Spin-polarized current-induced magnetization reversal in single nanowires

Using electrochemical deposition, 6 mum long Ni nanowires, with typical diameters of the order of 80 nm, are grown in ion-track etched membranes. Electric contacts are established during the growth, allowing resistance measurements of a single magnetic wire. Whatever the angle of the applied magnetic field with the wire, the full loops of magnetoresistance of a nickel nanowire can be described quantitatively on the basis of anisotropic magnetoresistance of a uniform magnet, and exhibit a jump of the magnetization at the so-called switching field. Hybrid wires made half with nickel and half with a Co/Cu multilayer were also produced. The multilayer could be grown using either a single bath technique or a multiple bath setup, with the result of a different magnetic anisotropy in the Co layers. When the multilayer is made of an optimal number of layers, the two parts of the hybrid wire act as two resistances in series, having no magnetic interaction onto each other. In contrast, the action of a current pulse on the nickel magnetization is to provoke a switch, when injected before the unstable state of the hysteresis cycle has been reached. But the amount of applied field discrepancy where the current still has an effect is given by a measured value H-max, which appears to be substantially dependent on the presence or not of a multilayer close enough to the nickel wire and on the orientation of the magnetization in the multilayer. The role of the multilayer's presence or state evidences the role of spin polarization in the current-induced switches of nickel. This is confirmed by measurements of the amplitude of H-max in homogeneous nickel wires that exclude spurious effects such as the induced oersted-field, heating, or a combination of the two to account for all the current-induced switches.