Magnetization dynamics of synthetic MRAM free layers: coupled precession and ultra fast magnetization reversal strategies

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The aim of this work is to study the magnetization dynamics of microscopic synthetic antiferromagnets (SyAF) cells on the 10 ps time scale. SyAF consist of two ferromagnetic thin films FM1, FM2 separated by an ultra thin non-magnetic exchange coupling layer (CL) which induces an antiparallel alignment of the magnetization M1, M2 of the two ferromagnets. Such SyAF are now used as the storage layer (or ¿free layer¿) in magnetic random access memories (MRAM) and magnetic logic. So far, the important question of the maximum write rate of a SyAF free layer device has not been answered. How fast can the magnetization of a SyAF free layer cell be reversed? To answer this question the coupled precessional dynamics of the magnetization M1, M2 of the two ferromagnets in the SyAF and their dependence on device parameters is studied. To get a complete picture of the SyAF dynamics the time resolved trajectories of the magnetization M1,M2 of both ferromagnets FM1, FM2, are derived from time resolved magneto transport measurements. For this purpose a novel sample design - consisting of a SyAF sandwiched between a magnetic tunnel junction and a spin valve ¿ is developed. It allows for the first time to derive the magnetization dynamics of both two ferromagnets FM1, FM2 independently in an all electrical setup. This experiment allows to fully track the magnetization dynamics of the SyAF in sub micron magnetic memory cells. The dynamics are studied for different sample parameters (exchange coupling strength, spin compensation, etc¿) and are compared to numerical simulations. Recently proposed ultra fast precessional SyAF MRAM reversal schemes are tested.