Perpendicular giant magnetoresistance in Co/Cu and permalloy/Cu multilayered nanowires (abstract)

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We have prepared Co/Cu and NiFe/Cu (Ni/Fe=permalloy) multilayered nanowires by electrodeposition into pores of membranes or holes made by e-beam lithography in PMMA layers. In both cases, pores and lithography, the diameter of the wires is around 100 nm and the layer thickness ranges between a few nm and several hundred nm. Transmission electron microscopy reveals that the nanowires are composed of long single-crystal grains with c axis (hcp Co) or (111) axis (fcc NiFe or Cu) perpendicular to the axis of the wire. A first series of samples is composed of conventional periodic multilayers. Their CPP-MR ratio can be as large as 80% at 4.2 K (NiFe 5 nm/Cu 5 nm) and giant magnetoresistance effects can be observed up to very large thicknesses (example: t_co=1 µm). At small thicknesses, we find the conventional behavior of the so-called "long spin diffusion length limit." More interesting are the results obtained out of this limit and used to determine the spin diffsion length SDL in Cu (140 nm at low T) and Co (44 nm at low T). For NiFe/Cu, the magnetic arrangement of successive layers is more difficult to control and we could not determine the SDL from data of the first series. A second series of samples is made with NiFe/Cu/NiFe trilayers (t_Cu=10 nm, 7 nmt_NiFe30 nm), separated from each other by Cu layers of 100 nm. As shown by superconducting quantum interference device measurements, the magnetization of the two NiFe layers in a trilayer are approximately antiparallel at zero field. We use the CPP-MR data on these samples to derive the SDL in permalloy. ©1997 American Institute of Physics.