Structural and magnetic studies of exchange bias films of Ir(20)Mn(80)

Thin films of IrMn were made by magnetron sputtering, using nominally 20 at. % Ir, and their structural and magnetic properties were evaluated for use as an exchange bias material. The magnetic properties of different combinations of Py and CoFe underlayers were determined by magnetometry and by using ferromagnetic resonance (FMR) in the temperature range 4-350 K; x-ray analyses and atomic force microscopy were used to assess the structures. The IrMn films have the AuCu3 structure with strong < 111 > texture. The internal interfaces of the multilayer structures are very smooth. They induce relatively strong exchange bias in Py and CoFe overlayers but can have negligible coercivity. The bias field is strongly dependent on the direction of the moment during cooling, even well below 300 K, and coercivity and FMR linewidth increase with cooling. Isotropic shifts of FMR are small at 300 K but increase rapidly below 150 K. Our data suggest that spin-flop models for exchange bias may not apply to IrMn, and that small spin structures dominate low temperature behavior. [S0021-8979(00)35808-X].