Perpendicular magnetic anisotropy for CoFeBZr/MgO

Abstract

Magnetic tunnel junctions (MTJs) using perpendicular magnetic anisotropy (PMA) have been studied for high density magnetoresistive random access memory (MRAM) with the expectations of scalability for driving current and reducing switching anomalies by local magnetization non-uniformity. CoFeB which has been well developed for MTJ using in-plane magnetization, is also a favorable choice for perpendicular magnetization with the stalking structure of Ta/CoFeB/MgO because its interfacial anisotropy results low current density (J<inf>c</inf>) for magnetization reversal by spin transfer torque (STT) [1]. However the practical MRAM technology requires further reduction of J<inf>c</inf> without degradation of thermal stability. The Gilbert damping measurement showed that Zr insertion provides reduction of the damping constant (α) for the Co film with in-plane magnetization [2]. We present the effects of Zr insertion (5%) in Co(65)Fe(20)B(10) for PMA due to interfacial anisotropy with MgO. Perpendicular magnetization is successfully formed up to 1.56 nm of CoFeBZr with the stalking structure of Ta/CoFeBZr/MgO. The damping is determined as α = 0.004 from the line width of ferromagnetic resonance (FMR) which is lower than value (∼ 0.008) for CoFeB [3]. Moreover, the effective anisotropy energy (K<inf>eff</inf>) for maximum value shows 0.163 MJ/m3 for CoFeBZr which is comparable to that 0.183 MJ/m of CoFeB [4]. This study results that insertion of Zr in CoFeB suggests a method for low current switching of MTJ using PMA.