Coupling between magnetism and transport properties in monoclinic Fe6.10±δGe5 single crystals

We report the synthesis of monoclinic Fe_6.10±δGe₅ single crystals, as well as their magnetic, transport and thermodynamic properties, sharing similar key features within the range of δ ≈ 0.25. The susceptibility and magnetization results reveal two distinct antiferromagnetic transitions at T_N1 = 340 K and T_N2 = 121 K, respectively, with the easy axis to be along the crystalline c direction, as implied both by the anisotropy in the susceptibility and by a spin-flop transition. Insulating behavior with a narrow band gap of ~1 meV is observed in resistivity measurement in the intermediate temperature range T_N2 < T < T_N1, whereas metalliclike behavior manifests at lower temperatures T < T_N2. These observations indicate that Fe_6.10±δGe₅ exhibits rich magnetic phases, with charge carrier scattering highly sensitive to spin configurations in different magnetic phases, calling for further high-resolution experiments on its local atomic environment and magnetic structure.