Cycloidal Domains in the Magnetization Reversal Process of Ni80Fe20/Nd16Co84/Gd12Co

Abstract

The magnetization reversal of each individual layer in magnetic trilayers (permalloy/NdCo/GdCo) is investigated in detail with x-ray microscopy and micromagnetic calculations. Two sequential inversion mechanisms are identified. First, magnetic vortex-antivortex pairs move along the field direction while inverting the magnetization of magnetic stripes until they are pinned by defects. The vortex-antivortex displacements are reversible within a field interval which allows their controlled motion. Second, as the reversed magnetic field increases, cycloidal domains appear in the permalloy layer as a consequence of the dissociation of vortex-antivortex pairs due to pinning. The field range where magnetic vortices and antivortices are effectively guided by the stripe pattern is of the order of tens of mT for the NiFe layer, as estimated from the stability of cycloid domains in the sample.

Revealing 3D magnetization of thin films with soft X-ray tomography: magnetic singularities and topological charges

“…The white and black arrows illustrate the magnetization pattern of the closure domains. X-rays tuned at the Fe L 3 energy (wavelength 1.754 nm) were chosen to probe only magnetic domains at the top and bottom layers, which are nominally of identical atomic composition and cannot be distinguished by element specific 2D X-ray transmission microscopy 20 , 28 ). A 3D method with in-depth sensitivity is necessary to separate their magnetizations and to characterize magnetic singularities within the striped domain pattern.…”

“…This has hindered a direct 3D visualization of the magnetization in thin films and multilayers of arbitrary magnetization configuration and it is a major limitation since most magnetic devices are fabricated on substrates with macroscopic lateral dimensions. Therefore, a variety of basic and applicationrelated topics such as the thickness dependence of magnetic textures in chiral multilayers 15 , or the optimization of spin torque oscillators 16 , have been addressed indirectly [15][16][17][18][19][20][21] by image simulations and clever sample designs. Thus, magnetic vector tomography in extended thin films can become an essential tool for the evolution of nanomagnetism from 2D configurations to the complex 3D magnetization textures and structures explored nowadays 2 including magnetic hopfions 22 and skyrmion dots 23 .…”

“…For Py films at the Fe L 3 resonance, Ni absorbs about six times less X rays than Fe resulting in a reasonable transmission of thick films compared to films of a pure element. The magnetic state was prepared by in-plane partial magnetization reversal from 3000 to −62 Oe, which is the magnitude of the coercive field, in order to generate relevant magnetic topological textures such as Vortex-Antivortex pairs, and meron-like configurations20,30,31 . After fabrication and magnetic preparation, commercial Au nanoparticles (NPs) with diameters around 100 nm were deposited on the trilayerTomographic reconstruction of magnetic singularities.…”

“…As a consequence, a variety of basic and application-related topics as e.g. the determination of the dependence with depth of the magnetic textures in chiral multilayers (11), or the optimization of spin-torque oscillators (12) have been addressed indirectly (11)(12)(13)(14)(15)(16) by image simulations and clever sample designs. Thus, magnetic tomography in extended thin film samples can become an essential tool in the evolution of nanomagnetism from the present basically 2D structures to 3D objects.…”

“…Characteristic features of closure domains. The most relevant feature of parallel stripe domains is the periodic pattern of My-Mz closure domains (16,19) sketched in Fig. 2 which means that the z resolution of the reconstruction may be estimated to be as a minimum one half i.e.…”