Noncentrosymmetric Nowotny Chimney Ladder Ferromagnet Cr₄Ge₇ with a High Curie Temperature of ∼207 K

Noncentrosymmetric magnets usually host intriguing magnetic interactions inherent in the crystal structure with broken inversion symmetry, which can give rise to rich magnetic behaviors. We report herein the high-pressure synthesis, crystal structure, magnetizations, and magnetic structure of a so-called Nowotny chimney ladder compound Cr₄Ge₇. Our analysis on the powder neutron diffraction data revises the crystal structure as a noncentrosymmetric space group (P4̅c2, No. 116). It exhibits two magnetic orders within the temperature range of 2-400 K. The first order at ∼207 K associated with a small magnetic moment of ∼0.75 μ_B is assigned to a commensurate ferromagnetic structure with a propagation vector k = (0, 0, 0). The weak itinerant ferromagnet nature should be caused by the complex Cr spin orders from different Wyckoff positions. The second order-like behavior at ∼18 K is assumed to arise from a competition between the Dzyaloshinskii-Moriya and Heisenberg interactions. The results provide an excellent platform for the study of intricate interactions among various magnetic exchanges as well as for the exploration of high-temperature exotic magnetic properties.