We investigate the magnetic symmetry of the topological antiferromagnetic material Mn3Ge by using torque measurements. Below the Néel temperature, detailed angle-dependent torque measurements were performed on Mn3Ge single crystals in directions parallel and perpendicular to the Kagome basal plane. The out-of plane torque data exhibit ± sin θ and sin 2θ behaviors, of which the former results from the spontaneous ferromagnetism within the basal plane and the latter from the in-and out-of-plane susceptibility anisotropy. The reversible component of the in-plane torque exhibits sin 6ϕ behavior, revealing the six-fold symmetry of the in-plane magnetic free energy. Moreover, we find that the free energy minima are pinned to the direction of spontaneous ferromagnetism, which correspond to the maxima of the irreversible component of the in-plane torque. We provide an effective spin model to describe the in-plane magnetic anisotropy. Our results demonstrate that the ground state of Mn3Ge is described by the coexistence of a strong six-fold antichiral order and a weak ferromagnetic order induced by second-order spin anisotropy.

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