Vector Magneto-Optical Generalized Ellipsometry on Passivated Permalloy Slanted Columnar Thin Films
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Vector Magneto-Optical Generalized Ellipsometry on Passivated Permalloy Slanted Columnar Thin Films Daniel Schmidt, Chad Briley, Eva Schubert and Mathias Schubert Department of Electrical Engineering and Center for Nanohybrid Functional Materials, University of Nebraska-Lincoln, Lincoln, NE 68588, U.S.A. ABSTRACT Vector magneto-optical generalized ellipsometry on passivated ferromagnetic permalloy slanted columnar thin films is reported. The nanostructured thin film was grown by electron-beam glancing angle deposition and subsequently coated with a thin Al2O3 layer by atomic layer deposition. Magneto-optical generalized ellipsometry data have been acquired while an external magnetic field H with constant amplitude was rotated with respect to the sample (spatial hysteresis loops). The magneto-optical coupling parameters, which are proportional to the sample magnetization M, reveal intriguing anisotropic magnetic behavior of the slanted columnar thin film. Three-dimensional graphs of the magneto-optical coupling parameters with respect to spatial hysteresis loops shown here are representative for the sample magnetization. INTRODUCTION Three-dimensionally shaped metal sculptured thin films made by glancing angle deposition (GLAD) resemble an artificial material class with interesting characteristics. Typically, physical properties are closely related to their geometry, and may vary significantly from bulk properties due to size and confinement effects [1]. Ferromagnetic materials such as permalloy (Ni80Fe20) are particularly interesting for future magneto-optical applications since magnetic and optical properties can be tailored at the same time. Slanted columnar thin films (SCTFs) comprise rather simple geometries yet show complex anisotropic optical, magnetic, and magneto-optical properties [2, 3, 4, 5, 6, 7], for example. Due to relatively small and anisotropic extinction coefficients, high penetration depths can be achieved in SCTFs for electromagnetic radiation at visible wavelengths. Hence, in contrast to highly absorbing solid metal films, the magnetic field-induced birefringence is no longer probed only at the near surface. Therefore, such ferromagnetic nanostructures may be interesting for thin film low-loss transmission magneto-optical modulators, for example. The challenge, however, is to understand the magnetic behavior of such threedimensionally shaped nanostructures with confined magnetic domains which possibly show coupling effects. Previously, magnetic force microscopy images of Co SCTFs reveal that regular stripe patterns parallel to the incoming vapor flux may be observed for small deposition angles (α < 75°); however, for large deposition angles (α > 75°) only randomly distributed spots were seen [6,8]. The authors conclude that due to large intercolumnar spacings magnetic interactions are too weak to form strip patterns [6]. Albrecht et al. performed superconducting quantum interference device (SQUID) measurements on tubular SCTFs comprising a Si core and a ferrimagnetic Fe3O4 shell. Upon in-plane r
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