Control of vortex pair states by post-deposition interlayer exchange coupling modification

Abstract

We report on both the global and micromagnetic properties of interlayer exchange coupled spin systems. Irradiation with Ne ions is employed to achieve a phase transition from antiferromagnetic to ferromagnetic coupling. For extended trilayer films a full quantitative analysis of the bilinear and biquadratic coupling constants is performed. With increasing ion fluence we observe a steady increase of the bilinear coupling constant at an almost negligible decrease in saturation magnetization. The mixing of atoms at the layer interfaces is identified as the origin for this. The effects of ion modification on the magnetic microstructure are studied for the model system of layered vortex pairs. X-ray microscopy is used to directly image the individual magnetization circulations in trilayer disks. The circulation configuration is found to be determined by the film coupling for both coupling orientations with a homogenous coupling angle throughout the structure. For the vortex cores, however, micromagnetic simulations indicate that due to the significant local demagnetization fields, parallel states are always energetically preferred. Nevertheless antiparallel configurations are metastable, having their signature in reduced core diameters. Our study provides new results on spin structures in interlayer exchange coupled trilayers and it demonstrates a promising way to control the local interlayer coupling post-deposition.

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

“…The thicknesses chosen for the ferromagnetic layers are expected to enforce the formation of vortex pair states in micron-sized elements. 24,25,44 In order to generate vortex pairs with ferromagnetic (fm) IEC, we made use of the ion-induced IEC modification, which had been pioneered by Demokritov et al 45 Irradiation of afm IEC disks with Ne ions results in a reorientation of the coupling from afm to fm and by this the C configuration of a vortex pair changes from AF to FM. 25 Empirically, IEC can be quantified by its bilinear (J L ) and biquadratic (J Q ) coupling constants with respect to the areal energy density (σ IEC ):…”

“…[16][17][18][19][20] From the viewpoint of these concepts, but also from a fundamental perspective, the coupling between spatially confined vortices is a key issue to address. 21,22 Especially, vortices that are coupled vertically via a nonmagnetic interlayer are of interest, [23][24][25][26][27][28][29][30][31][32][33][34] as significant magnetoresistance and spin-torque phenomena may occur. [35][36][37][38][39] The relevant coupling mechanisms for such geometries are the magnetodipolar interaction and, depending on the spacer material and thickness, also interlayer exchange coupling (IEC).…”

“…24 In addition, it was found that these C states can be predetermined by a control of IEC. 24,25 In this article, we will report on the response of individual vortex pairs (which are imaged directly by soft x-ray microscopy) to the application of quasistatic magnetic fields. We will discuss the behavior of different C states for pure dipolar coupling (PDC) as well as IEC.…”

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].…”

Coherence and modality of driven interlayer-coupled magnetic vortices

“…Indeed, utilizing such perturbations has demonstrated excellent linewidths with frequencies in the gigahertz range, and device compatible power generation using phase-locked vortices in carefully engineered geometries and materials 19,20 . Recently, the use of interlayercoupled (IC) solitons in multilayered structures has resulted in higher velocities, the reversal of magnetic ordering through ion irradiation, as well as independent control of the vortices' polarity and chirality in heterostructures with polarized spin currents [21][22][23] . To the best of our knowledge, the direct observation of HF dynamic motion in coaxial strongly coupled vortex system has yet to be reported and will provide significant insights for applications such as spin-torque vortex oscillators (STVO).…”