Switching characteristics and magnetoresistance of Co-based multilayered perpendicular magnetic tunnel junctions

Abstract

AbstractPerpendicularly magnetized magnetic tunnel junctions (pMTJ) using Co based multilayers as free and reference layers have been optimized for perpendicular magnetic anisotropy (PMA) and high tunneling magnetoresistance (TMR). The effect of seed layers, Co thickness and Co/Ni thickness ratio on the anisotropy of these multilayer films has been studied. Intermixing of these multilayers was analyzed by local electrode atom probe (LEAP). The effect of Co thickness, Pd thickness and number of Co/Pd bilayers on the anisotropy and coercivity of the [Co/Pd]n multilayer films have been studied for both free and reference layers. The magnetic behavior of these PMA systems was studied by alternating gradient magnetometer. CoFeB/MgO/CoFeB trilayers sandwiched between the PMA multilayer material systems were studied. The transport properties of the patterned MTJ stacks were measured by PPMS from 10K to 400 K. A maximum TMR of 10% at 10K (5-10% at 300 K) was obtained for these perpendicular MTJ’s (pMTJ), regardless of whether they were magnetically annealed for MgO-CoFeB crystallization or not, indicating that the fcc-bcc-fcc transitions from the fcc multilayers to the bcc CoFeB/MgO/CoFeB do not promote the “giant MgO TMR effect” caused by symmetry filtering.