Giant tunnel magnetoresistance and high annealing stability in CoFeB∕MgO∕CoFeB magnetic tunnel junctions with synthetic pinned layer

We investigated the relationship between tunnel magnetoresistance (TMR) ratio and the crystallization of CoFeB layers through annealing in magnetic tunnel junctions (MTJs) with MgO barriers that had CoFe∕Ru∕CoFeB synthetic ferrimagnet pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta=425°C, whereas the TMR ratio of the MTJs with pinned layers without Ru spacers decreased at Ta over 325°C. Ruthenium spacers play an important role in forming a (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through annealing at high temperatures.

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