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Precessional switching of the magnetisation is a convenient way to ensure sub-ns, reliable, energy cost efficient writing of an MRAM cell. In this technique, a controlled pulse of magnetic field is applied perpendicular to the easy magnetisation axis of the MRAM cell free layer, which switches the magnetisation from one direction to its reverse. Bit selection and fast direct overwrite can be obtained by superimposing another field pulse along the easy magnetisation axis. It is proposed to change the cell shape while reducing its size to postpone the onset of superparamagnetism. Based on the Landau-Lifshitz-Gilbert equation an analytical theory of this precessional switching process has been developed. This allows the understanding of the minimal switching field and accountingly for the bit selection scheme. A study of how the writing parameter window is affected by a distribution of cell parameters in a array and by the intercell dipolar coupling has been mode. A high-pass encoding, and a balanced encoding algorithm are proposed to reduce the maximum intercell dipolar field. [ABSTRACT FROM AUTHOR]

We have induced magnetization switching by spin transfer in pillar-shaped spin valves using nanosecond-scale current pulses combined with hard axis fields. Switching events requiring 100 ps pulses were obtained. In comparison with the switching induced by a single current pulse, biasing the device with a hard axis field decreases the pulse duration needed for error-free switching. The reduction of the cost in pulse amplitude scales with the magnitude of the applied field, and can be quantitatively understood from micromagnetic simulations and macrospin arguments taking into account the thermal fluctuations. [ABSTRACT FROM AUTHOR]

We have characterized the strength of the interfacial Dyzaloshinskii-Moriya interaction (DMI) in ultrathin perpendicularly magnetized CoFeB/MgO films, grown on different underlayers of W, TaN, and Hf, using two experimental methods. First, we determined the effective DMI field from measurements of field-driven domain wall motion in the creep regime, where applied in-plane magnetic fields induce an anisotropy in the wall propagation that is correlated with the DMI strength. Second, Brillouin light spectroscopy was employed to quantify the frequency nonreciprocity of spin waves in the CoFeB layers, which yielded an independent measurement of the DMI. By combining these results, we show that DMI estimates from the different techniques yield only qualitative agreement, which suggests that open questions remain about the underlying models used to interpret these results. [ABSTRACT FROM AUTHOR]