Thermal stability of spin valve sensors using artificial Co/Ir based ferrimagnets

Hard-soft spin valve structures have been grown by molecular beam epitaxy on MgO(0 0 1) substrates. The hard magnetic layer consists of an artificial Co/Ir/Co ferrimagnet system (AFi), while a Fe/Co bilayer from the buffer has been used as a soft detection layer. The Fe layer has been grown at 600°C giving rise to a monocrystalline layer with a BCC structure. Consequently, this layer presents a hard and a easy magnetization axis, respectively, along the BCC [1 1 0] and the [1 0 0] directions. The AFi system presents dramatic differences after successive annealing steps up to 350°C. An increase of the GMR from 3% to 3.5% is observed after annealing at 250°C while the coercive field of the AFi and the GMR plateau are strongly reduced. After further annealing at higher temperature the GMR drops down accompanied with a strong decrease in the antiparallel alignment amount in the AFi system. Rutherford back scattering measurements have been performed to investigate the changes in the interface morphology and to correlate it to the magneto-transport properties.