Generalized MagnetoOtpical Ellipsometry for Systems with Optical Anisotropy

CIC nanoGUNE Seminars

Juan González Díaz, nanomagnetism group
nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
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Generalized MagnetoOtpical Ellipsometry for Systems with Optical Anisotropy Ellipsometry is an advanced measurement and characterization technique for the investigation of optical materials properties and multilayer metrology. Its applications are very widespread, from basic research to industrial utilization, and besides other advantages it is non-destructive, fast, compatible with many environmental conditions, and can be implemented even through very simple experimental configurations [1]. A specific implementation and extension of this technique, named Generalized Magneto-Optical Ellipsometry (GME), has emerged in the last decade as a methodology to characterize magnetic materials with a high degree of precision, by means of utilizing the magneto-optical Kerr effect [2-3]. Compared to other magneto-optical characterization methods based on the same effect [4-5], GME has two key advantages: it can measure both the optical and magneto-optical constants, and it allows full vector magnetometry, all with one conceptionally simple experimental set-up. This method, based on measurements of the light reflection change upon applying a magnetic field, has been successfully utilized in the study of diverse magnetization reversal processes [6-7], the investigation of magneto- optical coupling in ferromagnetic films [8], and for the purpose of identifying spin-polarized electronic states in multiferroic materials [9], as well as for the measurement of the magnetization orientation using two- and three-dimensional vector magnetometry [3,10]. However, despite obtaining both the diagonal and off-diagonal constants of the dielectric tensor, this technique has not been demonstrated to fully characterize all kinds of materials. For instance, it has not been attempted to extract information from samples that in addition to being magneto-optically active also exhibit optical birefringence. In fact, all GME detection schemes and materials analysis frameworks to date have been based on the assumption that the non- magnetic optical properties of materials are isotropic. Here, we make the first attempt to extend GME beyond this limitation to increase its capabilities and possible applications, by conducting measurement of materials that are magneto-optically active and optically anisotropic at the same time. We will show that by using the same experimental setup and methodology utilized previously for GME measurements, we can determine the orientation of the optical axis of an anisotropic material, and in addition, distinguish between the magneto-optical and the birefringent contributions to the change in the polarization state of the reflected light. For this purpose, we have performed GME measurements on a multilayer structure that exhibits not only in-plane uniaxial magnetic anisotropy, but also uniaxial optical anisotropy. The corresponding magnetization reversal and optical axis orientation are both reflected in the polarizer orientation dependent maps of magnetically-induced intensity change (dI/I), from which the GME methodology extracts the optical and magneto-optical information (see Figure 1). As the sample is rotated perpendicular to the optical anisotropy axis, the dI/I maps exhibit a shift in their features with a periodicity of 180º, which is absent in optically isotropic materials. From these results, both optical and magneto-optical information can be extracted quantitatively. [1] H. Fujiwara, Spectroscopic Ellipsometry, John Wiley & Sons (2003) [2] A. Berger and M. R. Pufall,Appl. Phys. Lett. **71** (1997) 965 [3] A. Berger and M. R. Pufall, J. Appl. Phys. **85** (1999) 4583 [4] K. Sato, Jpn. J. Appl. Phys. **20** (1981) 2403 [5] W. S. Kim, M. Aderholz and W. Kleemann, Meas. Sci. Technol. **4** (1993) 1275 [6] Idigoras O, Vavassori P, Porro JM, et al., J. Magn. Magn. Mater. **322** (2010) L57 [7] M. R. Pufall and A. Berger, J. Appl. Phys. **87** (2000) 5834 [8] K. Mok, G. J. Kovacs, J. McCord, L. Li, M. Helm, and H. Schmidt, Phys. Rev. **B 84** (2011) 094413 [9] M. Bastjan, S.G. Singer, G. Neuber et al., Phys. Rev. **B 77** (2008) 193105 [10] K. Mok, N. Du and H. Schmidt, Rev. Sci. Inst. **82** (2011) 033112