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The perpendicular magnetic anisotropy (PMA) and crystalline structure of Ta/NiFeB/MgO stacks are investigated. When the stack is annealed, PMA is induced and the magnetic moment increases due to the crystallization of bcc NiFe from amorphous NiFeB. This structure is combined with [Pt/Co]6 multilayers to study the change in the magnetic coupling and PMA behavior with the change in the Ta thickness inserted in-between and the annealing temperature. Among the [Pt/Co]6/Ta/NiFeB/MgO stacks, the stack with a 0.5-nm-thick Ta layer shows the strongest PMA with an effective PMA energy density of 4.4 × 106 erg/cm3 upon annealing at 400 °C. Further, the X-ray diffraction study of the crystalline structures confirms the formation of the NiFe (001) phase, which is essential for achieving a high tunneling magnetoresistance ratio.

The individual strengths of perpendicular magnetic anisotropy (PMA) at the bottom and top interfaces in sputtered [Pt/Co/Pt] trilayers are determined. The PMA strength from the top Co/Pt interface is significantly weaker than that from the bottom Pt/Co interface, indicating a similar difference in the interface quality. The contribution to the total anisotropy strength from the top Co/Pt interface increases with decreasing top Pt layer thickness; for a stack of Co thickness 1 nm, the contribution is only 10% for a top Pt layer of thickness 3.0 nm, but it increases to 32% for a Pt layer of thickness 0.2 nm.

The effects of inserting an amorphous FeZr layer between the [Pt/Co] multilayer and the CoFeB/MgO layer in stacks possessing perpendicular magnetic anisotropy are examined. A 1-nm-thick FeZr layer is effective in forming a bcc (001)-textured CoFe layer during annealing by suppression of crystallization at the interface with the multilayer, which is terminated in a close-packed plane. Because FeZr is magnetic, it has an advantage over Ta, an alternative material used for the same purpose. Efficient magnetic coupling between the multilayer and CoFeB/MgO occurs even for large FeZr layer thicknesses, so the magnetic properties of the stack are only weakly affected.

The effects of Co layer thickness and annealing temperature on the perpendicular magnetic anisotropy (PMA) properties of inverted [Pt (0.2 nm)/Co (tCo)]6 multilayers (where tCo indicates the thickness of the Co layer) have been investigated. The cross-sectional microstructure, as observed from the high-resolution transmission electron microscope images, shows a clear layered structure with atomically flat interfaces both in the as-deposited state as well as after annealing, indicating the interface effects for PMA. The effective PMA energy density (Keff) increases significantly with an increase in tCo from 0.2 to 0.28 nm and then becomes almost saturated with further increases in tCo, followed by a slight reduction at the highest Co thickness, tCo = 0.6 nm. In order to explain the tCo dependence on Keff, the intrinsic PMA energy density (Ki) is calculated by additionally measuring a similar set of results for the saturation magnetization. The Ki value increases nearly linearly with the increase in tCo fro...