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• Polycrystalline β -FeB sample with zigzag boron chains substructure was fabricated by high pressure and high temperature. • β -FeB exhibits high saturation magnetization, good antioxidant capacity, high hardness and low resistivity. • Majority spin state electrons are the main participants in electrons transfer and bonding between Fe and zigzag boron chains. • Spin-selective electrons transfer effect in TMBs can effectively modulate the hardness, magnetism and conductivity. Complex boron substructures lead to diversity properties for transition metal borides (TMBs), that provides them many application possibilities in numerous fields. To clarify the actual effect of boron substructures on mechanical, magnetic and electrical properties, we prepared polycrystalline β -FeB samples with zigzag boron chains by high pressure and high temperature. β -FeB exhibits high saturation magnetization (79.54 emu/g), good antioxidant capacity (> 800 K), high hardness (15.62 GPa) and low resistivity (3.4 × 10−6 Ω m); thus, it is a promising magnetic material for extreme environmental applications. Subsequently, we performed first-principle calculations combined with X-ray photoelectron spectroscopy analysis and found that the free electrons transferred from Fe atoms stabilize the zigzag boron chains. Spin selection occurs during electron transfer and bonding, with majority spin state electrons as the main participants. The zigzag boron chain substructure provides excellent mechanical properties, at the expense of electrical and magnetic properties. Therefore, we speculate that the spin-selective electrons transfer between the metal and boron substructure can effectively modulate the electrical, mechanical, and magnetic properties of TMBs. This study introduces an effective route for the design, preparation, and applications of high-hardness multifunctional TMBs. [ABSTRACT FROM AUTHOR]

Higher boron concentration is generally recognized as the most direct method to improve the hardness of transition metal borides. Here, we report the synthesis of manganese tetraboride, a recently proposed superhard candidate, by high pressure and high temperature solid state reaction. Hardness measurement of MnB 4 yields an asymptotic hardness value of 20.1 GPa. The measured asymptotic hardness value of MnB 4 is far higher than that of low boron concentration manganese borides counterparts. On the basis the results of XPS and first principle calculations, the stabilization of this three-dimensional diamond-like boron net analogue is intimately related to the fact that B− ions are electronic isostructure to the carbon atoms in diamond. In addition, the atomic radius of transition metals, R TM , is relevant to the formation of B24 and B12 boron cages in transition metal dodecaborides and tetraborides, respectively. Given the crystal structure and bond configuration, its high hardness originates from its diamond-like boron net analogues frameworks which indicate its strong covalent feature. Unlabelled Image • Boron-rich transition metal tetraboride with three-dimensional boron cages was fabricated by high pressure and high temperature method. • The hardness value of MnB 4 is far higher than that of low boron concentration manganese borides counterparts because of its diamond-like boron net analogues frameworks. • Three-dimensional diamond-like boron net analogue is intimately related to the fact that B- ions are electronic isostructure to the carbon atoms in diamond • Transition metal with large R TM adopts B24 boron cages in dodecaborides and transition metal with small R TM will crystallize in B12 boron cages in tetraborides. [ABSTRACT FROM AUTHOR]