We use ${}^{51}\mathrm{V}$ nuclear magnetic resonance (NMR) spectroscopy to investigate the magnetic ground state of the lacunar spinel ${\mathrm{GeV}}_4{\mathrm{S}}_8$, which undergoes a structural distortion at $T_{\text{JT}}\approx 30\mathrm{K}$ followed by an antiferromagnetic (AFM) ordering at $T_N\approx 15\mathrm{K}$. According to our zero- and finite-field NMR data, the four V-sites of ${\mathrm{V}}_4$ clusters become magnetically inequivalent in the AFM state: Two of them share the same internal field, while the other two sites are characterized by different internal fields. The angular dependence of the ${}^{51}\mathrm{V}$ NMR lines, upon rotation of an external magnetic field about the pseudocubic [110] and [100] axes, reveals that the internal fields are either parallel to the orthorhombic $a$ axis at all four V-sites of the ${\mathrm{V}}_4$ tetrahedra, or they form an orthogonal pattern, where two V-sites have internal field along the $a$ axis and the other two along the $b$ axis. Based on these results, further supported by the observation of distinct spin-echo modulations of the inequivalent V-sites, we conclude that the magnetic space group of the AFM state is $P_{b}mn{2}_1$ or $Pm{n}^{\prime }{2}_1^{\prime }$.

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• Jahn-Teller effect
• Magnetic order
• Magnetic phase transitions
• Magnetic texture
• Molecular magnetism
• Spintronics
• Density functional calculations
• Nuclear magnetic resonance
• Nuclear quadrupole resonance