 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 Fe0.26TaS2 is a promising candidate of next-generation material of spintronics.