Determination of the magnetic structure of CePt${}_2$In${}_7$ by means of neutron diffraction

The magnetic structure of the heavy fermion antiferromagnet CePt${}_2$In${}_7$ is determined using neutron diffraction. We find a magnetic wave vector ${\mathbf{q}}_M=(1\mathrm{/}2,1\mathrm{/}2,1\mathrm{/}2)$, which is temperature independent up to $T_N=$ 5.5 K. A staggered moment of 0.45(1)${\mu }_B$ at 2 K resides on the Ce ion. The nearest-neighbor moments in the tetragonal basal plane are aligned antiferromagnetically. The moments rotate by 90${}^{\circ }$ from one CeIn${}_3$ plane to another along the $c$ axis. A much weaker satellite peak with an incommensurate magnetic wave vector ${\mathbf{q}}_M=(1\mathrm{/}2,1\mathrm{/}2,0.47)$ seems to develop at low temperature. However, the experimental data available so far are not sufficient to draw a definitive conclusion about the possible co-existence of commensurate and incommensurate magnetic structures in this material.