Spin-transfer-induced excitations in bilayer magnetic nanopillars at high fields: The effects of contact layers

Abstract

Current-induced excitations in bilayer magnetic nanopillars have been studied with large magnetic fields applied perpendicular to the layers at low temperatures. Junctions investigated all have Cu/Co/Cu/Co/Cu as core layer stacks. Two types of such junctions are compared, one with the core stack sandwiched between Pt layers (Type A), the other with Pt only on one side of the stack (Type B ). Transport measurements show these two types of junctions have similar magnetoresistances and slope of critical currents with respect to field, while A samples have higher resistance. The high field bipolar excitation, as was previously reported [ Özyilmaz et al. Phys. Rev. B, 71, 140403(R)] , is present in B samples only. This illustrates the importance of contact layers to spin-current-induced phenomena. This also confirms a recent prediction on such spin-wave excitations in bilayers.

Spin‐transfer in High Magnetic Fields and Single Magnetic Layer Nanopillars

“…Further, the results illustrate that at high currents the nanopillar resistance can be lower than that of a state of P magnetic alignment. Finally, modifying the contact geometry, by making the contacts more symmetric, is shown to suppress such excitations, consistent with theory (Chen et al, 2006a).…”

“…Further, in the model asymmetries in the spin diffusion to the left and right of the ferromagnets are the main origin of the short wavelength spin-wave excitations of the magnetization. Subsequently, we have prepared nanopillar samples with identical top and bottom leads with respect to spin diffusion, by inserting a thin Pt layer in the right Cu leads shown in Figure 16 (Chen et al, 2006a). In these structures, bipolar excitations are suppressed and no excitations are observed beyond the main peak in dV /dI , confirming theoretical predictions.…”