engleski

Magnetization reversal induced by a spin polarized current

The magnetic moment of a ferromagnetic layer can be reversed by spin transfer from a spin-polarized current (i.e. without applying a magnetic field), as predicted first by Slonczewski in 1996 and then in other contexts. This effect has been conrmed by recent experiments on nano-pillars at Cornell's University and at Orsay. We will present our latest experiments obtained on Co/Cu/Co nano-pillars in which we find that a positive current switches the magnetic conguration from AP to P whereas a negative one switches from P to AP. This asymmetry is the signature of reversal by spin injection. The required current density is about 10^7 A/cm . We will also show the variation of the critical current with the applied magnetic field. In fact, this study is of interest to decide between the different theoretical approaches as they predict quite different field dependence of the switching current. Our interpretation is based on the dynamical approach of Slonczewski with a calculation of the current spin polarization in a standard model of the CPP-GMR. We show how the spin asymmetry involved in Slonczewski's equations is infuenced by the thickness of the layer and the spin diffusion lengths in the magnetic and the nonmagnetic layers. Optimizing the parameters of the samples, the critical currents can certainly be reduced and be of interest for application to the switching of submicronic magnetic devices.

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