Sujet de stage / Master 2 Internship

The idea here is to run a home made magnetic atomistic simulation code and attempt in parallel to image nanostructures of BiFeO3, a room-temperature magneto-electric. The imaging is based on Second Harmonic Generation in near-field mode.

Antiferromagnets (AF) are currently in the limelight thanks to recent breakthroughs demonstrating the efficient effect of spin currents in interacting with the AF order parameter [1,2]. So far, due to the lack of net magnetization, controlling AF distributions has been rather challenging. On the materials side, antiferromagnets represent the majority of magnetic materials and some of them show several simultaneous coupled ordered phases. They are commonly called ‘multiferroics’. Multiferroic materials [3] are the focus of an intense research effort due to the significant technological interest of multifunctional materials as well as the rich fundamental physics stemming from the coupling of various order parameters. Among all multiferroics, BiFeO3 (BFO) is a material of choice because its two ordering temperatures (ferroelectric FE and AF) are well above room temperature. In addition, a large magnetoelectric (ME) coupling has been demonstrated in single crystals as well as in thin films. Beyond the ability to manipulate the AF order using an electric field, the ME interaction is the main ingredient to stabilize homochiral magnetic distributions, promoting BFO as an ideal host for topological multiferroic entities [4]. However, one downside of multiferroics is that these FE/AF textures can be rather challenging to assess, in particular with a required spatial resolution below 100 nm. Second harmonic generation, a non-linear optical approach, has proven to be a powerful and elegant way to image complex multiferroic textures and to untangle the different contributions at play [5]. In CEA/SPEC, we are experienced in assessing ferroelectric and antiferromagnetic distributions with sub-micron resolution [6].

We are now aiming at studying nanostructures (near 100 nm) of these materials. The object of the proposed internship is then twofold: 1) using a home-made micromagnetic simulation code adapted to BFO, the student will simulate some basic magnetic configurations depending on ferroelectric domains. 2) These structures (made in CNRS/Thales) will be imaged in the laboratory using near-field second harmonic generation microscopy.

During this internship, the student will be trained in laser optics, near-field optical microscopy and will have to use the simulation code developed internally. We are looking for a candidate who likes the duality between simulation and experiments, with a certain degree of proficiency in basic computer coding. Ideally, the internship would continue in a PhD as the proposed subject is part of a long-term effort on these materials.

[1] T. Jungwirth, X. Marti, P. Wadley and J. Wunderlich Nature Nanotech. 11, 231 (2016) [2] P. Wadley and al. Science 351, 587 (2016) [3] N. Spaldin and M. Fiebig, Science, 309, 391 (2005) [4] J.-Y. Chauleau & al., Nature Materials, 19, 386 (2020) [5] M. Fiebig & al., Nature, 419, 818 (2002) [6] J.-Y. Chauleau & al., Nature Materials, 16, 803 (2017)