Influence of barrier impurities on the magnetoresistance in ferromagnetic tunnel junctions

Abstract

The effect of barrier impurity atoms on the magnetoresistance of ferromagnetic tunnel junctions has been investigated. For that purpose, Co/Al2O3/Ni80Fe20 junctions were prepared with submonolayer amounts of Co, Pd, Cu, or Ni incorporated into the middle of the insulating oxide. The junction magnetoresistance (JMR) was measured at 77 and 300 K and referenced to that of simultaneously prepared control junctions without impurities. The JMR decays approximately linearly with increasing impurity content, the slope depending sensitively on the type of element. The decrease is most pronounced for Ni, with the normalized JMR going down at a rate of 0.39 Å−1 of material (at 77 K), whereas Co shows a relatively weak decay of only 0.08 Å−1. Pd and Cu represent intermediate cases. At 300 K, the suppression of JMR is slightly higher. Results are interpreted in terms of spin-flip scattering of tunneling electrons by the impurities.