Charge transfer effect at the La0.7Ca0.3MnO3/NiO heterojunction and the novel interface ferromagnetism

We report the formation of a new ferromagnetic (FM) states in the antiferromagnet (AFM) NiO at the interface with ferromagnet (FM) La_0.7Ca_0.3MnO₃ (LCMO). The new magnetization temperature at 80 K is observed and can be ascribed to Ni³⁺-O-Mn³⁺ superexchange interactions. Mn 3s and Ni 3p core-level spectra have been measured by x-ray photoelectron spectroscopy (XPS) which show a direct evidence of charge transfer effects of the type Mn⁴⁺-Ni²⁺ → Mn³⁺-Ni³⁺ at the interface region. The valence band offset (VBO) at the LCMO/NiO interface can be determined to be ΔE_VBO ~ 0.77 eV. The valence band of NiO is shifted to higher binding energy compared to LCMO. Thus, charge transfer occurred owing to the valence band edge shifting at the heterostructure interfaces.