Dependence of spin-transfer switching current on free layer thickness in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions

Magnetoresistance (MR) and spin-transfer switching (STS) properties were investigated in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions as a function of free layer thickness (d(Free)). The MR ratio was about 140% at d(Free)>= 2 nm. It decreased to about 80% at d(Free)=1.5 nm. Both switching currents and thermal stability were roughly proportional to d(Free). The averaged intrinsic switching current density (J(c0)(av)) was 1x10(7)-2x10(7) A/cm(2). The thermal stability of parallel magnetization state was greater than that of antiparallel state. The feasibility of the STS write scheme for nonvolatile magnetic random access memory was discussed. (c) 2006 American Institute of Physics.