Measurements of ultrafast spin-profiles and spin-diffusion properties in the domain wall area at a metal/ferromagnetic film interface

Abstract

Exciting a ferromagnetic material with an ultrashort IR laser pulse is known to induce spin dynamics by heating the spin system and by ultrafast spin diffusion processes. Here, we report on measurements of spin-profiles and spin diffusion properties in the vicinity of domain walls in the interface region between a metallic Al layer and a ferromagnetic Co/Pd thin film upon IR excitation. We followed the ultrafast temporal evolution by means of an ultrafast resonant magnetic scattering experiment in surface scattering geometry, which enables us to exploit the evolution of the domain network within a 1/e distance of 3 nm to 5 nm from the Al/FM film interface. We observe a magnetization-reversal close to the domain wall boundaries that becomes more pronounced closer to the Al/FM film interface. This magnetization-reversal is driven by the different transport properties of majority and minority carriers through a magnetically disordered domain network. Its finite lateral extension has allowed us to measure the ultrafast spin-diffusion coefficients and ultrafast spin velocities for majority and minority carriers upon IR excitation.

Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co88Tb12 thin film with stripe domains

“…A more reliable strategy to observe superdiffusive spin transfer between domains would consist in unveiling the possible ultrafast changes of the domain wall structure, where an enhanced demagnetization due to an accumulation of minority electrons is expected to take place [15,42]. As will be shown in the next section, our experiments, where the first-and thirdorder magnetic diffraction peaks are recorded simultaneously, allow us to directly monitor the impact of the pump pulse on the magnetic structure of the CoTb thin films, thereby providing more reliable evidence for the presence or absence of superdiffusive interdomain spin transport.…”

Faster chiral versus collinear magnetic order recovery after optical excitation revealed by femtosecond XUV scattering

“…1a . Circularly polarized XUV radiation of 60 fs pulse duration was tuned to a wavelength of 23.0 nm corresponding to the Fe M 2,3 dichroic transition, which exhibits magnetic scattering contrast due to the X-ray magnetic circular dichroism (XMCD) effect 27 , 28 , 31 , 32 . The limited transmission in the XUV regime required us to perform the experiment in reflection geometry with an incident angle of Θ = 44° 28 yielding an effective XUV penetration depth of ≈8 nm.…”

“…Circularly polarized XUV radiation of 60 fs pulse duration was tuned to a wavelength of 23.0 nm corresponding to the Fe M 2,3 dichroic transition, which exhibits magnetic scattering contrast due to the X-ray magnetic circular dichroism (XMCD) effect 27 , 28 , 31 , 32 . The limited transmission in the XUV regime required us to perform the experiment in reflection geometry with an incident angle of Θ = 44° 28 yielding an effective XUV penetration depth of ≈8 nm. Owing to an isotropic disordered domain structure we observe the typical ring-like diffraction feature well known from magnetic transmission small angle x-ray scattering (SAXS) experiments representing a broad distribution of Fourier components of the magnetic domain pattern 27 , 28 .…”

“…The limited transmission in the XUV regime required us to perform the experiment in reflection geometry with an incident angle of Θ = 44° 28 yielding an effective XUV penetration depth of ≈8 nm. Owing to an isotropic disordered domain structure we observe the typical ring-like diffraction feature well known from magnetic transmission small angle x-ray scattering (SAXS) experiments representing a broad distribution of Fourier components of the magnetic domain pattern 27 , 28 . The sample is pumped with a 60 fs IR laser pulse of 780 nm wavelength impinging on the sample with a small 2 degree offset with respect to the XUV beam (further setup information can be found in the “Methods” section).…”

Coherent x-ray scattering in an XPEEM setup

“…It should be underlined that the reflection at incidence angles away from the surface normal approaching grazing geometry introduces further considerations, among which those due to the surface roughness and the elongated beam footprint can be counted. On 2 the other hand, recent studies taking advantage of the element selectivity in coherent x-ray scattering at selected absorption thresholds show that the information coded in the diffraction pattern can be put to use even without the need for a real-space reconstruction [8].…”