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The metal borides, Hf 2 MOs 5 B 2 (M = Mn, Fe, Co), which are the first Os-rich quaternary variants of the prolific Ti 3 Co 5 B 2 structure type, were investigated computationally and experimentally. In their crystal structures, osmium builds a network of prisms, in which the other elements are located. The magnetic M elements are found in face-connected Os 8 square prisms leading to M-chains with intra- and interchain distances of about 3.0 and 6.5 Å, respectively. Density functional theory (DFT) showed that magnetic ordering is hugely favored for M = Mn and Fe but only slightly favored for M = Co. Experimental investigations then confirmed and extended the DFT predictions as a metamagnetic behavior was found for the M = Mn and Fe phases, whereby the antiferromagnetic interactions ( T N = 19 and 90 K) found at low magnetic fields change to ferromagnetic at higher fields. A very broad transition ( T N = 45 K) is found for M = Co, suggesting spin-glass behavior for this phase. For M = Fe, a hard-magnet hysteresis at 5 K is found with a 40 kA/m coercivity, and even at room temperature, a significant hysteresis is found. This study paves the way for the discovery of Os-based magnets in this structure type and other intermetallics.

The complex metal-rich boride Ti 5- x Fe 1- y Os 6+ x+y B 6 (0 < x , y < 1), crystallizing in a new structure type (space group Cmcm , no. 63), was prepared by arc-melting. The new structure contains both isolated boron atoms and zigzag boron chains (B-B distance of 1.74 Å), a rare combination among metal-rich borides. In addition, the structure also contains Fe-chains running parallel to the B-chains. Unlike in previously reported structures, these Fe-chains are offset from each other and arranged in a triangular manner with intrachain and interchain distances of 2.98 and 6.69 Å, respectively. Density functional theory (DFT) calculations predict preferred ferromagnetic interactions within each chain but only small energy differences for different magnetic interactions between them, suggesting a potentially weak long-range order. This new structure offers the opportunity to study new configurations and interactions of magnetic elements for the design of magnetic materials.

Materials "design" is increasingly gaining importance in the solid-state materials community in general and in the field of magnetic materials in particular. Density functional theory (DFT) predicted the competition between ferromagnetic (FM) and antiferromagnetic (AFM) ground states in a ruthenium-rich Ti 3 Co 5 B 2 -type boride (Hf 2 MnRu 5 B 2 ) for the first time. Vienna ab initio simulation package (VASP) total energy calculations indicated that the FM model was marginally more stable than one of the AFM models (AFM1), indicating very weak interactions between magnetic 1D Mn chains that can be easily perturbated by external means (magnetic field or composition). The predicted phase was then synthesized by arc-melting and characterized as Hf 2 Mn 1-x Ru 5+x B 2 (x = 0.27). Vibrating-scanning magnetometry shows an AFM ground state with T N ≈ 20 K under low magnetic field (0.005 T). At moderate-to-higher fields, AFM ordering vanishes while FM ordering emerges with a Curie temperature of 115 K. These experimental outcomes confirm the weak nature of the interchain interactions, as predicted by DFT calculations.

Na 2 Au 3 Al, the first experimentally prepared compound in the ternary Na-Au-Al system, crystallizes in the cubic crystal system with space group P4 1 32 (a = 771.42(2) pm). It can be described as a P-centered ternary ordered variant of the F-centered Laves phase MgCu 2 and is isostructural to Mo 3 Al 2 C. A phase width was found for the series Na 2 Au 4-x Al x allowing a successive substitution of Au by Al. The primitive structure forms for x ≥ 0.5. Na 2 Au 3 Al is diamagnetic at room temperature but metallic in nature, as seen from susceptibility and electrical resistivity measurements. Band structure calculations and X-ray photoelectron spectroscopy confirm the metallic nature of the title compound as states are found at the Fermi level of the DOS, along with its "auride" character. 23 Na and 27 Al solid-state-NMR investigations show the existence of both a disordered (x = 0.5 and 0.75) and a fully ordered (x = 1.0) representative within this series. Both COHP and Bader charge analyses suggest the presence of strong Au-Al interactions forming an anionic [Au 3 Al] δ- network, with the Na cations occupying the cavities.

The new quaternary boride series FeRh 6-n Ru n B 3 (n = 1-5) was synthesized by arc melting and characterized by powder and single-crystal X-ray diffraction (XRD), energy-dispersive X-ray analysis, and superconducting quantum interference device magnetometry. Single-crystal structure refinement showed the distribution of the iron atoms in two of three possible crystallographic 4d metal sites in the structure (Th 7 Fe 3 -type, space group P6 3 mc). Rietveld refinements of the powder XRD data indicated single-phase synthesis of all the members. A linear decrease of the lattice parameters and the unit cell volume with increasing Ru content was found, indicating Vegard's behavior. Susceptibility measurements show decreasing Curie temperature and magnetic moment (μ a ) recorded at 5 T with increasing Ru content from T 5T ) recorded at 5 T with increasing Ru content from T C = 295 K and μ a 5T = 3.35 μ B ) to T 5 RuB 3 ) to T C = 205 K and μ a 5T = 0.70 μ B (FeRhRu 5 B 3 ). The measured coercivities lie between 1.0 and 2.2 kA/m indicating soft to semihard magnetic materials.

The intermetallic compound EuAu3Al2 has been prepared by reaction of the elements in tantalum ampules. The structure was refined from single-crystal data, indicating that the title compound crystallizes in the orthorhombic crystal system (a = 1310.36(4), b = 547.87(1), c = 681.26(2) pm) with space group Pnma (wR2 = 0.0266, 1038 F(2) values, 35 parameters) and is isostructural to SrAu3Al2 (LT-SrZn5 type). Full ordering of the gold and aluminum atoms was observed. Theoretical calculations confirm that the title compound can be described as a polar intermetallic phase containing a polyanionic [Au3Al2](δ-) network featuring interconnected strands of edge-sharing [AlAu4] tetrahedra. Magnetic measurements and (151)Eu Mössbauer spectroscopic investigations confirmed the divalent character of the europium atoms. Ferromagnetic ordering below TC = 16.5(1) K was observed. Heat capacity measurements showed a λ-type anomaly at T = 15.7(1) K, in line with the ordering temperature from the susceptibility measurements. The magnetocaloric properties of EuAu3Al2 were determined, and a magnetic entropy of ΔSM = -4.8 J kg(-1) K(-1) for a field change of 0 to 50 kOe was determined. Band structure calculations found that the f-bands of Eu present at the Fermi level of non-spin-polarized calculations are responsible for the ferromagnetic ordering in this phase, whereas COHP chemical bonding coupled with Bader charge analysis confirmed the description of the structure as covalently bonded polyanionic [Au3Al2](δ-) network interacting ionically with Eu(δ+).

Spin-frustrated chains of Cr3 triangles are found in the new metal boride TiCrIr2B2 by synergistic experimental and theoretical investigations. Although magnetic ordering is found at 275 K, competing ferro- and anti-ferromagnetic interactions coupled with spin frustration induce a rather small total magnetic moment (0.05 μB at 5 T), and density functional theory (DFT) calculations propose a canted, nonlinear magnetic ground-state ordering in the new phase. TiCrIr2B2 crystallizes in the hexagonal Ti1+xOs2-xRuB2 structure type (space group P6̅2m, No. 189, Pearson symbol hP18). The structure contains trigonal planar B4 boron fragments with B-B distances of 1.76(3) Å alternating along the c-direction with Cr3 triangles with intra- and intertriangle Cr-Cr distances of 2.642(9) and 3.185(1) Å, respectively. Magnetization measurements of TiCrIr2B2 reveal ferrimagnetic behavior and a large, negative Weiss constant of -750 K. DFT calculations demonstrate a strong site preference of Cr for the triangle sites, as well as magnetic frustration due to indirect anti-ferromagnetic interactions within the Cr3 triangles.

Ba3Pt4Al4 was prepared from the elements in niobium ampules and crystallizes in an orthorhombic structure, space group Cmcm (oP44, a = 1073.07(3), b = 812.30(3), c = 1182.69(3) pm) isopointal to the Zintl phase A2Zn5As4 (A = K, Rb). The structure features strands of distorted [Pt4Al4] heterocubane-like units connected by condensation over Pt/Al edges. These are arranged in a hexagonal rod packing by further condensation over Pt and Al atoms with the barium atoms located inside cavities of the [Pt4Al4](δ-) framework. Structural relaxation confirmed the electronic stability of the new phase, while band structure calculations indicate metallic behavior. Crystal orbital Hamilton bonding analysis coupled with Bader effective charge analysis suggest a polar intermetallic phase in which strong Al-Pt covalent bonds are present, while a significant electron transfer from Ba to the [Pt4Al4](δ-) network is found. By X-ray photoelectron spectroscopy measurements the Pt 4f5/2 and 4f7/2 energies for Ba3Pt4Al4 were found in the range of those of elemental Pt due to the electron transfer of Ba, while PtAl and PtAl2 show a pronounced shift toward a more cationic platinum state. (27)Al magic-angle spinning NMR investigations verified the two independent crystallographic Al sites with differently distorted tetrahedrally coordinated [AlPt4] units. Peak assignments could be made based on both geometrical considerations and in relation to electric field gradient calculations.

Analysis of the electronic density of states of the hypothetical ternary double-perovskite-like phases "Sc2T6B (T = Ir, Pd, Ni)" reveals the presence of deep and large pseudogaps between 61 and 68 valence electrons (VE) as well as a strong peak at 69 VEs. Subsequently, crystal orbital Hamilton population (COHP) bonding analysis shows that the heteroatomic T-B and Sc-T interactions are optimized in Sc2Ir6B (63 VE) but not in "Sc2Pd6B (69 VE)" and "Sc2Ni6B (69 VE)", thus indicating less stability for these VE-richer phases. These findings point out the possibility of discovering new double-perovskite-like borides through chemical substitution and lead to the study of the Sc2Ir6-xPdxB and Sc2Ir6-xNixB (x = 0-6; VE = 63-69) series, for which powder samples and single crystals were synthesized by arc melting the elements. Superstructure reflections were observed in the powder diffractograms of Sc2Ir6-xPdxB and Sc2Ir6-xNixB for x = 0-5 and VE = 63-68, thereby showing that these phases crystallize in the double-perovskite-like Ti2Rh6B-type structure (space group Fm3̅m, Z = 4). Single-crystal and Rietveld refinement results confirm and extend these findings because Pd (or Ni) is found to mix exclusively with Ir in all quaternary compositions. For x = 6, no superstructure reflections were observed, in accordance with the theoretical expectation for the 69 VE phases.