Antiferromagnetically coupled CoFe/MgO/CoFe stacks

Exchange coupling (EC) in as-deposited and annealed Co 80 Fe 20 (CoFe)/MgO/Co 80 Fe 20 (CoFe) for MgO thickness spanning 0.45 to 4.5 nm has been studied. Unlike relevant existing results and theories, antiferromagnetic EC behaviors were observed in annealed CoFe/MgO/CoFe with 2.7-nm MgO insulating barrier. Interestingly, a transition from antiferromagnetic to nearly paramagnetic response to applied magnetic field was found around 520 °C corresponding to Néel temperature of CoFe 2 O 4 . Based on grazing incidence x-ray diffraction study, oxide phases of CoO, Co 3 O 4 , and CoFe 2 O 4 starts to be built in the interface annealed at 150 °C and then those of CoO, Fe 3 O 4 , Fe 2 O 3 , and CoFe 2 O 4 are mostly distributed over the interface annealed at 250 °C. This indicates CoO and CoFe 2 O 4 formed at the Co-rich interface act as antiferromagnetic sources giving rise to the exchange-coupled antiferromagnetic/ferromagnetic (AFM/FM) interface and then AFM EC into the CoFe/MgO/CoFe.