“…Future works are in place to understand the spin filtering effect as well as to investigate the feasibility of Ho 2 O 3 as a tunnel barrier. With regards to the loss of magnetic properties of the free layer, we postulate the effect to be the strong oxygen scavenging effect of Ho due to its high enthalpy of formation of Ho 2 O 3 , previously established to be -1883.3 kJ/mol [252][253][254]. It has been well reported that equiatomic stoichiometry of Mg:O is crucial to ensure the formation of defect-free bcc-MgO responsible for the lattice matching and growth of bcc-CoFe [255,256].…”