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超快退磁的发现提供了一种使用超短激光产生超快自旋流的新手段, 从而可能更快地操纵材料磁性. 然而, 这一过程仍未被理解, 尤其是超快自旋流在层间转移中的影响因素尚不明晰. 本文利用超扩散自旋输运模型对Ni/Ru/Fe自旋阀结构体系的超快自旋输运机制进行了深入研究, 尤其关注层间自旋转移效率对铁磁层超快磁动力学的影响. 本研究计算出铁磁层在不同磁化排列下的退磁差异, 并通过调节间隔层厚度, 揭示出超快自旋输运在磁动力学中的关键作用. 此外, 还确定了热电子自旋流在间隔层中的自旋衰减长度. 通过控制激光的薄膜吸收, 进一步发现了能够引起铁磁层瞬态磁化增强的条件. 这些结果对于理解热电子自旋流的输运机制具有重要意义, 为未来控制超快自旋流提供了理论基础.The discovery of ultrafast demagnetization has provided a new means for generating ultrafast spin currents by using an ultrashort laser, potentially enabling faster manipulation of material magnetism. This has sparked research on the transport mechanisms of ultrafast spin currents. However, the basic processes are still poorly understood, especially the factors influencing interlayer spin transfer. In this work, a superdiffusive spin transport model is used to investigate the ultrafast spin transport mechanism in the Ni/Ru/Fe spin valve system, with a particular focus on how interlayer spin transfer affects the ultrafast magnetization dynamics of the ferromagnetic layer. First, by calculating the laser-induced magnetization dynamics of the Ni/Ru/Fe system under different magnetization alignments, the recent experimental findings are validated. Further analysis shows that reducing the thickness of the Ru spacer layer will significantly enhance the spin current intensity and increase the demagnetization difference in the Fe layer, confirming the key role of the hot electron spin current generated by the Ni layer in interlayer spin transport. In addition, the spin decay length of hot electron spin currents in the spacer Ru layer is determined to be approximately 0.5 nm. This work also shows that laser-induced transient magnetization enhancement can be achieved by adjusting the relative laser absorption in the films. These results provide theoretical support for ultrafast magnetic control of future spin valve structures and contribute to the development of spintronics in high-speed information processing and storage applications.
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Keywords:
- spintronics /
- ultrafast magnetic dynamics /
- spin-polarized transport
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图 1 飞秒激光脉冲诱导的Ni/Ru/Fe自旋阀结构中层间自旋输运示意图. 自旋极化热电子从Ni层通过Ru层转移至Fe层, 引起超快磁动力学. Ni层和Fe层的磁化方向可以为平行或反平行排列
Fig. 1. Schematic of ultrafast interlayer spin transport in a Ni/Ru/Fe trilayer structure induced by femtosecond laser pulses. Spin-polarized hot electrons transfer from the Ni layer through the Ru spacer to the Fe layer, triggering ultrafast magnetic dynamics. The magnetization directions of the Ni and Fe layers can be either parallel or antiparallel.
图 2 (a)—(f)计算得到激光激发后的磁动力学, Ni层和Fe层初始的磁化方向为平行(红线)和反平行(蓝线)排列. (a)与(b), (c)与(d), (e)与(f)分别为间隔层dRu = 2, 1.5, 1 nm厚的结果
Fig. 2. (a)–(f) Calculated magnetic dynamics after laser excitation, with initial magnetization directions of the Ni and Fe layers aligned parallel (red line) and antiparallel (blue line). (a) and (b), (c) and (d), (e) and (f) show the results for spacer layer thicknesses of dRu = 2, 1.5, and 1 nm, respectively.
图 3 (a) Ru层各位置自旋流js随时间的演化曲线, 以Ni/Ru界面处最大值进行归一化, 插图是以自旋流最大值对位置进行的指数拟合; (b)为图(a)中自旋流所对应的自旋极化率
Fig. 3. (a) Time evolution of the spin current js at various positions in the Ru layer, normalized to the maximum at the Ni/Ru interface. The inset shows an exponential fit of the spin current maximum values as a function of position. (b) The corresponding spin polarization of the spin current in panel (a).
图 4 计算得到不同初始磁化方向下Fe层的磁动力学行为, 其中, 飞秒激光仅激发 Ni 层产生非平衡热电子, 浅灰色阴影表示激光脉冲的时间分布
Fig. 4. Calculated magnetic dynamics of Fe layer under different initial magnetization directions. The femtosecond laser excites only the Ni layer, generating nonequilibrium hot electrons. The light gray shading indicates the temporal profile of the laser pulse.
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[1] Wolf S A, Awschalom D D, Buhrman R A, Daughton J M, von Molnár V S, Roukes M L, Chtchelkanova A Y, Treger D M 2001 Science 294 1488
Google Scholar
[2] Žutić I, Fabian J, Sarma S D 2004 Rev. Mod. Phys. 76 323
Google Scholar
[3] Bader S D, Parkin S S P 2010 Annu. Rev. Condens. Matter Phys. 1 71
Google Scholar
[4] 许涌, 张帆, 张晓强, 杜寅昌, 赵海慧, 聂天晓, 吴晓君, 赵巍胜 2022 69 200703
Google Scholar
Xu Y, Zhang F, Zhang X Q, Du Y C, Zhao H H, Nie T X, Wu X J, Zhao W S 2022 Acta Phys. Sin. 69 200703
Google Scholar
[5] Seifert T S, Cheng L, Wei Z X, Kampfrath T, Qi J B 2022 Appl. Phys. Lett. 120 180401
Google Scholar
[6] 芦闻天, 袁喆 2022 中国科学: 物理学 力学 天文学 52 270007
Google Scholar
Lu W T, Yuan Z 2022 Sci. Sin. -Phys. Mech. Astron. 52 270007
Google Scholar
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Google Scholar
Yang X, Feng H M, Liu J N, Zhang X Q, He W, Cheng Z H 2024 Acta Phys. Sin. 73 157501
Google Scholar
[8] Kirilyuk A, Kimel A V, Rasing T 2010 Rev. Mod. Phys. 82 2731
Google Scholar
[9] 李杭, 张新惠 2015 64 177503
Google Scholar
Li H, Zhang X H 2015 Acta Phys. Sin. 64 177503
Google Scholar
[10] Liu B, Xiao HJ, Weinelt M 2023 Sci. Adv. 9 eade0286
Google Scholar
[11] Jin Z M, Guo Y Y, Peng Y, Zhang Z Y, Pang J Y, Zhang Z Z, Liu F, Ye B, Jiang Y X, Ma G H, Zhang C, Balakin A V, Shkurinov A P, Zhu Y M, Zhuang S L 2023 Adv. Phys. Res. 2 2200049
Google Scholar
[12] Wang C T, Liu Y M 2020 Nano Converg. 7 35
Google Scholar
[13] Wu N, Zhang S J, Wang Y X, Meng S 2023 Prog. Surf. Sci. 98 100709
Google Scholar
[14] Wu X Q, Meng H, Zhang H Y, Xu N 2021 New J. Phys. 23 103007
Google Scholar
[15] Ghising P, Biswas C, Lee Y H 2023 Adv. Mater. 35 2209137
Google Scholar
[16] Gusev N A, Dgheparov D I, Pugach N G, Belotelov V I 2021 Appl. Phys. Lett. 118 232601
Google Scholar
[17] Beaurepaire E, Merle J C, Daunois A, Bigot J Y 1996 Phys. Rev. Lett. 76 4250
Google Scholar
[18] Stanciu C D, Hansteen F, Kimel A V, KirilyukA, Tsukamoto A, Itoh A, Rasing T 2007 Phys. Rev. Lett. 99 047601
Google Scholar
[19] Malinowski G, Dalla Longa F, Rietjens J H H, Paluskar P V, Huijink R, Swagten H J M, Koopmans B 2008 Nat. Phys. 4 855
Google Scholar
[20] Rudolf D, La-O-Vorakiat C, Battiato M, Adam R, Shaw J M, Turgut E, Maldonado P, Mathias S, Grychtol P, Nembach H T, Silva T J, Aeschlimann M, Kapteyn H C, Murnane M M, Schneider C M, Oppeneer P M 2012 Nat. Commun. 3 1037
Google Scholar
[21] Turgut E, La-o-Vorakiat C, Shaw J M, Grychtol P, Nembach H T, Rudolf D, Adam R, Aeschlimann M, Schneider C M, Silva T J, Murnane M M, Kapteyn H C, Mathias S 2013 Phys. Rev. Lett. 110 197201
Google Scholar
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Google Scholar
[23] Ji B Y, Jin Z M, Wu G J, Li J G, Wan C H, Han X F, Zhang Z Z, Ma G H, Peng Y, Zhu Y M 2023 Appl. Phys. Lett. 122 111104
Google Scholar
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Google Scholar
[27] Stamm C, Murer C, Wörnle M S, Reid A H, Higley D J, Wandel S F, Schlotter W F, Gambardella P 2020 J. Appl. Phys. 127 223902
Google Scholar
[28] Battiato M, Carva K, Oppeneer P M 2010 Phys. Rev. Lett. 105 027203
Google Scholar
[29] Zhukov V P, Chulkov E V, Echenique P M 2005 Phys. Rev. B 72 155109
Google Scholar
[30] Zhukov V P, Chulkov E V, Echenique P M 2006 Phys. Rev. B 73 125105
Google Scholar
[31] Battiato M, Maldonado P, Oppeneer P M 2014 J. Appl. Phys. 115 172611
Google Scholar
[32] Battiato M, Carva K, Oppeneer P M 2012 Phys. Rev. B 86 024404
Google Scholar
[33] Lu W T, Yuan Z, Xu X H 2023 Sci. Chin. -Phys. Mech. Astron. 66 127511
Google Scholar
[34] Gorchon J, Mangin S, Hehn M, Malinowski G 2022 Appl. Phys. Lett. 121 012402
Google Scholar
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