Magnetic properties of Dy nano-islands on graphene

We have determined the magnetic properties of epitaxially grown Dy islands on graphene/SiC(0001) that are passivated by a gold film (deposited in the ultra-high vacuum growth chamber) for ex-situ X-ray magnetic circular dichroism (XMCD). Our sum-rule analysis of the Dy M_4,5 XMCD spectra at low temperatures (T=15 K) as a function of magnetic field assuming Dy³⁺ (spin configuration 6H_15/2) indicate that the projection of the magnetic moment along an applied magnetic field of 5 T is 3.5(3) μ_B. Temperature dependence of the magnetic moment (extracted from the M₅ XMCD spectra) shows an onset of a change in magnetic moment at about 175 K in proximity of the transition from paramagnetic to helical magnetic structure at T_H=179 K in bulk Dy. No feature at the vicinity of the ferromagnetic transition of hcp bulk Dy at T_c = 88 K is observed. However, below ∼130 K, the inverse magnetic moment (extracted from the XMCD) is linear in temperature as commonly expected from a paramagnetic system suggesting different behavior of Dy nano-island than bulk Dy.