Laser induced THz emission from femtosecond photocurrents in Co/ZnO/Pt and Co/Cu/Pt multilayers

The ultrashort laser excitation of Co/Pt magnetic heterostructures can effectively generate spin and charge currents at the interfaces between magnetic and nonmagnetic layers. The direction of these photocurrents can be controlled by the helicity of the circularly polarized laser light and an external magnetic field. Here, we employ THz time-domain spectroscopy to investigate further the role of interfaces in these photo-galvanic phenomena. In particular, the effects of either Cu or ZnO interlayers on the photocurrents in Co/X/Pt (X = Cu, ZnO) have been studied by varying the thickness of the interlayers up to 5 nm. The results are discussed in terms of spin-diffusion phenomena and interfacial spin-orbit torque.Comment: 15 pages, 6 figures, 2 table

The ultra-diffuse dwarf galaxies NGC 1052-DF2 and 1052-DF4 are in conflict with standard cosmology

Funding Information: IB is supported by an Alexander von Humboldt postdoctoral research fellowship. KG was supported by the German-Russian Interdisciplinary Science Center funded by the German Federal Foreign Office via the German Academic Exchange Service.Recently van Dokkum et al. reported that the galaxy NGC 1052-DF2 (DF2) lacks dark matter if located at 20 Mpc from Earth. In contrast,DF2 is a dark-matter-dominated dwarf galaxy with a normal globular cluster population if it has a much shorter distance near 10 Mpc. However, DF2 then has a high peculiar velocity wrt. the cosmic microwave background of 886 km s-1, which differs from that of the Local Group (LG) velocity vector by 1298 km s-1 with an angle of 117°.Taking into account the dynamical M/L ratio, the stellar mass, half-light radius, peculiar velocity, motion relative to the LG, and the luminosities of the globular clusters, we show that the probability of finding DF2-like galaxies in the lambda cold dark matter (CDM) TNG100-1 simulation is at most 1.0 × 10-4 at 11.5 Mpc and is 4.8 × 10-7 at 20.0 Mpc. At 11.5 Mpc, the peculiar velocity is in significant tension in the TNG100-1, TNG300-1, and Millennium simulations, but naturally in a Milgromian cosmology. At 20.0 Mpc, the unusual globular cluster population would challenge any cosmological model. Estimating that precise measurements of the internal velocity dispersion, stellar mass, and distance exist for 100 galaxies, DF2 is in 2.6σ (11.5 Mpc) and 4.1σ (20.0 Mpc) tension with standard cosmology. Adopting the former distance for DF2 and assuming that NGC 1052-DF4 is at 20.0 Mpc, the existence of both is in tension at ≥4.8σ with the ΛCDM model. If both galaxies are at 20.0 Mpc the ΛCDM cosmology has to be rejected by ≥5.8σ.Publisher PDFPeer reviewe

Assessment of Impact of Economic Sustainability on Shareholder Return and Economic Profit of BRICS Industrial Companies Following Digital Transformation Strategy

We investigated the impact of Economic Sustainability (ES) practices of digitally oriented industrial companies in BRICS (Brazil, Russia, India, China, and South Africa) in various horizons. The relevance is underpinned by numerous controversies in the literature on the topic. The sample included 257 industrial companies from BRICS in 2017-2021. Economic profit in the long-term and short-term was measured by Total Shareholder Return (TSR) and Economic Value Added (EVA), respectively. We found that the improvements in resource use, enhancements in the workforce and responsible product development had a positive and significant influence on the TSR of BRICS companies. Conversely, we discovered the negative impact of social practices on companies’ EVA. Firms from Brazil and India with stronger ESG practices provided higher returns for shareholders, while there was a significant and negative linkage between ES and EVA for Chinese firms. Cross-industry analysis showed that ESG practices had an additional positive and significant impact on the TSR of firms in the basic materials and technology sectors. However, there was an additional negative and significant impact of ES practices on EVA in consumer cyclical and energy sectors. The novelty is driven by (1) exploring the impact of ESG practices on companies’ value at BRICS; (2) considering previously overlooked metrics of TSR and EVA; and (3) applying granular ES metrics instead of aggregated ones. &nbsp

The Cost Management of Innovative Products in an Industrial Enterprise Given the Risks in the Digital Economy

This study aims to develop a mechanism for the cost management of innovative products in an industrial enterprise given the inherent risks. Under the conditions of the high volatility of the digital economy, risk assessment in cost management, as well as the development of some mechanisms for staying flexible and adaptable with regard to continual changes, is a priority for the further development of cost management systems for an industrial enterprise. The research results include: (1) a mechanism for assessing and considering the changes in the key cost drivers, which continuously controls the target cost level that has been achieved and can be used for taking into account the risk factors in cost management and for increasing the effectiveness of the business processes of industrial enterprises operating in the digital economy; and (2) a description of the methods recommended for implementing each stage of the mechanism suggested. The mechanism is based on the synthesis of the cost driver concept and the risk-controlling concept. The following tools were used to develop the mechanism: target-costing, kaizen-costing, variance analysis for cost planning, accounting and analysis, an Ishikawa diagram, a fault tree for identifying risk factors for key cost drivers, and simulation modeling using the Monte Carlo method. The mechanism: (1) makes it possible to consider the high uncertainty level of the external environment and the effect of risks in the cost management system; (2) can be used to control the level of target costs reached in real time and introduce prompt corrections regarding the planned costs according to external and internal changes; and (3) is based on using modern, high-precision tools for assessing risks and the effect they produce on the costs and profitability of an industrial enterprise. The advantages above help to increase the dynamics and flexibility of the process of the cost management of innovative products and to maintain such products’ competitiveness.&nbsp

Excitation and Detection of THz Coherent Spin Waves in Antiferromagnetic α−Fe2O3\mathrm{\alpha-Fe_2O_3}

The efficiency of ultrafast excitation of spins in antiferromagnetic $\mathrm{\alpha-Fe_{2}O_{3}}$ using nearly single-cycle THz pulse is studied as a function of the polarization of the THz pulse and the sample temperature. Above the Morin point the most efficient excitation is achieved when the magnetic field of the THz pulse is perpendicular to the antiferromagnetically coupled spins. Using the experimental results and equations of motion for spins, we show that the mechanism of the spin excitation above and below the Morin point relies on magnetic-dipole interaction of the THz magnetic field with spins and the efficiency of the coupling is proportional to the time derivative of the magnetic field

Stages and Fracture Mechanisms of Lamellar Pearlite of 100-m-Long Differentially Hardened Rails Under Long-Term Operation Conditions

Using the methods of transmission electron microscopy, the carbide phase evolution in surface layers of the differentially quenched rails is studied after the passed tonnage of 691.8 million tons at the depth up to 10 mm along the central axis and fillet of rail head. The action of two mutual supplement mechanisms of steel carbide phase transformation in surface layers at rail operation is established: (1) cutting mechanism of cementite particles with the following departure in the volume of ferrite grains or plates (in pearlite structure); (2) cutting mechanism and following dissolution of cementite particles, transfer of carbon atoms on dislocations (in Cottrell atmospheres and dislocation cores), transfer of carbon atoms by moving dislocations into ferrite grains volume (or plates) with the following repeated formation of nanosized cementite particles. The first mechanism is accompanied by the change in linear sizes and morphology of carbide particles. Cementite element composition change is not essential. Carbide structure change can take place during the second mechanism

Terahertz Optomagnetism:Nonlinear THz Excitation of GHz Spin Waves in Antiferromagnetic FeBO3

A nearly single cycle intense terahertz (THz) pulse with peak electric and magnetic fields of 0.5 MV/cm and 0.16 T, respectively, excites both modes of spin resonances in the weak antiferromagnet FeBO3. The high frequency quasiantiferromagnetic mode is excited resonantly and its amplitude scales linearly with the strength of the THz magnetic field, whereas the low frequency quasiferromagnetic mode is excited via a nonlinear mechanism that scales quadratically with the strength of the THz electric field and can be regarded as a THz inverse Cotton-Mouton effect. THz optomagnetism is shown to be more energy efficient than similar effects reported previously for the near-infrared spectral range

Two-dimensional THz spectroscopy of nonlinear phononics in the topological insulator MnBi2Te4\mathrm{MnBi}_2\mathrm{Te}_4

The interaction of a single-cycle THz electric field with the topological insulator $\mathrm{MnBi}_2\mathrm{Te}_4$ triggers strongly anharmonic lattice dynamics, promoting fully coherent energy transfer between the otherwise non-interacting Raman-active $E_g$ and infrared (IR)-active $E_u$ phononic modes. Two-dimensional (2D) THz spectroscopy combined with modeling based on the classical equations of motion and symmetry analysis reveals the multi-stage process underlying the excitation of the Raman-active $E_g$ phonon. In this process, the THz electric field first prepares a coherent IR-active $E_u$ phononic state and subsequently interacts with this state to efficiently excite the $E_g$ phonon.Comment: 27 pages, 20 figure