Abstrakt
An effective tool for the characterization of thin magnetic films is the magneto-optic Kerr effect (MOKE), which can provide information about fundamental magnetic properties, such as magnetic anisotropy or domain structure. MOKE linear-in-magnetization is only applicable in ferromagnets (FM) and certain canted antiferromagnets (AFM). In contrast, the quadratic-in-magnetization MOKE (QMOKE) is also employable for the fully compensated AFM. According to our study, the QMOKE signal exhibits a remarkable anisotropy depending on the polarization of incident light. This anisotropy reflects in the amplitude and shape of the QMOKE signal. Our contribution describes how to measure the anisotropy of QMOKE comprehensively.
To demonstrate our approach, we chose a 20 nm thin layer of FeRh, prepared on the MgO substrate, FeRh is particularly interesting as a potential candidate for spintronic devices owing to its specific magnetic ordering, having FM phase above and a compensated AFM phase below the Neel temperature of 380 K. We used an in-house built MOKE setup to measure the QMOKE anisotropy of the sample at different wavelengths in its FM state (T= 420 K). We illuminated the sample with a wide-spectral range light source (supercontinuum laser, 460-1600 nm) under near-normal incidence. We detected polarization rotation (Δβ) of the light reflected from the sample while applying a magnetic field of 50mT under variable angles (φ_H=0 to 360deg) using home-made vectorial electromagnet. The method is described in detail in [1]. In order to study the impact of different polarization of incident light (β) on the polarization rotation Δβ, we measured the QMOKE signal Δβ(φ_H) for different initial polarizations β. An example of the QMOKE signal, obtained at wavelength 810 nm is shown in Fig 1 (a). Clearly, there is a remarkable change in the amplitude of the MO signal for different β, indicating a strong anisotropy of the magneto-optical response. Since the QMOKE is known to be strongly wavelength-dependent [2], we measured the full spectrum of the QMOKE anisotropy (see Fig1 (b)). The spectral dependence is in accord with QMOKE in thin Fe films, as presented in the work of Silber et al. [3]. By measuring QMOKE, we are able to extract local magnetic properties, e.g. magnetic anisotropy of FeRh in full spectral dependence.
References
[1] GAMNAS paper ---- in preparation (we need the name of the paper approved by Prof. Nemec)
[2] N.Tesařová, , T.Ostatnický, , V.Novák, , K.Olejník, , J.Šubrt, , H.Reichlová, , ... & K.Výborný, Physical Review B, 89(8), 085203.(2014).
[3] R.Silber , O.Stejskal, L.Beran, P.Cejpek, R.Antoš, T.Matalla-Wagner, ... & Hamrle, J. Physical Review B, 100(6), 064403.(2019).