Real-space imaging of non-collinear antiferromagnetic order with a single spin magnetometer (2011.12399v1)

Abstract: While ferromagnets are at the heart of daily life applications, their large magnetization and resulting energy cost for switching bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem and often possess remarkable extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or produce emergent spin-orbit effects, which enable efficient spin-charge interconversion. To harness these unique traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive scanning nanomagnetometer based on a single nitrogen-vacancy (NV) defect in diamond, we demonstrate the first real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film, at room temperature. We image the spin cycloid of a multiferroic BiFeO$_3$ thin film and extract a period of $\sim70$ nm, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO$_3$ to manipulate the cycloid propagation direction by an electric field. Besides highlighting the unique potential of NV magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO$_3$ can be used as a versatile platform for the design of reconfigurable nanoscale spin textures.

• The paper demonstrates that a scanning NV magnetometer images non-collinear antiferromagnetic order in BiFeO₃ with ~70 nm spatial resolution.
• It reveals that electric fields can manipulate the spin cycloid via intrinsic magnetoelectric coupling in the multiferroic thin film.
• The method overcomes traditional imaging limitations, advancing research in low-power spintronics and reconfigurable magnetic textures.

Real-space Imaging of Non-collinear Antiferromagnetic Order with a Single Spin Magnetometer

The paper explores the paper of non-collinear antiferromagnetic systems, which have garnered attention due to their potential applications in low-power spintronic devices. Unlike ferromagnets, antiferromagnets exhibit negligible magnetization, thus leading to more energy-efficient operations. Specifically, the research employs a scanning nanomagnetometer based on a single nitrogen-vacancy (NV) defect in diamond for imaging purposes. This allows for real-space visualization of the spin cycloid in a multiferroic BiFeO₃ thin film at the nanoscale.

This work is notable for its ability to map the antiferromagnetic order in thin films with a spatial resolution of approximately 70 nm. The findings reveal that the spin cycloid propagation direction in BiFeO₃ can be manipulated via electric fields, thanks to the material's intrinsic magnetoelectric coupling. Such a capability is crucial for advancing the design of reconfigurable nanoscale spin textures in spintronic applications.

Several challenges impede the mapping of antiferromagnetic orders, especially at the nanoscale. Traditional techniques such as magnetic force microscopy and x-ray photoemission electron microscopy, while useful, lack the necessary sensitivity for detecting weak magnetic signals typical of antiferromagnets. The paper showcases that NV magnetometry, with its high sensitivity and spatial resolution, can effectively overcome these limitations, thus offering valuable insights into complex magnetic textures.

The implications of this research extend to both spintronics and magnonics, where the electric control of magnetism through an electric field is highly sought after. BiFeO₃ emerges as a promising platform due to its preserved multiferroic phase above room temperature. The paper suggests that understanding the spin structure and order at the nanoscale could lead to significant advancements in low-power spintronic technology.

Furthermore, the research provides a quantitative analysis of the spin cycloid's magnetic texture using NV magnetometry under ambient conditions. This analysis aids in understanding the spin density wave's properties and confirms that magnetoelectric coupling is efficient in manipulating antiferromagnetic order. The work prompts further exploration into the local magnetoelectric interactions in multiferroics, especially in contexts where inversion symmetry is broken at interfaces.

In summary, the paper demonstrates a significant step forward in the real-space imaging and control of antiferromagnetic orders. Future work may explore the nanoscale phenomena prevalent in multiferroics, potentially unveiling new functionalities and efficiencies in spintronic devices. The successful application of NV magnetometry in this context underscores its potential as a versatile tool for exploring complex magnetic orders across a range of material systems.