Role of antisite disorder, electron-electron correlations, and a surface valence transition in the electronic structure of CeMnNi4

CeMnNi4 exhibits an unusually large spin polarization, but its origin has baffled researchers for more than a decade. We use bulk sensitive hard x-ray photoelectron spectroscopy (HAXPES) and density functional theory based on the Green's function technique to demonstrate the importance of electron-electron correlations of both the Ni 3d (UNi) and Mn 3d (UMn) electrons in explaining the valence band of this multiply correlated material. We show that Mn-Ni antisite disorder as well as UNi play a crucial role in enhancing its spin polarization: Antisite disorder broadens a Ni 3d minority-spin peak close to the Fermi level (EF), while an increase in UNi shifts it toward EF, both leading to a significant increase of minority-spin states at EF. Furthermore, the rare occurrence of a valence state transition between the bulk and the surface is demonstrated highlighting the importance of HAXPES in resolving the electronic structure of materials unhindered by surface effects.