The microwave power and the critical current of spin torque oscillator (STO) devices with a built-in hard axis polarizer have been studied. This design allows for an external-field-free STO. The time domain oscillation signals give direct evidence of higher output from the hard axis polarizer STO, which agrees with spectroscopic results. The hard axis polarizer STO generates a higher power because of the larger slope of the magnetoresistance-angle curve at the lowest energy potential. Furthermore, the hard axis polarizer STO shows a low critical current indicating the large spin torque effect when two magnetic layers are in the 90 configuration.
Bibliographical noteFunding Information:
This work was supported primarily by the MRSEC Program of the National Science Foundation under Award No. DMR-0819885. We acknowledge Dr. Jaesang Oh, Professor Anand Gopinath, and Professor Rhonda Franklin from University of Minnesota and Jerry Mendez from Tektronix for technical assistance with the microwave measurements. H.Z. and J.P.W. also acknowledge the support from the DARPA STT-RAM program and Intel.