We report on the study of the cycloidal antiferromagnetic state in bulk single crystals of the multiferroic bismuth ferrite using a combination of real-space and reciprocal magnetic imaging techniques [1]. We first discuss the origin of the magnetic stray field allowing us to image the cycloidal modulation of the antiferromagnetic state. This stray field is produced by the small uncompensated moment arising from the spin density wave which is locked to the cycloid [2]. We then use scanning NV center magnetometry to image the magnetic texture, with additional resonant X-ray diffraction measurements to obtain a larger scale insight. We observe the unexpected coexistence inside a single ferroelectric domain of magnetic domains hosting different cycloid wavevectors. We show that the direction of these wavevectors is not strictly locked to the preferred crystallographic axes as continuous rotations bridge different wavevectors. Making profit of the nanoscale spatial resolution of scanning NV-center magnetometry, we show that topological defects form at the junction between the magnetic domains. These defects are identical to those found in a broad variety of lamellar physical systems with rotational symmetries (liquid crystals, magnetic helix [3], ferromagnetic garnets, copolymers, etc.). The presence of these objects in such a multiferroic antiferromagnet offers new opportunities in terms of robustness and electrical control towards their use in spintronic devices.<br>

**References:**<br>

[1] Finco et al, Phys. Rev. Lett. 128, 187201 (2022)
[2] Ramazanoglu et al, Phys. Rev. Lett. 107, 207206 (2011)
[3] Schönherr et al, Nat. Phys. 14, 465 (2018)


Topological Defects in a multiferroic Antiferromagnet

To improve magnetic memories, significant efforts are made to reduce the size and spacing of magnetic bits. This implies that failures and defects can only be discovered with a non-invasive technique that can resolve small magnetic fields with high spatial resolution. Scanning NV magnetometry (SNVM) is the emerging quantum sensing technique that offers the required sensitivity.<br/>We will demonstrate magnetic images of a few hot candidate materials for future magnetic memory devices. We will look at memory bits in antiferromagnetic chromia, antiferromagnetic cycloids in BiFeO3 [1], cobalt nanomagnets and ultra-scaled CoFeB nanowires [2]. We will reveal magnetic textures that are undetectable with standard characterization techniques. In this context, we will more broadly discuss the potential of SNVM as a powerful magnetic characterization tool.

Investigation of Ferro and Antiferromagnetic Memory Structures using Scanning NV Magnetometry

Experimental methods allowing for the detection of single spins in the solid-state, which were initially developed for quantum information science, open new avenues for the development of highly sensitive quantum sensors [1]. In that context, the electronic spin of a single nitrogen-vacancy (NV) defect in diamond can be used as an atomic-sized magnetometer, providing an unprecedented combination of spatial resolution and magnetic sensitivity under ambient conditions [2]. In this talk, I will illustrate how scanning-NV magnetometry can be used as a powerful tool for exploring condensed-matter physics, focusing on chiral spin textures in antiferromagnetic materials [3-5].

Exploring antiferromagnetic order at the nanoscale with a single spin microscope


***Supported by***<br>

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SC: Imaging Magnetic Textures at the Nanoscale

technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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MMM 2022

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

ROB: Recent Advances In Magnetic Imaging

**Session chair:** Patrick Maletinsky, University of Basel

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Symposium SC: Exploring Magnetism at the Nanoscale with Scanning NV Magnetometry

symposium

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Vincent Jacques

3

40

SHORT BIO

Presentations

Topological Defects in a multiferroic Antiferromagnet

Investigation of Ferro and Antiferromagnetic Memory Structures using Scanning NV Magnetometry

Exploring antiferromagnetic order at the nanoscale with a single spin microscope

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