title: Coresonant enhancement of spin-torque critical currents in spin valves with a synthetic-ferrimagnet free layer.
abstract: It is experimentally shown that the critical current for onset of spin torque instability in current-perpendicular-to-plane spin valves can be strongly increased using "synthetic-ferrimagnet" free layers of form FM1/Ru/FM2 (FM=ferrromagnet). However, this increase occurs for only one polarity of bias current. A two-macrospin model is shown to reproduce the observations. The model suggests that this phenomenon is related to a polarity-dependent, spin torque-induced coresonance between the two natural dynamic modes of the FM1/FM2 couple. The coresonance condition facilitates energy transfer out of the spin-torque destabilized mode into the other stable mode whose effective damping (or line width) is strongly enhanced by spin torques.
authors.affiliation: San Jose Research Center, Hitachi Global Storage Technologies, San Jose, California 95135, USA.
authors.forename: Neil
authors.initials: N
authors.lastname: Smith
authors.forename: Stefan
authors.initials: S
authors.lastname: Maat
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Carey
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Childress