Interlayer-coupled spin vortex pairs and their response to external magnetic fields

Abstract

We report on the response of multilayer spin textures to static magnetic fields. Coupled magnetic vortex pairs in trilayer elements (ferromagnetic/nonmagnetic/ferromagnetic) are imaged directly by means of layer-selective magnetic x-ray microscopy. We observe two different circulation configurations with parallel and opposing senses of magnetization rotation at remanence. Upon application of a field, all of the vortex pairs investigated react with a displacement of their cores. For purely dipolar coupled pairs, the individual core displacements are similar to those of an isolated single-layer vortex, but also a noticeable effect of the mutual stray fields is detected. Vortex pairs that are linked by an additional interlayer exchange coupling (IEC), which is either ferromagnetic or antiferromagnetic, mainly exhibit a layer-congruent response. We find that, apart from a possible decoupling at higher fields, these strict IEC vortex pairs can be described by a single-layer model with effective material parameters. This result implies the possibility to design multilayer spin structures with arbitrary effective magnetization.

Topology and Origin of Effective Spin Meron Pairs in Ferromagnetic Multilayer Elements

“…In addition to fundamental aspects, these investigations have led to the proposal of vortex based memory cells [14] and spin-torque driven nano-oscillators [15][16][17]. For both concepts the integration of vortices into lateral arrays [18,19] or multilayer systems is a crucial point [20][21][22][23][24][25][26][27][28][29].…”

Two-body problem of core-region coupled magnetic vortex stacks

“…As shown in the inset we observe both possible combinations (c 1 c 2 = 1 and c 1 c 2 = −1), indicating that the silicon spacer decreases interlayer exchange coupling between the vortices. For interlayer exchange-coupled vortices only one state would occur [33]. Stray fields at the side surfaces of the disks emerge when the vortices are deflected from their equilibrium position indicated in Fig.…”

Determination of magnetic vortex chirality by local field excited gyration

“…15 The chirality of the magnetic vortex is the rotational direction of the whirling magnetic moments with two degenerated states of the clockwise (CW) and counterclockwise (CCW) directions. Several techniques such as Lorentz transmission electron microscopy, 4,16,17 SP-STM, 7 nonlocal spin valve measurement, 18,19 and MTXM 12,20,21 have been employed to determine the chirality.…”

“…Among the existing techniques for determining the vortex chirality, low temperature is usually needed for the SP-STM, 7 and a synchrotron beamline is required for the MTXM. 12,20,21 Our proposed method using the local field excited frequency measurement can be performed at room temperature in a university laboratory.…”

“…In practice, the local field on magnetic vortex can be generated by, for example, the dipolar field from an adjacent magnetic layer 21,32 or the neighboring magnetic element in a patterned nanostructure, 33-37 the stray field from a magnetic tip, 7,15 or point contact, 38 and the Oersted field from an electrode. [9][10][11]20,39,40 Spin-polarized current induced torque in nanostructure can also act like a local field on vortex.…”