UC Riverside

Theoretical screening of hypothetical compounds based on a known structure type is a promising approach to facilitate the design of new materials in solid-state chemistry. Electronic structure calculation on Ti3Co5B2 structure type ternaries yields a large pseudo-gap at the Fermi level in the density of states (DOS) plot, indicating electronic stability and offers the possibility of tuning the Fermi level via chemical substitutions to derive new isostructural phases. Following this pathway, new promising magnetic materials in this structure type were first predicted by DFT, then prepared by high-temperature synthetic techniques, and finally characterized by X-ray diffraction, EDX analysis, and magnetic measurements.

Total energy calculations by Vienna Ab initio simulation package (VASP) for the quaternary Hf2MnRu5B2 predicted a competition for antiferro- and ferromagnetic states in a ruthenium-rich compound of this structure type for the first time. Temperature-dependent magnetization measurements of this compound showed an antiferromagnetic transition at a low magnetic field (0.005 T), whereas dominating ferromagnetic interactions observed at higher fields confirmed the competition between antiferro- and ferromagnetic states predicted by VASP.

Next, a complete theoretical and experimental study of the ruthenium-rich quaternary series of borides A2MRu5B2 (A = Hf, Zr; M = Fe, Mn) established the fundamental difference between the Mn and Fe-based Ru-rich compounds in this structure type: Mn enhances ferromagnetic interactions whereas Fe-based compounds clearly prefer antiferromagnetic ground states. Additionally, it was understood that the 5d element Hf was assisting Mn to further enhance the ferromagnetic interactions, making 5d-rich compounds promising targets.

Lastly, 5d-rich Hf2FeIr5B2 and Hf2MnIr5B2 were predicted to have strong magnetic anisotropy (i.e. permanent magnet candidates). Experiments confirmed and extended these predictions: Hf2FeIr5B2 orders at TC ~ 901 K and has a coercivity value of 12 kA/m whereas Hf2MnIr5B2 orders at about 590 K and has a coercivity of 62 kA/m (the highest value reported for this structure type). Hf2MnIr¬5B2 is the first hard magnetic material in this structure type showing ordering temperature far above room temperature. The good coercivity values of both compounds coupled with their high ordering temperatures make them viable candidates for achieving competitive room temperature permanent magnetic properties in the future.