Ultrafast optical manipulation of magnetic order

Kirilyuk, Andrei; Kimel, A.V.; Rasing, T.H.M.

doi:10.1103/revmodphys.82.2731

Cited by 1,700 publications

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References 247 publications

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“…On a longer timescale (a few nanoseconds), the three subsystems cool down because of heat transfer to the surrounding material, and the magnetization recovers completely. How exactly these processes occur at the microscopic level is still actively debated 2,13 . In our experiment, the initial heating of the spin system seems to be very fast, because within the first 100 fs, more than two-thirds of the magnetic scattering signal is lost.…”

Section: Methodsmentioning

confidence: 99%

“…Figure 3 shows the magnetization (M normalized to the unpumped magnetization, M 0 ) as a function of time delay for a series of increasing pump fluences. The solid lines reproduce fits by a double exponential expression (Equation (2)) to the data (triangles) based on a semi-empirical model (see Methods), which allows us to extract parameters like the maximum demagnetization, the thermalization time (τ th ) and the relaxation time from the spin degrees of freedom to others (τ s − ph ) 20 . To obtain accurate values for τ s − ph , long-delay scans have been performed (Fig.…”

Section: Methodsmentioning

confidence: 99%

“…T he phenomenon of ultrafast demagnetization 1 , first discovered in 1996, resulting from excitation by an intense femtosecond infrared laser pulse, has been extensively investigated, yet its underlying mechanism remains poorly understood 2 . Additionally, it has attracted considerable interest as a possible path to magnetization control on a femtosecond timescale 3 .…”

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confidence: 99%

“…Additionally, it has attracted considerable interest as a possible path to magnetization control on a femtosecond timescale 3 . Most commonly, the magneto-optical Kerr effect (MOKE) is exploited as a femtosecond probe of the temporal evolution of magnetization 2 . Despite some controversy about the validity of MOKE as a probe of the magnetization of an excited system on the femtosecond timescale [4][5][6][7] , significant progress has been made: the importance of subtle effects, such as direct transfer of spin angular momentum 8 or coherent magneto-optical processes 9 , have been revealed.…”

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confidence: 99%

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Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network

et al. 2012

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Femtosecond magnetization phenomena have been challenging our understanding for over a decade. most experiments have relied on infrared femtosecond lasers, limiting the spatial resolution to a few micrometres. With the advent of femtosecond X-ray sources, nanometric resolution can now be reached, which matches key length scales in femtomagnetism such as the travelling length of excited 'hot' electrons on a femtosecond timescale. Here we study laser-induced ultrafast demagnetization in [Co/Pd] 30 multilayer films, which, for the first time, achieves a spatial resolution better than 100 nm by using femtosecond soft X-ray pulses. This allows us to follow the femtosecond demagnetization process in a magnetic system consisting of alternating nanometric domains of opposite magnetization. no modification of the magnetic structure is observed, but, in comparison with uniformly magnetized systems of similar composition, we find a significantly faster demagnetization time. We argue that this may be caused by direct transfer of spin angular momentum between neighbouring domains.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network

et al. 2012

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“…Second, we note that our pump pulse also induces an ultrafast quenching of the sample magnetic moment 27 by about 7%. This modulation leads to the emission of magnetic dipole radiation 28,29,30,31 and the generation of an additional spin current along z via spin pumping 6,24 .…”

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confidence: 86%

Terahertz spin current pulses controlled by magnetic heterostructures

et al. 2013

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In spin-based electronics, information is encoded by the spin state of electron bunches 1,2,3,4 . Processing this information requires the controlled transport of spin angular momentum through a solid 5,6 , preferably at frequencies reaching the so far unexplored terahertz (THz) regime 7,8,9 . Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin-current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is employed to drive spins 10,11,12 from a ferromagnetic Fe thin film into a nonmagnetic cap layer that has either low (Ru) or high (Au) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter 13 based on the inverse spin Hall effect 14,15 that converts the spin flow into a THz electromagnetic pulse. We find that the Ru cap layer yields a considerably longer spin-current pulse because electrons are injected in Ru d states that have a much smaller mobility than Au sp states 16 . Thus, spin current pulses and the resulting THz transients can be shaped by tailoring magnetic heterostructures, which opens the door for engineering high-speed spintronic devices as well as broadband THz emitters 7,8,9 , in particular covering the elusive range from 5 to 10THz.Contemporary electronics is based on the electron charge as information carrier whose presence or absence encodes the value of a bit. Much more efficient devices for low-power data storage and processing could be realized if the spin degree of freedom were used in addition 1,2,3,4 . The spintronics approach requires the generation and control of spin currents, that is, the transport of spin angular momentum through space 5,6 . Spintronic operations should be performed at a pace exceeding that of today's computers, which ultimately requires the generation of spin current pulses with terahertz (1 THz = 10 12 Hz) bandwidths 7,8 as well as the possibility to manipulate them in novel structures 17,18 . To date, femtosecond spin-current pulses have been successfully launched by optically exciting electrons in semiconductors 10 or ferromagnetic metals 11,12 . However, to enable ultrafast basic operations on these transients (such as buffering or delaying), their shape and propagation have to be controlled on subpicosecond time scales.Here, we employ magnetic heterostructures containing an optimally chosen nonmagnetic metallic layer whose electron mobility allows us either to trap or to transmit electrons and, thus, to engineer ultrafast spin pulses. The spin flow is probed in a contactless manner using the inverse spin Hall effect 14,15 (ISHE) that converts the spin current into a detectable THz electromagnetic pulse 13 . Our findings open up a route to device-oriented femtosecond spintronics as well as novel broadband emitters of THz radiation 7,8,9 .Our idea is illustrated in Fig. 1a, which shows a schematic of a ferromagnetic Fe film capped by a thin layer of Ru or Au. Absorption of a femtosecond laser pulse (photon energy 1...

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Magneto‐Optical Characterization of Magnetic Thin Films, Surfaces, and Interfaces at Small Length and Short Timescales

Kirilyuk

Kimel

Savoini

et al. 2012

Characterization of Materials

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The understanding of magnetism at its fundamental length and timescales related to the exchange interaction, that is, at nanometer (nm) length and femtosecond (fs) timescales, is becoming essential as future magnetic recording aims at Tbit densities switched at THz rates, which is exactly this regime. Magnetization‐sensitive second harmonic generation (MSHG) is a nonlinear optical technique that, due to the dipole selection rules, is specifically sensitive to surfaces and interfaces of centrosymmetric media. This surface/interface sensitivity of MSHG in combination with very large magneto‐optical effects has lead to a fast development of this technique over the past decade, demonstrating atomic scale resolution in the direction perpendicular to the interfaces. To increase the lateral resolution of magneto‐optics beyond the diffraction limit, scanning near‐field optical microscopy techniques are more appropriate. The development of novel probes that preserve the polarization has led to the possibility of magneto‐optical characterization of magnetic nanostructures with spatial resolution beyond 100 nm. The combination of these and other magneto‐optical techniques with pump–probe approaches finally allows one to include time resolution down to the femtosecond range in the magneto‐optical characterization of magnetic structures. The main attention of the present chapter is on the application of the MSHG, SNOM, and pump–probe techniques to magnetic thin films and surfaces, with a focus on the achieved progress in understanding of magnetic phenomena at the smallest length and shortest timescales. On the one hand, an extreme sensitivity of MSHG to the electronic and magnetic structure of clean surfaces has been successfully demonstrated. On the other hand, the penetration depth of light has allowed to use this sensitivity to study buried interfaces in multilayer systems. Various phenomena, such as surface states on magnetic metals, enhanced magnetic moments of low‐coordinated atoms, and quantum well states, have been studied. Complimentary to these developments, we show how SNOM gives in‐plane information about submicron magnetic domain structures. Finally, we demonstrate how magneto‐optical pump–probe techniques can be used to study the dynamics of magnetic phenomena with a time resolution down to femtoseconds.

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Ultrafast optical manipulation of magnetic order

Cited by 1,700 publications

References 247 publications

Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network

Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network

Terahertz spin current pulses controlled by magnetic heterostructures

Magneto‐Optical Characterization of Magnetic Thin Films, Surfaces, and Interfaces at Small Length and Short Timescales

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