R3Au9Pn (R = Y, Gd-Tm; Pn = Sb, Bi): A Link between Cu10Sn3 and Gd14Ag51

A new series of intermetallic compounds R3Au9Pn (R = Y, Gd-Tm; Pn = Sb, Bi) has been discovered during the explorations of the Au-rich parts of rare-earth-containing ternary systems with p-block elements. The existence of the series is strongly restricted by both geometric and electronic factors. R3Au9Pn compounds crystallize in the hexagonal crystal system with space group P63/m (a = 8.08-8.24 \uc5, c = 8.98-9.08 \uc5). All compounds feature Au-Pn, formally anionic, networks built up by layers of alternating edge-sharing Au@Au6 and Sb@Au6 trigonal antiprisms of overall composition Au6/2Pn connected through additional Au atoms and separated by a triangular cationic substructure formed by R atoms. From a first look, the series appears to be isostructural with recently reported R3Au7Sn3 (a ternary ordered derivative of the Cu10Sn3-structure type), but no example of R3Au9M is known when M is a triel or tetrel element. R3Au9Pn also contains Au@Au6Au2R3 fully capped trigonal prisms, which are found to be isostructural with those found in the well-researched R14Au51 series. This structural motif, not present in R3Au7Sn3, represents a previously unrecognized link between Cu10Sn3 and Gd14Ag51 parent structure types. Magnetic property measurements carried out for Ho3Au9Sb reveal a complex magnetic structure characterized by antiferromagnetic interactions at low temperature (TN = 10 K). Two metamagnetic transitions occur at high field with a change from antiferromagnetic toward ferromagnetic ordering. Density functional theory based computations were performed to understand the materials' properties and to shed some light on the stability ranges. This allowed a better understanding of the bonding pattern, especially of the Au-containing substructure, and elucidation of the role of the third element in the stability of the structure type

Experimental Evidence for Static Charge Density Waves in Iron Oxypnictides

In this Letter we report high-resolution synchrotron x-ray powder diffraction and transmission electron microscope analysis of Mn-substituted LaFeAsO samples, demonstrating that a static incommensurate modulated structure develops across the low-temperature orthorhombic phase, whose modulation wave vector depends on the Mn content. The incommensurate structural distortion is likely originating from a charge-density-wave instability, a periodic modulation of the density of conduction electrons associated with a modulation of the atomic positions. Our results add a new component in the physics of Fe-based superconductors, indicating that the density wave ordering is charge driven

Formation, Stability and Magnetism of New Gd3TAl3Ge2 Quaternary Compounds (T = Mn, Cu)

A study on the formation and stability of new quaternary compounds with the general chemical formula Gd3TAl3Ge2 (T = Mn, Cu) has been undertaken by experimental investigations (SEM-EDX, DTA and XRD) and density functional theory (DFT) calculations. These compounds crystallize in the hexagonal Y3NiAl3Ge2-type structure (hP9, P–62m, Z = 1) (an ordered, quaternary derivative of the ternary ZrNiAl or of the binary Fe2P prototypes), with lattice parameters values a = 7.0239(2) Å and c = 4.2580(1) Å for Gd3MnAl3Ge2 and a = 7.0434(1) Å and c = 4.2089(1) Å for Gd3CuAl3Ge2. DTA suggests a peritectic reaction for the formation of these compounds (at 1245°C for Gd3CuAl3Ge2). The existence and stability of these phases has been explained on the basis of DFT calculations, and a comparison of ground state properties of the studied compounds with the earlier known Gd3CoAl3Ge2 phase is outlined. The negative formation energies in all three cases govern the stability of compounds from theory as well, predicting Gd3MnAl3Ge2 as the most stable phase with highest formation energy (–13.01 eV/f.u.). The total DOS are generic in nature and suggest the robust magnetism, with the Gd-f moments of ≈7 μB. An antiparallel coupling among Gd-f and T-d states is observed for all compounds, as usually seen in rare earth (R) - transition metal (T) compounds. Preliminary magnetization measurements on Gd3MnAl3Ge2 show two ferromagnetic/ferrimagnetic (FM/FIM) like transitions at TC1 = 142 K and TC2 = 97 K, with another anomaly seen at ≈15 K. Isothermal magnetization data show no hysteresis even at 5 K, and the magnetization does not saturate up to 50 kOe, further suggesting a possible FIM behavior

Stability, Crystal Chemistry, and Magnetism of U2+xNi21–xB6 and Nb3–yNi20+yB6 and the Role of Uranium in the Formation of the Quaternary U2–zNbzNi21B6 and UδNb3−δNi20B6 Systems

We investigated the U–Ni–B and Nb–Ni–B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of U2Ni21B6 and Nb3–yNi20+yB6 [ternary derivatives of the cubic Cr23C6-type (cF116, Fm3̅m)] have been studied; the formation of the hypothetical “U3Ni20B6” and “Nb2Ni21B6” has been disproved. U2Ni21B6 [a = 10.6701(2) Å] crystallizes in the ordered W2Cr21C6-type, whereas Nb3–yNi20+yB6 [a = 10.5842(1) Å] adopts the Mg3Ni20B6-type. Ni in U2Ni21B6 can be substituted by U, leading to the solid solution U2+xNi21–xB6 (0 ≤ x ≤ 0.3); oppositely, Nb in Nb3Ni20B6 is partially replaced by Ni, forming the solution Nb3–yNi20+yB6 (0 ≤ y ≤ 0.5), none of them reaching the limit corresponding to the hypothetically ordered “U3Ni20B6” and “Nb2Ni21B6”. These results prompted us to investigate quaternary compounds U2–zNbzNi21B6 and UδNb3−δNi20B6: strong competition in the occupancy of the 4a and 8c sites by U, Nb, and Ni atoms has been observed, with the 4a site occupied by U/Ni atoms only and the 8c site filled by U/Nb atoms only. U2Ni21B6, U2.3Ni20.7B6, and Nb3Ni20B6 are Pauli paramagnets. Interestingly, Nb2.5Ni20.5B6 shows ferromagnetism with TC ≈ 11 K; the Curie–Weiss fit gives an effective magnetic moment of 2.78 μB/Ni, suggesting that all Ni atoms in the formula unit contribute to the total magnetic moment. The M(H) data at 2 K further corroborate the ferromagnetic behavior with a saturation moment of 10 μB/fu (≈0.49 μB/Ni). The magnetic moment of Ni at the 4a site induces a moment in all of the Ni atoms of the whole unit cell (32f and 48h sites), with all atoms ordering ferromagnetically at 11 K. Density functional theory (DFT) shows that the formation of U2Ni21B6 and Nb3Ni20B6 is energetically preferred. The various electronic states generating ferromagnetism on Nb2.5Ni20.5B6 and Pauli paramagnetism on U2Ni21B6 and Nb3Ni20B6 have been identified

Unusual magnetic and transport properties in HoMn6_6Sn6_6 kagome magnet

With intricate lattice structures, kagome materials are an excellent platform to study various fascinating topological quantum states. In particular, kagome materials, revealing large responses to external stimuli such as pressure or magnetic field, are subject to special investigation. Here, we study the kagome-net HoMn$_6$Sn$_6$ magnet that undergoes paramagnetic to ferrimagnetic transition (below 376 K) and reveals spin-reorientation transition below 200 K. In this compound, we observe the topological Hall effect and substantial contribution of anomalous Hall effect above 100 K. We unveil the pressure effects on magnetic ordering at a low magnetic field from the pressure tunable magnetization measurement. By utilizing high-resolution angle-resolved photoemission spectroscopy, Dirac-like dispersion at the high-symmetry point K is revealed in the vicinity of the Fermi level, which is well supported by the first-principles calculations, suggesting a possible Chern-gapped Dirac cone in this compound. Our investigation will pave the way to understand the magneto-transport and electronic properties of various rare-earth-based kagome magnets

Investigation on the Power Factor of Skutterudite Sm-y(FexNi1-x)(4)Sb-12 Thin Films: Effects of Deposition and Annealing Temperature

Filled skutterudites are currently studied as promising thermoelectric materials due to their high power factor and low thermal conductivity. The latter property, in particular, can be enhanced by adding scattering centers, such as the ones deriving from low dimensionality and the presence of interfaces. This work reports on the synthesis and characterization of thin films belonging to the Sm-y(FexNi1-x)(4)Sb-12-filled skutterudite system. Films were deposited under vacuum conditions by the pulsed laser deposition (PLD) method on fused silica substrates, and the deposition temperature was varied. The effect of the annealing process was studied by subjecting a set of films to a thermal treatment for 1 h at 423 K. Electrical conductivity sigma and Seebeck coefficient S were acquired by the four-probe method using a ZEM-3 apparatus performing cycles in the 348-523 K temperature range, recording both heating and cooling processes. Films deposited at room temperature required three cycles up to 523 K before being stabilized, thus revealing the importance of a proper annealing process in order to obtain reliable physical data. XRD analyses confirm the previous result, as only annealed films present a highly crystalline skutterudite not accompanied by extra phases. The power factor of annealed films is shown to be lower than in the corresponding bulk samples due to the lower Seebeck coefficients occurring in films. Room temperature thermal conductivity, on the contrary, shows values comparable to the ones of doubly doped bulk samples, thus highlighting the positive effect of interfaces on the introduction of scattering centers, and therefore on the reduction of thermal conductivity

Phases in the Al-Yb-Zn system between 25 and 50 at% Yb

Phases YbZn1-xAlx, YbZn2-xAlx and YbZn3-xAlx were studied by electron microprobe analysis and X-ray single crystal and powder methods. The compound YbZn0.8Al0.2 crystallizes with the CsCl-type, a=3.635(2) \uc5. Four phases were investigated by single crystal X-ray diffraction: YbZn0.996(6)Al1.004(6), MgNi2-type, P63/mmc, a=5.573(1), c=18.051(3) \uc5, Z=8, wR2=0.040 and YbZn0.88(3)Al1.12(3), MgCu2-type, Fd over(3, -) m, a=7.860(2) \uc5, Z=8, wR2=0.060, both showing mixed Zn/Al occupancy; YbZn2.50(1)Al0.50(1), CeNi3-type, P63/mmc, a=5.496(1), c=17.336(2) \uc5, Z=6, wR2=0.036 and YbZn1.92(2)Al1.08(2), PuNi3- or NbBe3-type, R over(3, -) m, a=5.499(1), c=26.134(5) \uc5, Z=9, wR2=0.053, where the zinc atoms are ordered in the CaCu5 segment, while share the sites with aluminium in the Laves phase segment. In the pseudobinary section YbZn2-xAlx four structures occur in sequence with increasing the electron concentration: CeCu2 or KHg2 (x=0-0.3), MgZn2 (x=0.33-0.54), MgNi2 (x=0.68-1.01) and MgCu2 (x=1.12-2). This sequence agrees with the results of first-principles calculations, already reported in the literature for other similar series. In the YbZn3-xAlx section CeNi3-type compounds occur with x=0.40-0.88 followed by PuNi3-type compounds with x=0.92-1.10. The stability ranges of these phases are related to the valence electron concentration

A neutron diffraction study of the R15Ge9C compounds (R = Ce, Pr, Nd)

In this work we report the results of the neutron diffraction investigation performed on the germanides R15Ge9C, for R = Ce, Pr and Nd (La15Ge9Fe-type, hP50, P63mc, Z = 2), to refine the crystal superstructure of these compounds and determine their magnetic structures. The interstitial carbon atoms occupy mainly the 2b Wyckoff site in the position (1/3 2/3 ∼1/2) and also, with a smaller occupancy rate, the Wyckoff site 2a at (0 0 ∼1/2). In the magnetic state, the three compounds display predominantly a ferromagnetic behavior with the propagation vector k = [0 0 0]. These results are in agreement with the magnetization measurements, with TC = 10, 30 and 80 K as Curie temperature of Ce15Ge9C, Pr15Ge9C and Nd15Ge9C, respectively. Ce15Ge9C and Nd15Ge9C present a ferromagnetic alignment of the R moments along the c-axis and an antiferromagnetic spin arrangement within the (a-b) plane. For Pr15Ge9C the ferromagnetic contribution is found within the (a-b) plane, as previously observed for the isotypic compound Tb15Si9C. The carbides crystal structure possesses four inequivalent rare earth sites carrying different magnetic moments, leading to mean values of 0.9 μB/Ce, 1.1 μB/Pr and 2.2 μB/Nd for Ce15Ge9C, Pr15Ge9C and Nd15Ge9C, respectively. The magnetic structures of these R15Ge9C compounds differ strongly from those of their parent R5Ge3 germanides, but present strong similarities with the structures of the R15Si9C compounds. The overall results indicate and confirm the drastic influence of carbon insertion in the rare earth environment

The phase diagram of the Yb-Si system

none4A. Palenzona; P. Manfrinetti; S. Brutti; G. BalducciA., Palenzona; Manfrinetti, Pietro; S., Brutti; G., Balducc