Co-resonant enhancement of spin-torque critical currents in spin-valves with 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 enhanced using "synthetic ferrimagnet" free-layers of form FM1/Ru/FM2 (FM=ferrromagnet). However, this enhancement 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 co-resonance between the two natural dynamic modes of the FM1/FM2 couple. The resonance condition facilitates energy transfer out of the spin-torque destabilized mode into the other stable mode whose effective damping is actually enhanced by spin-torques, thereby delaying the onset of instability of this coupled system to larger critical currents.

arXiv comment10 pages (manuscript form), with 4 embedded figures. Submitted for publication. Version #2 contains one additional equation (Eq. 4)

References in corpus (6)

• Spin Transfer Torques
• Spin-Diffusion Lengths in Metals and Alloys, and Spin-Flipping at Metal/Metal Interfaces: an Experimentalist's Critical Review
• Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal
• Angular Dependence of Spin-Torque Critical Currents in CPP-GMR Read Heads
• Spin-transfer in bilayer magnetic nanopillars at high fields as a function of free layer thickness
• Basic considerations for magnetization dynamics in the combined presence of spin-transfer torques and thermal fluctuations

Cited by in corpus (6)

• CPP Magnetoresistance of Magnetic Multilayers: A critical review
• Interplay between non equilibrium and equilibrium spin torque using synthetic ferrimagnets
• Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin-valves
• Current-induced dynamics of composite free layer with antiferromagnetic interlayer exchange coupling
• Switching of biaxial synthetic antiferromagnets: a micromagentic study
• Current Perpendicular-to-Plane (CPP) Magnetoresistance (MR)