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非晶态稀土-过渡金属合金亚铁磁薄膜具有很强的垂直磁各向异性、超快的磁矩翻转速度以及磁矩和角动量补偿的特性, 是当前自旋电子学以及超快信息存储领域的重要研究对象. 本文采用磁控溅射制备了系列X/Tbx(Fe0.75Co0.25)1–x/X三明治结构薄膜(
$0.13 \leqslant x \leqslant 0.32$ , X = SiO2, Pt和W), 系统地研究了重金属Pt, W作为TbFeCo超薄膜的缓冲层和覆盖层(统称包覆层)对其室温下磁性和热稳定性的影响. 实验结果显示, 被SiO2包覆的TbFeCo薄膜具有垂直磁各向异性, 磁矩补偿成分在$0.21 < x < 0.24$ 范围内. 用Pt包覆的3 nm 和5 nm TbFeCo超薄膜, 则不出现磁矩补偿现象, 在整个研究成分范围对应薄膜的磁矩始终由FeCo主导, 且在250 ℃高真空退火后垂直磁各向异性消失; 当以W作为包覆层时, 超薄TbFeCo的磁矩补偿点复现, 在补偿点成分附近, 其有效垂直各向异性场超过11.5 T, 且经过350—400 ℃退火后TbFeCo依然保持良好的垂直磁各向异性. 最后, 通过[Pt/TbFeCo]5/Pt和[W/TbFeCo]5/W多周期多层膜的宏观磁性测量和结构表征, 发现Pt/TbFeCo存在界面晶化, 导致以Pt作为包覆层时TbFeCo超薄膜不存在磁矩补偿, 且在垂直磁各向异性方面和热稳定性等方面的严重弱化. 重金属W/TbFeCo超薄膜体系具有磁矩补偿、巨大垂直磁各向异性场和高热稳定性的特点, 研究结果对今后设计基于非晶态稀土-过渡金属合金纳米磁性超薄膜的自旋电子学器件具有重要参考价值.-
关键词:
- 亚铁磁/重金属异质结 /
- 磁矩补偿 /
- 垂直磁各向异性 /
- 热稳定性
Amorphous rare earth (RE)-transition metal (TM) ferrimagnetic alloy films have been intensively studied recently in spintronics and ultrafast information storage due to the large perpendicular magnetic anisotropy (PMA), ultrafast magnetization switching, and the presence of magnetization compensation and angular momentum compensation. In this work, we fabricate X/Tbx(Fe0.75Co0.25)1–x/X (0.13 ≤ x ≤ 0.32, X = SiO2, Pt and W) trilayers by magnetron sputtering, and systematically investigate the magnetic properties and thermal stabilities of the ultrathin TbFeCo films encapsulated by heavy metals Pt and W at room temperature. The 5–50-nm-thick TbFeCo films sandwiched by SiO2 exhibit PMA with magnetic compensation occurring in Tb concentration x between 0.21 with 0.24. For 3-nm- and 5- nm-thick TbFeCo ultrathin films encapsulated by Pt, however, there is no magnetic compensation observed throughout the composition range 0.13 ≤ x ≤ 0.32 with the film magnetization dominated by the FeCo moment. Nevertheless, the weakened PMA for the Pt/ultrathin TbFeCo/Pt trilayers is completely destroyed after annealing at 250 ℃. When the buffer layer and capping layer of Pt are replaced by W, the ultrathin TbFeCo films show magnetic compensation at 0.21 < x < 0.24, so do the thick TbFeCo films. The effective PMA field (HK) exceeds 11.5 T for the W/ultrathin TbFeCo/W films near the compensation composition, and remarkably, the HK decreases slowly on annealing, with PMA maintained even after annealing at 350–400℃. We further prepare [Pt/TbFeCo]5/Pt and [W/TbFeCo]5/W multilayers to clarify the origin of the huge difference between Pt/ultrathin TbFeCo/Pt and the W counterpart. It is found that there are partial recrystallization and phase separation for TbFeCo layer around the Pt/TbFeCo interface, leading to the disappearance of magnetic compensation and the deterioration of the PMA in the Pt/ultrathin TbFeCo/Pt films. With large PMA, W/ultrathin TbFeCo/W films show the presence of magnetic compensation, and excellent thermal robustness. The present study provides a promising heavy metal/RE-TM heterostructure for spintronic applications.-
Keywords:
- ferrimagnetic alloy/heavy metal heterostructure /
- magnetic compensation /
- perpendicular magnetic anisotropy /
- thermal stability
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图 1 (a) SiO2(3 nm)/Tb0.16(Fe0.75Co0.25)0.84(50 nm)/SiO2(3 nm)的面外方向磁滞回线; (b) SiO2(3 nm)/Tb0.24(Fe0.75Co0.25)0.76(50 nm)/SiO2(3 nm)的面外方向磁滞回线; (c) SiO2(3 nm)/Tbx(Fe0.75Co0.25)1–x(50 nm)/SiO2(3 nm) 的饱和磁化强度和垂直矫顽力随Tb含量的变化; (d) SiO2(3 nm)/Tb0.16(Fe0.75Co0.25)0.84(50 nm)/SiO2(3 nm)的霍尔电阻回线; (e) SiO2(3 nm)/ Tb0.24(Fe0.75Co0.25)0.76(50 nm)/SiO2(3 nm)的霍尔电阻回线
Fig. 1. The out plane of M-H loops of the samples of (a) SiO2(3 nm)/Tb0.16(Fe0.75Co0.25)0.84(50 nm)/SiO2(3 nm) and (b) SiO2(3 nm)/Tb0.24(Fe0.75Co0.25)0.76(50 nm)/SiO2(3 nm); (c) the saturation magnetization and perpendicular coercivity as a function of Tb concentration for SiO2(3 nm)/ Tbx(Fe0.75Co0.25)1–x(50 nm)/SiO2(3 nm). The Hall resistance loops of the samples (e) SiO2(3 nm)/Tb0.16(Fe0.75Co0.25)0.84(50 nm)/SiO2(3 nm) and (f) SiO2(3 nm)/Tb0.24(Fe0.75Co0.25)0.76(50 nm)/SiO2(3 nm).
图 2 (a) Pt(3 nm)/Tb0.13(Fe0.75Co0.25)0.87(3, 5 nm)/Pt(3 nm)的霍尔电阻回线; (b) Pt(3 nm)/Tb0.24(Fe0.75Co0.25)0.76(3, 5 nm)/Pt(3 nm)的霍尔电阻回线; (c) Pt(3 nm)/Tbx (Fe0.75Co0.25)1–x(5 nm)/Pt(3 nm)的矫顽力随Tb含量的变化; (d) Pt(3 nm)/Tbx(Fe0.75Co0.25)1–x(3, 5 nm)/Pt(3 nm)的饱和反常霍尔电阻随Tb含量的变化. 图(c)的插图为Pt(3 nm)/Tb0.21 (Fe0.75Co0.25)0.79 (5 nm)/Pt(3 nm)样品在制备态和250 ℃ 退火后的归一化霍尔电阻回线
Fig. 2. The Hall loops of the samples of (a) Pt(3 nm)/Tb0.13(Fe0.75Co0.25)0.87(3, 5 nm)/Pt(3 nm), and (b) Pt(3 nm)/Tb0.24(Fe0.75Co0.25)0.76(3, 5 nm)/Pt(3 nm); (c) the coercivity as a function of Tb concentration for Pt(3 nm)/Tbx(Fe0.75Co0.25)1–x(5 nm)/Pt(3 nm); (d) the saturated anomalous Hall resistance as a function of Tb concentration in Pt(3 nm)/Tbx(Fe0.75Co0.25)1–x(3, 5 nm)/Pt(3 nm). The inset in Figure (c) shows the normalized Hall resistance loops of the sample Pt(3 nm)/Tb0.21(Fe0.75Co0.25)0.79(5 nm)/Pt(3 nm) in the as-deposited state and after annealed 250 ℃.
图 3 (a) W(5 nm)/Tb0.21(Fe0.75Co0.25)0.79(3, 5 nm)/W(5 nm)的霍尔电阻回线; (b) W(5 nm)/Tb0.24(Fe0.75Co0.25)0.76(3, 5 nm)/W(5 nm)的霍尔电阻回线; (c) W(5 nm)/Tbx(Fe0.75Co0.25)1–x(3, 5 nm)/W(5 nm)的反常霍尔电阻随Tb含量的变化; (d) W(5 nm)/Tb0.24(Fe0.75Co0.25)0.76(5 nm)/W(5 nm)经过300和350 °C退火后的霍尔电阻回线; (e) W(5 nm)/ Tb0.16(Fe0.75Co0.25)0.84(5 nm)/W(5 nm)的横向霍尔电阻随面内纵向外磁场的变化; (f) W(5 nm)/ Tbx(Fe0.75Co0.25)1–x(5 nm)/W(5 nm)在制备态和300 ℃ 退火后的垂直矫顽力和有效垂直磁各向异性场随Tb含量的变化, 蓝线和深黄线分别代表制备态下的矫顽力和有效垂直各向异性场, 橙线和黑线分别代表退火后矫顽力和有效各向异性场
Fig. 3. The Hall loops of the samples of (a) W(5 nm)/Tb0.21(Fe0.75Co0.25)0.79(3, 5 nm)/W(5 nm) and (b) W(5 nm)/Tb0.24(Fe0.75Co0.25)0.76(3, 5 nm)/W(5 nm); (c) the anomalous Hall resistance as a function of the Tb concentration in samples W(5 nm)/Tbx(Fe0.75Co0.25)1–x(3, 5 nm)/W(5 nm); (d) the Hall loops of the sample W(5 nm)/Tb0.24(Fe0.75Co0.25)0.76(5 nm)/W(5 nm) after annealed at 300 and 350 ℃; (e) the transverse Hall resistance as a function of longitudinal in-plane field for the sample W(5 nm)/ Tb0.16(Fe0.75Co0.25)0.84(5 nm)/W(5 nm); (f) the coercivity and effective perpendicular anisotropic field as a function of Tb concentration in W(5 nm)/Tbx(Fe0.75Co0.25)1–x(5 nm)/W(5 nm), where blue circle and dark yellow circle represent the coercivity and effective perpendicular anisotropic fields in the as-deposited samples, respectively, and orange circle and black circle represent the corresponding parameters for the 300 ℃ annealed samples.
图 4 (a) [Pt(3 nm)/Tb0.16(Fe0.75Co0.25)0.84(5 nm)]5/Pt(3 nm)多层膜和Pt(3 nm)/ Tb0.16(Fe0.75Co0.25)0.84(25 nm)/Pt(3 nm)三层膜的面外方向磁滞回线; (b) [W(5 nm)/ Tb0.16(Fe0.75Co0.25)0.84(5 nm)]5/W(5 nm)多层膜和W(5 nm)/Tb0.16(Fe0.75Co0.25)0.84(25 nm)/W(5 nm)三层膜的面外方向磁滞回线; (c) 上述Pt, W多层膜和三层膜样品的X射线衍射图, 插图为对应衍射峰的放大图
Fig. 4. The out plane of M-H loops of samples of (a) [Pt(3 nm)/Tb0.16(Fe0.75Co0.25)0.84(5 nm)]5/Pt(3 nm), Pt(3 nm)/Tb0.16(Fe0.75Co0.25)0.84(25 nm)/Pt(3 nm), and (b) [W(5 nm)/Tb0.16(Fe0.75Co0.25)0.84(5 nm)]5/W(5 nm), W(5 nm)/ Tb0.16(Fe0.75Co0.25)0.84(25 nm/ W(5 nm). (c) The X-ray diffraction patterns of above four samples. The inset shows the zoom of the diffraction peaks.
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[1] Ishibashi M, Yakushiji K, Kawaguchi M, Tsukamoto A, Nakatsuji S, Hayashi M 2022 Appl. Phys. Lett. 120 022405
Google Scholar
[2] Seung Ham W, Kim S, Kim D H, Kim K J, Okuno T, Yoshikawa H, Tsukamoto A, Moriyama T, Ono T 2017 Appl. Phys. Lett. 110 242405
Google Scholar
[3] Li W, Yan J, Tang M, Lou S, Zhang Z, Zhang X L, Jin Q Y 2018 Phys. Rev. B 97 184432
Google Scholar
[4] Radu I, Vahaplar K, Stamm C, Kachel T, Kimel A V 2011 Nature 472 205
Google Scholar
[5] Kim D H, Okuno T, Kim S K, Oh S H, Nishimura T, Hirata Y, Futakawa Y, Yoshikawa H, Tsukamoto A, Tserkovnyak Y, Shiota Y, Moriyama T, Kim K J, Lee K J, Ono T 2019 Phys. Rev. Lett. 122 127203
Google Scholar
[6] Chaudhari P, Cuomo J J, Gambino R J 1973 Appl. Phys. Lett. 22 337
Google Scholar
[7] Ota S, Van Thach P, Awano H, Ando A, Toyoki K, Kotani Y, Nakamura T, Koyama T, Chiba D 2021 Sci. Rep. 11 6237
Google Scholar
[8] Ceballos A, Charilaou M, Molina-Ruiz M, Hellman F 2022 J. Appl. Phys. 131 033901
Google Scholar
[9] Hebler B, Hassdenteufel A, Reinhardt P, Karl H, Albrecht M 2016 Front. Mater. 3 8
[10] Mizoguchi T, III G S C 1979 J. Appl. Phys. 50 3570
Google Scholar
[11] Suzuki Y, Takayama S, Kirino F, Ohta N 1987 IEEE Trans. Magn. 23 2275
Google Scholar
[12] III G S C, Mizoguchi T 1978 J. Appl. Phys. 49 1753
Google Scholar
[13] Harris V G, Aylesworth K D, Das B N, Elam W T, Koon N C 1992 IEEE Trans. Magn. 28 2958
Google Scholar
[14] Harris V G, Aylesworth K D, Das B N, Elam W T, Koon N C 1992 Phys. Rev. Lett. 69 1939
Google Scholar
[15] Takagi H, Tsunashima S, Uchiyama S, Fujii T 1979 J. Appl. Phys. 50 1642
Google Scholar
[16] Leamy H J, Dirks A G 1979 J. Appl. Phys. 50 2871
Google Scholar
[17] Suzuki, Takao 1985 J. Magn. Magn. Mater. 50 265
Google Scholar
[18] Egami T, Graham C, Dmowski W, Zhou P, Flanders P, Marinero E, Notarys H, Robinson C 2003 IEEE Trans. Magn. 23 2269
[19] Meiklejohn W H 1986 Proc. IEEE 74 1570
Google Scholar
[20] Wang Y J, Leng Q W 1990 Phys. Rev. B 41 651
Google Scholar
[21] Mergel D, Heitmann H, Hansen P 1993 Phys. Rev. B 47 882
Google Scholar
[22] Shan Z S, Sellmyer D J 1990 Phys. Rev. B 42 10433
Google Scholar
[23] Cheng S C N, Kryder M H 1991 J. Appl. Phys. 69 7202
Google Scholar
[24] Manchon A, Železný J, Miron I M, Jungwirth T, Sinova J, Thiaville A, Garello K, Gambardella P 2019 Rev. Mod. Phys. 91 035004
Google Scholar
[25] Dyakonov M I, Perel V I 1971 Phys. Lett. A 35 459
Google Scholar
[26] Miron I M, Gaudin G, Auffret S, Rodmacq B, Schuhl A, Pizzini S, Vogel J, Gambardella P 2010 Nat. Mater. 9 230
Google Scholar
[27] Ueda K, Mann M, de Brouwer P W P, Bono D, Beach G S D 2017 Phys. Rev. B 96 064410
Google Scholar
[28] Je S G, Rojas-Sánchez J C, Pham T H, Vallobra P, Malinowski G, Lacour D, Fache T, Cyrille M C, Kim D Y, Choe S B, Belmeguenai M, Hehn M, Mangin S, Gaudin G, Boulle O 2018 Appl. Phys. Lett. 112 062401
Google Scholar
[29] Lee J W, Park J Y, Yuk J M, Park B G 2020 Phys. Rev. Appl. 13 044030
Google Scholar
[30] Kim S K, Beach G S D, Lee K J, Ono T, Rasing T, Yang H 2022 Nat. Mater. 21 24
Google Scholar
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