Underlayer Effect on Perpendicular Magnetic Anisotropy in Co(sub20)Fe(sub60)B(sub20)/MgO
Andrew P. Chen, Yury Y. Iunin, S F. Cheng, Robert D. Shull
Perpendicular Magnetic Tunneling Junctions (pMTJs) with Ta\CoFeB\MgO have been extensively studied in recent years. However, the effects of the underlayer on the formation of the CoFeB perpendicular magnetic anisotropy (PMA) are still not well understood. Here we report the results of our systematic use of a wide range of elements (Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt and Au) encompassed by columns IVA, VA, VIA, VIIA, and VIIIA of the periodic table as the underlayer in a underlayer\Co(sub20)Fe(sub60)B(sub20)\MgO stack. Our goals are to find more elements which can create PMA in CoFeB and to explore the mechanisms for these underlayers to enhance or create the PMA. We found underlayer elements having both an outer shell of 4d electrons (Zr, Nb Mo, and Pd) and 5d electronics (Hf, Ta, W, Re, Ir, and Pt) resulted in the development of PMA in the MgO capped Co(sub20)Fe(sub60)B(sub20). Hybridization between the 3d electrons of the Fe or Co (in the Co(sub20)Fe(sub60)B(sub20) at the interface with the 4d or 5d electrons of the underlayer is throught to be the cause of the PMA development.