Abstract
The magnetic structure of holmium exhibits an incommensurate spin spiral below the Néel temperature of 131.5 K. We have studied the effect of hydrogen on the magnetic properties of antiferromagnetic holmium. Combining thin-film deposition techniques with resonant magnetic X-ray scattering at the Ho LIII absorption edge, we were able to follow the magnetic properties of HoHx, with a small X-ray beam along a lateral hydrogen gradient in the sample. The results show that the period for the spin spiral increases with increasing hydrogen concentration while the Néel temperature decreases. Both effects can be related to a weakening of the RKKY interaction caused by a depletion of the mediating conduction electrons, which fill a low-lying hydrogen band.