Magnetic properties and structure of CoFe/MnN films with Ta layers

Abstract

Structure and magnetic properties of CoFe/MnN films with Ta underlayer and MnN/CoFe films with Ta toplayer through annealing at various temperatures (Tann = 300–450 °C) and then field cooling to room temperature at 1.5 kOe are studied. Different samples annealed at Tann below 400 °C mainly consist of θ-MnN(002) phase; with increasing Tann, stress relaxation and grain growth of MnN(002) takes place. Distinct phase composition is found for 4 series of films annealed at higher Tann. The phase composition of MnN layer in the films with Tann is related to the escape of N from MnN layer and the compounding of Ta with N. The increase of exchange bias field (HE) with Tann is related to the promoted crystallinity and stress relaxation of θ-MnN phase, but the vanish of HE for the films annealed at higher Tann is due to the disappearance of θ-MnN phase. In this study, Ta/CoFe/MnN/Ta films annealed at Tann = 375 °C exhibits the largest HE = 562 Oe due to the optimization of θ-MnN phase and flatter interface. The results in this work provide useful information to fabricate exchange bias system with θ-MnN as an antiferromagnetic layer.