Crystal electric field and properties of 4f magnetic moments at the surface of the rare-earth compound TbRh2Si2

By means of 4$f$ photoemission measurements and first-principles calculations, the authors demonstrate here how the crystal electric field (CEF) and related magnetic properties can be modified at the surface of rare-earth materials. For TbRh${}₂$Si${}₂$, CEF at the Tb surface makes the 4$f$ moments orthogonal to those in the bulk. For the Tb layer below the Si termination, the temperature-dependent photoemission data reveal larger CEF splitting relative to the bulk. The methodology used here can facilitate unveiling of the surface magnetic properties of layered 4$f$ systems.