Control of speed and efficiency of ultrafast demagnetization by direct transfer of spin angular momentum

Malinowski, Grégory; Longa, F. Dalla; Rietjens, Jeroen; Paluskar, P. V.; Huijink, R.; Swagten, H.J.M.; Koopmans, B.

doi:10.1038/nphys1092

Cited by 320 publications

(299 citation statements)

References 25 publications

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“…This idea is supported by the recent publication of Malinowski et al 8 These authors noticed that in a magnetic bilayer, spaced by a thin non-magnetic conductive layer, the demagnetization seems to be faster for an antiparallel orientation of the magnetization directions in the two layers. This led them to conclude that the laser-induced demagnetization process could be sped up by direct transfer of spin angular momentum between the two magnetic layers 8 . The magnetic domain structure of our sample can be seen as a network of such junctions.…”

Section: Discussionmentioning

confidence: 65%

“…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. Phenomenological and microscopic models have been proposed and further refined [10][11][12][13] .…”

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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: Discussionmentioning

confidence: 65%

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confidence: 99%

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

et al. 2012

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“…Battiato et al 20 proposed that spin-dependent relaxation and fast transport of hot electrons play a crucial role and suggested that ultrafast demagnetization produces spinpolarized hot electrons, which move to an adjacent metallic layer by a so-called 'superdiffusive current'. The findings of several subsequent experiments have been interpreted as supporting this hypothesis [21][22][23][24][25] . However, the superdiffusive model is based on non-thermal electronic motion 20 and the transport of thermal energy is not considered in these experiments [21][22][23][24][25] .…”

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confidence: 77%

Spin current generated by thermally driven ultrafast demagnetization

Choi

Min

Lee³

et al. 2014

Nat Commun

192

203

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Spin current is the key element for nanoscale spintronic devices. For ultrafast operation of such nano-devices, generation of spin current in picoseconds, a timescale that is difficult to achieve using electrical circuits, is highly desired. Here we show thermally driven ultrafast demagnetization of a perpendicular ferromagnet leads to spin accumulation in a normal metal and spin transfer torque in an in-plane ferromagnet. The data are well described by models of spin generation and transport based on differences and gradients of thermodynamic parameters. The temperature difference between electrons and magnons is the driving force for spin current generation by ultrafast demagnetization. On longer timescales, a few picoseconds following laser excitation, we also observe a small contribution to spin current by a temperature gradient and the spin-dependent Seebeck effect.

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“…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 .…”

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confidence: 99%

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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Control of speed and efficiency of ultrafast demagnetization by direct transfer of spin angular momentum

Cited by 320 publications

References 25 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

Spin current generated by thermally driven ultrafast demagnetization

Terahertz spin current pulses controlled by magnetic heterostructures

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