Competing Magnetic Phases in Li-Fe-Ge Kagome Systems

TL;DR

This study combines first-principles calculations and experiments to explore competing magnetic phases in Li-Fe-Ge kagome systems, revealing diverse magnetic ground states and transitions relevant for topological magnetic properties.

Contribution

The paper presents the first combined theoretical and experimental investigation of magnetic phases in Li-Fe-Ge kagome compounds, identifying collinear AFM and incommensurate spiral states.

Findings

LiFe6Ge4 and LiFe6Ge5 favor collinear AFM ground states.

LiFe6Ge6 stabilizes an incommensurate cycloidal spin spiral.

Experimental AFM ordering observed at ~540 K with phase transition below ~270 K.

Abstract

Competing interlayer magnetic interactions in kagome magnets can lead to diverse magnetic phases, which enable various promising topological or quantum material properties. Here, the electronic structure and magnetic properties have been studied using first-principles calculations for the LiFe$_6$Ge$_6$, LiFe$_6$Ge$_4$, and LiFe$_6$Ge$_5$ compounds sharing the kagome Fe$_3$Ge layer motif but with different interlayer arrangements. For LiFe$_6$Ge$_4$ and LiFe$_6$Ge$_5$, the predicted magnetic ground states are collinear antiferromagnetic (AFM) states involving a mix of ferromagnetic (FM) and AFM interlayer orientations. Whereas for LiFe$_6$Ge$_6$, an incommensurate cycloidal spin spiral is stabilized as a ground state, being close to a collinear A-type AFM state. The analysis of magnetic RKKY exchange coupling confirms the results of electronic structure calculations. The values of atomic magnetic moments are in good agreement with existing experimental estimations. Our experiments on LiFe$_6$Ge$_6$ single crystals have observed AFM ordering at ~540 K and transition to another magnetic phase, with a small FM component (possibly with spin canting), below ~270 K. Thus, our theory and experiment suggest the existence and sequence of collinear and noncollinear magnetic states in kagome LiFe$_6$Ge$_6$. Our findings provide a platform for exploring various novel magnetic phases and associated unconventional or topological magnetism.