Coexistence of Bloch and Néel walls in a collinear antiferromagnet

Abstract

We resolve the domain-wall structure of the model antiferromagnet Cr 2 O 3 using nanoscale scanning diamond magnetometry and second-harmonic-generation microscopy. We find that the 180 • domain walls are predominantly Bloch-like, and can coexist with Néel walls in crystals with significant in-plane anisotropy. In the latter case, Néel walls that run perpendicular to a magnetic easy axis acquire a well-defined chirality. We further report quantitative measurement of the domain-wall width and surface magnetization. Our results provide fundamental input and an experimental methodology for the understanding of domain walls in pure, intrinsic antiferromagnets, which is relevant to achieve electrical control of domain-wall motion in antiferromagnetic compounds.

Boundary conditions for the Néel order parameter in a chiral antiferromagnetic slab

“…The envisioned devices rely on AFM textures moving in spatially confined channels [5][6][7][8][9][10] similarly to ferromagnetic racetracks [11]. One of the most efficient ways to control their dynamics are spin-orbit staggered torques, which require specific symmetry of antiferromagnets rendering them chiral with Dzyaloshinskii-Moriya interaction (DMI) [12][13][14][15]. In this respect, the technological progress in design and optimization of AFM racetracks requires a fundamental understanding of the interaction of magnetic solitons with boundaries of a chiral AFM slab.…”

Scanning gradiometry with a single spin quantum magnetometer

“…While the magnetic imaging of ferromagnetic and ferrimagnetic textures is well-established [10][11][12], detection of the much weaker stray fields of, for example, antiferromagnets, multiferroics or nanoscale current distribution is a relatively new development. Quantum magnetometers based on single nitrogen-vacancy (NV) centers have recently led to exciting advances in this direction [13][14][15][16][17][18][19]. In their standard configuration, NV magnetometers image stray fields by scanning a sharp diamond probe over the sample surface and monitoring the static shift of the NV spin resonance frequency [20,21].…”

“…In their standard configuration, NV magnetometers image stray fields by scanning a sharp diamond probe over the sample surface and monitoring the static shift of the NV spin resonance frequency [20,21]. State-ofthe-art scanning NV magnetometers reach a sensitivity to static fields of a few µT/ √ Hz [16,22]. This sensitivity is sufficient for imaging the domain structure of monolayer ferromagnets [22][23][24] and uncompensated antiferromagnets [14][15][16][17], however, it remains challenging to detect the even weaker stray fields of isolated magnetic defects, spin chains or ideally compensated antiferromagnets.…”

“…State-ofthe-art scanning NV magnetometers reach a sensitivity to static fields of a few µT/ √ Hz [16,22]. This sensitivity is sufficient for imaging the domain structure of monolayer ferromagnets [22][23][24] and uncompensated antiferromagnets [14][15][16][17], however, it remains challenging to detect the even weaker stray fields of isolated magnetic defects, spin chains or ideally compensated antiferromagnets. While higher sensitivities, on the order of 50 nT/ √ Hz, have been demonstrated using dynamic (ac) detection of fields [25,26], this approach is limited to the few systems whose magnetization can be modulated, like isolated spins [27,28].…”

“…The microscope apparatus additionally includes an objective to optically polarize and read-out the NV center spin state and a bond wire acting as a microwave antenna for spin manipulation (see Methods for details). In the conventional mode of operation, we record a spin resonance spectrum at each pixel location to build up a map of the sample's static stray field [16].…”