Direct evidence of helifan structures in holmium by single crystal neutron diffraction

We give direct evidence of the existence of helifan structures, an intermediate phase between helix and fan, in holmium at 50 K in a magnetic field by single-crystal neutron-diffraction experiments. Two types of helifan structures, helifan(3/2) and helifan(2) have been observed at 1.4 and 2.0 T, respectively. The magnetic structure successively changes with increasing magnetic field, from a normal helix at zero field to a helifan(3/2) structure, to a helifan(2) structure, to a fan structure and, finally, to an induced ferromagnetic structure