Bert Koopmans (SIMES Seminar)

Date/Time
Date(s) - Mar 30 2015
11:00 AM - 12:00 PM

Location
Shasta Room, Bldg. 40, Room 361

Category(ies)


Ultrafast Laser-Induced Spin-Transfer  

Bert Koopmans 

Department of Applied Physics, Center for NanoMaterials,

Eindhoven University of Technology,

P.O. Box 513, 5600 MB Eindhoven , the Netherlands

A hot topic in the field of ultrafast laser-induced manipulation of the magnetic state is that of the role and exploitation of laser-induced spin currents. Intense debate has been triggered by claims that such a spin-transfer, e.g. in the form of super-diffusive spin currents over tens of nanometers, is driving the complete demagnetization process in ferromagnetic thin films after femtosecond laser excitation [1]. Yet, a number of rather unambiguous experimental indications for a finite transfer of optically excited spin-polarized carriers have been reported. Laser-induced spin transfer has been found to change the sub-ps demagnetization profile of magnetic bilayers coupled in an anti-parallel orientation [2], while it even has been reported that optical excitation of such bilayers can lead to a ‘super-magnetized’ state [3].   In this presentation the underlying concepts will be introduced and recent developments reviewed. Then a number of our recent results will be discussed. First it will be shown that in single ferromagnetic Ni layers super-diffusive spin currents play a minor role [4]. Then, an application to fs laser-induced dynamics in a tri-layer Fe/Ru/Ni structure will be discussed, resolving the demagnetization due to local dissipation of angular momentum via spin-orbit interaction and due to interlayer spin-transfer [5]. Finally, we demonstrate the possibility to apply a true laser-induced spin transfer torque on a free magnetic layer, using a collinear multilayer configuration consisting of a free in-plane layer on top of a PMA injection layer and separated by a nonmagnetic spacer. Interestingly, this approach allows for a quantitative measure of the amount of spin transfer. Careful analysis of the resulting precession of the free layer allows us to quantify the applied torque, and distinguish between driving mechanisms based on laser-induced transfer of hot electrons versus a spin Seebeck effect due to the large thermal gradients [6].

 

[1] M. Battiato, K. Carva, and P. M. Oppeneer, Phys. Rev. Lett. 105, 027203 (2010).

[2] G. Malinowski, F. Dalla Longa, J.H.H. Rietjens, P.V. Paluskar, R. Huijink, H.J.M. Swagen and B. Koopmans, Nature Physics 4, 855 (2008).

[3] D. Rudolf et al., Nature Communications 3, 1037 (2012).

[4] A.J. Schellekens, W. Verhoeven, T.N. Vader, B. Koopmans, Appl. Phys. Lett. 102, 252408 (2013).

[5] A.J. Schellekens, N. de Vries, J. Lucassen, and B. Koopmans, Phys. Rev. B 90, 104429 (2014).

[6] A.J. Schellekens, K.C. Kuiper, R.R.J.C. de Wit, and B. Koopmans, Nature Communications 5, 4333 (2014).