Simultaneous Development of Antiferromagnetism and Local Symmetry Breaking in a Kagome Magnet (CoFe)Sn.

CoSn and FeSn, two kagome-lattice metals, have recently attracted significant attention as hosts of electronic flat bands and emergent physical properties. However, current understandings of their physical properties are limited to knowledge of the average crystal structure. Here, we report the Fe-doping induced coemergence of the antiferromagentic (AFM) order and local symmetry breaking in (CoFe)Sn.

Large magnon-induced anomalous Nernst conductivity in single-crystal MnBi.

Thermoelectric modules are a promising approach to energy harvesting and efficient cooling. In addition to the longitudinal Seebeck effect, transverse devices utilizing the anomalous Nernst effect (ANE) have recently attracted interest. For high conversion efficiency, it is required that the material have a large ANE thermoelectric power and low electrical resistance, which lead to the conductivity of the ANE.

Direct visualization of anionic electrons in an electride reveals inhomogeneities.

Electrides are an unusual family of materials that feature loosely bonded electrons that occupy special interstitial sites and serve as anions. They are attracting increasing attention because of their wide range of exotic physical and chemical properties. Despite the critical role of the anionic electrons in inducing these properties, their presence has not been directly observed experimentally.

Additive Manufacturing of Isotropic NdFeB PPS Bonded Permanent Magnets.

Extrusion based additive manufacturing of polymer composite magnets can increase the solid loading volume fraction with greater mechanical force through the printing nozzle as compared to traditional injection molding process. About 63 vol% of isotropic NdFeB magnet powders were compounded with 37 vol% of polyphenylene sulfide and bonded permanent magnets were fabricated while using Big Area Additive Manufacturing without any degradation in magnetic properties. The polyphenylene sulfide bonded magnets have a tensile stress of 20 MPa, almost double than that of nylon bonded permanent magnets.

Effect of Oxygen Interstitial Ordering on Multiple Order Parameters in Rare Earth Ferrite.

Oxygen interstitials and vacancies play a key role in modulating the microstructure and properties of nonstoichiometric oxide systems, such as those used for superconductors and multiferroics. Key to understanding the tuning mechanisms resulting from oxygen doping is a knowledge of the precise positions of these lattice defects, and of the interaction both between these defects and with many order parameters. Here, we report how such information can, for the first time, be obtained from a sample of LuFe_{2}O_{4.

Supporting adults to support youth: An evaluation of two social justice trainings.

The current research examined pre- and post survey data in two social justice trainings for adults who support youth, including staff and volunteers (Study 1, N = 44) at youth-serving organizations and adults who mentor young Black men and boys (Study 2, N = 72). We investigate whether training participants' self-report scores of cultural competences (studies 1 and 2), self-efficacy for race equity (Study 1) and racial self-efficacy to support mentee (Study 2) changed between the beginning of the training and after the training. Furthermore, we examine whether the changes depend upon whether training participants share cultural background with the youth with whom they work.

Antisite Pairs Suppress the Thermal Conductivity of BAs.

BAs was predicted to have an unusually high thermal conductivity with a room temperature value of 2000  W m^{-1} K^{-1}, comparable to that of diamond. However, the experimentally measured thermal conductivity of BAs single crystals is still lower than this value. To identify the origin of this large inconsistency, we investigate the lattice structure and potential defects in BAs single crystals at the atomic scale using aberration-corrected scanning transmission electron microscopy (STEM).

Mn-induced Ferromagnetic Semiconducting Behavior with Linear Negative Magnetoresistance in Sr(RuMn)O Single Crystals.

Triple-layered SrRuO is a unique ferromagnet with the central RuO layer behaving differently from two outer layers both crystallographically and magnetically. We report that the partial substitution of Ru by smaller Mn gives rise to modification in crystal structure, electronic and magnetic properties of Sr(RuMn)O. Through the single crystal X-ray diffraction refinement, we find that (Ru/Mn)O octahedral rotation is no longer detectable at x ≥ 0.

Two-channel model for ultralow thermal conductivity of crystalline TlVSe.

Solids with ultralow thermal conductivity are of great interest as thermal barrier coatings for insulation or thermoelectrics for energy conversion. However, the theoretical limits of lattice thermal conductivity (κ) are unclear. In typical crystals a phonon picture is valid, whereas lowest κ values occur in highly disordered materials where this picture fails and heat is supposedly carried by random walk among uncorrelated oscillators.

Competing magnetic ground states and their coupling to the crystal lattice in CuFeGe.

Identifying and characterizing systems with coupled and competing interactions is central to the development of physical models that can accurately describe and predict emergent behavior in condensed matter systems. This work demonstrates that the metallic compound CuFeGe has competing magnetic ground states, which are shown to be strongly coupled to the lattice and easily manipulated using temperature and applied magnetic fields. Temperature-dependent magnetization M measurements reveal a ferromagnetic-like onset at 228 (1) K and a broad maximum in M near 180 K.

Quantum Critical Behavior in a Concentrated Ternary Solid Solution.

The face centered cubic (fcc) alloy NiCoCrx with x ≈ 1 is found to be close to the Cr concentration where the ferromagnetic transition temperature, Tc, goes to 0. Near this composition these alloys exhibit a resistivity linear in temperature to 2 K, a linear magnetoresistance, an excess -TlnT (or power law) contribution to the low temperature heat capacity, and excess low temperature entropy. All of the low temperature electrical, magnetic and thermodynamic properties of the alloys with compositions near x ≈ 1 are not typical of a Fermi liquid and suggest strong magnetic fluctuations associated with a quantum critical region.

Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2.

Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba(1-x)Tl(x)Fe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (T(N) = T(s) = 133 K) increase for x = 0.

Magnetic Ordering in Sr3YCo4O10+x.

Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt's ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3YCo4O10+x (SYCO) has attracted considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism.

Influence of chemical disorder on energy dissipation and defect evolution in concentrated solid solution alloys.

A grand challenge in materials research is to understand complex electronic correlation and non-equilibrium atomic interactions, and how such intrinsic properties and dynamic processes affect energy transfer and defect evolution in irradiated materials. Here we report that chemical disorder, with an increasing number of principal elements and/or altered concentrations of specific elements, in single-phase concentrated solid solution alloys can lead to substantial reduction in electron mean free path and orders of magnitude decrease in electrical and thermal conductivity. The subsequently slow energy dissipation affects defect dynamics at the early stages, and consequentially may result in less deleterious defects.

Room-Temperature Ba(Fe1-x Cox)2 As2 is not Tetragonal: Direct Observation of Magnetoelastic Interactions in Pnictide Superconductors.

Lattice distortions corresponding to Ba displacements with respect to the FeAs sublattice are revealed to break the room-temperature tetragonal symmetry in Ba(Fe1-x Cox)2 As2. The displacements yield twin domains of the size of ≈10 nm. The domain size correlates with the magnitude of the local Fe magnetic moment and its non-monotonic dependence on Co concentration.

Ferromagnetism of Fe3Sn and alloys.

Hexagonal Fe(3)Sn has many of the desirable properties for a new permanent magnet phase with a Curie temperature of 725 K, a saturation moment of 1.18 MA/m. and anisotropy energy, K1 of 1.

Orbital occupancy and charge doping in iron-based superconductors.

The intrinsic Fe local magnetic moment and Fe orbital occupations of iron-based superconductors are unveiled through the local, real-space capability of aberration-corrected scanning transmission electron microscopy/electron energy loss spectroscopy (STEM/EELS). Although the ordering of Fe moments needs to be suppressed for superconductivity to arise, the local, fluctuating Fe magnetic moment is enhanced near optimal superconductivity.

Atomically resolved spectroscopic study of Sr2IrO4: experiment and theory.

Particularly in Sr2IrO4, the interplay between spin-orbit coupling, bandwidth and on-site Coulomb repulsion stabilizes a J(eff) = 1/2 spin-orbital entangled insulating state at low temperatures. Whether this insulating phase is Mott- or Slater-type, has been under intense debate. We address this issue via spatially resolved imaging and spectroscopic studies of the Sr2IrO4 surface using scanning tunneling microscopy/spectroscopy (STM/S).

Local crystallography analysis for atomically resolved scanning tunneling microscopy images.

Scanning probe microscopy has emerged as a powerful and flexible tool for atomically resolved imaging of surface structures. However, due to the amount of information extracted, in many cases the interpretation of such data is limited to being qualitative and semi-quantitative in nature. At the same time, much can be learned from local atom parameters, such as distances and angles, that can be analyzed and interpreted as variations of local chemical bonding, or order parameter fields.

Direct probe of interplay between local structure and superconductivity in FeTe₀.₅₅Se₀.₄₅.

The relationship between atomically defined structures and physical properties in functional materials remains a subject of constant interest. We explore the interplay between local crystallographic structure, composition, and local superconductive properties in iron chalcogenide superconductors. Direct structural analysis of scanning tunneling microscopy data allows local lattice distortions and structural defects across an FeTe0.

Spin reorientation in TlFe1.6Se2 with complete vacancy ordering.

The relationship between vacancy ordering and magnetism in TlFe(1.6)Se(2) has been investigated via single crystal neutron diffraction, nuclear forward scattering, and transmission electron microscopy. The examination of chemically and structurally homogeneous crystals allows the true ground state to be revealed, which is characterized by Fe moments lying in the ab plane below 100 K.

Crystallographic and magnetic phase transitions in the layered ruthenium oxyarsenides TbRuAsO and DyRuAsO.

The crystallographic and physical properties of TbRuAsO and DyRuAsO at and below room temperature are reported, including full structure refinements from powder X-ray diffraction data and measured electrical and thermal transport properties, magnetic susceptibility, and heat capacity. Both compounds are isostructural to LaFeAsO (ZrCuSiAs-type, P4/nmm) at room temperature. However, DyRuAsO undergoes a symmetry-lowering crystallographic phase transition near 25 K, and adopts an orthorhombic structure (Pmmn) below this temperature.

Dielectric-constant-enhanced hall mobility in complex oxides.

The high dielectric constant of doped ferroelectric KTa(1-x)Nb(x)O(3) is shown to increase dielectric screening of electron scatterers, and thus to enhance the electronic mobility, overcoming one of the key limitations in the application of functional oxides. These observations are based on transport and optical measurements as well as band structure calculations.

Formation of collapsed tetragonal phase in EuCo₂As₂ under high pressure.

The structural properties of EuCo₂As₂ have been studied up to 35 GPa, through the use of x-ray diffraction in a diamond anvil cell at a synchrotron source. At ambient conditions, EuCo₂As₂ ) (I4/mmm) has a tetragonal lattice structure with a bulk modulus of 48 ± 4 GPa. With the application of pressure, the a axis exhibits negative compressibility with a concurrent sharp decrease in c-axis length.