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오영완,박경웅,박병국 한국물리학회 2019 Current Applied Physics Vol.19 No.1
We report the dependence of voltage-controlled magnetic anisotropy (VCMA) effect and its volatility on an underlayer (UL) in CoFeB/MgO structures. For a sample with Ta or Pt UL, the VCMA effect occurs when the applied gate voltage (Vg) exceeds a critical value, and it persists even after removing Vg. This is in contrast to the volatile VCMA effect and its linear dependence on Vg in a sample with W UL. Furthermore, we demonstrate that the volatility of the VCMA effect can be modified by introducing a Ta/W bilayer, enabling arbitrary control of the magnetic properties via VCMA effect.
Luong Chi Hieu,심윤수,이예림,정종율,오영완,박병국 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.7
The magneto-optical polar Kerr spectra of CoFeB/MgO thin films on different kinds of underlayers (Hf, Pt) were investigated in order to understand the origin of the interfacial perpendicular magnetic anisotropy (PMA) in that structure. The Kerr spectra were measured by using real-time Kerr spectroscopy based on a fiber-coupled high-speed spectrometer in the photon energy range of 1.5 2.9 eV. The magneto-optical studies revealed that the magneto-optical proximity effect due to the Hf underlayer to CoFeB was weak, but the interfacial contribution of the Pt underlayer to the CoFeB was strong. The variation of the PMA as a function of the annealing conditions was also investigated, and a gradual enhancement of the PMA was observed with increasing annealing temperature for the Pt underlayer sample, but a gradual decay of the PMA was observed for the Hf underlayer sample. The magneto-optical studies showed that the formation of CoPt alloys at the Pt/CoFeB interface played an important role in the PMA of the Pt/CoFeB/MgO structure at higher annealing temperature.