Spin-torque-induced RF oscillations in MgO-based magnetic tunnel junctions (MTJs) were investigated at two different in-plane angles of applied magnetic field. The RF spectra with the magnetic field applied in the hard axis direction of the MTJ showed a simple Lorentzian-type peak structure, while those measured in the easy axis direction had a complicated peak structure. It was found by analyzing Lorentzian-type RF spectra that the linewidth decreased linearly as the injected dc current was increased. The linear decrease of the linewidth indicates the reduction of effective damping in the magnetization dynamics due to spin-transfer-torque. The RF output power measured with the magnetic field in the hard axis direction was 32 nW, which was larger than that measured with the magnetic field in the easy axis direction.
