2013, Zhao, G., Wang, H., Sanchez, S., Schmidt, O.G., Pumera, M.

In this work, we will show that ferromagnetic microjets can pick-up paramagnetic beads while not showing any interaction with diamagnetic silica microparticles for the active separation of microparticles in solution.

2019, Zhu, H., Mao, J., Li, Y., Sun, J., Wang, Y., Zhu, Q., Li, G., Song, Q., Zhou, J., Fu, Y., He, R., Tong, T., Liu, Z., Ren, W., You, L., Wang, Z., Luo, J., Sotnikov, A., Bao, J., Nielsch, K., Chen, G., Singh, D.J., Ren, Z.

Discovery of thermoelectric materials has long been realized by the Edisonian trial and error approach. However, recent progress in theoretical calculations, including the ability to predict structures of unknown phases along with their thermodynamic stability and functional properties, has enabled the so-called inverse design approach. Compared to the traditional materials discovery, the inverse design approach has the potential to substantially reduce the experimental efforts needed to identify promising compounds with target functionalities. By adopting this approach, here we have discovered several unreported half-Heusler compounds. Among them, the p-type TaFeSb-based half-Heusler demonstrates a record high ZT of ~1.52 at 973 K. Additionally, an ultrahigh average ZT of ~0.93 between 300 and 973 K is achieved. Such an extraordinary thermoelectric performance is further verified by the heat-to-electricity conversion efficiency measurement and a high efficiency of ~11.4% is obtained. Our work demonstrates that the TaFeSb-based half-Heuslers are highly promising for thermoelectric power generation.

2019, Gabler, F., Karnaushenko, D.D., Karnaushenko, D., Schmidt, O.G.

Self-assembly of two-dimensional patterned nanomembranes into three-dimensional micro-architectures has been considered a powerful approach for parallel and scalable manufacturing of the next generation of micro-electronic devices. However, the formation pathway towards the final geometry into which two-dimensional nanomembranes can transform depends on many available degrees of freedom and is plagued by structural inaccuracies. Especially for high-aspect-ratio nanomembranes, the potential energy landscape gives way to a manifold of complex pathways towards misassembly. Therefore, the self-assembly yield and device quality remain low and cannot compete with state-of-the art technologies. Here we present an alternative approach for the assembly of high-aspect-ratio nanomembranes into microelectronic devices with unprecedented control by remotely programming their assembly behavior under the influence of external magnetic fields. This form of magnetic Origami creates micro energy storage devices with excellent performance and high yield unleashing the full potential of magnetic field assisted assembly for on-chip manufacturing processes.

2023, Gallop, Nathaniel. P., Maslennikov, Dmitry R., Mondal, Navendu, Goetz, Katelyn P., Dai, Zhenbang, Schankler, Aaron M., Sung, Woongmo, Nihonyanagi, Satoshi, Tahara, Tahei, Bodnarchuk, Maryna I., Kovalenko, Maksym V., Vaynzof, Yana, Rappe, Andrew M., Bakulin, Artem A.

Vibrational control (VC) of photochemistry through the optical stimulation of structural dynamics is a nascent concept only recently demonstrated for model molecules in solution. Extending VC to state-of-the-art materials may lead to new applications and improved performance for optoelectronic devices. Metal halide perovskites are promising targets for VC due to their mechanical softness and the rich array of vibrational motions of both their inorganic and organic sublattices. Here, we demonstrate the ultrafast VC of FAPbBr3 perovskite solar cells via intramolecular vibrations of the formamidinium cation using spectroscopic techniques based on vibrationally promoted electronic resonance. The observed short (~300 fs) time window of VC highlights the fast dynamics of coupling between the cation and inorganic sublattice. First-principles modelling reveals that this coupling is mediated by hydrogen bonds that modulate both lead halide lattice and electronic states. Cation dynamics modulating this coupling may suppress non-radiative recombination in perovskites, leading to photovoltaics with reduced voltage losses.

2024, Fedorov, Pavel, Soldatov, Ivan, Neu, Volker, Schäfer, Rudolf, Schmidt, Oliver G., Karnaushenko, Daniil

Modification of the magnetic properties under the induced strain and curvature is a promising avenue to build three-dimensional magnetic devices, based on the domain wall motion. So far, most of the studies with 3D magnetic structures were performed in the helixes and nanowires, mainly with stationary domain walls. In this study, we demonstrate the impact of 3D geometry, strain and curvature on the current-induced domain wall motion and spin-orbital torque efficiency in the heterostructure, realized via a self-assembly rolling technique on a polymeric platform. We introduce a complete 3D memory unit with write, read and store functionality, all based on the field-free domain wall motion. Additionally, we conducted a comparative analysis between 2D and 3D structures, particularly addressing the influence of heat during the electric current pulse sequences. Finally, we demonstrated a remarkable increase of 30% in spin-torque efficiency in 3D configuration.

2024, Cheng, Erjian, Yan, Limin, Shi, Xianbiao, Lou, Rui, Fedorov, Alexander, Behnami, Mahdi, Yuan, Jian, Yang, Pengtao, Wang, Bosen, Cheng, Jin-Guang, Xu, Yuanji, Xu, Yang, Xia, Wei, Pavlovskii, Nikolai, Peets, Darren C., Zhao, Weiwei, Wan, Yimin, Burkhardt, Ulrich, Guo, Yanfeng, Li, Shiyan, Felser, Claudia, Yang, Wenge, Büchner, Bernd

The noncentrosymmetric ferromagnetic Weyl semimetal CeAlSi with simultaneous space-inversion and time-reversal symmetry breaking provides a unique platform for exploring novel topological states. Here, by employing multiple experimental techniques, we demonstrate that ferromagnetism and pressure can serve as efficient parameters to tune the positions of Weyl nodes in CeAlSi. At ambient pressure, a magnetism-facilitated anomalous Hall/Nernst effect (AHE/ANE) is uncovered. Angle-resolved photoemission spectroscopy (ARPES) measurements demonstrated that the Weyl nodes with opposite chirality are moving away from each other upon entering the ferromagnetic phase. Under pressure, by tracing the pressure evolution of AHE and band structure, we demonstrate that pressure could also serve as a pivotal knob to tune the positions of Weyl nodes. Moreover, multiple pressure-induced phase transitions are also revealed. These findings indicate that CeAlSi provides a unique and tunable platform for exploring exotic topological physics and electron correlations, as well as catering to potential applications, such as spintronics.

2019, Güttler, M., Generalov, A., Fujimori, S.I., Kummer, K., Chikina, A., Seiro, S., Danzenbächer, S., Koroteev, Y.M., Chulkov, E.V., Radovic, M., Shi, M., Plumb, N.C., Laubschat, C., Allen, J.W., Krellner, C., Geibel, C., Vyalikh, D.V.

Application of the Luttinger theorem to the Kondo lattice YbRh 2 Si 2 suggests that its large 4f-derived Fermi surface (FS) in the paramagnetic (PM) regime should be similar in shape and volume to that of the divalent local-moment antiferromagnet (AFM) EuRh 2 Si 2 in its PM regime. Here we show by angle-resolved photoemission spectroscopy that paramagnetic EuRh 2 Si 2 has a large FS essentially similar to the one seen in YbRh 2 Si 2 down to 1 K. In EuRh 2 Si 2 the onset of AFM order below 24.5 K induces an extensive fragmentation of the FS due to Brillouin zone folding, intersection and resulting hybridization of the Fermi-surface sheets. Our results on EuRh 2 Si 2 indicate that the formation of the AFM state in YbRh 2 Si 2 is very likely also connected with similar changes in the FS, which have to be taken into account in the controversial analysis and discussion of anomalies observed at the quantum critical point in this system.

2019, Borisenko, S., Evtushinsky, D., Gibson, Q., Yaresko, A., Koepernik, K., Kim, T., Ali, M., van den Brink, J., Hoesch, M., Fedorov, A., Haubold, E., Kushnirenko, Y., Soldatov, I., Schäfer, R., Cava, R.J.

Spectroscopic detection of Dirac and Weyl fermions in real materials is vital for both, promising applications and fundamental bridge between high-energy and condensed-matter physics. While the presence of Dirac and noncentrosymmetric Weyl fermions is well established in many materials, the magnetic Weyl semimetals still escape direct experimental detection. In order to find a time-reversal symmetry breaking Weyl state we design two materials and present here experimental and theoretical evidence of realization of such a state in one of them, YbMnBi2. We model the time-reversal symmetry breaking observed by magnetization and magneto-optical microscopy measurements by canted antiferromagnetism and find a number of Weyl points. Using angle-resolved photoemission, we directly observe two pairs of Weyl points connected by the Fermi arcs. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties.

2023, Han, Liuliu, Maccari, Fernando, Soldatov, Ivan, Peter, Nicolas J., Souza Filho, Isnaldi R., Schäfer, Rudolf, Gutfleisch, Oliver, Li, Zhiming, Raabe, Dierk

Fast growth of sustainable energy production requires massive electrification of transport, industry and households, with electrical motors as key components. These need soft magnets with high saturation magnetization, mechanical strength, and thermal stability to operate efficiently and safely. Reconciling these properties in one material is challenging because thermally-stable microstructures for strength increase conflict with magnetic performance. Here, we present a material concept that combines thermal stability, soft magnetic response, and high mechanical strength. The strong and ductile soft ferromagnet is realized as a multicomponent alloy in which precipitates with a large aspect ratio form a Widmanstätten pattern. The material shows excellent magnetic and mechanical properties at high temperatures while the reference alloy with identical composition devoid of precipitates significantly loses its magnetization and strength at identical temperatures. The work provides a new avenue to develop soft magnets for high-temperature applications, enabling efficient use of sustainable electrical energy under harsh operating conditions.

2024, He, Ge, Peis, Leander, Cuddy, Emma Frances, Zhao, Zhen, Li, Dong, Zhang, Yuhang, Stumberger, Romona, Moritz, Brian, Yang, Haitao, Gao, Hongjun, Devereaux, Thomas Peter, Hackl, Rudi

The formation of charge density waves is a long-standing open problem, particularly in dimensions higher than one. Various observations in the vanadium antimonides discovered recently further underpin this notion. Here, we study the Kagome metal CsV3Sb5 using polarized inelastic light scattering and density functional theory calculations. We observe a significant gap anisotropy with 2Δmax/kBTCDW≈20, far beyond the prediction of mean-field theory. The analysis of the A1g and E2g phonons, including those emerging below TCDW, indicates strong phonon-phonon coupling, presumably mediated by a strong electron-phonon interaction. Similarly, the asymmetric Fano-type lineshape of the A1g amplitude mode suggests strong electron-phonon coupling below TCDW. The large electronic gap, the enhanced anharmonic phonon-phonon coupling, and the Fano shape of the amplitude mode combined are more supportive of a strong-coupling phonon-driven charge density wave transition than of a Fermi surface instability or an exotic mechanism in CsV3Sb5.