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SYMS: Magnetic Switching

SYMS 2: Magnetic Switching II

SYMS 2.3: Hauptvortrag

Montag, 27. März 2006, 17:50–18:20, HSZ 04

Spin torque: wall dynamics in nanowires vs. switching in nanopillars — •Jacques Miltat and André Thiaville — Laboratoire de Physique des Solides, Univ. Paris-Sud and CNRS, ORSAY, France

Spin transfer induced switching in nanopillars may be viewed as an efficient process mainly due to the existence of a parametric pumping phase preceeding switching. Thus, a minute torque combined to the micromagnetic response of the nanoelement allows for switching at relatively low current densities. Spin pressure may also induce wall motion in ferromagnetic nanowires. Assuming current polarization adiabaticity and full transfer of angular momentum to the local magnetization, the usual spin torque term translates into − ( u^→ · ∇^→ ) M^→ , where u^→ represents a velocity vector proportional to the current density and impinging electrons polarization. Unfortunately, according to the adiabatic theory, walls in nanowires, be it of the Transverse or Vortex type, are found to move only for current densities about one order of magnitude larger than experimental values. Also, wall structures are found to transform continuously during motion, a phenomenon directly linked to the so-called Walker velocity limit. A better agreement between theory and experiment may be achieved via the introduction of an additional torque term, the origin of which remains unclear at this stage. It is anticipated that theory and experiments might be best compared under pulsed current conditions, special attention being paid to the displacement of a depinned wall during the time necessary for a structure transition at a specified current density.