Evidence for a devil’s staircase in holmium produced by an applied magnetic field

The magnetic structure of holmium has been studied using neutron diffraction when a magnetic field is applied along the c axis. The field has the effect of suppressing the onset of the commensurate cone phase found at low temperatures in zero field, and instead produces a series of spin-slip structures. In contrast to the zero-field diffraction experiments, where a continuous variation of the magnetic wave vector q was observed, we find that below {}15 K the wave vector q is always commensurate and forms a devil's staircase with increasing field.