11:30 〜 11:45
▼ [6a-C18-11] Efficient excitation of ferromagnetic resonance for radio-frequency amplification in magnetic tunnel junctions
キーワード：rf amplifier, magnetic tunnel junction, ferromagnetic resonance
Radio-frequency (rf) devices using magnetic tunnel junctions (MTJs) have attracted attention in spintronics. Recently, rf-amplification has been investigated in MTJs by S parameter measurement [1, 2]. The rf-signal can be amplified at ferromagnetic resonance (FMR) frequency in the direct-current (dc) biased MTJ. However, the rf-signal has not been amplified, i.e. observed rf-gain is less than 1 (0.5~0.6 in Ref. 1 and 0.07 in Ref. 2). To increase rf-gain, efficient excitation of FMR is required. In the present study, we have employed giant spin-torque induced by Joule heating in MTJs while applying magnetic field normal to the film plane to prepare quite shallow magnetization potential for efficient FMR excitation.
Figure 1 shows the experimental design. The film stack, Ta(3) | PtMn(15) | FeCo(2.5) | Ru(0.9) | FeCo(1) | Ta(0.3) | CoFeB(2) reference layer | MgO(1.1) | FeB(1.7) free layer | MgO(1.0) | TaB(2) | Ta(5) | Ru(7), was deposited on thermally oxidized Si substrate (nm in thickness). The multilayer was fabricated with the designed junction size of 80 nm in diameter. The dc and rf-current are applied to the MTJ through bias-tee. The external magnetic field is applied along tilted direction at 8° from perpendicular to the film plane to cancel out shape anisotropy of the free layer and coupling field from the reference layer. Figure 2 shows the magnetic field dependence of S11 intensity. The FMR peaks from the free layer are observed by S11 spectra. The maximum S11 intensity of 1.26 was observed at the magnetic field of 50 mT, which can be explained by spin-torques from spin-transfer as well as magnetic anisotropy change induced by Joule heating. This work was supported by ImPACT program and JSPS KAKENHI (Grant No. JP16H03850).
Figure 1 shows the experimental design. The film stack, Ta(3) | PtMn(15) | FeCo(2.5) | Ru(0.9) | FeCo(1) | Ta(0.3) | CoFeB(2) reference layer | MgO(1.1) | FeB(1.7) free layer | MgO(1.0) | TaB(2) | Ta(5) | Ru(7), was deposited on thermally oxidized Si substrate (nm in thickness). The multilayer was fabricated with the designed junction size of 80 nm in diameter. The dc and rf-current are applied to the MTJ through bias-tee. The external magnetic field is applied along tilted direction at 8° from perpendicular to the film plane to cancel out shape anisotropy of the free layer and coupling field from the reference layer. Figure 2 shows the magnetic field dependence of S11 intensity. The FMR peaks from the free layer are observed by S11 spectra. The maximum S11 intensity of 1.26 was observed at the magnetic field of 50 mT, which can be explained by spin-torques from spin-transfer as well as magnetic anisotropy change induced by Joule heating. This work was supported by ImPACT program and JSPS KAKENHI (Grant No. JP16H03850).