THz emission from Fe/Pt spintronic emitters with L10_{0}-FePt alloyed interface

Recent developments in nanomagnetism and spintronics have enabled the use of ultrafast spin physics for terahertz (THz) emission. Spintronic THz emitters, consisting of ferromagnetic FM / non-magnetic (NM) thin film heterostructures, have demonstrated impressive properties for the use in THz spectroscopy and have great potential in scientific and industrial applications. In this work, we focus on the impact of the FM/NM interface on the THz emission by investigating Fe/Pt bilayers with engineered interfaces. In particular, we intentionally modify the Fe/Pt interface by inserting an ordered L1$_{0}$-FePt alloy interlayer. Subsequently, we establish that a Fe/L1$_{0}$-FePt (2\,nm)/Pt configuration is significantly superior to a Fe/Pt bilayer structure, regarding THz emission amplitude. The latter depends on the extent of alloying on either side of the interface. The unique trilayer structure opens new perspectives in terms of material choices for the next generation of spintronic THz emitters

Enhanced thermally-activated skyrmion diffusion with tunable effective gyrotropic force

Magnetic skyrmions, topologically-stabilized spin textures that emerge in magnetic systems, have garnered considerable interest due to a variety of electromagnetic responses that are governed by the topology. The topology that creates a microscopic gyrotropic force also causes detrimental effects, such as the skyrmion Hall effect, which is a well-studied phenomenon highlighting the influence of topology on the deterministic dynamics and drift motion. Furthermore, the gyrotropic force is anticipated to have a substantial impact on stochastic diffusive motion; however, the predicted repercussions have yet to be demonstrated, even qualitatively. Here we demonstrate enhanced thermally-activated diffusive motion of skyrmions in a specifically designed synthetic antiferromagnet. Suppressing the effective gyrotropic force by tuning the angular momentum compensation leads to a more than 10 times enhanced diffusion coefficient compared to that of ferromagnetic skyrmions. Consequently, our findings not only demonstrate the gyro-force dependence of the diffusion coefficient but also enable ultimately energy-efficient unconventional stochastic computing

Coupling of ferromagnetic and antiferromagnetic spin dynamics in Mn2_{2}Au/NiFe thin-film bilayers

We investigate magnetization dynamics of Mn$_{2}$Au/Py (Ni$_{80}$Fe$_{20}$) thin film bilayers using broadband ferromagnetic resonance (FMR) and Brillouin light scattering spectroscopy. Our bilayers exhibit two resonant modes with zero-field frequencies up to almost 40 GHz, far above the single-layer Py FMR. Our model calculations attribute these modes to the coupling of the Py FMR and the two antiferromagnetic resonance (AFMR) modes of Mn2Au. The coupling-strength is in the order of 1.6 T$\cdot$nm at room temperature for nm-thick Py. Our model reveals the dependence of the hybrid modes on the AFMR frequencies and interfacial coupling as well as the evanescent character of the spin waves that extend across the Mn$_{2}$Au/Py interfac

Enhanced thermally-activated skyrmion diffusion with tunable effective gyrotropic force

Magnetic skyrmions, topologically-stabilized spin textures that emerge in magnetic systems, have garnered considerable interest due to a variety of electromagnetic responses that are governed by the topology. The topology that creates a microscopic gyrotropic force also causes detrimental effects, such as the skyrmion Hall effect, which is a well-studied phenomenon highlighting the influence of topology on the deterministic dynamics and drift motion. Furthermore, the gyrotropic force is anticipated to have a substantial impact on stochastic diffusive motion; however, the predicted repercussions have yet to be demonstrated, even qualitatively. Here we demonstrate enhanced thermally-activated diffusive motion of skyrmions in a specifically designed synthetic antiferromagnet. Suppressing the effective gyrotropic force by tuning the angular momentum compensation leads to a more than 10 times enhanced diffusion coefficient compared to that of ferromagnetic skyrmions. Consequently, our findings not only demonstrate the gyro-force dependence of the diffusion coefficient but also enable ultimately energy-efficient unconventional stochastic computing

Integrated Concentrating Solar/Photovoltaic Hybrid Concepts—Technological Discussion, Energy Yield, and Cost Considerations

Concentrating solar thermal (CST) technologies are a sustainable way to produce high-temperature heat. Four concepts of integrating photovoltaics (PV) into CST plants, namely Rear-PV, PV-Mirror, bifacial PV-Mirror and Spillage-concentrating PV (CPV), are compared and the technological and economic outcome is discussed. The concepts are presented for the use with solar tower systems, but can also be applied to other configurations. In this work, parameters for each concept to quantify annual energy production and investment costs are derived. It is determined that implementing Rear-PV, PV-Mirror, bifacial PV-Mirror, and Spillage-CPV in a concentrating solar power tower plant leads to an additional energy yield as high as 23%, 29%, 40%, and 36%, respectively, on the same mirror aperture size. For the concepts of the Rear-PV, PV-Mirror, and bifacial PV-Mirror, maximum allowable cost per aperture area can be 3.0, 4.8, and 5.7 times the cost of conventional mirrors, to reach a break-even of the specific investment cost per annually produced energy. Such values are considered to be achievable for PV-Mirror and bifacial PV-Mirror, but not for Rear-PV. For Spillage-CPV, a break-even of investment cost can be achieved if installed in areas with spillage radiation flux exceeding ≈350 kWm-2 at peak

Concepts for combining concentrating solar mirrors with PV modules

Concentrating solar thermal (CST) technologies produce renewable, sustainable heat at elevated temperature. In this work four concepts are compared to integrate photovoltaic cells into CST heliostats and at tower receivers to increase efficiency and decrease cost of the systems. Based on previous research, parameters are derived which describe energy production and investment cost of the concepts. It is found that the integrated concepts can increase the total annual energy production of a concentrating solar power plant by 23% to 40%, justifying investment cost increase compared to the conventional configurations. According to this the concepts utilizing a spectrally selective mirror on top of PV cells to replace the concentrating mirrors are expected to be economically feasible. The concentrating PV concept produces electricity at lower cost than separate stand-alone PV if the spillage radiation flux around the receiver of CST tower plants is higher than around 350 kW/m2

Fast long-wavelength exchange spin waves in partially compensated Ga:YIG

Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant λex⁠. Using wave vector resolved Brillouin light scattering spectroscopy, we directly measure λex in Ga-substituted YIG thin films and show that it is about three times larger than for pure YIG. Consequently, the spin-wave group velocity overcomes the one in pure YIG for wavenumbers k > 4 rad/μm, and the ratio between the velocities reaches a constant value of around 3.4 for all k > 20 rad/μm. As revealed by vibrating-sample magnetometry and ferromagnetic resonance spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert damping (⁠α<10−3⁠), a decreased saturation magnetization μ0MS≈20 mT, and a pronounced out-of-plane uniaxial anisotropy of about μ0Hu1≈95 mT, which leads to an out-of-plane easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport for all wavelengths in nano-scale systems independently of dipolar effects