An x-ray powder diffraction study of polycrystalline Dy was performed over the temperature interval from 5 to $300\mathrm{K}$ in applied magnetic fields up to $40\mathrm{kOe}$. A complex first-order magnetostructural transformation, which occurs below $\sim 8\mathrm{kOe}$ and above $\sim 20\mathrm{kOe}$, is decoupled into a first-order magnetic (helix-fan) transition and a second-order magnetostructural (hexagonal-orthorhombic) transition between $\sim 135$ and $\sim 175\mathrm{K}$ in magnetic fields between $\sim 8$ and $\sim 20\mathrm{kOe}$. The transition to the ferromagnetic (FM) state is always accompanied by an orthorhombic distortion of the hexagonal lattice, including a transition from the paramagnetic (PM) to the FM state in magnetic fields exceeding $20\mathrm{kOe}$.

• Received 29 November 2007

DOI:https://doi.org/10.1103/PhysRevB.77.094132