Effect of overlayer material and thickness in Ta/CoFeB/MgO/overlayer structures

Interest in spintronic memory has sustained research efforts on materials systems such as CoFeB/ MgO, which exhibit high tunneling magnetoresistance necessary for readout while also possessing perpendicular magnetic anisotropy (PMA) necessary for the continued downscaling of low-power, non-volatile memory devices . Several requirements have already been identified in order to obtain PMA, including MgO quality and CoFeB thickness, among others . In seed/CoFeB/MgO or MgO/CoFeB/cap stacks, appropriate seed or cap materials that help induce PMA when placed adjacent to CoFeB have also been identified. In the former stack configuration, a protective overlayer is often deposited above MgO, the effect of which on magnetic properties may not be immediately apparent nor expected as this overlayer has no contact with the magnetic layer . In this work, we show that overlayer material and thickness can affect magnetic properties significantly, even resulting in the loss of PMA .