4f and 5d magnetic moments in highly correlated [Ce/La/Fe] and [La/Ce/Fe] multilayers studied by x-ray magnetic circular dichroism

Experiments are reported of x-ray absorption and x-ray magnetic circular dichroism at the L-2,L-3(2p --> 5d) and M-4,M-5(3d --> 4f) absorption edges of Ce and La in the multilayers [La/Ce(10 Angstrom)/La/Fe(30 Angstrom)] x n and [Ce/La(10 Angstrom)/Ce/Fe(30 Angstrom)] x n. In these layers, Ce adopts an alpha-phase-like electronic structure. Strong 3d-5d and 3d-4f hybridization is effective at the interfaces. It induces an ordered magnetic moment on the 5d and 4f states in the ground state of Ce and of the 5d states of La at room temperature, in antiparallel orientation to the Fe moment. By choosing the special laminar structure of the two lanthanides intercalated in between the Fe layers, the spatial extension of the Fe-induced magnetic order is directly probed, The 4f polarization of Ce and the 5d polarization of La are limited to the direct interface with Fe. In contrast, the polarization of Ce-5d states extends deeply into the layers. There is evidence that the 5d states of cu-like Ce in these layered structures are very close to a ferromagnetic instability. Remarkably, magnetic order on the Ce-5d states can exist without a polarization of the 4f states. Apparently the 4f-(5d,6s) hybridization wins over the intraatomic 4f-5d exchange interaction, and stabilizes a nonmagnetic 4f ground state. Comparative studies on alloys CexFe1-x confirm this observation: near x = 0.34 the polarization of the 4f states gets lost, but the 5d states are magnetically ordered. The special electronic and magnetic properties of Ce and La in the multilayer systems are reflected in the reversal of the macroscopic magnetization studied by the magneto-optical Kerr effect.