The power angular dependence for spin torque oscillators (STOs) is systematically investigated in magnetic tunnel junctions by varying the in-plane polarizer angle (IPPA) which refers to the angle between the free and fixed layer. The polarizer angle is adjusted by integrating a lithography process and a post-annealing process. An increase of power with increasing IPPA is experimentally demonstrated. STOs with a 30 and 60 IPPA show a 2-3 and 5-6 times higher efficiency in the power spectral density of the main peak than that with the traditional 0 IPPA, respectively. This increase of the power efficiency with IPPA for STOs can be explained by the power dependence on the precession angle at different IPPA.
Bibliographical noteFunding Information:
This work was supported primarily by the MRSEC Program of the National Science Foundation under Award No. DMR-0819885. We thank Professor Paul Crowell, Mr. Te-Yu Chen, Dr. Jaesang Oh, Professor Anand Gopinath, and Professor Rhonda Franklin for their technical assistance with the microwave measurements and Professor Ilya Krivorotov from UC Irvine for his useful discussions.