Influence of a uniform current on collective magnetization dynamics in a ferromagnetic metal

Abstract

We discuss the influence of a uniform current j ជ on the magnetization dynamics of a ferromagnetic metal. We find that the magnon energy ⑀(q ជ ) has a current-induced contribution proportional to q ជ •J ជ , where J ជ is the spin current, and predict that collective dynamics will be more strongly damped at finite j ជ . We obtain similar results for models with and without local moment participation in the magnetic order. For transition metal ferromagnets, we estimate that the uniform magnetic state will be destabilized for jտ10 9 A cm Ϫ2 . We discuss the relationship of this effect to the spin-torque effects that alter magnetization dynamics in inhomogeneous magnetic systems.

Spin pumping by a field-driven domain wall

“…47 Equation ͑4͒ is most easily understood as arising from the Berry phase picked up by the spin of the electrons as they drift adiabatically through a noncollinear magnetization texture. 16,17 Variation of this term with respect to the magnetization direction gives the reactive spin transfer torque in Eq. ͑1͒.…”

“…Perturbation theory in these terms then amounts to performing a gradient expansion in the magnetization direction. 17 Hence, the fact that Barnes and Maekawa consider the case that spin is fully conserved is demonstrated mathematically by noting that in Eq. ͑5͒ of Ref.…”

“…The first is the reactive spin transfer torque, 16,17 which corresponds to the term proportional to ٌ⍀ on the left-hand side of the above equation. It is characterized by the velocity v s that is linear in the current and related to the external electric field E by…”

“…11 The opposite effect, i.e., the manipulation of magnetization with spin current, is called spin transfer. [12][13][14][15] Recently, the possibility of manipulating with current the position of a magnetic domain wall via spin transfer torques has attracted a great deal of theoretical [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and experimental [31][32][33][34][35][36][37][38] interest. Although the subject is still controversial, 18,21 it is by now established that in the longwavelength limit, the equation of motion for the magnetization direction ⍀, which in the absence of current describes damped precession around the effective field −␦E MM ͓⍀͔ / ͑ប␦⍀͒, is given by…”

Reversal-mechanism of perpendicular switching induced by an in-plane current

“…For the first condition, as shown below, we experimentally demonstrate that, without any external fields, a large current can break a uniform magnetization state by forming 50% ↑ and ↓ domains in HM/FM structures. Generally, the current-induced domain nucleation can be caused by Joule heating and current-induced spin torques [11][12][13][14] . However, by monitoring the sample resistance change during the applied current pulses, we show that the current-induced temperature rise is only several K, which cannot dominate the domain nucleation process.…”