Electric field tunable high-frequency performance in high-resistivity Fe0.5Co0.5-MgO/lead zinc niobate-lead titanate nanogranular film multiferroic heterostructures

Abstract

Fe0.5Co0.5-MgO films with composition gradient were fabricated by sputter deposition onto (011) lead zinc niobate-lead titanate substrates. The addition of MgO in excess of its solubility in the FeCo alloy results in the formation of amorphous grain boundaries, leading to a dramatic increase of the resistivity with values over 20 times that of pure FeCo films. As a result, a large self-bias ferromagnetic resonance frequency fFMR of up to 9.87 GHz is obtained in the absence of an external magnetic field (H = 0 A/m) and an electric field tuning frequency range of 4.55 GHz was achieved in the as-deposited films at an electric field of 7 kV/cm. The high resistivity and high fFMR in these heterostructures provide great opportunities for application in self-bias tunable monolithic microwave integrated circuit devices.