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. 

**References:** 

[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. 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

Antiferromagnetic thin films attract significant interest for future low-power spintronic devices. They are largely insensitive to external magnetic fields, exhibit negligible cross-talk between neighboring memory cells and they can be switched at THz frequencies [1]. Multiferroics, such as bismuth ferrite BiFeO3, in which antiferromagnetism and ferroelectricity coexist at room temperature, appears as a unique platform for spintronic [2] and magnonic devices [3]. The nanoscale structure of its ferroelectric domains has been widely investigated with piezoresponse force microscopy (PFM), revealing unique domain structures and domain wall functionalities [4, 5], but nanoscale magnetic textures present in BiFeO3 and their potential for spin-based technology remain concealed. Depending on the strain, growth conditions and crystal orientation, the magnetic state of BiFeO3 thin films can either show different types of non-collinear cycloids, canted G-type antiferromagnetic orders, or even a mixture of these [6]. In this report, we present two different antiferromagnetic spin textures in multiferroic BiFeO3 thin films with different epitaxial strains, using a non-invasive scanning Nitrogen-Vacancy magnetometer (Qnami, ProteusQTM) based on a single nitrogen-vacancy (NV) defect in diamond (Qnami, QuantileverTM MX), with a calibrated NV flying height of ~35 nm and proven dc field sensitivity of ~1 μT/√Hz. The two BiFeO3 samples were grown on DyScO3 (110) and SmScO3 (110) substrates using pulsed laser deposition. The striped ferroelectric domains in both samples are first observed by the in-plane PFM as shown in Figs. (a) and (b), respectively. The corresponding scanning NV images in Figs. (c) and (d) confirm the existence of the spin cycloid texture, with zig-zag wiggling angles of 90° and 127°, and the propagation wavelength of λDSO≈64 nm and λSSO≈94 nm, respectively. At the local scale, the combination of PFM and scanning NV magnetometry allows to identify the relative orientation of the ferroelectric polarization and cycloid propagation directions on both sides of a domain wall. For the BiFeO3 grown on DyScO3 (110) substrate, the 90-degree in-plane rotation of the ferroelectric polarization imprints the 90-degree in-plane rotation of the cycloidal propagation direction along k1=[-1 1 0] direction, corresponding to the type-I cycloid as shown in Fig. (c). On the contrary, in the BiFeO3 film grown on SmScO3 (110) substrate, the propagation vectors are found to be along k1’=[-2 1 1] and k2’= [1 -2 1] directions in the neighboring domains separated by the 71° domain wall, cf. Fig. (d). It is worth to mentioned that in the previous report [6], BiFeO3 grown on SmScO3 (110), prepared in another growth chamber, showed G-type antiferromagnetic textures, compared to the observed type-II cycloid here in Fig (d). Our results here shed the light on future potential for reconfigurable nanoscale spin textures on multiferroic systems by strain engineering.

**References:**

 [1] V. Baltz, et al., Rev. Mod. Phys. 90, 015005 (2018). [2] J. T. Heron et al., Nature 516, 370–373 (2014). [3] P. Rovillain et al., Nat. Mater. 9, 975–979 (2010). [4] N. Balke et al., Nat. Phys. 8, 81–88 (2011). [5] G. Catalan, et al., Rev. Mod. Phys. 84, 119–156 (2012). [6] A. Haykal, et al., Nat. Commun. 11, 1704 (2020).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/b5b38edff0eaadbc038640f26e71f1fc.jpg)
Figure: (a-b) In-plane PFM phase images of BiFeO3 films grown on DyScO3 (110) and SmScO3 (110) substrates with resulted strains of -0.35% and +0.5%, respectively. (c-d) NV magnetometry images corresponding to the ferroelectric domains depicted in (a-b). The dashed lines in (c–d) are guides to the eyes, reflecting a change of the cycloid propagation vector associated to the ferroelectric domain walls.

Quantitative Imaging of Antiferromagnetic Spin Cycloidal Textures on Strain Engineered BiFeO3 Thin Films with a Scanning Nitrogen-Vacancy Magnetometer

Antiferromagnets attract a great interest for spintronics owing to the robustness of their magnetic textures and their fast dynamics. However, since they exhibit no net magnetization, antiferromagnets are challenging to work with. NV-center magnetometry, which provides a sensitivity of a few µT/Hz-1/2 combined with a nanoscale spatial resolution, has emerged in the last years as a powerful technique to investigate them [1]. Here we introduce a new imaging mode of the NV-center magnetometer which does not rely on the measurement of the static magnetic stray field but on the detection of magnetic noise originating from spin waves inside the non-collinear antiferromagnetic textures of interest. The presence of magnetic noise accelerates the NV spin relaxation. As a consequence, the emitted photoluminescence is reduced, allowing a simple detection of the noise sources [2]. We demonstrate this new technique on synthetic antiferromagnets (SAF) [3] consisting of two ferromagnetic Co layers antiferromagnetically coupled through a Ru/Pt spacer. We first image domain walls and prove that we perform noise-based imaging by measuring a shorter NV spin relaxation time above an antiferromagnetic domain than above a domain wall. Calculations of the spin waves dispersion both in the antiferromagnetic domains and in the domains walls as well as maps of simulated magnetic noise intensity enable us to conclude that the noise which we probe arises from spin waves channelled in the domain walls. Going further, we tune the composition of the SAF stacks in order to stabilize spin spirals or antiferromagnetic skyrmions. In both cases, our relaxometry-based technique is able to image the non-collinear structures, demonstrating its efficiency and opening new avenues of exploration in the characterization of complex structures in magnetically-compensated materials. This work was performed in collaboration with the UMR CNRS/Thalès and the Center for Nanoscience and Nanotechnology (C2N) in Palaiseau, France. It has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 846597 and from the DARPA TEE Program.References: [1] I. Gross et al, Nature, Vol 549, p 252 (2017) [2] A. Finco et al, arXiv:2006.13130 (2020) [3] W. Legrand et al, Nature Materials, Vol 19, p 34 (2020)

Imaging non-collinear antiferromagnetic textures via single spin relaxometry INVITED

***Supported by*** 

![](https://assets.underline.io/uploads/markdown_image/1/image/e6439ec743887b20761082e75ed2d3a7.jpg)

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.

<iframe width="560" height="315" src="https://s3.amazonaws.com/pf-user-files-01/u-59356/uploads/2022-11-02/un13zp7/MMM%20Welcome%20Video%20v5.mp4" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

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

Please register for the MMM 2022 conference to join the event.

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: Trevor Almeida, CEA-SPINTEC*

These on-demand presentations are available to view at your leisure. 

AB: Magnetic Microscopy and lmaging

INTERMAG 2021 Welcome Video



	
<figure class="video_container">
 <iframe src="https://screencast-o-matic.com/player/crflqFVnUpZ?v=6&ff=1&title=0&controls=1" width=640 height=360 frameborder="0" allowfullscreen="true"> </iframe>
</figure>

Want to buy a ticket? 

Register for INTERMAG 2021 here

[![](https://assets.underline.io/uploads/markdown_image/1/image/17ce76e7960db633258024eef8d6da7f.png)](https://intermag.org/register)

Got your ticket, but still can’t access the event?

Contact us and our team will look into it.

INTERMAG 2021

L1: Magnetic Microscopy and Imaging I

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

We were reluctant to give up the benefits of meeting face-to-face, and know that shifting to a virtual conference is a significant change for this community. Nevertheless, we are first and foremost concerned about the health and safety of all our Conference participants and their loved ones on returning home after travelling.

The MMM 2020 Steering Committee was working exceptionally hard, along with our sponsors, the IEEE Magnetics Society and AIP Publishing, to make this event serve the needs of our participants, who live in time zones all around the globe, in the best possible way. 

You need a ticket to explore this event.

If you have already registered for MMM 2020, and you have already created an account, then you
just need to login (above).

If you have already registered for MMM 2020, but you have not yet created an account, then you
need to click on &quot;create an account&quot; (above) and then login.

Forgot your password? Go to
https://www.underline.io/log-in

If you have not yet registered for MMM 2020 but would like to do so, go to
https://magnetism.org/register

Still need help? Contact our team!


Aurore Finco

4

44

1

SHORT BIO

Presentations

Topological Defects in a multiferroic Antiferromagnet

Investigation of Ferro and Antiferromagnetic Memory Structures using Scanning NV Magnetometry

Quantitative Imaging of Antiferromagnetic Spin Cycloidal Textures on Strain Engineered BiFeO3 Thin Films with a Scanning Nitrogen-Vacancy Magnetometer

Imaging non-collinear antiferromagnetic textures via single spin relaxometry INVITED

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES