Itinerant Magnetism in Hydride-Synthesized CaCo₁₂B₆

A new compound in the underexplored Ca-Co-B phase space has been discovered, validating high-throughput computations from the Open Quantum Materials Database, which predicted thermodynamic stability for CaCo₁₂B₆ in the SrNi₁₂B₆ structure type. The synthetic effects of different boron precursors and the advantages of using CaH₂ instead of Ca metal were demonstrated by the short synthesis duration and high purity of CaCo₁₂B₆, in contrast with traditional synthesis routes. Powder X-ray diffraction (PXRD) confirmed that CaCo₁₂B₆ shares the SrNi₁₂B₆ structure (R3̅m (#166), a = 9.469(4) Å, c = 7.468(2) Å, Z = 3) and is water- and air-stable. High-temperature in situ PXRD indicates that CaCo₁₂B₆ is stable below 1050 K under vacuum in a silica capillary. CaCo₁₂B₆ decomposes between 693 and 773 K during spark-plasma sintering. Density functional theory calculations indicate that CaCo₁₂B₆ is metallic with a ferromagnetic ground state. X-ray absorption near-edge spectroscopy and Bader charge analysis indicate that Co atoms in CaCo₁₂B₆ lack ionic character. Magnetometry reveals room-temperature paramagnetism with μ_eff = 1.7(1)μ_B per Co atom and a Weiss constant of +190(10)K. Ferromagnetic ordering occurs below 172(1)K, resulting in a saturation moment of 0.46 μ_B per Co atom. Our findings demonstrate that the hydride route is a viable strategy for discovery of new ternary alkaline-earth-transition metal borides analogous to rare-earth-containing counterparts.