Direct Imaging and Manipulation of Antiferromagnets

Project Information

DIMAF

Grant agreement ID: 846597

DOI

10.3030/846597

Project closed

EC signature date 3 May 2019

Start date 1 September 2019

End date 31 August 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 184 707,84

EU contribution

€ 184 707,84

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 1 - DIMAF (Direct Imaging and Manipulation of Antiferromagnets)

Reporting period: 2019-09-01 to 2021-08-31

Summary of the context and overall objectives of the project

With the growing energy comsuption of digital technologies, new routes are explored in order to develop efficient and low power consuming devices. In particular, spintronics is now turning to antiferromagnets, materials with fast dynamics, robust to parasitic fields and which can be manipulated at low power.
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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first part of the project, the phase diagram describing the magnetic states of thin films of bismuth ferrite depending on epitaxial strain was established from real-space measurement using NV center magnetometry. Epitaxial strain was varied by changing the growth substrate of the films.

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.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The complete characterization of the effect of epitaxial strain on bismuth ferrite thin film is unprecedented for such antiferromagnetic material. It is a first step towards strain control of antiferromagnetic textures. In the next phase of the project, direct control of the magnetic texture with strain will be performed using a film grown on a piezoelectric substrate. In addition, manipulation of the antiferromagnetic state by electric field and spin current will also be realized and imaged directly in the scanning NV setup.

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.

Phase diagram of the magnetic state in BiFeO3 depending on epitaxial strain