Nickel on Lead, Magnetically Dead or Alive.pdf

a r X i v : 0 8 0 9 .0 7 1 5 v 1 [ c o n d - m a t .m e s - h a l l ] 3 S e p 2 0 0 8 Nickel on Lead, Magnetically Dead or Alive? Go Tateishi and Gerd Bergmann Department of Physics University of Southern California Los Angeles, California 90089-0484 e-mail: bergmann@usc.edu September 3, 2008 Abstract Two atomic layers of Ni condensed onto Pb films behave, according to anomalous Hall effect measurements, as magnetic dead layers. However, the Ni lowers the super- conducting Tc of the Pb film. This has lead to the conclusion that the Ni layers are still very weakly magnetic. In the present paper the electron dephasing due to the Ni has been measured by weak localization. The dephasing is smaller by a factor 100 than the pair-breaking. This proves that the Tc-reduction in the PbNi films is not due magnetic Ni moments. PACS: 75.20.Hr, 73.20.Fz, 74.45.+c, 74.78.Fk When a thin superconductor is condensed onto a normal conducting film then the first layers loose their superconductivity. This phenomenon is called the ”superconducting prox- imity effect”. A similar question arises if one condenses a thin ferromagnetic metal onto a normal metal. If the first layers of the ferromagnet loose their magnetism they are denoted as ”magnetic dead layers” (MDL). The first dead layers were observed almost 30 years ago for two to three atomic layers of Ni condensed onto amorphous Bi films [1]. For Ni layers on top of noble metals there were originally contradicting results. Liebermann et al. [2] observed two dead layers of Ni on Cu and Au while Pierce and Siegmann [3] observed ferromagnetism already in mono-layers of Ni on Cu (by means of spin polarized photo electrons). Kramer and Bergmann [4] investigated the magnetic properties of Ni on the surface of Mg, In, Sn, and the noble metals Cu, Ag and Au by means of the anomalous Hall effect (AHE). They observed between two and three dead Ni layers on the polyvalent substrate, while Ni on top of the noble metals showed ferromagneti