09:45 〜 10:00
▼ [14a-2J-4] CoFeB thickness dependence of electric-field effects on magnetic anisotropy and damping constant in Ta/CoFeB/MgO structures
キーワード：electric-field effect,magnetic anisotropy,damping constant
Magnetic anisotropy and damping constant \alpha are important parameters characterizing spintronics materials and devices. They are expected to be related to each other through the spin-orbit interaction, and thus the correlation between them has been studied in various materials. We investigated the correlation in Ta/CoFeB/MgO structures by modulating the anisotropy through the application of the electric field E, where clear modulation of \alpha was observed for one device with the largest perpendicular magnetic anisotropy among studied devices. In order to clarify the trend experimentally, we investigate here the electric-field effect on a in devices with thinner CoFeB and thus larger magnetic anisotropy than that in the previous study.
Stack structures, Ta/Ru/Ta/Co0.2Fe0.6B0.2 (t = 1.30, 1.36 nm)/MgO (2 nm)/Al2O3(5 nm), are deposited on a Si (001)/SiO2 substrate by rf magnetron sputtering, and are annealed at 300oC for 1 h in vacuum under perpendicular magnetic field of 0.4 T. The stacks are processed into a 1-mm diameter circular mesa, and a 57-nm-thick Al2O3 insulator and a Cr (3)/Au (50) counter electrode were deposited to complete electric-field-effect devices. Positive voltage is defined as the Cr/Au layer positive with respect to the CoFeB layer.
The magnetic field angle /thetaH dependence of ferromagnetic resonance spectra are measured as a function of E at room temperature. The magnetic anisotropy and \alpha are determined from the analysis of the angle dependence of resonant field and linewidth, respectively. The effective perpendicular magnetic anisotropy energy constant K1eff and a decrease by the application of positive E for the two devices, and their modulation ratios increase with decreasing t. The present result along with the previous result indicates that the modulation of K1eff is observed for all the devices, whereas that of \alpha is observed only in devices with a perpendicular easy axis (K1eff > 0). The modulation ratio of \alpha increases with increasing K1eff and thus decreasing t. These results suggest that the modulation of a is related to the interfacial effect and the direction of easy axis plays a role in the emergence of the electric field effect.
Stack structures, Ta/Ru/Ta/Co0.2Fe0.6B0.2 (t = 1.30, 1.36 nm)/MgO (2 nm)/Al2O3(5 nm), are deposited on a Si (001)/SiO2 substrate by rf magnetron sputtering, and are annealed at 300oC for 1 h in vacuum under perpendicular magnetic field of 0.4 T. The stacks are processed into a 1-mm diameter circular mesa, and a 57-nm-thick Al2O3 insulator and a Cr (3)/Au (50) counter electrode were deposited to complete electric-field-effect devices. Positive voltage is defined as the Cr/Au layer positive with respect to the CoFeB layer.
The magnetic field angle /thetaH dependence of ferromagnetic resonance spectra are measured as a function of E at room temperature. The magnetic anisotropy and \alpha are determined from the analysis of the angle dependence of resonant field and linewidth, respectively. The effective perpendicular magnetic anisotropy energy constant K1eff and a decrease by the application of positive E for the two devices, and their modulation ratios increase with decreasing t. The present result along with the previous result indicates that the modulation of K1eff is observed for all the devices, whereas that of \alpha is observed only in devices with a perpendicular easy axis (K1eff > 0). The modulation ratio of \alpha increases with increasing K1eff and thus decreasing t. These results suggest that the modulation of a is related to the interfacial effect and the direction of easy axis plays a role in the emergence of the electric field effect.