Abstract-Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt, W and Cu80Ir20

T. Seifert, N. M. Tran, O. Gueckstock, S. M. Rouzegar,
 L. Nadvornik, S. Jaiswal, G. Jakob. V. Temnov, M. Münzenberg,  M. Wolf,  M. Kläui, T. Kampfrath

https://arxiv.org/ftp/arxiv/papers/1805/1805.02193.pdf

 Identifying materials with an efficient spin-to-charge conversion is crucial for future spintronic applications. The spin Hall effect is a central mechanism as it allows for the interconversion of spin and charge currents. Spintronic material research aims at maximizing its efficiency, quantified by the spin Hall angle 𝛩 and the spin-current relaxation length 𝜆୰ୣ୪. We develop an all-optical method with large sample throughput that allows us to extract 𝛩 and 𝜆୰ୣ୪. and 𝜆୰ୣ୪. Employing terahertz spectroscopy, we characterize magnetic metallic heterostructures involving Pt, W and Cu80Ir20 in terms of their optical and spintronic properties. We furthermore find indications that the interface plays a minor role for the spin-current transmission. Our analytical model is validated by the good agreement with literature DC values. These findings establish terahertz emission spectroscopy as a reliable tool complementing the spintronics workbench.  

Abstract-Launching magnons at the terahertz speed of the spin Seebeck effect

T. Seifert, S. Jaiswal, J. Barker, I. Razdolski, J. Cramer, O. Gueckstock, S. Watanabe, C. Ciccarelli, A. Melnikov, G. Jakob, S.T.B. Goennenwein, G. Woltersdorf, P.W. Brouwer, M. Wolf, M. Kläui, T. Kampfrath

(Submitted on 3 Sep 2017)

https://arxiv.org/abs/1709.00768

Transport of spin angular momentum is an essential operation in spintronic devices. In magnetic insulators, spin currents are carried by magnons and can be launched straightforwardly by heating an adjacent metal layer. Here, we study the ultimate speed of this spin Seebeck effect with 10-fs time resolution in prototypical bilayers of ferrimagnetic yttrium iron garnet and platinum. Upon exciting the metal by a laser pulse, the spin flow is measured using the inverse spin Hall effect and terahertz electrooptic sampling. The spin Seebeck current reaches its peak within ~200 fs, a hallmark of the photoexcited metal electrons approaching a Fermi-Dirac distribution. Analytical modeling shows the spin Seebeck response is virtually instantaneous because the ferrimagnetic spins react without inertia and the metal spins impinging on the interface have a correlation time of only ~4 fs. Novel applications for material characterization, interface probing, spin-noise detection and terahertz spin pumping emerge.

Abstract-Efficient metallic spintronic emitters of ultrabroadband terahertz radiation

T. Seifert,

S. Jaiswal,

U. Martens,

J. Hannegan,

L. Braun,

P. Maldonado,

F. Freimuth,

A. Kronenberg,

J. Henrizi,

I. Radu,

E. Beaurepaire,

Y. Mokrousov,

P. M. Oppeneer,

M. Jourdan,

G. Jakob,

D. Turchinovich,

L. M. Hayden,

M. Wolf,

M. Münzenberg,

M. Kläui

& T. Kampfrath 

(some author names deleted from Labels at the bottom due to blogger word limit)

http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2016.91.html

Terahertz electromagnetic radiation is extremely useful for numerous applications, including imaging and spectroscopy. It is thus highly desirable to have an efficient table-top emitter covering the 1–30 THz window that is driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source that relies on three tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photoinduced spin currents, the inverse spin-Hall effect and a broadband Fabry–Pérot resonance. Guided by an analytical model, this spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort pulses fully covering the 1–30 THz range. Our novel source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals in terms of bandwidth, terahertz field amplitude, flexibility, scalability and cost.

Abstract-Efficient metallic spintronic emitters of ultrabroadband terahertz radiation

T. Seifert, S. Jaiswal, U. Martens, J. Hannegan, L. Braun, P. Maldonado, F. Freimuth, A. Kronenberg, J. Henrizi, I. Radu, E. Beaurepaire, Y. Mokrousov, P. M. Oppeneer, M. Jourdan, G. Jakob,D. Turchinovich, L. M. Hayden, M. Wolf, M. Münzenberg, M. Kläui, T. Kampfrath

http://www.mathpubs.com/detail/1510.03729v1/Efficient-metallic-spintronic-emitters-of-ultrabroadband-terahertz-radiation

Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source based on tailored fundamental spintronic/photonic phenomena in magnetic metal multilayers: a spin-dependent generalization of the photo-Dember effect, the inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an analytical model, such spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort THz pulses fully covering the 1-to-30-THz range. Our novel source outperforms standard emitters such as ZnTe(110) crystals in terms of bandwidth, conversion efficiency, flexibility, scalability and cost.

Abstract-Ultrafast Spin Precession and Transport Controlled and Probed with Terahertz Radiation

T. Kampfrath, 

M. Battiato, 

A. Sell, 

F. Freimuth, 

A. Leitenstorfer, 

M. Wolf, 

R. Huber, 

P. M. Oppeneer,

M. Münzenberg

http://link.springer.com/chapter/10.1007/978-3-319-07743-7_100
We present examples of how terahertz (THz) electromagnetic transients can be used to control spin precession in antiferromagnets (through the THz Zeeman torque) and to probe spin transport in magnetic heterostructures (through the THz inverse spin Hall effect), on femtosecond time scales.

Abstract-Terahertz spin current pulses controlled by magnetic heterostructures

Nature Nanotechnology. doi:10.1038/nnano.2013.43
Authors: T. Kampfrath, M. Battiato, P. Maldonado, G. Eilers, J. Nötzold, S. Mährlein, V. Zbarsky, F. Freimuth, Y. Mokrousov, S. Blügel, M. Wolf, I. Radu, P. M. Oppeneer & M. Münzenberg
http://www.chem8.org/forum.php?mod=viewthread&tid=87025&from=portal
In spin-based electronics, information is encoded by the spin state of electron bunches1, 2, 3, 4. Processing this information requires the controlled transport of spin angular momentum through a solid5, 6, preferably at frequencies reaching the so far unexplored terahertz regime7, 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 used to drive spins10, 11, 12 from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter13 based on the inverse spin Hall effect14, 15, which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states16. Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters7, 8, 9.

Abstract-Engineering ultrafast spin currents and terahertz transients by magnetic heterostructures

http://arxiv.org/abs/1210.5372
T. Kampfrath, M. Battiato, P. Maldonado, G. Eilers, J. Nötzold, I. Radu, F. Freimuth, Y. Mokrousov, S. Blügel, M. Wolf, P. M. Oppeneer, M. Münzenberg

In spin-based electronics, information is encoded by the spin state of electron bunches. Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz (THz) regime. 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 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 based on the inverse spin Hall effect 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. 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 in particular covering the elusive range from 5 to 10THz.

Subjects:	Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other)
Cite as:	arXiv:1210.5372 [cond-mat.mes-hall]
	(or arXiv:1210.5372v1 [cond-mat.mes-hall] for this version)