Dependence of exchange coupling on IrMn microstructures in IrMn/Fe65Co35 films

The exchange coupling strength and microstructure of the multilayers, Si/Ta(22)/Cu(t)/IrMn(10)/FeCo(4 nm) with tCu=1-30 nm, have been investigated using XRD and high-resolution TEM. It has been found that randomly oriented small IrMn crystallites embedded in amorphous-like matrix are observed for tCu=1 and 5 nm, with their size increasing with increasing tCu, while columnar IrMn crystallites grow epitaxially for tCu=10 nm. It has turned out that the exchange coupling strength depends on the number and size of the IrMn crystallites directly coupled with the FeCo layer rather than the orientation of the IrMn crystallites.