valet - Thales Group

Jeudi 4 juin à 14h
Auditorium de l’IOTA, en face de Thales TRT, Palaiseau
Micro-magnetic Theories of Linear Stability and Non
Linear Magnetization Dynamics in Magnetic
Nanostructures under Spin Transfer Induced Torques
Thierry Valet
In Silicio, Parc de la Duranne, Les Pléiades II,
730 rue René Descartes, 13857 Aix en Provence, France
Considering the pretty general case of a three dimensional (3D) multi-terminal
magnetic nano-device, we introduce new theories solving two fundamental classes of
problems central to spin transfer induced magnetization dynamics:
(1). What is the zero temperature critical current value for loss of stability of a general 3D
non uniform micro-magnetic state?
(2). How can we “best” approximate the stochastic non linear magnetization dynamic at
finite temperature “near” a critical current value?
First, we demonstrate how a new perturbation theory of the zero temperature linearized
magnetization dynamic in the vicinity of general non uniform (meta)stable micro-magnetic
states can be established. Illuminating analogies (and differences) with stationary perturbation
theory in elementary quantum mechanic are discussed. Applied to problem (1), we show how
the new theory enables to derive general formal expressions for the critical current(s). We
discuss the relation with classical macro-spin critical current theory.
Second, near a critical current value, we demonstrate how one can systematically reduce the
infinite dimensional stochastic micro-magnetic dynamic equations at finite temperature into a
much more tractable universal non linear stochastic complex amplitude equation. We compare
the newly derived universal amplitude equation with previously proposed reduced dynamic
equations, and we show how the new theory allows establishing and discussing generic
features of the non linear stochastic magnetization dynamic and associated magneto-resistive
noise “near” a critical current value.
Finally, we demonstrate how the derived formal theories are amenable to practical numerical
calculations. We introduce the newly available software package SpinFlow 3D™, and
illustrate its capabilities on selected applications:
 Magnetic noise modeling for TMR and CPP GMR hard disk drive readers
Oscillation threshold current prediction and spectral metric modeling for spin transfer
nano-pillar oscillators
Contributions to STT RAM cell modeling