Magnetic, structural, and electronic properties of NiFe2O4 ultrathin films

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The physical properties of transition-metal oxides are influenced by the competition among charge, spin, and orbital degrees of freedom. Advances in deposition techniques enable the growth of thin film heterostructures with atomically sharp interfaces, allowing for the exploration of novel nanoelectronic functionalities and phenomena unique to these interfaces. Oxides that exhibit both magnetic and insulating properties present a promising avenue for enhancing spintronic devices through effective spin-filter effects generated by spin-dependent tunneling. The spinel ferrite NiFe2O4 is particularly promising due to its dual properties at room temperature. This research investigates the interplay between magnetic, electronic, and structural properties in NiFe2O4. Thin films are deposited on Nb-doped SrTiO3 substrates using pulsed laser deposition, with careful evaluation of growth conditions to achieve high-quality, epitaxial films. Emphasis is placed on the effects of reduced dimensionality in ultrathin films (d < 4nm), revealing enhanced saturation magnetization coinciding with reduced lattice constants under compressive strain. Various analyses, including HAXPES, XANES, and XMCD spectroscopy, confirm a consistent cationic coordination across film thickness, ruling out cationic inversion as a cause for enhanced magnetization. Instead, a novel interfacial magnetism is discovered, driven by ferromagnetic ordering of Ti electrons,