Prediction of Van Hove singularity systems in ternary borides

TL;DR

This study computationally identifies stable ternary boride structures with Van Hove singularities near the Fermi level, revealing tunable electronic and magnetic properties, and discusses experimental synthesis challenges and future directions.

Contribution

It introduces a new family of stable or nearly stable ternary borides with Van Hove singularities, highlighting their tunable electronic and magnetic behaviors.

Findings

Identification of stable α-ATB4 borides with specific elements.

Presence of Van Hove singularities near the Fermi level.

Magnetic instabilities and spin glass-like states in certain compounds.

Abstract

A computational search for stable structures among both $\alpha$ and $\beta$ phases of ternary ATB4 borides (A= Mg, Ca, Sr, Ba, Al, Ga, and Zn, T is 3d or 4d transition elements) has been performed. We found that $\alpha$-ATB4 compounds with A=Mg, Ca, Al, and T=V, Cr, Mn, Fe, Ni, and Co form a family of structurally stable or almost stable materials. These systems are metallic in non-magnetic states and characterized by the formation of the localized molecular-like state of 3d transition metal atom dimers, which leads to the appearance of numerous Van Hove singularities (VHS) in the electronic spectrum. The closeness of these VHS to the Fermi level can be easily tuned by electron doping. For the atoms in the middle of the 3d row (Cr, Mn, and Fe), these VHS led to magnetic instabilities and new magnetic ground states with a weakly metallic or semiconducting nature. The magnetic ground states in these systems appear as an analog of the spin glass state. Experimental attempts to produce MgFeB4 and associated challenges are discussed, and promising directions for further synthetic studies are formulated.