Magnetization switching and tunneling magnetoresistance effects of MTJs with synthetic antiferromagnet free layers consisting of amorphous CoFeSiB

Magnetic tunnel junctions (MTJs), which consisted of amorphous CoFeSiB layers, were investigated. The CoFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with an emphasis given on understanding the effect of the amorphous free layer on the switching characteristics of the MTJs. CoFeSiB has a lower saturation magnetization (M_s:560 emu/cm³) and a higher anisotropy constant (K_u:2 800 erg/cm³) than CoFe and NiFe, respectively. An exchange coupling energy (J_ex) of -0.003 erg/cm² was observed by inserting a 1.0 nm Ru layer in between CoFeSiB layers. In the Si-SiO₂-Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO_x/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in nanometers) MTJs structure, it was found that the size dependence of the switching field originated in the lower J_ex using the experimental and simulation results. The CoFeSiB synthetic antiferromagnet structures were proved to be beneficial for the switching characteristics such as reducing the coercivity (H_c) and increasing the sensitivity in micrometer size, even in submicrometer sized elements.