  Low-temperature neutron diffraction experiments at P = 8 GPa have been
conducted to investigate the magnetic structures of metallic Holmium at high
pressures by employing a long d-spacing highflux diffractometer and a
Paris-Edinburgh press cell inside a cryostat. We find that at P = 8 GPa and T =
5 K, no nuclear symmetry change is observed, keeping therefore the hexagonal
closed packed (hcp) symmetry at high pressure. Our neutron diffraction data
confirm that the ferromagnetic state does not exist. The magnetic structure
corresponding to the helimagnetic order, which survives down to 5 K, is fully
described by the magnetic superspace group formalism. These results are
consistent with those previously published using magnetization experiments.
