Search

A phase transition is found in Ti$_3$C$_2$T$_x$ MXene at 350 K, by measuring the complex Young's modulus of self-standing thick films. A step-like softening and increase of the mechanical losses is found below 350 K, indicative of a phase transition, where the square of the order parameter is coupled to strain. It is argued that it should be a ferroelectric transition, most likely of the sliding (moir\'e) type, due to charge transfer between facing flakes sliding with respect to each other. If the transition will be confirmed to be ferroelectric, Ti$_3$C$_2$T$_x$ will be added to the class of metallic ferroelectrics and open new perspectives of applications, in addition to the numerous already studied.

New generation concentrated solar power (CSP) plants require new solar receiver materials with selective optical properties and excellent corrosion resistance against molten salts. MAX phases are promising materials for CSP applications due to their optical properties and resistance to thermal shocks. Herein, we report a solar absorptance >/= 0.5 and a thermal emittance of 0.17-0.31 between 600 and 1500 K for Cr2AlC, Ti2AlC, and Ti3AlC2. These compositions were also exposed to solar salt corrosion at 600{\deg}C for up to 4 weeks. Cr2AlC exhibited superior corrosion resistance due to the formation of a protective nanometric layer., Comment: 17 pages, 5 figures, 1 table

MAX phases have great potential under demands of both high-temperature and high-stress performance, with their mixed atomic bonding producing the temperature and oxidation resistance of ceramics with the mechanical resilience of metals. Here, we measure the mechanical properties up to 980C by nanoindentation on highly dense and pure Cr$_2$AlC, as well as after oxidation with a burner rig at 1200C for more than 29 hours. Only modest reductions in both hardness and modulus up to 980C were observed, implying no change in deformation mechanism. Furthermore, micro-cantilever fracture tests were carried out at the Cr$_2$AlC/Cr$_7$C$_3$ and Cr$_7$C$_3$/Al$_2$O$_3$ interfaces after the oxidation of the Cr$_2$AlC substrates with said burner rig. The values are typical of ceramic-ceramic interfaces, below 4 MPa/m, leading to the hypothesis that the excellent macroscopic behaviour is due to a combination of low internal strain due to the match in thermal expansion coefficient as well as the convoluted interface.

An influence of a time dependent external tensile stress on the remagnetization process of a bistable wire is investigated experimentally and numerically. The dependence of the magnetization on the frequency of the tensile stress is analyzed in terms of the magnetic domain structure of Fe-rich wires. The dependence of the switching field on the phase of the tensile stress is presented and reproduced by a straightforward numerical simulation of the remagnetization process in a bistable wire. There, the input is the experimental static dependences of the switching field and of the magnetization of the wire on an external tensile stress. The presented dependences of the switching field and the magnetization on the periodic tensile stress allow to tune the shape of the hysteresis loop, what can be useful in constructing a phase sensor.

We calculated the main dynamic parameters of the spin polarized current induced magnetic vortex oscillations in nanopillars, such as the range of current density, where a vortex steady oscillations exist, the oscillation frequency and orbit radius. We accounted for both the non-linear vortex frequency and non-linear vortex damping. To describe the vortex excitations by the spin polarized current we used a generalized Thiele approach to motion of the vortex core as a collective coordinate. All the calculation results are represented via the free layer sizes, saturation magnetization, Gilbert damping and the degree of the spin polarization of the fixed layer. Predictions of the developed model can be checked experimentally., Comment: 12 pages, 3 figures

We introduce a topological gauge vector potential which influences spin wave excitations over arbitrary non-uniform, slowly moving magnetization distribution. The time-component of the gauge potential plays a principal role in magnetization dynamics, whereas its spatial components can be often neglected for typical magnetic nanostructures. As an example, we consider spin modes excited in the vortex state magnetic dots. It is shown that the vortex/ spin wave interaction can be described as a consequence of the gauge field arising due to non uniform moving vortex magnetization distribution. The coupled equations of motion of the vortex and spin waves are solved within small excitation amplitude approximation. The model yields a giant frequency splitting of the spin wave modes having non-zero overlapping with the vortex mode as well as a finite vortex mass of dynamical origin., Comment: 14 pages, 2 figures