High TMR ratio in perpendicular MTJs using fe-based Heusler alloy Fe2Cr1−xCoxSi

Perpendicular magnetic tunnel junctions (p-MTJs) have attract immense attention due to high thermal stability and low critical current for spin-transfer torque induced magnetization switching, as compared to in-plane MTJs. The conventional perpendicular magnetic anisotropy (PMA) materials explored so far include rare-earth/transition metal alloys, Co/(Pd, Pt, Ni) multilayers, and L1₀-or-dered (Co, Fe)Pt alloys. However, these materials suffer from some limitations including insufficient chemical and/or thermal stability and low spin polarization. Further, the interfacial PMA induced by MgO interface was shown as an efficient way to realize PMA for conventional magnetic storage materials, such as CoFeB. Nonethelss, the damping constant of CoFeB increases sharply as its thickness decreases (less than 2 nm) and leads to an increase in the intrinsic critical switching current density. Recently, full Heusler alloys have attracted much attention as PMA materials due to high spin polarization, low damping constant and good lattice match with MgO, such as Co₂FeAl and Co₂FeAl_0.5Si_0.5. So far, only Co₂FeAl in Heusler alloys has been demonstrated with a TMR ratio of 91% in p-MTJs [1] and there is no report on the PMA in Fe-based Heusler alloys such as Fe₂Cr_1-xCo_xSi (FCCS).