Showing papers in "Physica Status Solidi B-basic Solid State Physics in 2020"

Magnetic and Electronic Properties of Complex Oxides from First-Principles

Abstract: The theoretical treatment of complex oxide structures requires a combination of efficient methods to calculate structural, electronic, and magnetic properties, due to special challenges such as str ...

Validation of a Finite Element Modeling Process for Auxetic Structures under Impact

Abstract: Auxetic materials behave unconventionally under deformation, which enhances material properties such as resistance to indentation and energy absorption. Auxetics, therefore, have the potential to enhance sporting protective equipment. This study explores finite element modeling, additive manufacturing and impact testing of three auxetic lattices, and a conventional equivalent, with a view to advance auxetic implementation within sports equipment. The lattices are modeled and impacts are simulated between 1 J and 5 J, for flat and hemispherical drop hammers. Simulation outputs, including peak impact force, impact duration, maximum axial strain and Poisson’s ratio are compared to experimental results from equivalent impact energies on additively manufactured lattices, using an instrumented drop tower and a high‐speed camera. The simulation and experimental results show broad agreement for all lattices and scenarios, demonstrated by comparative force vs time plots and maximum compression images. The benefits of developing and validating finite element models of three auxetic lattices (as well as the conventional honeycomb lattice) under various impact scenarios as a process is discussed, including material characterization of an exemplar thermoplastic polyurethane. Future work could use the models to investigate auxetic lattices further, selecting and tailoring candidates to further explore their potential application to specific personal protective equipment in sport.

Defect-Induced Magnetism in Nonmagnetic Oxides: Basic Principles, Experimental Evidence, and Possible Devices with ZnO and TiO 2

Abstract: Nowadays, the magnetic properties of solids play a main role in different kinds of applications. In particular, magnetic order, like ferromagnetism (FM) or antiferromagnetism (AFM), is a phenomenon that attracts the interest of a large scientific community. From the materials research side, there is still the need of new materials with magnetic order above room temperature (RT). Interestingly, although there are a large number of magnetic compounds including oxides with ordering temperatures above RT (especially with transition metals like Fe, Co, Ni, etc.), its percentage with respect to the total number of magnetically ordered materials remains rather small. From the theoretical side, magnetic order still belongs to one of the most complex phenomena in solid-state physics. Its origin is given by the exchange interaction, a quantum mechanical mechanism

Oxygen Incorporation in the Molecular Beam Epitaxy Growth of Sc x Ga 1−x N and Sc x Al 1−x N

Abstract: III-nitride semiconductors such as GaN, AlN, InN, and their corresponding alloys have displayed promising optical and electronic device performance. Recently, scandium and other transition metals (e.g., yttrium, niobium, tantalum, manganese, etc.) have gained attention to increase the functionality of nitride semiconductors through piezoelectric, ferroelectric, superconducting, and magnetic behavior. Sc-III nitrides in particular have shown promise for extremely large increases in piezoelectric coefficients and spontaneous polarizations and even ferroelectric behavior. These attractive properties have allowed Sc-III nitrides to find use in applications such as bulk acoustic wave (BAW) resonators and microelectromechanical systems (MEMS). Magnetron sputtering has been utilized to deposit thin film ScxAl1 xN, [11–14] and more recently, molecular beam epitaxy (MBE) to grow Sc-III nitrides films. However, few reports provide information of the oxygen content in the scandiumcontaining films. Due to the large oxygen affinity of scandium, refractory nature of Sc2O3, and lack of extremely high-purity scandium source material that quotes oxygen concentration, integration of scandium into a nitride semiconductor crystal structure without incorporating significant amounts of oxygen and impurities would need special attention. Oxygen incorporation has been readily observed in the binary semiconductor ScN and has been shown to act as an electron donor and is related to degenerate electron carrier concentrations in ScN films. Moram et al. showed that Sc2O3 can form during sputterdeposition of ScN if the chamber pressure vacuum is raised above 7.5 10 7 torr, illustrating the need for ultrahigh vacuum conditions to limit oxygen incorporation in ScN. In that study, similar behavior was not seen for Ti or Zr, indicating Sc has a large affinity for oxygen. Here, we present a secondary-ion mass spectrometry (SIMS) study calibrated by Rutherford backscattering spectrometry (RBS) on MBE-grown Sc-III nitride semiconductor multilayer heterostructures. The results indicate that the oxygen incorporation into Sc-III nitrides alloys is significant and correlates with the scandium content. The evidence of the observed densities of oxygen is a first step toward an investigation of its effects on the electronic properties of ScGaN and ScAlN.

Impact of Defects on Magnetic Properties of Spinel Zinc Ferrite Thin Films

Abstract: through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/pssb.201900630 This article is protected by copyright. All rights reserved Impact of Defects on Magnetic Properties of Spinel Zinc Ferrite Thin Films Vitaly Zviagin, Marius Grundmann, and Rüdiger Schmidt-Grund Universität Leipzig, Felix-Bloch-Institut für Festkörperphysik, Linnéstraß e 5, D-04103 Leipzig, Germany Present address: Technische Universität Ilmenau, Institut für Physik, Weimarer Straß e 32, D-98684 Ilmenau, Germany Received XXXX, revised XXXX, accepted XXXX Published online XXXX

Growth and Magnetotransport in Thin-Film α-Sn on CdTe

Abstract: We report growth and characterization of epitaxial $\\alpha$-Sn thin films grown on CdTe(111)B. Noninvasive techniques verify the film's pseduomorphic growth before fabrication of magnetotransport devices, overcoming ex-situ obstacles on uncapped films for measurement in the Hall bar geometry. We identify a transition to metallic behavior at low temperature with large magnetoresistance, high mobility, and quantum oscillations tentatively suggesting an n-type Dirac semimetallic channel. A parallel p-type dopant channel with high carrier density is seen to dominate at thinner film thicknesses. Careful preparation of the CdTe surface before growth is considered crucial to attain a low dopant density and accessible topological states on an insulating substrate.

Numerical Analysis of Binding Yarn Float Length for 3D Auxetic Structures

Abstract: This study uses finite element analysis (FEA) numerical tool to determine the Poisson's ratio of different three‐dimensional (3D) woven structures. The simulation results reveal a coupled auxetic and bending behavior when a tensile force is applied. This study will help to choose the best 3D structure as reinforcement for ballistic grade impact applications in the area of wearable protection.

Enhanced Auxetic and Viscoelastic Properties of Filled Reentrant Honeycomb

Abstract: Honeycombs or foams with reentrant microstructures exhibit effective negative Poisson's ratio. Although they are light weight due to inherently empty space, their overall stiffness and damping are somewhat limited. With judiciously chosen filler material to fill the voids in star-shaped honeycomb, it is numerically demonstrated its auxeticity may be enhanced. By combining the filler and skeleton, the hierarchical composite materials are constructed. The magnitude of the enhancement depends on inner and outer filler's modulus mismatch, as well as the types of filling. Filler's auxeticity also largely enhances overall auxeticity of the outer- and all-filled honeycomb. In addition, for outer-filled honeycomb, its effective viscoelastic modulus and damping are significantly increased, while maintaining relatively light weight, due to local stress concentration. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim