Bilayer Kagome Ferrimagnet Exhibiting Exceptional Spontaneous Exchange Bias in TbMn₆(Ge,Ga)₆

Abstract

Manipulating interlayer interactions in two-dimensional (2D) materials has led to intriguing behaviors. Borrowing these 2D signatures to bulk materials is likely to unlock exceptional properties. Here, we report an emergent 2D-like bilayer Kagome ferrimagnet through reducing the interbilayer magnetic interaction to nearly zero. This concept is realized within bulk TbMn₆(Ge,Ga)₆ compounds, characterized by an isolated and pure Mn Kagome lattice, simply by the chemical substitution of Ge with Ga. Specifically, the targeted compound TbMn₆Ge₅Ga₁ exhibits a giant spontaneous exchange bias (SEB) of approximately 1.6 T, which is more than twice that observed in known materials. Field-dependent neutron diffraction reveals the robust nature of the compensated ferrimagnetic (FiM), characterized by almost two-thirds of the moments being pinned and irreversible under fields up to 9 T. Through magnetic and structural analysis, alongside theoretical calculations, we demonstrate that the substantial SEB is related to the intense competition between local robust and weak FiM states within the bilayer Kagome configuration, which are stabilized by an incommensurate spin arrangement. The concept of a bilayer Kagome magnet offers new opportunities for discovering attractive properties in 2D-like materials.