Superparamagnetic ground state of CoFeB/MgO magnetic tunnel junction with dual-barrier

Tran Thanh Nga^1*, Tu Ngoc Lam¹, Chao Yao Yang¹, Wen Chin Lin², Po Wen Chen³, Yuan Chieh Tseng¹

¹Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan
²Department of Physics, National Taiwan Normal University, Taipei, Taiwan
³Division of Physics, Institute of Nuclear Engineer Research, TaoYuan, Taiwan

* Presenter:Tran Thanh Nga, email:tranthithanhnga91@gmail.com

CoFeB/MgO-based magnetic tunnel junctions (MTJs) have considerable potential in magnetic random access memory (MRAM), thanks to their tunable perpendicular magnetic anisotropy (PMA). Interface, electronic and transport characterizations were utilized to approach the modified magnetic properties driven by the dual-MgO structure in this work. We found significant reduction of dead-layer by inserting additional MgO into the MTJ structure. The dual-MgO structure appeared to hinder boron (B) diffusion into the metallic layer and prevent capping-layer (Ta) penetration across the interface, compared with single-MgO. This suppressed the dead-layer effect and promoted overall magnetization despite PMA degradation. A robust BOx phase that formed within the dual-MgO structure presented a superparamagnetic ground state (SPM). In the single-MgO structure, any reduction in the thickness of the CoFeB promoted PMA, albeit at the cost of spin-polarization. The dual-MgO structure could restore spin-polarization by preferentially populating spin electrons into Fe/Co minority states. X-ray magnetic spectroscopy and anomalous Hall effect suggest that, the dual-MgO differs from the single-MgO with a favorable longitudinal polarized spin-channel. This makes the dual-MgO structure applicable to applications requiring in-plane rather than out-of-plane sensing.

Keywords: Magnetic tunnel junction, Perpendicular magnetic anisotropy, Superparamagnetic