Thermal degradation of spin valve multilayers caused by Mn migration

We have investigated the thermal degradation of spin valve multilayers caused by annealing at 250–300 °C, and determined that it significantly depended on selection of antiferromagnetic layers. Spin valves with a CuAu-I type ordered PtMn antiferromagnetic layer exhibited better thermal stability than those with a disordered Rh17–Mn83 or an Ir20–Mn80 layer. Comparing the magnetoresistance ratio dR/R of those spin valves after annealing at 280 °C for 5 h, that of PtMn spin valves was more than 60% higher than the others, even though the same stack of layers was used, except the antiferromagnetic layer. Such an excellent thermal stability of PtMn spin valves was attributed to less Mn migration over the existing layers after annealing. This indicated that Mn impurities in ferromagnetic layers such as Co90–Fe10 or Ni81–Fe19 deleteriously affected the spin-dependent scattering of conduction electrons.