Collapse of itinerant ferromagnetism in CoS2 under pressure: An x-ray absorption spectroscopy study

Cobalt L-edge x-ray absorption spectra (XAS) and x-ray magnetic circular dichroism (XMCD) of CoS2 have been measured at low temperature (4 K) in order to characterize the electronic and magnetic structure with a significant improvement in resolution as compared with previous measurements. The branching ratio of L3 and L2 x-ray absorption near-edge spectra was found to be consistent with a low-spin configuration (S=1/2). A total magnetic moment ⟨m⟩=0.78μB/Co atom with the orbital part ⟨ml⟩=0.049μB has been obtained from the XMCD signal, consistent with the nearly half-metallic character of CoS2 and with the itinerant nature of the ferromagnetism. The behavior under pressure of CoS2 was studied by Co K-edge XAS and XMCD experiments performed up to a pressure of about 30 GPa using diamond-anvil cell at a temperature of 10 K. No evidence of structural phase transition was observed, while the intensity of the XMCD signal was found to decrease continuously for increasing pressures, becoming negligible in the 8∼10 GPa pressure range, a fact consistent with the collapse of itinerant ferromagnetic ordering. The gradual change in the electronic and magnetic structure upon application of pressure was also monitored by the near-edge XAS evolution, found to be in agreement with full multiple-scattering calculations under uniform contraction of distances, and by the blue-shift of the K-edge energy. The Co K-edge energy was found to shift to higher energies (up to 0.64 eV at 30 GPa) and a change of slope was observed at pressures around 5 GPa that may correspond to the disappearance of half-metallicity, in agreement with previous studies.