Structural-Distortion-Driven Magnetic Transformation from Ferro- to Ferrimagnetic Iron Chains in B 6 -based Nb 6 FeIr 6 B 8 .

We report on a structural distortion of kinetically stable B6 -based ferromagnetic Nb6 FeIr6 B8 that induces an unprecedented transformation of a ferromagnetic Fe chain into two ferrimagnetic Fe chains through superstructure formation. Density functional theory calculations showed that the ferromagnetic Fe-Fe intrachain interactions found in the undistorted structure become ferrimagnetic in the distorted superstructure, mainly because the two independent iron atoms building each chain interact antiferromagnetically and carry different magnetic moments. High-temperature SQUID magnetometry confirmed ferrimagnetic ordering at 525 K with a high and negative Weiss constant of -972 K indicating the presence of strong antiferromagnetic interactions, as predicted. This finding paves the way for the development of low-dimensional magnetic intermetallic systems based on Heisenberg ferrimagnetic chains, which have previously been studied only in molecular-based compounds.