Intrinsic, two-dimensional (2D) ferromagnetic semiconductors are an important class of materials for spin-charge conversion applications. Cr$_2$Ge$_2$Te$_6$ retains long-range magnetic order in bilayer at cryogenic temperatures and shows complex magnetic interactions with considerable magnetic anisotropy. Here, we performed a series of structural, magnetic, X-ray scattering, electronic, thermal transport and first-principles calculation studies which reveal that localized electronic charge carriers in Cr$_2$Ge$_2$Te$_6$ are dressed by surrounding lattice and are involved in polaronic transport via hopping that is sensitive on details of magnetocrystalline anisotropy. This opens possibility for manipulation of charge transport in Cr$_2$Ge$_2$Te$_6$ - based devices by electron-phonon- and spin-orbit coupling-based tailoring of polaron properties.
Iron antimonide (FeSb$_2$) is a mysterious material with peculiar colossal thermopower of about $-45$ mV/K at 10 K. However, a unified microscopic description of this phenomenon is far from being achieved. The understanding of the electronic structure in details is crucial in identifying the microscopic mechanism of FeSb$_2$ thermopower. Combining angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations we find that the spectrum of FeSb$_2$ consists of two bands near the Fermi energy: the nondispersive strongly renormalized $\alpha$-band, and the hole-like $\beta$-band that intersects the first one at $\Gamma$ and Y points of the Brillouin zone. Our study reveals the presence of sizable correlations, predominantly among electrons derived from Fe-3d states, and considerable anisotropy in the electronic structure of FeSb$_2$. These key ingredients are of fundamental importance in the description of colossal thermopower in FeSb$_2$.
We present a systematical study on single crystalline FeSb2 using electrical transport and magnetic torque measurements at low temperatures. Nonlinear magnetic field dependence of Hall resistivity demonstrates a multi-carrier transport instinct of the electronic transport. Current-controlled negative differential resistance (CC-NDR) observed in current–voltage characteristics below ~ 7 K is closely associated with the intrinsic transition ~ 5 K of FeSb2, which is, however, mediated by extrinsic current-induced Joule heating effect. The antimony crystallized in a preferred orientation within the FeSb2 lattice in the high-temperature synthesis process leaves its fingerprint in the de Haas-Van Alphen (dHvA) oscillations, and results in the regular angular dependence of the oscillating frequencies. Nevertheless, possible existence of intrinsic non-trivial states cannot be completely ruled out. Our findings call for further theoretical and experimental studies to explore novel physics on flux-free grown FeSb2 crystals.
In all Fe superconductors the maximal $T_c$ correlates with the average anion height above the Fe plane, i.e. with the geometry of the FeAs$_4$ or FeCh$_4$ (Ch = Te, Se, S) tetrahedron. By synthesizing FeSe$_{1-x}$S$_x$ (0 $\leq$ x $\leq$ 1) single crystal alloys and by performing a series of experiments we find that $T_c$ does scale with the average anion height for $x$ in the presence of nematic order and near FeS, whereas superconductivity changes for all other $x$ track local crystallographic disorder and disorder-related scattering. Our findings demonstrate the strong coupling between disorder and $T_c$ as $x$ is tuned beyond the nematic critical point (NCP) and provide evidence of a $T_c$ tuning mechanism related to local bond disorder.
We report a magnetotransport study on type-II Weyl semimetal ${\mathrm{WP}}_{2}$ single crystals. Magnetoresistance exhibits a nonsaturating ${H}^{n}$ field dependence (14 300% at 2 K and 9 T), whereas systematic violation of Kohler's rule was observed. Quantum oscillations reveal a complex multiband electronic structure. The cyclotron effective mass close to the mass of free electron ${m}_{e}$ was observed in quantum oscillations along the $b$ axis, while a reduced effective mass of about $0.5{m}_{e}$ was observed in $a$-axis quantum oscillations, suggesting Fermi surface anisotropy. The temperature dependence of the resistivity shows a large upturn that cannot be explained by the multiband magnetoresistance of conventional metals. Even though the crystal structure of ${\mathrm{WP}}_{2}$ is not layered as in transition-metal dichalcogenides, quantum oscillations suggest partial two-dimensional character.
We present simultaneous suppression of FeSb2 thermal conductivity and electronic correlations in Fe1−xRuxSb2 (0 ≤x≤ 0.6) single crystal alloys. Small energy gap Δ1 in Kondo-insulator-like semiconductor FeSb2 associated with impurity in-gap state increases whereas the intrinsic bandgap Δ2 decreases upon Ru substitution on Fe atomic site. Thermopower is suppressed along with the intrinsic bandgap and with the thermal conductivity. The more delocalized 4d character of atomic orbital of Ru brings suppression of electronic correlations, but also an increase in impurity density which reduces phonon mean free path and surface scattering length. Our results indicate a range of Ru doping x where nanostructuring could be used to suppress thermal conductivity further, potentially toward the amorphous limit.
The structure and magnetic properties of MnCoSi1− x Px (x = 0.05–0.50) are systematically investigated. With P content increasing, the lattice parameter a increases monotonically while both b and c decrease. At the same time, the temperature of metamagnetic transition from a low-temperature non-collinear ferromagnetic state to a high-temperature ferromagnetic state decreases and a new magnetic transition from a higher-magnetization ferromagnetic state to a lower-magnetization ferromagnetic state is observed in each of these compounds for the first time. This is explained by the changes of crystal structure and distance between Mn and Si atoms with the increase of temperature according to the high-temperature XRD result. The metamagnetic transition is found to be a second-order magnetic transition accompanied by a low inversed magnetocaloric effect (1.0 Jkg−1K−1 at 5 T) with a large temperature span (190 K at 5 T) compared with the scenario of MnCoSi. The changes in the order of metamagnetic transition and structure make P-doped MoCoSi compounds good candidates for the study of magnetoelastic coupling and the modulation of magnetic phase transition.
Transition metal dichalcogenides attract considerable attention due to a variety of interesting properties, including long-range magnetism in nanocrystals. Here we investigate the magnetic, thermal, and electrical properties of an ${\mathrm{FeTe}}_{2}$ single crystal with iron vacancy defects. Magnetic measurements show a paramagnetic state and the absence of magnetic order with low anisotropy in the magnetic susceptibility. Fe $3d$ orbitals are well hybridized, contributing to the bad metal electrical resistivity. Observed thermal conductivity values below room temperature are rather low and comparable to those of high-performance thermoelectric materials. Our results indicate that ${\mathrm{FeTe}}_{2}$ can form in a highly defective marcasite crystal structure which can be exploited in future materials design.
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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