Effect of heavy metal (HM) stacking on magnetic anisotropy of HM/CoFeB/MgO structures

We investigated the effect of heavy metal (HM) stacking on magnetic anisotropy (MA) in HM/CoFeB(CFB)/MgO films. Perpendicular MA (PMA) is observed at as-deposited Ta/Pt/CFB/MgO and Ta/CFB/MgO films annealed at 300 °C for 2 hours. Irrespective of annealing conditions, in-plane MA (IMA) is detected in films with Ta/Ru and Ta/Cu HM stacks, respectively. X-Ray diffraction and reflectivity measurements evidence that in the case of Ta HM, CFB/MgO develops the bcc structure, while Ta/Cu and Ta/Ru HM stacks induce fcc and hcp structures, respectively, indicating HM-stacking affects epitaxial relation between MgO and CFB layers. XRR simulation shows that the thickness of CFB layer leads to structural changes of CFB layer together with those of MgO layer. This is consistent with a bond-oriented anisotropy through the thickness of amorphous CFB films with respect to HM stacks.