HRTEM study of microstructure-coercivity relationship in perpendicular Co25Pd75 thin films

Abstract

The microstructure of 20 nm thick polycrystalline Co25Pd75 alloy films exhibiting perpendicular magnetic anisotropy (PMA), studied on the atomic scale by analytical transmission electron microscopy (TEM) techniques, is presented. Thin CoPd alloy films are considered promising candidates for pinning MgO-based perpendicular magnetic tunnel junctions (pMTJs) for spin- transfer torque magnetic tunnel junctions (STT-MRAM). The CoPd alloy films studied were grown by DC magnetron sputtering on four different seed layers: MgO, Ta, and Ta/Ru/Ta trilayer and Ta/Pd bilayer. The effect of the seed layers on the Co25Pd75 structural quality, the size and texture of crystallites as well as their compositional homogeneity and structural coherency of the grain boundaries formed between adjacent crystallites, are investigated. The detailed structural analysis reveals that Co25Pd75 layers grown on the Ta/Pd bilayer and Ta/Ru/Ta trilayer seeds consist of larger crystalline columns, with sizes ranging from 25 nm to 15 nm respectively, compared to the other two samples. Correlation of the Co25Pd75 crystalline quality with coercivity is suggested.