Structural, electron transportation and magnetic behavior transition of metastable FeAlO granular films

Abstract

Metal-insulator granular film is technologically important for microwave applications. It has been challenging to obtain simultaneous high electrical resistivity and large saturation magnetization due to the balance of insulating non-magnetic and metallic magnetic components. FeAlO granular films satisfying both requirements have been prepared by pulsed laser deposition. The as-deposited film exhibits a high resistivity of 3700 μδ cm with a negative temperature coefficient despite that Fe content (0.77) exceeds the percolation threshold. This originates from its unique microstructure containing amorphous Fe nanoparticles embedded in Al 2 O 3 network. By optimizing the annealing conditions, superior electromagnetic properties with enhanced saturation magnetization (>1.05 T), high resistivity (>1200 μδ cm) and broadened Δf (>3.0 GHz) are obtained. Phase separation with Al 2 O 3 aggregating as inclusions in crystallized Fe(Al) matrix is observed after annealing at 673 K, resulting in a metallic-like resistivity. We provide a feasible way to achieve both high resistivity and large saturation magnetization for the FeAlO films with dominating metallic component and show that the microstructure can be tuned for desirable performance.