# MFe6 X4 system (M = Mg, Sc, Zr; X = Al, Si, P, Ga, Ge, In, Sn, Sb) as possible ‘gap’ magnets

## TL;DR

This paper investigates LiFe6Ge4's magnetic properties and finds that element substitution can improve its performance as a rare-earth-free permanent magnet.

## Contribution

The study resolves the structural origin of magnetism in LiFe6Ge4 and proposes element substitution strategies for better permanent magnets.

## Key findings

- LiFe6Ge4 has a trigonal crystal structure with an antiferromagnetic ground state.
- Substituting Al or Ga for Ge stabilizes a ferromagnetic state with high magnetization and anisotropy.
- Data-driven modeling combined with synthesis helps design improved rare-earth-free magnets.

## Abstract

LiFe6Ge4, with a theoretically predicted saturation magnetization of 1 T, a magnetocrystalline anisotropy energy of 1.78 MJ/m3 and a Curie temperature of 620 K was suggested to be a promising permanent magnet as an outcome of a data-mining search. Magnetic measurements of the synthesized sample are reported here. Unfortunately, experiments revealed a weak ferromagnetic behaviour with magnetization values much below that predicted by theory. This discrepancy is analyzed in detail, and is attributed to the trigonal crystal symmetry that was missed in the previous characterisation of the material. The correct crystal structure is R3‾
mH (space group 166) and it is found here to have an antiferromagnetic ground state, as opposed to a theoretically predicted ferromagnetic state of the previously reported monoclinic crystal structure. Theoretical calculations show that element substitution can stabilize a ferromagnetic state of the trigonal crystal structure, with high values of saturation magnetization and magnetocrystalline anisotropy. The best results are seen for the Al or Ga substitution for Ge of the LiFe6
X4 compound.

Combining data-driven modeling with synthesis, we resolve the structural origin of magnetism in LiFe6Ge4 and propose element substitution strategies for sustainable, rare-earth-free permanent magnets with enhanced performance.