The mysterious magnetic ground state of Ba14MnBi11 is likely altermagnetic

TL;DR

This study investigates the magnetic ground state of Ba14MnBi11, revealing its susceptibility to charge doping and proposing altermagnetic ordering as a key feature, which helps reconcile experimental and theoretical discrepancies.

Contribution

The paper demonstrates that Ba14MnBi11's magnetic state is highly sensitive to doping and introduces altermagnetic order as a novel magnetic phase in this compound.

Findings

Stoichiometric Ba14MnBi11 is ferromagnetic and metallic.

Electron doping induces semiconducting and weakly antiferromagnetic states.

Hole doping leads to altermagnetic ordering.

Abstract

Mn-based transition metal Zintl compounds in the 14-1-11 phase are known to host complex atomic and magnetic structures owing to their intricate crystal structure. Among them, Ba14MnBi11 stands out as one of the least understood compounds, with experimental measurements and theoretical findings largely inconsistent. Following up on the earlier attempt [D. Sanchez-Portal et al., PRB 65, 144414 (2002)] at establishing a connection between metallicity and magnetism through a DFT-based analysis, our work aims to provide additional insights to resolve the existing contradictions. Our key finding is that the magnetic ground state is very susceptible to charge doping. DFT calculations for stoichiometric Ba14MnBi11 give a rather stable ferromagnetic metallic ground state. However, by adding exactly one additional electron per Mn, the system becomes semiconducting and the magnetic ground state becomes weakly antiferromagnetic (AF). On the other hand, upon small hole doping the system transitions to a special type of AF state known as altermagnetic ordering. The observed trends suggest that hole and electron doping-induced phase transitions likely result from different underlying mechanisms, influencing various exchange pathways. Additionally, our projected density-of-states along with bandstructure analyses indicate that, besides the largest hole contribution coming from the tetrahedral unit of Bi, the isolated Bi sites also play a substantial role and the dispersive bands near VBM suggest a rather complex hybridization network involving both Bi band characters. Through a comprehensive comparison of available data and our analysis, we propose that the inconsistency in magnetic states between experimental findings and DFT calculations is due to nonstoichiometric effects, likely impurities or defects.