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
$300~^{\circ }$
C for 2 h. Irrespective of annealing conditions, in-plane MA (IMA) is detected in films with Ta/Ru and Ta/Cu HM stacks. X-ray diffraction (XRD) and reflectivity measurements evidence that in the case of Ta HM, CFB/MgO develops the body-centered-cubic (bcc) structure, while Ta/Cu and Ta/Ru HM stacks induce face-centered-cubic (fcc) and hcp structures, respectively, indicating HM stacking affects epitaxial relation between MgO and CFB layers. The X-ray reflectivity (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.