60% magnetoresistance at room temperature in Co–Fe/Al–O/Co–Fe tunnel junctions oxidized with Kr–O2 plasma

The influence of the mixed inert gas species for plasma oxidization process of a metallic Al layer on the tunnel magnetoresistance (TMR) was investigated for a magnetic tunnel junction (MTJ), $\mathrm{Ta}\text{\hspace{0.17em}50\hspace{0.17em}Å/}\mathrm{Cu}\text{\hspace{0.17em}200\hspace{0.17em}Å/}\mathrm{Ta}\text{\hspace{0.17em}200\hspace{0.17em}Å/}\mathrm{Ni}–\mathrm{Fe}\text{\hspace{0.17em}50\hspace{0.17em}Å/}\mathrm{Cu}\text{\hspace{0.17em}50\hspace{0.17em}Å/}{\mathrm{Mn}}_{75}{\mathrm{Ir}}_{25}\text{\hspace{0.17em}100\hspace{0.17em}Å/}{\mathrm{Co}}_{70}{\mathrm{Fe}}_{30}\text{\hspace{0.17em}25\hspace{0.17em}Å/}\mathrm{Al}–\mathrm{O}/{\mathrm{Co}}_{70}{\mathrm{Fe}}_{30}\text{\hspace{0.17em}25\hspace{0.17em}Å/}\mathrm{Ni}–\mathrm{Fe}\text{\hspace{0.17em}100\hspace{0.17em}Å/}\mathrm{Cu}\text{\hspace{0.17em}200\hspace{0.17em}Å/}\mathrm{Ta}\text{\hspace{0.17em}50\hspace{0.17em}Å.}$ Using $\mathrm{Kr}–{\mathrm{O}}_2$ plasma, a 58.8% of TMR ratio was obtained at room temperature after annealing the junction at $\text{300\hspace{0.05em}°}\mathrm{C},$ while the achieved TMR ratio of the MTJ fabricated with usual $\mathrm{Ar}–{\mathrm{O}}_2$ plasma remained 48.6%. A faster oxidization rate of the Al layer by using $\mathrm{Kr}–{\mathrm{O}}_2$ plasma is a possible cause to prevent the over oxidization of the Al layer, which depolarizes the surface of the underlaid ferromagnetic electrode, and to realize a large magnetoresistance.