Domain wall propagation in magnetic nanowires by spin-polarized current injection

Abstract

We demonstrate movement of a head-to-head domain wall through a magnetic nanowire simply by passing an electrical current through the domain wall and without any external magnetic field applied. The effect depends on the sense and magnitude of the electrical current and allows direct propagation of domain walls through complex nanowire shapes, contrary to the case of magnetic field induced propagation. The efficiency of this mechanism has been evaluated and the effective force acting on the wall has been found equal to 0.88x10 -9 N.A -1 .Controlling magnetization directly with an electric current rather than a magnetic field is one of the recent exciting developments within spintronics. The main expectations are a very fast reversal of magnetization (< 100 ps) and the ability to control individual magnetic elements without affecting neighbouring structures. In ferromagnetic/nonmagnetic/ferromagnetic multilayer structures, several experiments have demonstrated magnetization reversal of one layer purely by applying a pulsed current and without any externally applied magnetic field [1]. This concept could be also very interesting in the framework of recently demonstrated magnetic logic [2], where logic operations are performed by domain wall propagation through ferromagnetic nanowire junctions, resulting in magnetization reversal. Until now, this propagation has been induced by an external applied field. A potential alternative is current-induced dragging of a domainwall, which does not rely on a generated magnetic field and is now well known in quasiinfinite thin film [3,4]. However, the effect of nanopatterning has never been studied, despite introducing several new conditions and raising important questions. First, the shape anisotropy of certain nanowires (e.g. 5 nm thick, 100 -200 nm wide permalloy) dictates that its magnetization is parallel to the wire axis, and domain walls become headto-head rather than the Bloch walls studied previously. Second, the profile of the domain wall is modified; its width has been shown to be much smaller in nanostructures [5].Third, the edge roughness of nanowires could become very important, possibly severely impairing domain wall propagation. Fourth, can domain walls propagate through nanowires that are not straight?Here, we address these questions and demonstrate experimentally that domain walls can be moved through magnetic nanowire circuits and even around corners by spin

Depinning probability of a magnetic domain wall in nanowires by spin-polarized currents

“…There are mainly two ways to utilize the STT: one is current-induced magnetization switching (CIMS) in magnetic nanopillars 2,[7][8][9][10][11][12] , and the other is current-induced domain wall motion (CIDWM) in magnetic nanowires 1,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] . In particular, the latter is promising for applications in which a domain wall (DW) moves numerous times within several nanoseconds' duration 4 , or in which numerous DWs are shifted simultaneously 6 .…”

Direct observation of the coherent precession of magnetic domain walls propagating along permalloy nanowires

“…Depending on the driving force, conventionally magnetic field and, more recently, spin-polarized current [4][5][6][7][8][9][10][11][12][13] , the propagation of DWs changes from a simple translation to more complex precessional modes 14 . Experimentally, indirect evidence of this transition is found from a sudden drop in the wall's velocity [15][16][17][18] , but direct observation of the precessional modes is lacking.…”

Dependence of Domain-Wall Depinning Threshold Current on Pinning Profile

“…Experimental work on this subject includes studies on ferromagnetic thin films [2,3], nanowires [4][5][6][7][8], and wires with patterned pinning sites [9][10][11][12][13]. In addition to the early theoretical work [14,15], recent reformulations have been proposed, based on a microscopic approach [16][17][18][19].…”