This experimental study demonstrates that with transverse magneto-optical Kerr effect (T-MOKE) ellipsometry, it is possible to determine the magneto-optical and magnetic properties of insertion layers, even if they are superimposed onto much larger magnetic signals from the surrounding structure. Hereby, it turns out to be especially valuable that with T-MOKE ellipsometry one has full and precise quantitative access to the complex value of the magneto-optical reflection matrix component β, because small magneto-optical insertion layer signals do not necessarily increase the absolute size of β, but can lead to observable phase changes of this complex quantity instead. We demonstrate the ability of T-MOKE ellipsometry to precisely detect such small effects and hereby allow for an accurate determination of the alloy concentration dependent onset of ferromagnetism in ultrathin Co x Ru 1−x insertion layers, that are embedded into a much thicker ferromagnetic structure. In addition, a detailed and quantitative signal analysis allowed us to demonstrate that the Co x Ru 1−x insertion layers in our samples exhibit a magnetization reversal behavior that is independent of the adjacent Y 3 Fe 5 O 12 layers, clearly indicating that both magnetic entities are either not or only very weakly coupled.

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We report a comprehensive experimental study to analyze the limiting factors and physical mechanisms that determine the achievable performance of Transverse Magneto-Optical Kerr Effect (T-MOKE) ellipsometry. Specifically, we explore different approaches to achieve high sensitivity and reduced acquisition times. The best sensitivity is observed for an incident light polarization with balanced s-p components. We also verify experimentally that the method’s theoretical description is accurately describing data for any s-p combination of the incoming light. Furthermore, two alternative measurement strategies are explored by using different measurement sequences for the polarization sensitive optics, which both achieve a very comparable, high quality of results. Signal-to-noise ratios and systematic deviations are measured and analyzed based on a large number of nominally identical measurement repeats, both for entire signal sequences as well as for individual Fourier components of the magneto-optical signal generated by a sinusoidal magnetic field sequence. Hereby, we observe that while higher order Fourier components have a significantly reduced signal amplitude and correspondingly exhibit reduced signal-to-noise and repeatability performance, signal-to-noise ratios always exceed values of 100 even for the lowest signal Fourier component and the lowest signal sample that we investigated, illustrating the extremely precise nature of T-MOKE ellipsometry.

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