Controlling the magnetic reversal mechanism of exchange biased Mn _x O _y /Ni ₈₀ Fe ₂₀ bilayers through O ⁺ implantation

This work investigates the different magnetic reversal mechanisms of as-grown and oxygen-ion (O ⁺ ) implanted Mn _x O _y /Ni ₈₀ Fe ₂₀ bilayers. A Mn _x O _y /Ni ₈₀ Fe ₂₀ bilayer was prepared by ion-beam sputter deposition in an Ar ⁺ atmosphere using a partially oxidised Mn target. Oxygen implantations were then performed using 8 keV O ⁺ ions at fluences of 10 ¹⁶ , 10 ¹⁷ and 10 ¹⁸ ions/cm ² to modify the exchange bias strength at the Mn _x O _y /Ni ₈₀ Fe ₂₀ interface. The magnetic, crystallographic and chemical properties of the bilayers before and after O ⁺ implantation were studied using transmission electron microscopy, X-ray reflectometry, magnetometry and polarised neutron reflectometry. The results show an overall improved exchange bias and coercivity for the O ⁺ implanted bilayers. The 10 ¹⁷ ions/cm ² implanted sample shows the greatest improvement in exchange bias and was further studied for its detailed spin-reversal behaviour using polarised neutron reflectometry. Data analysis in the magnetically-trained state reveals a coexistence of coherent rotational and non-coherent magnetic spin reversal in the as-grown sample and a solely coherent spin rotation reversal mechanism for the O ⁺ implanted Mn _x O _y /Ni ₈₀ Fe ₂₀ bilayer.