Improved performance of polycrystalline antiferromagnet/ferromagnet stack by nitrogen-assisted deposition

Abstract

The deposition process of the IrMn3/Co70Fe30 bilayer of antiferromagnet/ferromagnet (AF/FM) type was modified by introducing a nitrogen additive in argon plasma during the magnetron sputtering of the Co70Fe30 layer. This slight modification significantly enhanced the exchange bias energy density and reduced coercivity of an AF/FM bilayer for the AF IrMn layer thickness ranging from 20 to 50 Å. Calculations indicate that the boost in exchange bias energy density and the reduction in coercivity can be attributed to the increased anisotropy energy of the AF layer, resulting in more effective pinning of the FM layer by AF grains. The increase in anisotropy is caused by the diffusion of nitrogen from the FM into the AF layer, as established by x-ray diffraction, neutron reflectometry, and x-ray magnetic circular dichroism. Our research allows us to improve magnetic characteristics of exchange-coupled FM/AF structures through minor modifications in the sputtering process and/or save up to 20% of the costly IrMn3 target by reducing the thickness of the AF layer.