arXiv subjects

Martin Veis

Publications and source records attributed to Martin Veis.

24 records · Page 2Linked to original sources

arXiv2019

Magnetic domain wall motion in SrRuO$_3$ thin films

Influence of substrate miscut on magnetization dynamics in SrRuO$_3$ (SRO) thin films was studied. Two films were grown on SrTiO$_3$ substrates with high ($\sim1^{\circ}$) and low ($\sim0.1^{\circ}$) miscut angles, respectively. As expected, high miscut angle leads to suppression of multi-variant growth. By means of SQUID magnetometry, comparable relaxation effects were observed in both the multi-variant and the nearly single-variant sample. Differences in the magnetization reversal process were revealed by magnetic force microscopy. It showed that the multi-variant growth leads to higher density of defects acting as pinning or nucleation sites for magnetic domains, which consequently results in deterioration of magnetic properties. It was demonstrated that the use of high miscut substrate is important for fabrication of high quality SRO thin films with low density of crystallographic defects and excellent magnetic properties.

cond-mat.mtrl-sci↗

arXiv2019

Quadratic magnetooptic Kerr effect spectroscopy of Fe epitaxial films on MgO(001) substrates

The magnetooptic Kerr effect (MOKE) is a well known and handy tool to characterize ferro-, ferri- and antiferromagnetic materials. Many of the MOKE techniques employ effects solely linear in magnetization $\bm{M}$. Nevertheless, a higher-order term being proportional to $\bm{M}^2$ and called quadratic MOKE (QMOKE) can additionally contribute to the experimental data. Here, we present detailed QMOKE spectroscopy measurements in the range of 0.8 -- 5.5\,eV based on a modified 8-directional method applied on ferromagnetic bcc Fe thin films grown on MgO substrates. From the measured QMOKE spectra, two further complex spectra of the QMOKE parameters $G_s$ and $2G_{44}$ are yielded. The difference between those two parameters, known as $ΔG$, denotes the strength of the QMOKE anisotropy. Those QMOKE parameters give rise to the QMOKE tensor $\bm{G}$, fully describing the perturbation of the permittivity tensor in the second order in $\bm{M}$ for cubic crystal structures. We further present experimental measurements of ellipsometry and linear MOKE spectra, wherefrom permittivity in the zeroth and the first order in $\bm{M}$ are obtained, respectively. Finally, all those spectra are described by ab-initio calculations.

physics.optics↗

arXiv2018

Investigation of the quality of an As35S65 grating by spectroscopic ellipsometry

The quality of an As35S65 chalcogenide glass (ChG) grating fabricated by electron beam lithography (EBL) was characterized by optical scatterometry based on spectroscopic ellipsometry (SE) in the visible and near infrared spectral range and complementary techniques providing direct images, especially atomic force microscopy (AFM). The geometric dimensions and the shape of patterned grating lines were determined by fitting modeled values (calculated by the Fourier modal method) to SE experimental data. A simple power-dependent function with only one variable parameter was successfully used to describe the shape of the patterned lines. The result yielded by SE is shown to correspond to AFM measurement with high accuracy, provided that optical constants of ChG modified by EBL were used in the fitting procedure. The line edge roughness (LER) of the grating was also investigated by further fitting the SE data to find out that no LER is optically detectable in the spectral range used, which is essential for the functionality of optical tools fabricated by EBL.

physics.optics↗

arXiv2018

Quadratic magnetooptic spectroscopy setup based on photoelastic light modulation

In most of the cases the magnetooptic Kerr effect (MOKE) techniques rely solely on the effects linear in magnetization ($\bm{M}$). Nevertheless, a higher-order term being proportional to $\bm{M}$$^2$ and called quadratic MOKE (QMOKE) can additionally contribute to experimental data. Handling and understanding the underlying origin of QMOKE could be the key to utilize this effect for investigation of antiferromagnetic materials in the future due to their vanishing first order MOKE contribution. Also, better understanding of QMOKE and hence better understanding of magnetooptic (MO) effects in general is very valuable, as the MO effect is very much employed in research of ferro- and ferrimagnetic materials. Therefore, we present our QMOKE and longitudinal MOKE spectroscopy setup with a spectral range of 0.8--5.5\,eV. The setup is based on light modulation through a photoelastic modulator and detection of second-harmonic intensity by a lock-in amplifier. To measure the Kerr ellipticity an achromatic compensator is used within the setup, whereas without it Kerr rotation is measured. The separation of QMOKE spectra directly from the measured data is based on measurements with multiple magnetization directions. So far the QMOKE separation algorithm is developed and tested for but not limited to cubic (001) oriented samples. The QMOKE spectra yielded by our setup arise from two quadratic MO parameters $G_s$ and $2G_{44}$, being elements of quadratic MO tensor $\bm{G}$, which describe perturbation of the permittivity tensor in the second order in $\bm{M}$.

physics.ins-det↗

arXiv2016

Principal spectra describing magnetooptic permittivity tensor in cubic crystals

We provide unified phenomenological description of magnetooptic effects being linear and quadratic in magnetization. The description is based on few principal spectra, describing elements of permittivity tensor up to the second order in magnetization. Each permittivity tensor element for any magnetization direction and any sample surface orientation is simply determined by weighted summation of the principal spectra, where weights are given by crystallographic and magnetization orientations. The number of principal spectra depends on the symmetry of the crystal. In cubic crystals owning point symmetry we need only four principal spectra. Here, the principal spectra are expressed by ab-initio calculations for bcc Fe, fcc Co and fcc Ni in optical range as well as in hard and soft x-ray energy range, i.e. at the 2p- and 3p-edges. We also express principal spectra analytically using modified Kubo formula.

cond-mat.mtrl-sci↗

arXiv2010

Fourier factorization with complex polarization bases in the plane-wave expansion method applied to two-dimensional photonic crystals

We demonstrate an enhancement of the plane wave expansion method treating two-dimensional photonic crystals by applying Fourier factorization with generally elliptic polarization bases. By studying three examples of periodically arranged cylindrical elements, we compare our approach to the classical Ho method in which the permittivity function is simply expanded without changing coordinates, and to the normal vector method using a normal-tangential polarization transform. The compared calculations clearly show that our approach yields the best convergence properties owing to the complete continuity of our distribution of polarization bases. The presented methodology enables us to study more general systems such as periodic elements with an arbitrary cross-section or devices such as photonic crystal waveguides.

physics.optics↗