Tomasz Blachowicz

Crystalline phases in the GeSb2Te4 alloy system: Phase transitions and elastic properties

Chalcogenide alloys are attracting considerable interest as phase-change materials. Their elastic properties are investigated here. A film of stoichiometric GeSb2Te4 is amorphous as deposited; under annealing at increasing temperatures it crystallizes into a cubic phase and then into a hexagonal phase. The elastic properties of the three phases have been investigated nondestructively by Brillouin light scattering. Measurements detect frequency dispersion relations of Rayleigh and Sezawa acoustic modes. All the elastic moduli can be derived: they increase, together with mass density, upon transition from the amorphous to the cubic and to the hexagonal phase. The measured moduli provide a benchmark for computational predictions of film properties.

Fourfold nanosystems for quaternary storage devices

In nano-magnetic coupled systems of wires, pronounced magnetization steps in the hysteresis loops have been found by micromagnetic simulations. The steps can be attributed to stable intermediate states, similar to flux-closed vortex states in ferromagnetic nano-rings. Due to the fourfold anisotropy of the system of four crossed nanowires, these states can be distinguished even by measuring the magnetization of the whole system, giving rise to four separated states without application of external magnetic field. Opposite to actual trials with nano-rings or layered structures, no additional method of symmetry breaking is necessary. Such an easily created system can be utilized, e.g., in quaternary (four states, i.e., two bits per magnetic nano-object) magnetic storage applications.

Magnetic properties of square Py nanowires: Irradiation dose and geometry dependence

Arrays of ferromagnetic patterned nanostructures with single particle lateral dimensions between 160 nm and 400 nm were created by electron-beam lithography. The fourfold particles with rectangular-shaped walls around a square open area were produced from permalloy. Their magnetic properties were measured using the longitudinal magneto-optical Kerr effect. The article reports about the angle-dependent coercive fields and the influence of the e-beam radiation dose on sample shapes. It is shown that a broad range of radiation dose intensities enables reliable creation of nanostructures with parameters relevant for the desired magnetization reversal scenario. The experimental results are finally compared with micromagnetic simulations to explain the findings.

Examination of the sintering process-dependent properties of TiO2 on glass and textile substrates

Abstract. In recent years, the development of smart textiles has attracted great attention. Such textiles can contain small electrical devices, which need a power supply. Dye-sensitized solar cells, which can be produced from nontoxic, cheap, low-purity materials, could fill this purpose. However, to reach reasonable cell properties, sintering the TiO2 layer on the substrate is necessary. Unfortunately, only a few textile materials can withstand a sintering process at high temperatures. Therefore, it is important to find an optimal temperature leading to a reasonable improvement of the cell characteristics without damaging the textile substrate. The influence of the sintering temperature on different properties is investigated. For this, the surface properties of the TiO2 coating, such as adhesion to the substrate, dye adsorption characteristic, and film stability, are investigated on different substrates, i.e., a glass plate, a stainless steel nonwoven fabric, and a carbon woven fabric. Two commercially available TiO2 sources are used: a TiO2 dispersion obtained from Man Solar and a water-based solution of TiO2 particles purchased from Kronos. The influence of the sintering temperature on short-circuit current and open-circuit voltage of solar cells on the aforementioned substrates is also examined.

Image processing and analysis of textile fibers by virtual random walk

An algorithm for extracting material shape and spatial information from non-uniform background, and for generating object skeletons for statistical two-dimensional experiments using random walk approach, is presented. This finds applications in textile analysis and microscopic analysis of various materials like hairs and allows for further precise determination of textile yarn dimensions as well as other geometrical characteristics like a fractal dimension.

Elastic constants of the lithium tantalate crystal in the hypersonic range

Elastic constants of the lithium tantalate LiTaO3 crystal were determined in the hypersonic range by the use of the Brillouin laser light scattering method. Obtained values show variation with respect to ultrasonic measurements. Results are interesting because the same effects are qualitatively different in isomorphic lithium niobate LiNbO3 crystal.

Adjusting exchange bias and coercivity of magnetic layered systems with varying anisotropies

The impact of a variation of anisotropy constants on the resulting coercivity and exchange bias has been analyzed modeling the total energy density in thin layered ferromagnetic/antiferromagnetic in-plane systems. For a broad range of fourfold, uniaxial, and unidirectional anisotropies, our results illustrate that the exchange bias can grow significantly for a sample rotation off the cooling field direction, while for other combinations of anisotropies, a positive exchange bias can be found near or even in the cooling field direction. These findings allow identification of anisotropies based on superconducting quantum interference device or magneto-optical Kerr effect measurements as well as tailoring desired angular dependencies for magnetoelectronic applications.

Examination of hairiness changes due to washing in knitted fabrics using a random walk approach

The relaxation of knitted fabrics is usually described in terms of dimensional changes of knitted loop widths and heights or fabric widths and heights, respectively. Due to washing, however, additional changes in the optical appearance and the haptic properties of a knitted fabric can occur, such as a change in the regularity or the hairiness. This article uses the random walk statistical approach to estimate the structural complexity of knitted fabrics directly after production and up to 10 washing cycles and shows that the Hurst exponent, resulting from the random walk process, is partly related to the cover factor of the knitted fabrics under investigation; however, it depicts significant contributions of the hairiness. Thus, this novel approach offers a quantitative measure of structural changes in knitted fabrics that cannot be described by cover factor or dimensional changes.

Directional-dependent coercivities and magnetization reversal mechanisms in fourfold ferromagnetic systems of varying sizes

Different types of reversal processes, including either uniform-rotation or domain-wall driven processes, were indentified in magnetic nano-wires of four-fold symmetry using micromagnetic simulations. Iron wires were tested for diameters ranging from 6 nm up to 20 nm, while their lengths were taken from 30 nm to 70 nm range, and for several directions of externally applied magnetic field. Physical parameters of presented low-dimensional structures enabled reversal via intermediate states, which can lead to additional stable states at remanence, contrary to instable vortexes observed in magnetic nano-rings or cylindrical nanodots.

Walking or running in the rain—a simple derivation of a general solution

The question whether to walk slowly or to run when it starts raining in order to stay as dry as possible has been considered for many years—and with different results, depending on the assumptions made and the mathematical descriptions for the situation. Because of the practical meaning for real life and the inconsistent results depending on the chosen parameters, this problem is well suited to undergraduate students learning to decide which parameters are important and choosing reasonable values to describe a physical problem. Dealing with physical parameters is still useful at university level, as students do not always recognize the connection between pure numbers and their qualitative and quantitative influence on a physical problem. This paper presents an intuitive approach which offers the additional advantage of being more detailed, allowing for more parameters to be tested than the simple models proposed in most other publications.