Periodic Reporting for period 1 - DIMAF (Direct Imaging and Manipulation of Antiferromagnets)
Okres sprawozdawczy: 2019-09-01 do 2021-08-31
However, the study of the magnetic states in antiferromagnets is hindered by the difficulty to image them in real space with most of the available microscopy techniques. The recently developed nitrogen-vacancy (NV) center magnetometry appears to be a solution to this problem. It probes the magnetic order via the measurement of the stray field present at the surface of the sample. The field is measured using the Zeeman shifts of the electronic spin sublevels of a single nitrogen-vacancy defect in diamond. The single NV defect is placed at the apex of a nanopillar in a diamond tip integrated into an atomic force microscope, allowing to scan in close proximity to the sample surface.
The project aims at the direct imaging of nanoscale antiferromagnetic textures using NV-center magnetometry, in particular in synthetic antiferromagnets as well as in bismuth ferrite. A further objective is the demonstration of the manipulation of the magnetic states using epitaxial strain, electric field and spin currents.
Since NV magnetometry measurements are non-perturbative, they allowed the demonstration that magnetic skyrmions can be stabilized in a ferromagnetic layer in the absence of an external magnetic field. In this case, an effective magnetic field was introduced in the system by exchange bias at the interface between hte ferromagnet and an antiferromagnet.
Investigations of domain walls and skyrmions in synthetic antiferromagnets have brought to light a new operating mode of the NV center magnetometer. It relies on the enhancement of the NV center spin relaxation in the presence of magnetic noise generated by spin waves inside the magnetic texture.
The demonstration of a magnetic-noise-based operating mode of the NV magnetometer is a significant step towards faster and simpler imaging of antiferromagnetic states. It opens new perspectives for the characterization of magnetic textures and the study of spin waves, as well in ferromagnets as in antiferromagnets.
This work establishes NV-center magnetometry as a relevant technique for the investigation of new materials for spintronics.