Centre d’Élaboration de Matériaux et d’Etudes Structurales

Accueil > Faits marquants

Complex 3D magnetic configurations revealed by an original holography-tomography method

A 3D study at the nanoscale of multi-vortex magnetic states

par Guy Molénat - publié le

CEMES researchers have studied the 3D magnetic configuration of longitudinal and transverse multi-vortex states of different chiralities in CoNi magnetic nanowires using a unique holographic vector-field electron tomography method. This study has revealed the complex distribution of the magnetization and highlighted an unexpected domain wall separating two vortex domains of opposite chirality.

Cylindrical magnetic nanowires in which the direction of easy magnetization is perpendicular to the wire axis (or close to), exhibit peculiar magnetic configurations resulting from the competition between the exchange and anisotropy (magnetocrystalline and shape) energies.

In a collaboration with the IFW in Dresden, the University of Berlin, ICMM Madrid, and University del Valle de Cali, CEMES researchers used the unique holographic vector-field electron tomography (VFET) method to study the 3D magnetic configurations of hcp/fcc CoNi nanowires in the remanent state.

The 3D structure of magnetic domains has been revealed with a spatial resolution of 10 nm. By tuning the applied magnetic field direction perpendicular or parallel to the wire axis before the observations, they could stabilize respectively a transverse-vortex chain with a zig-zag modulation of the vortex lines or a longitudinal vortex configuration separated by an unexpected chiral domain wall (CDW).

This CDW exhibits a complex 3D shape characterized by the expulsion of the opposite vortex lines from the nanowire (see figure). It is demonstrated to reduce both the exchange and the anisotropy energies compared to conventional DWs.

By combining the experimental results and the micromagnetic simulations carried out on both perfectly cylindrical nanowires, the “ideal” case, and of the real shape nanowire obtained experimentally by VFET, they demonstrated the impact of the crystalline properties and real shape real at the nanometric scale on resulting magnetic configurations of the nano-objects.

3D reconstruction of the magnetic B-field inside CoNi NW by holographic VFET and comparison with micromagnetic simulation after magnetizing the NW in axial x-direction. The z-direction corresponds to the electron beam trajectory. Central slices in axial (xy) and (xz) direction through the 3D B-field inside the NW visualized by arrow-plots and color-coded volume rendering of Bx and By reveal a complex configuration in the hcp region with the appearance of Chiral Domain Walls (CDW).


Publication : 

Field tunable three-dimensional magnetic nanotextures in cobalt-nickel nanowires. M. Andersen, D. Wolf, L. A. Rodriguez, A. Lubk, D. Oliveros, C. Bran, T. Niermann, U. K. Rößler, M. Vazquez, C. Gatel, and E. Snoeck - Phys. Rev. Research 3, 033085 (published 23 July 2021)



Contacts :

Christophe Gatel, christophe.gatel [at] cemes.fr

Etienne Snoeck, etienne.snoeck [at] cemes.fr