Exchange coupling in FeTaN/IrMn/FeTaN and NiFe/IrMn/NiFe trilayer films

The dependence of the exchange bias field H-eb in FeTaN/IrMn and NiFe/IrMn systems on the microstructure has been investigated. Bilayer and trilayer films of 50 nm thick FeTaN and NiFe and 10 nm thick IrMn were prepared by dc magnetron sputtering. The glass/FeTaN/IrMn/FeTaN trilayer showed that the top FeTaN did not influence H-eb in the bottom FeTaN, closest to the substrate, during deposition and annealing. High-resolution transmission electron microscopy results showed limited evidence of epitaxial growth with both columnar single IrMn grains and multiple IrMn grains. In contrast, in the glass/NiFe/IrMn/NiFe trilayer, the top NiFe significantly influenced H-eb in the bottom NiFe during deposition and annealing. X-ray diffraction data for both systems showed no detectable changes in either the crystallinity or (111) texture of the IrMn layer during annealing. In the NiFe system, the trend in H-eb in the as-deposited and annealed states may be explained by assuming single columnar grains in the IrMn which couple the top and bottom NiFe layers. In the FeTaN system, the trend in H-eb in the as-deposited state may be explained by assuming multiple IrMn grains which decouple the top and bottom FeTaN layers. However, the behavior on annealing is a mystery. (C) 2002 American Institute of Physics.