Structural and Magnetic Properties of CoPd Alloys for Non-Volatile Memory Applications

We have intensively studied perpendicular magnetic anisotropy (PMA) CoPd alloys, both structurally and magnetically, as a simple means of pinning MgO-based perpendicular magnetic tunnel junctions (pMTJs) for spin-transfer torque magnetic tunnel junction (STT-MRAM) applications. A compositional study of the Co _x Pd _100-x alloys at 50 nm thickness showed that the maximum coercivity and anisotropy was found for Co ₂₅ Pd ₇₅ . Perpendicular magnetic tunnel junction stacks were deposited using different compositions of CoPd. Current-in-plane tunneling measurements indicated that the TMR values roughly correlated with the coercivity and anisotropy of the single layers. A thickness study indicated that the alloy was fully perpendicular for thicknesses as low as 20 nm. Various seed layers were employed to optimize the coercivity of the Co ₂₅ Pd ₇₅ layer. Magnetometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were carried out to relate the magnetic and structural properties of these layers.