Unveiling atomic-scale transport for giant tunnel magnetoresistance in Co$_{47}$Mn$_{32}$Si$_{21}$/MgO/Co$_{47}$Mn$_{32}$Si$_{21}$ magnetic tunnel junctions

Mn diffusion in Co$_{47}$Mn$_{32}$Si$_{21}$/MgO/Co$_{47}$Mn$_{32}$Si$_{21}$ magnetic tunnel junctions (MTJs) plays a crucial role in interface stability, spin polarization, and tunnel magnetoresistance (TMR). Up to 823 K, Mn remains confined to grain boundaries, preserving structural order and facilitating coherent tunneling. The extracted activation energy of 73.11 kJ/mol confirms grain boundary diffusion as the dominant atomic transport mechanism. Beyond this, Mn migration into MgO barrier contributes to structural degradation and a reduction in tunnel magnetoresistance (TMR) performance. Maximum TMR ratios of 1995% at 4.2 K and 378% at room temperature, exceeding those of MTJs with nearly stoichiometric CoMnSi electrodes, highlight the critical importance of interface engineering. The observed TMR enhancement correlates primarily with annealing-driven improvements in crystallinity and interface quality, while Mn redistribution provides additional mechanistic insight into thermally activated interfacial diffusion processes.