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The quinary members in the solid solution Hf2Fe1−δRu5−xIrx+δB2 (x=1–4, VE=63–66) have been investigated experimentally and computationally. They were synthesized via arc‐melting and analyzed by EDX and X‐ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro‐ and antiferromagnetism arising from interchain Fe−Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness for x=1 and 3 and the highest for x=2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering (TN=55–70 K) found at low magnetic fields changed to ferromagnetic (TC=150–750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf2FeRu3Ir2B2 has the highest intrinsic coercivity (Hc=74 kA/m) reported to date for Ti3Co5B2‐type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf2FeIr5B2, indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members (x=1 and 4) maintain intrinsic coercivities in the semi‐hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low‐dimensional rare‐earth‐free magnetic materials. [ABSTRACT FROM AUTHOR]

Transition‐metal borides (TMBs) containing Bn‐fragment (n>3) have recently gained interest for their ability to enable exciting magnetic materials. Herein, we show that the B4‐containing TiFe0.64(1)Os2.36(1)B2 is a new ferromagnetic TMB with a Curie temperature of 523(2) K and a Weiss constant of 554(3) K, originating from the chain of M3‐triangles (M=64 %Fe+36 %Os). The new phase was synthesized from the elements by arc‐melting, and its structure was elucidated by single‐crystal X‐ray diffraction. It belongs to the Ti1+xOs2−xRuB2‐type structure (space group P6‾ 2 m, no. 189) and contains trigonal‐planar B4 boron fragments [B−B distance of 1.87(4) Å] interacting with M3‐triangles [M–M distances of 2.637(8) Å and 3.0199(2) Å]. The experimental results were supported by computational calculations based on the ideal TiFeOs2B2 composition, which revealed strong ferromagnetic interactions within and between the Fe3‐triangles. This discovery represents the first magnetically ordered Os‐rich TMB, thus it will help expand our knowledge of the role of Os in low‐dimensional magnetism of intermetallics and enable the design of such materials in the future. [ABSTRACT FROM AUTHOR]

Metal‐rich borides with the Ti3Co5B2‐type structure represent an ideal playground for tuning magnetic interactions through chemical substitutions. In this work, density functional theory (DFT) and experimental studies of Ru‐rich quaternary borides with the general composition A2MRu5B2 (A=Zr, Hf, M=Fe, Mn) are presented. Total energy calculations show that the phases Zr2FeRu5B2 and Hf2FeRu5B2 prefer ground states with strong antiferromagnetic (AFM) interactions between ferromagnetic (FM) M‐chains. Manganese substitution for iron lowers these antiferromagnetic interchain interactions dramatically and creates a strong competition between FM and AFM states with a slight preference for AFM in Zr2MnRu5B2 and for FM in Hf2MnRu5B2. Magnetic property measurements show a field dependence of the AFM transition (TN): TN is found at 0.1 T for all phases with predicted AFM states whereas for the predicted FM phase it is found at a much lower magnetic field (0.005 T). Furthermore, TN is lowest for a Hf‐based phase (20 K) and highest for a Zr‐based one (28 K), in accordance with DFT predictions of weaker AFM interactions in the Hf‐based phases. Interestingly, the AFM transitions vanish in all compounds at higher fields (>1 T) in favor of FM transitions, indicating metamagnetic behaviors for these Ru‐rich phases. [ABSTRACT FROM AUTHOR]

Four new MPtAl2 (M=Ca, Sr, Ba, Eu) compounds, adopting the orthorhombic MgCuAl2‐type structure, have been synthesized from the elements using tantalum ampoules. All compounds are obtained as platelet‐shaped crystallites and exhibit an increasing moisture sensitivity with increasing size of the formal M cation. Structural investigations indicate a pronounced elongation of the crystallographic b‐axis, which results in a significant distortion of the [PtAl2]δ− polyanion. Within the polyanion, layer‐like arrangements can be found with bonding Pt−Al interactions within the slab; the increase of the b‐axis can be attributed to increasing Al−Al distances and therefore decreasing interactions between the slabs, caused by the differently‐sized formal M cations. While the alkaline earth (M=Ca, Sr) representatives exhibit Pauli paramagnetism, BaPtAl2 shows diamagnetic behavior, finally EuPtAl2 is ferromagnetic with TC=54.0(5) K. The effective magnetic moment indicates that the Eu atoms are in a divalent oxidation state, which is confirmed by 151Eu Mössbauer spectroscopic investigations. Measurements below the Curie‐temperature show a full magnetic hyperfine field splitting with Bhf=21.7(1) T. 27Al and 195Pt magic‐angle spinning NMR spectroscopy corroborates the presence of single crystallographic sites for the Pt and Al atoms. The large 27Al nuclear electric quadrupolar coupling constants confirm unusually strong electric field gradients, in agreement with the structural distortions and the respective theoretical calculations. X‐ray photoelectron spectroscopy has been utilized to investigate the charge transfer within the polyanion. The Pt 4f binding energy decreases with decreasing electronegativity / ionization energy of the alkaline earth elements, suggesting an increasing electron density at the Pt atoms. Theoretical investigations underline the platinide character of the investigated compounds by Bader charge calculations. The analysis of the integrated crystal orbital Hamilton population (ICOHP) values, electron localization function (ELF) and isosurface analyses lead to a consistent structural picture, indicating stable layer‐like arrangements of the [PtAl2]δ− polyanion. [ABSTRACT FROM AUTHOR]

The quinary members in the solid solution Hf2Fe1−δRu5−xIrx+δB2 (x=1–4, VE=63–66) have been investigated experimentally and computationally. They were synthesized via arc‐melting and analyzed by EDX and X‐ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro‐ and antiferromagnetism arising from interchain Fe−Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness for x=1 and 3 and the highest for x=2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering (TN=55–70 K) found at low magnetic fields changed to ferromagnetic (TC=150–750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf2FeRu3Ir2B2 has the highest intrinsic coercivity (Hc=74 kA/m) reported to date for Ti3Co5B2‐type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf2FeIr5B2, indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members (x=1 and 4) maintain intrinsic coercivities in the semi‐hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low‐dimensional rare‐earth‐free magnetic materials. [ABSTRACT FROM AUTHOR]

Transition‐metal borides (TMBs) containing Bn‐fragment (n>3) have recently gained interest for their ability to enable exciting magnetic materials. Herein, we show that the B4‐containing TiFe0.64(1)Os2.36(1)B2 is a new ferromagnetic TMB with a Curie temperature of 523(2) K and a Weiss constant of 554(3) K, originating from the chain of M3‐triangles (M=64 %Fe+36 %Os). The new phase was synthesized from the elements by arc‐melting, and its structure was elucidated by single‐crystal X‐ray diffraction. It belongs to the Ti1+xOs2−xRuB2‐type structure (space group P6‾ 2 m, no. 189) and contains trigonal‐planar B4 boron fragments [B−B distance of 1.87(4) Å] interacting with M3‐triangles [M–M distances of 2.637(8) Å and 3.0199(2) Å]. The experimental results were supported by computational calculations based on the ideal TiFeOs2B2 composition, which revealed strong ferromagnetic interactions within and between the Fe3‐triangles. This discovery represents the first magnetically ordered Os‐rich TMB, thus it will help expand our knowledge of the role of Os in low‐dimensional magnetism of intermetallics and enable the design of such materials in the future. [ABSTRACT FROM AUTHOR]