  We have developed and optimized two categories of spin transfer torque
magnetic tunnel junctions (STT-MTJs) that exhibit a high tunnel
magnetoresistance (TMR) ratio, low critical current, high outputpower in the
micro watt range, and auto-oscillation behavior. These characteristics
demonstrate the potential of STT-MTJs for low-power, high-speed, and reliable
spintronic applications, including magnetic memory, logic, and signal
processing. The only distinguishing factor between the two categories, denoted
as A-MTJs and B-MTJs, is the composition of their free layers, 2 CoFeB/0.21
Ta/6 CoFeSiB for A-MTJs and 2 CoFeB/0.21 Ta/7 NiFe for B-MTJs. Our study
reveals that B-MTJs exhibit lower critical currents for auto-oscillation than
A-MTJs. We found that both stacks have comparable saturation magnetization and
anisotropy field, suggesting that the difference in auto-oscillation behavior
is due to the higher damping of A-MTJs compared to B-MTJs. To verify this
hypothesis, we employed the all-optical time-resolved magneto-optical Kerr
effect (TRMOKE) technique, which confirmed that STT-MTJs with lower damping
exhibited auto-oscillation at lower critical current values. Additionally, our
study aimed to optimize the STT-MTJ performance by investigating the impact of
the capping layer on the device's response to electronic and optical stimuli.
