Field-dependent domain structure evolution in artificial ferrimagnets analyzed by spin-polarized tunnel transport in magnetic tunnel junctions

A powerful technique for investigating field-dependent micromagnetism in thin magnetic layers is presented. The technique uses the spin-polarized tunnel-transport mechanism in magnetic-tunnel junctions. We used this technique to study the micromagnetic-reversal mechanism in an artificial ferrimagnetic system, which consists of two ferromagnetic layers strongly antiferromagnetically coupled through a nonmagnetic interlayer. We show that the high sensitivity of the spin-polarized current to the fluctuations of magnetization allows to probe the magnetic-domain structure in the magnetic electrodes. As a contrast to standard M-$H$ and giant-magnetoresistance measurements, which are only able to probe the global magnetic state of this artificial ferrimagnet, we show here that the tunnel magnetoresistance discriminates the field-dependent evolution of the domain phases in selective magnetic layers. Furthermore, we demonstrate the capability of a tunnel-magnetoresistance signal to be used as a quantitative probe for investigating residual walls during the reversal process.