Enhancement of exchange bias in thin PtMn antiferromagnets by Ru and Cr nano-lamination

In this work, we report a novel approach to facilitate the phase transformation, namely the introduction of ultrathin Ru and Cr nanolayers inside the PtMn layer. The concept is to bury one or more very thin (<1 monolayer) Ru or Cr layers in the PtMn at some distance from the interface. The effect of these insertion layers is to aid the FCC to FCT transformation by suppressing the constraining effect from the interface. Experimental results show an enhancement of the exchange bias field by adding these ultrathin insertion layers. The enhancement of the exchange bias field can be up to 10% compared to the structure without the insertion layer. From these results, it can be seen that significant exchange bias field enhancement can indeed be obtained with as little as 2 Å of Ru insertion at 10 Å from the interface. Similar results have been obtained with 1 Å Cr insertion at the same PtMn layer position. These results illustrate the potential of nano-lamination of antiferromagnets as an avenue toward creation of novel spin valve and spintronic materials.