Study of obliquely deposited 57Fe layer on organic semiconductor (Alq3); interface resolved magnetism under x-ray standing wave

Ultra-thin Fe film is deposited obliquely on the Tris(8-hydroxyquinolinato) aluminum (Alq3) layer to study the interface magnetism and compared with the normally deposited film of the same thickness. The overall magnetic property of the film, as observed using magneto-optic Kerr effect measurements, is understood precisely through interface resolved grazing incident nuclear resonance scattering (GINRS) measurements under x-ray standing wave (XSW) conditions. To excite XSW modes, the bilayer is deposited between high dense Ag and Pt layers to make a waveguide structure, where the position of the antinode is varied by changing incident angles. The Fe layer is enriched with 57Fe isotope during deposition to make it active for GINRS measurements. Compared with obliquely deposited 57Fe film, reduced hyperfine fields at the interface of normally deposited 57Fe/Alq3 film, providing evidence for the deep penetration of 57Fe atoms into Alq3 film. Due to the large shadowing effect at oblique angle deposition, Fe atoms try to organize into isolated superparamagnetic clusters to minimize their surface/interface energy. On the other hand, besides the relatively deep penetration in the normally deposited thin film, ferromagnetism is observed due to the connecting bigger 57Fe clusters. Our results demonstrate that deposition geometry has a direct and crucial bearing on the interfacial microstructure, which can control diffusion at the Alq3 interfaces and tune magnetic anisotropy in the ferromagnetic layer.