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摘要:
与外加磁场和热辅助磁反转相比,全光磁反转将磁化反转时间缩短至100 ps之内,得到了人们的广泛关注。其中,亚铁磁材料GdFeCo是能够实现单脉冲全光磁反转的重要材料,在全光磁存储领域中具有巨大的潜在应用价值。本文利用微观三温度模型(M3TM)理论模拟并实验验证了GdFeCo材料因热效应所引起的全光磁反转过程。具体研究了GdFeCo材料在单脉冲激发下磁化场的全光磁动力学过程,以及GdFeCo材料的全光磁响应末状态随激光脉冲能量与脉宽的变化关系。与原子自旋模型和Landau-Lifshitz-Bloch(LLB)模型相比,M3TM更简洁地给出了单脉冲激发下GdFeCo材料磁化场随时间的变化关系以及角动量转移的量子化关系,为基于热效应的全光磁反转的快速、大面积计算提供了有效手段。
Abstract:Compared with magnetic switching by an external magnetic field or by a heat-assisted manner, all-optical switching (AOS) can complete the switching process within 100 ps, which has attracted extensive attention from researchers. Among the magneto-optical materials which can realize AOS, the ferrimagnetic GdFeCo has the ability to realize single-shot AOS and possesses great potential in all-optical magnetic storage. In this paper, a microscopic three-temperature model (M3TM) is utilized to simulate the AOS process of GdFeCo, which is also demonstrated experimentally, under the excitation of a single laser pulse based on the heating effect. By using this M3TM, the AOS dynamics and the final magnetization states of GdFeCo induced by single laser pulses with different energy and pulse widths are calculated and analyzed concretely. Compared with the atomic spin model and the Landau- Lifshitz-Bloch (LLB) model, M3TM provides a more concise time-varying expression of the magnetization of GdFeCo and explicitly addresses the dissipation of angular momentum after the laser-pulse excitation, which enables faster calculations of the heat-induced magnetization dynamics in magneto-optical materials with large areas.
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Key words:
- microscopic three-temperature model /
- GdFeCo /
- all-optical switching
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Overview: All-optically manipulating the orientations of the magnetization or the spins in magnetic materials has aroused intensive research interests for the attractive applications in ultrafast data storage, spin dynamics, and magnetic holography. Among these applications, all-optical switching (AOS) has emerged as a promising alternative way to realize ultrafast perpendicular magnetic recording. Compared with magnetic switching by an external magnetic field or by a heat-assisted manner, AOS can complete the switching process within 100 ps, which has attracted extensive attention from researchers. Among the magneto-optical materials which can realize AOS, the ferrimagnetic GdFeCo has the ability to realize single-shot AOS and possesses great potential in all-optical magnetic storage. Currently, the atomic spin model and the Landau-Lifshitz-Bloch (LLB) model are the basic and frequently-used mathematical methods to describe the dynamics of GdFeCo after the laser-pulse excitation. However, these two models only use the damping parameters to phenomenologically describe the transfer process of angular momentum, and hence it is impossible to give the quantized information of angular momentum transfer during the switching process. In 2009, B. Koopmans et al. proposed a simple-form model which is called the microscopic three-temperature model (M3TM) to unify two contradictory ultrafast laser-induced demagnetization processes. This model is especially suitable for magnetic materials with the easy axis perpendicular to the surface and has been applied to calculate the ultrafast dynamics of multisublattice magnets, to demonstrate the spin-orbit enhanced demagnetization rate in Co/Pt-multilayers, and to explain the AOS in ferromagnets. In this model, the switching of electron spins is achieved by emitting or absorbing a phonon with a certain probability and hence the quantized information of angular momentum is explicitly given. In this paper, the M3TM is utilized to simulate the AOS process of GdFeCo, which is also demonstrated experimentally, under the excitation of a single laser pulse based on the heating effect. By using the M3TM, the AOS dynamics and the final magnetization states of GdFeCo induced by single laser pulses with different energy and pulse widths are calculated and analyzed concretely. Compared with the atomic spin model and the LLB model, M3TM provides a more concise time-varying expression of the magnetization of GdFeCo and explicitly addresses the dissipation of angular momentum after the laser-pulse excitation, which enables faster calculations of the heat-induced magnetization dynamics in magneto-optical materials with large areas.
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图 4 Gd27Fe63.87Co9.13材料全光磁反转的动力学过程。(a)实验装置图。BS:分束器、M:反射镜、P:起偏器、A:检偏器、PP:脉冲选择器、SH:光开关、F:滤色片、λ/2:半波片、L:透镜、S:样品、O:物镜;(b)室温下的实验结果;(c)数值模拟结果
Figure 4. Dynamics of the all-optical switching of Gd27Fe63.87Co9.13. (a) Scheme of the experimental setup. BS: Beam splitter), M: Mirror, P: Polarizer, A: Analyzer, PP: Pulse picker, SH: Shutter, F: Color filter, λ/2: Halfwave plate, L: Lens, S: Sample, O: Objective; (b) The experimental results at room temperature; (c) The calculated results
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[1] Iwasaki S. Perpendicular magnetic recording - Evolution and future[J]. IEEE Transactions on Magnetics, 1984, 20(5): 657-662. doi: 10.1109/TMAG.1984.1063563
[2] Schewe H, Stephani D. Thin-film inductive heads for perpendicular recording[J]. IEEE Transactions on Magnetics, 1990, 26(6): 2966-2971. doi: 10.1109/20.102874
[3] Nakamura Y, Iwasaki S. On the resolution of perpendicular magnetic head[J]. IEEE Transactions on Magnetics, 1984, 20(1): 105-107. doi: 10.1109/TMAG.1984.1063024
[4] Cumpson S R, Hidding P, Coehoorn R. A hybrid recording method using thermally assisted writing and flux sensitive detection[J]. IEEE Transactions on Magnetics, 2000, 36(5): 2271-2275. doi: 10.1109/20.908391
[5] Rottmayer R E, Batra S, Buechel D, et al. Heat-assisted magnetic recording[J]. IEEE Transactions on Magnetics, 2006, 42(10): 2417-2421. doi: 10.1109/TMAG.2006.879572
[6] Kirilyuk A, Kimel A V, Rasing T. Ultrafast optical manipulation of magnetic order[J]. Reviews of Modern Physics, 2010, 82(3): 2731-2784. doi: 10.1103/RevModPhys.82.2731
[7] Stanciu C D, Hansteen F, Kimel A V, et al. All-optical magnetic recording with circularly polarized light[J]. Physical Review Letters, 2007, 99(4): 047601. doi: 10.1103/PhysRevLett.99.047601
[8] Ostler T A, Barker J, Evans R F L, et al. Ultrafast heating as a sufficient stimulus for magnetization reversal in a ferrimagnet[J]. Nature Communications, 2012, 3: 666. doi: 10.1038/ncomms1666
[9] Gerrits T, van den Berg H A M, Hohlfeld J, et al. Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping[J]. Nature, 2002, 418(6897): 509-512. doi: 10.1038/nature00905
[10] Scholl A, Baumgarten L, Jacquemin R, et al. Ultrafast spin dynamics of ferromagnetic thin films observed by fs spin-resolved two-photon photoemission[J]. Physical Review Letters, 1997, 79(22): 5146-5149. doi: 10.1103/PhysRevLett.79.5146
[11] Gilbert L T. A lagrangian formulation of the gyromagnetic equation of the magnetization field[J]. Physical Review, 1955, 100: 1243.
[12] Landau L D, Lifshitz E. On the theory of the dispersion of magnetic permeability in ferromagnetic bodies[M]. Perspectives in Theoretical Physics. Pergamon, 1992: 51-65.
[13] Gilbert L T, Kelly M J. Proceedings of the Pittsburgh Conference on Magnetism and Magnetic Materials[M]. New York: American Institute of Electrical Engineers, 1955: 253.
[14] Dillon F J, Jr. Magnetism Ⅱ[M]. New York: Academic Press, 1963.
[15] Kazantseva N, Hinzke D, Nowak U, et al. Towards multiscale modeling of magnetic materials: simulations of FePt[J]. Physical Review B, 2008, 77(18): 184428. doi: 10.1103/PhysRevB.77.184428
[16] Garanin A D. Generalized equation of motion for a ferromagnet[J]. Physica A: Statistical Mechanics and its Applications, 1991, 172(3): 470-491. doi: 10.1016/0378-4371(91)90395-S
[17] Rebei A, Simionato M. Fluctuations of the magnetization in thin films due to conduction electrons[J]. Physical Review B, 2005, 71(17): 174415. doi: 10.1103/PhysRevB.71.174415
[18] Kuiper C K, Roth T, Schellekens J A. Spin-orbit enhanced demagnetization rate in Co/Pt-multilayers[J]. Applied Physics Letters, 2014, 105(20): 202402. doi: 10.1063/1.4902069
[19] Koopmans B, Malinowski G, Dalla Longa F, et al. Explaining the paradoxical diversity of ultrafast laser-induced demagnetization[J]. Nature Materials, 2009, 9(3): 259-265. doi: 10.1038/nmat2593
[20] Cornelissen T D, Córdoba R, Koopmans B. Microscopic model for all optical switching in ferromagnets[J]. Applied Physics Letters, 2016, 108(14): 142405. doi: 10.1063/1.4945660
[21] Khorsand R A, Savoini M, Kirilyuk A. Role of magnetic circular dichroism in all-optical magnetic recording[J]. Physical Review Letters, 2012, 108(12): 127205. doi: 10.1103/PhysRevLett.108.127205
[22] Wang S C, Wei C, Feng Y H. All-optical helicity-dependent magnetic switching by first-order azimuthally polarized vortex beams[J]. Physical Review Letters, 2018, 113(17): 171108.
[23] Wang S C, Cao Y Y, Li X P. Generation of uniformly oriented in-plane magnetization with near-unity purity in 4π microscopy[J]. Optics Letters, 2017, 42(23): 5050-5053. doi: 10.1364/OL.42.005050
[24] Wang S C, Li X P, Zhou J Y, et al. Ultralong pure longitudinal magnetization needle induced by annular vortex binary optics[J]. Optics Letters, 2014, 39(17): 5022-5025. doi: 10.1364/OL.39.005022
[25] Wang S C, Li X P, Zhou J Y, et al. All-optically configuring the inverse Faraday effect for nanoscale perpendicular magnetic recording[J]. Optics Express, 2015, 23(10): 13530-13536. doi: 10.1364/OE.23.013530
[26] Wang S C, Luo J J, Zhu Z Q, et al. All-optical generation of magnetization with arbitrary three-dimensional orientations[J]. Optics Letters, 2018, 43(22): 5551-5554. doi: 10.1364/OL.43.005551
[27] Radu I, Vahaplar K, Stamm C, et al. Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins[J]. Nature, 2011, 472(7342): 205-208. doi: 10.1038/nature09901
[28] Evans R F L, Fan W J, Chureemart P. Atomistic spin model simulations of magnetic nanomaterials[J]. Journal of Physics: Condensed Matter, 2014, 26(10): 103202. doi: 10.1088/0953-8984/26/10/103202
[29] Atxitia U, Chubykalo-Fesenko O. Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model[J]. Physical Review B, 2011, 84(14): 144414. doi: 10.1103/PhysRevB.84.144414
[30] Kazantseva N. Dynamic response of the magnetisation to picosecond heat pulses[D]. York, UK: The University of York, 2008: 1-128.
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