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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.
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关键词:
- Fe0.26TaS2 /
- 层状铁磁体 /
- 磁性 /
- 输运 /
- Andreev反射谱 /
- 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 FexTaS2, we fabricate an FexTaS2/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. -
Keywords:
- Fe0.26TaS2 /
- layered magnetic materials /
- magnetism /
- electronics transport /
- Andreev reflection spectroscopy /
- spin polarization
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图 1 Fe0.26TaS2单晶样品的磁性测量结果 (a) 外加磁场垂直于ab面(H⊥ab)时的FC和ZFC磁化曲线, 测量磁场为100 Oe (1 Oe = 103/(4π) A/m); (b)外加磁场平行于ab面时 (H//ab)的FC和ZFC磁化曲线, 测量磁场为100 Oe; (c) H⊥ab的等温磁化曲线随外加磁场的变化; (d) H//ab的等温磁化曲线随外加磁场的变化(为清楚起见, 在垂直方向做了等间距平移)
Fig. 1. Magnetization measurement results of Fe0.26TaS2: (a) Magnetization measurement with ZFC and FC process while H⊥ab, the measurement field is 100 Oe; (b) magnetization measurement with ZFC and FC process while H//ab, the measurement field is 100 Oe; (c) isothermal magnetization measurements for H⊥ab; (d) isothermal magnetization measurements for H//ab. For clarify, the data is shift equally in Fig. 1(d).
图 2 Fe0.26TaS2等温磁化曲线和电阻-温度曲线(1 emu = 10–3 A·m2) (a) H⊥ab方向Fe0.26TaS2等温磁化曲线的Arrott图, 居里温度为115 K; (b) Fe0.26TaS2的电阻-温度曲线
Fig. 2. Isothermal magnetization and temperature dependence of resistance of Fe0.26TaS2: (a) Arrot plot for isothermal magnetization in H⊥ab; (b) temperature dependence of resistance.
图 3 磁电阻和霍尔电阻随外加磁场的变化 (a) H⊥ab时, 磁电阻随外加磁场的变化; (b) H//ab时, 磁电阻随外加磁场的变化; (c) H⊥ab时, 霍尔电阻随外加磁场的变化; (d) H//ab时, 霍尔电阻随外加磁场的变化
Fig. 3. Magnetic field dependence of magnetoresistance and Hall effect: (a) Magnetic field dependence of magnetoresistance, H⊥ab; (b) magnetic field dependence of magnetoresistance, H//ab; (c) magnetic field dependence of Hall effect, H⊥ab; (d) magnetic field dependence of Hall effect, H//ab.
图 4 Fe0.26TaS2/Pb的Andreev反射谱 (a)不同温度下Andreev结的归一化微分电导谱; (b) T = 1.6 K, 修正的BTK理论对微分电导谱的拟合结果; (c) T = 2 K, 修正的BTK理论对微分电导谱的拟合结果; (d) T = 4 K, 修正的BTK理论对微分电导谱的拟合结果. 黑色点为实验数据, 红色线为理论计算结果
Fig. 4. Andreev reflection spectroscopy of Fe0.26TaS2/Pb: (a) Normalization of Andreev reflection spectroscopy from T = 2 K to 8 K; (b) modified BTK fitting for normalized Andreev reflection spectroscopy, T = 1.6 K; (c) modified BTK fitting for normalized Andreev reflection spectroscopy, T = 2 K; (d) modified BTK fitting for normalized Andreev reflection spectroscopy, T = 4 K. The black dot is experimental data and red line is fitting.
图 5 Fe0.26TaS2/Al/Pb异质结的Andreev反射谱 (a)不同温度下的归一化微分电导谱; (b) T = 0.36 K, 修正的BTK理论对微分电导谱的拟合结果; (c) T = 1 K, 修正的BTK理论对微分电导谱的拟合结果; (d) T = 6 K, 修正的BTK理论对微分电导谱的拟合结果; 黑色点为实验数据, 红色线为理论计算结果, 自旋极化率P ≠ 0
Fig. 5. Andreev reflection spectroscopy of Fe0.26TaS2/Al/Pb: (a) Normalization of Andreev reflection reflection spectroscopy from T = 0.36 K to 9 K; (b) modified BTK fitting for normalized Andreev reflection spectroscopy, T = 0.36 K; (c) modified BTK fitting for normalized Andreev reflection spectroscopy, T = 1 K; (d) modified BTK fitting for normalized Andreev reflection spectroscopy, T = 6 K. The black dot is experimental data and red line is fitting. Spin polarization is fixed to none-zero (P ≠ 0).
图 6 修正的BTK理论对不同温度下微分电导谱的拟合结果 (a) T = 0.36 K; (b) T = 1 K; (c) T = 3 K; (d) T = 6 K; 黑色点为实验数据, 红色线为理论计算结果; 自旋极化率固定为零(P = 0)
Fig. 6. Modified BTK fitting for normalized Andreev reflection spectroscopy of Fe0.26TaS2/Al/Pb: (a) T = 0.36 K; (b) T = 1 K; (c) T = 3 K; (d) T = 6 K. The black dot is experimental data and the red line is fitting. Spin polarization is fixed to zero (P = 0).
图 7 Fe0.26TaS2/NbSe2的Andreev反射谱 (a)不同温度下的归一化微分电导谱和修正的BTK拟合; (b) T = 4 K的微分电导谱和修正的BTK拟合; (c) T = 1.7 K下, 负偏压的归一化微分电导谱及修正的BTK拟合; (d) T = 1.7 K下, 正偏压的归一化微分电导谱及修正的BTK拟合; 黑色点为实验数据, 红色线为理论计算结果
Fig. 7. Andreev reflection spectroscopy of Fe0.26TaS2//NbSe2: (a) Normalization of Andreev reflection spectroscopy from T = 1.7 K to 8 K; (b) modified BTK fitting for normalized Andreev reflection spectroscopy at T = 4 K; (c) modified BTK fitting for normalized Andreev reflection spectroscopy at T = 1.7 K; (d) modified BTK fitting respectively for negative bias or positive bias Andreev reflection spectroscopy at T = 1.7 K. The black dot is experimental data and red line is fitting.
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[1] Wolf S A, Awschalom D D, Buhrman R A, Daughton J M, Molna S V, Roukes M L, Chtchelkanova A Y, Treger D M 2001 Science 294 1488
Google Scholar
[2] Fert A 2008 Rev. Mod. Phys. 80 1517
Google Scholar
[3] 刘兴翀, 路忠林, 任尚坤, 张凤鸣, 都有为, 刘存业, 匡安龙 2005 物理学报 54 2934
Liu X C, Lu Z L, Ren S K, Zhang F M, Du Y W, Liu C Y, Kuang A L 2005 Acta Phys. Sin. 54 2934
[4] Coey J M D, Chien C L 2003 MRS Bull. 28 720
Google Scholar
[5] Johnson P D 1997 Rep. Prog. Phys. 60 1217
Google Scholar
[6] Meservey R, Tedrow P M 1994 Phys. Rep. 238 173
Google Scholar
[7] Soulen Jr R J, Byers J M, Osofsky M S, Nadgorny B, Ambrose T, Cheng S F, Broussard P R, Tanaka C T, Nowak J, Moodera J S, Barry A, Coey J M D 1998 Science 282 85
Google Scholar
[8] Jong M J M, Beenakker C W J 1995 Phys. Rev. Lett. 74 1657
Google Scholar
[9] Blonder G E, Tinkham M 1983 Phys. Rev. B 27 112
[10] Blonder G E, Tinkham M, Klapwijk T M 1982 Phys. Rev. B 25 4515
Google Scholar
[11] Mazin I I 1999 Phys. Rev. Lett. 83 1427
Google Scholar
[12] 吴义华, 王振彦, 沈瑞 2009 物理学报 58 8591
Wu Y H, Wang Z Y, Shen R 2009 Acta Phys. Sin. 58 8591
[13] Strijkers G J, Ji Y, Yang F Y, Chien C L, Byers J M 2001 Phys. Rev. B 63 104510
Google Scholar
[14] Woods G T, Soulen Jr R J, Mazin I I, Nadgorny B, Osofsky M S, Sanders J, Srikanth H 2004 Phys. Rev. B 70 054416
Google Scholar
[15] Duif A M, Jansen A G M, Wyder P 1989 J. Phys. Condens. Mat. 1 3157
Google Scholar
[16] Ji Y, Strijkers G J, Yang F Y, Chien C L, Byers J M, Anguelouch A, Xiao G, Gupta A 2001 Phys. Rev. Lett. 86 5585
Google Scholar
[17] Ren C, Trbovic J, Kallaher R L, Braden J G, Parker J S, von Molnár S, Xiong P 2007 Phys. Rev. B 75 205208
Google Scholar
[18] Parker J S, Watts S M, Ivanov P G, Xiong P 2002 Phys. Rev. Lett. 88 196601
Google Scholar
[19] Stokmaier M, Goll G, Weissenberger D, Sürgers C, von Löhneysen H 2008 Phys. Rev. Lett. 101 147005
Google Scholar
[20] Bugoslavsky Y, Miyoshi Y, Clowes S K, Branford W R, Lake M, Brown I, Caplin A D, Cohen L F 2005 Phys. Rev. B 71 104523
Google Scholar
[21] Zhang X H, Yu L Q, von Molnár S, Fisk Z, Xiong P 2009 Phys. Rev. Lett. 103 106602
Google Scholar
[22] Guan T, Lin C, Yang C, Shi Y, Ren C, Li Y, Weng H, Dai X, Fang Z, Yan S, Xiong P 2015 Phys. Rev. Lett. 115 087002
Google Scholar
[23] Morosan E, Zandbergen H W, Li L, Lee M, Checkelsky J G, Heinrich M, Siegrist T, Ong N P, Cava R J 2007 Phys. Rev. B 75 104401
Google Scholar
[24] Narita H, Ikuta H, Hinode H, Uchida T, Ohtani T, Wakihara M 1994 J. Solid State Chem. 108 148
Google Scholar
[25] Gong C, Li L, Li Z, Ji H, Stern A, Xia Y, Cao T, Bao W, Wang C, Wang Y, Qiu Z Q, Cava R J, Louie S G, Xia J, Zhang X 2017 Nature 546 265
Google Scholar
[26] Novoselov K S, Mishchenko A, Carvalho A, Castro Neto A H 2016 Science 353 aac9439
Google Scholar
[27] Deng Y, Yu Y, Song Y, Zhang J, Wang N Z, Sun Z, Yi Y, Wu Y Z, Wu S, Zhu J, Wang J, Chen X H, Zhang Y 2018 Nature 563 94
Google Scholar
[28] Mankovsky S, Chadova K, Ködderitzsch D, Minár J, Ebert H, Bensch W 2015 Phys. Rev. B 92 144413
Google Scholar
[29] Ko K T, Kim K, Kim S B, Kim H D, Kim J Y, Min B I, Park J H, Chang F H, Lin H J, Tanaka A, Cheong S W 2011 Phys. Rev. Lett. 107 247201
Google Scholar
[30] Arai M, Moriya R, Yabuki N, Masubuchi S, Ueno K, Machida T 2015 Appl. Phys. Lett. 107 103107
Google Scholar
[31] Horibe Y, Yang J, Cho Y H, Luo X, Kim S B, Oh Y S, Huang F T, Asada T, Tanimura M, Jeong D, Cheong S W 2014 J. Am. Chem. Soc. 136 8368
Google Scholar
[32] Checkelsky J G, Lee M, Morosan E, Cava R J, Ong N P 2008 Phys. Rev. B 77 014433
Google Scholar
[33] Chen C W, Chikara S, Zapf V S, Morosan E 2016 Phys. Rev. B 94 054406
Google Scholar
[34] Hardy W J, Chen C W, Marcinkova A, Ji H, Sinova J, Natelson D, Morosan E 2015 Phys. Rev. B 91 054426
Google Scholar
[35] Reefman D, Baak J, Brom H B, Wiegers G A 1990 Solid State Commun. 75 47
Google Scholar
[36] Zhang X, von Molnár S, Fisk Z, Xiong P 2008 Phys. Rev. Lett. 100 167001
Google Scholar
[37] Nowack A, Heinz A, Oster F, Wohlleben D, Güntherodt G, Fisk Z, Menovsky A 1987 Phys. Rev. B 36 2436(R)
Google Scholar
[38] Rodrigo J G, Guinea F, Vieira S, Aliev F G 1997 Phys. Rev. B 55 14318
Google Scholar
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