High pressure neutron diffraction studies of the magnetic structures of erbium

The magnetic structures of single crystal Er were investigated by neutron diffraction at 11.5 and 14 kbar hydrostatic pressure. At 4.5 K, the spin structure is cycloidal in the ac-plane, not conical. At 14 kbar, the cycloidal configuration persists up to T_CY^P = (46 ± 1) K, where it changes to a longitudinal modulated structure which finally becomes paramagnetic above T_N = (82 ± 1) K. The modulation vector Q = 2 7 × ( 2π c) × c ̂ at 4.5 K, and remains nearly constant up to ∼ 30 K. Above ∼ 30 K, Q increases to reach a maximum slightly above T_CY^P . For further increase in temperature, Q decreases. The data at 11.5 and 14 kbar agree qualitatively.