Magnetic oxides EuO and NiFe2O4 for spintronics

Magnetic oxides provide the rare combination of electrical insulation and ferromagnetism and - prepared as thin films - are well-suited as tunnel barriers in efficient spinfilters. We optimize thin films of EuO and NiFe2O4 in crystal structure, magnetic and electronic properties. EuO thin films were prepared using an oxide MBE system. EuO single-crystalline thin films can be grown epitaxially on MgO and lattice-matched YSZ substrates, where on the latter a sustained layer-by-layer growth was achieved. A meticulous regulation of the oxygen supply renders EuO thin films possible (tEuO≥20 nm) with bulk-like magnetization msat=7μB and TC=69 K. The chemical states of EuO on silicon were studied in detail by HAXPES which clearly confirmed the high stoichiometric quality of EuO. The room temperature ferromagnetic spinel NiFe2O4 (NFO) was prepared by pulsed laser deposition (PLD). The chemical oxidation states and site occupancy (octahedral vs. tetrahedral) of the metal cations (Ni, Fe), investigated by Core-level XPS experiments, determine the magnetic behavior of NFO. In our NiFe2O4 samples exhibit msat=1.2μB. Magnetic oxides EuO and NiFe2O4 with high-quality magnetic, structural and chemical properties were prepared to be exerted as tunnel barriers in spinfilters.