Revealing channel polarization of atomic contacts of ferromagnets and strong paramagnets by shot-noise measurements

Abstract

We report measurements of the shot noise of atomic contacts of the ferromagnets cobalt and gadolinium and the strong paramagnets palladium, platinum, and iridium. The contacts are fabricated using the mechanically controlled break-junction technique at 4 K. Single-atom contacts of Co and Gd with conductance smaller than the conductance quantum show reduced noise compared to the expectation for the spin-degenerate single-channel case. We discuss by how far this observation gives evidence for spin-polarized transport. Pd, Pt, and Ir reveal noise levels which are above, but close to the threshold to the spin-degenerate single-channel situation. Since for such multivalent metals more than one channel is expected to contribute to the transport, our findings do not exclude spin-polarized transport for these elements. We observe an anticorrelation between the minimum noise and the bulk Stoner parameter of these elements, supporting that spin polarization might be reflected in the shot-noise signal in strong paramagnets.