Soft X-ray ARPES investigation of the nickelate Fermi surface in exchange biased LaNiO$_{3}$-LaMnO$_{3}$ superlattices

We investigate (111)-oriented superlattices consisting of paramagnetic LaNiO$_{3}$ (LNO) and ferromagnetic LaMnO$_{3}$ (LMO). The field dependence of the magnetization in these heterostructures was measured at 5 K after cooling the sample in the presence of a 0.4 T field. Surprisingly, a shift of 15 mT in the magnetization loop towards negative fields along the magnetic field axis was observed [1]. If the same measurement is repeated in a (111) LMO thin film, no exchange bias is observed which implies that LNO is the driving force for the biasing effect exhibited by the heterostructures. Since LNO is a well-known paramagnetic material, the existence of exchange bias in the superlattices implies the existence of an interface-induced magnetic order. Here we use soft x-ray angle resolved photoemission spectroscopy --SX ARPES- to study the electronic band structure of LNO layers in these heterostructures. Due to the increase in photoelectron escape depth in the 500 -- 1000 eV energy range, we are able to map the LNO Fermi surface below 7 u.c. of LMO. In this talk we will discuss the similarities and differences in the electronic structure between thin films of (111)-LNO and buried LNO-LMO interfaces.\\[4pt] [1] M.Gibert, et al, Nat. Materials, 11, 195 (2012).