|Title||Direct measurement of the static and transient magneto-optical permittivity of cobalt across the entire|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Zusin, D, Tengdin, PM, Gopalakrishnan, M, Gentry, C, Blonsky, A, Gerrity, M, Legut, D, Shaw, JM, Nembach, HT, Silva, TJ, Oppeneer, PM, Kapteyn, HC, Murnane, MM|
|Journal||Physical Review B|
The microscopic state of a magnetic material is characterized by its resonant magneto-optical response through the off-diagonal dielectric tensor component ∈xy . However, the measurement of the full complex ∈xy in the extreme ultraviolet spectral region covering the M absorption edges of 3d ferromagnets is challenging due to the need for either a careful polarization analysis, which is complicated by a lack of efficient polarization analyzers, or scanning the angle of incidence in fine steps. Here, we propose and demonstrate a technique to extract the complex resonant permittivity ∈xy simply by scanning the polarization angle of linearly polarized high harmonics to measure the magneto-optical asymmetry in reflection geometry. Because this technique is more practical and faster to experimentally implement than previous approaches, we can directly measure the full time evolution of ∈xy (t) during laser-induced demagnetization across the entire M2,3 absorption edge of cobalt with femtosecond time resolution. We find that for polycrystalline Co films on an insulating substrate, the changes in ∈xy are uniform throughout the spectrum, to within our experimental precision. This result suggests that, in the regime of strong demagnetization, the ultrafast demagnetization response is primarily dominated by magnon generation. We estimate the contribution of exchange-splitting reduction to the ultrafast demagnetization process to be no more than 25%.
|Short Title||Phys. Rev. B|