Multiple Field-Induced Phases in the Frustrated Triangular Magnet Cs3Fe2Br9

Abstract

The recently discovered material Cs3Fe2Br9 contains Fe2Br9 bi-octahedra forming triangular layers with hexagonal stacking along the c axis. In contrast to isostructural Cr-based compounds, the zero-field ground state is not a nonmagnetic S=0 singlet-dimer state. Instead, the Fe2Br9 bi-octahedra host semiclassical S=52Fe3+ spins with a pronounced easy-axis anisotropy along c, and interestingly, the intradimer spins are ordered ferromagnetically. The high degree of magnetic frustration due to (various) competing intradimer and interdimer couplings leads to a surprisingly rich magnetic phase diagram. The zero-field ground state is already reached via an intermediate phase, and the high-field magnetization and thermal expansion data for H∥c identify 10 different ordered phases. Among them are phases with constant magnetization of 13, respectively 12, of the saturation value, and several transitions are strongly hysteretic with pronounced length changes, reflecting strong magnetoelastic coupling. © 2021 American Physical Society.