Element-specific observation of the ferromagnetic ordering process in UCoAl via soft x-ray magnetic circular dichroism

Abstract

We have performed soft x-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U 4d-5f(N4,5) and Co 2p-3d(L2,3) absorption edges in order to investigate the magnetic properties of the U 5f and Co 3d electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co 3d electrons is unusually large. Through the systematic temperature (T)- and magnetic field (H)-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of H and T (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was clearly observed under 15 K at HM. The value of the HM and its T dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings clearly show that the role of the Co 3d electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.