Zero-field ${}^{115}\mathrm{In}$-nuclear magnetic resonance (NMR) has been used to study single crystals of CePt${}_2$In${}_7$, a heavy-fermion antiferromagnet with a Néel temperature ($T_{\mathrm{N}}$) of 5.2 K at ambient pressure. Narrow linewidths of ${}^{115}\mathrm{In}$-nuclear quadrupolar resonance spectra are observed from each of three crystallographically inequivalent In(1), In(2), and In(3) sites. The NMR spectra under zero field near the 3${\nu }_{\mathrm{Q}}$ line of the orthorhombic In(3) sites are tracked by temperatures down to 1.6 K and by hydrostatic pressures up to 2.4 GPa. These data reveal the coexistence of commensurate and incommensurate antiferromagneic orders at ambient pressure and that the commensurate ordering is stabilized by increasing pressures where bulk superconductivity emerges.

• Received 25 January 2011

DOI:https://doi.org/10.1103/PhysRevB.83.140408