Composite phases have been shown to improve both the thermoelectric efficiency and mechanical properties of materials. Here, we demonstrate an improved thermoelectric figure of merit, power factor, and mechanical properties for the high-temperature p-type Zintl phase Yb 14 MgSb 11 . Composites with 0, 1, 2, 3, 4, 6, and 8 vol % 6−10 μm reduced Fe powder were prepared via a fast, scalable, mechanical milling and spark plasma sintering procedure. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that Fe is not incorporated into the Yb 14 MgSb 11 structure. First-order reversal curves and scanning electron microscopy images show that the Fe inclusions are larger and closer together with increasing Fe content. Thermogravimetric and differential scanning calorimetry show that the composites are stable up to 1273 K. The elastic constants of the 8 vol % Fe composite were measured by resonant ultrasound spectroscopy and show that Yb 14 MgSb 11 becomes stiffer with increasing Fe volume % and SEM after indentations show crack arresting occurs at the Fe interface. Thermoelectric properties on dense pellets are measured from 300 K − 1273 K. The thermoelectric power factor (PF = S 2 /ρ) increases with increasing Fe content, with the 8 vol % Fe resulting in 40% higher PF than pristine Yb 14 MgSb 11 . The increase in PF is attributed to a systematic reduction in electrical resistivity. Peak thermoelectric figure of merit [zT = (S 2 T)/(κρ)] is observed at 3 vol % Fe, an 11% improvement in zT compared to Yb 14 MgSb 11 . Yb 14 MgSb 11 composites with Fe are compatible with Ce 0.9 Fe 3.5 Co 0.5 Sb 12 for thermoelectric generator couple segmentation. KEYWORDS: composite, thermoelectric, transport properties, Zintl phase, SPS synthesis, first-order reversal curves PFS 2 =ρ by band structure engineering, such as band convergence, tuning the electronic states with resonance levels, or simple substitutional alloying. There has also been significant research

Two-dimensional (2D) magnetic van der Waals materials provide a powerful platform for studying the fundamental physics of low-dimensional magnetism, engineering novel magnetic phases, and enabling thin and highly tunable spintronic devices. To realize high-quality and practical devices for such applications, there is a critical need for robust 2D magnets with ordering temperatures above room temperature that can be created via exfoliation. Here, the study of exfoliated flakes of cobalt-substituted Fe 5 GeTe 2 (CFGT) exhibiting magnetism above room temperature is reported. Via quantum magnetic imaging with nitrogen-vacancy centers in diamond, ferromagnetism at room temperature was observed in CFGT flakes as thin as 16 nm corresponding to 16 layers. This result expands the portfolio of thin roomtemperature 2D magnet flakes exfoliated from robust single crystals that reach a thickness regime relevant to practical spintronic applications. The Curie temperature T c of CFGT ranges from 310 K in the thinnest flake studied to 328 K in the bulk. To investigate the prospect of high-temperature monolayer ferromagnetism, Monte Carlo calculations were performed, which predicted a high value of T c of ∼270 K in CFGT monolayers. Pathways toward further enhancing monolayer T c are discussed. These results support CFGT as a promising platform for realizing high-quality room-temperature 2D magnet devices.

Interconnected magnetic nanowire (NW) networks offer a promising platform for three-dimensional (3D) information storage and integrated neuromorphic computing. Here we report discrete propagation of magnetic states in interconnected Co nanowire networks driven by magnetic field and current, manifested in distinct magnetoresistance (MR) features. In these networks, when only a few interconnected NWs were measured, multiple MR kinks and local minima were observed, including a significant minimum at a positive field during the descending field sweep. Micromagnetic simulations showed that this unusual feature was due to domain wall (DW) pinning at the NW intersections, which was confirmed by off-axis electron holography imaging. In a complex network with many intersections, sequential switching of nanowire sections separated by interconnects was observed, along with stochastic characteristics. The pinning/depinning of the DWs can be further controlled by the driving current density. These results illustrate the promise of such interconnected networks as integrated multistate memristors.

The rapid rise of atmospheric CO2 has spurred keen research interest in sustainable energy technologies including thermoelectric materials which can reliably and robustly turn heat directly to electricity. Yb14MnSb11 has been the material of intense study because of its high thermoelectric figure of merit, zT. A structural analogue, Yb14MgSb11, is also of interest as it has a higher average zT ( ) and a comparable peak zT (1.3 vs 1.2) to Yb14MnSb11. We have shown that Yb14MgSb11 can be composited with micron-sized iron particles with significant improvements to the thermoelectric power factor (PF) and mechanical properties. In this work, we successfully employ a rapid high-temperature in situ reaction to create well-dispersed nanoscale (<100 nm) iron inclusions in the bulk Yb14MgSb11 matrix via the decomposition of FeSb2 into Fe and Sb. The incorporation of nanoscale iron into Yb14MgSb11 further reduces the lattice thermal conductivity (κl), when compared to the previously published micron iron composites, due to an increase in phonon scattering. As a result of the synchronous decrease in thermal conductivity and resistivity, the 7.3 vol % Fe sample retains the zT of Yb14MgSb11 while achieving a 43% PF improvement.

The spin-momentum locking of surface states in topological materials can produce a resistance that scales linearly with magnetic and electric fields. Such a bilinear magnetoelectric resistance (BMER) effect offers a new approach for information reading and field sensing applications, but the effects demonstrated so far are too weak or for low temperatures. This article reports the first observation of BMER effects in topological Dirac semimetals; the BMER responses were measured at room temperature and were substantially stronger than those reported previously. The experiments used topological Dirac semimetal α-Sn thin films grown on silicon substrates. The films showed BMER responses that are 10 6 times larger than previously measured at room temperature and are also larger than those previously obtained at low temperatures. These results represent a major advance toward realistic BMER applications. Significantly, the data also yield the first characterization of three-dimensional Fermi-level spin texture of topological surface states in α-Sn.

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