Surface magnetization of Cr2O3 (104) quantified via scanning NV magnetometry

Magneto-electric antiferromagnets are candidate materials for future spintronic
devices. While antiferromagnets offer high speed, low power consumption and
robustness to external fields, magneto-electrics allow manipulation of the magnetic
order parameter not only via magnetic signals, but also via electric signals [1, 2].
Readout and manipulation of the antiferromagnetic order on the nanoscale typically
relies on local probes sensitive to the surface magnetization. Therefore, its optimization
is key challenge in device engineering. Here we investigate the surface magnetization
of an oblique cut of single crystal Cr 2 O3 using scanning probe nitrogen-vacancy center
magnetometry. The (104) surface normal is at an angle of 38.5° to the uniaxial
anisotropy axis of Cr 2 O3. By magneto-electric annealing [3], a homogeneous
antiferromagnetic order is initialized. We then measure the stray magnetic fields
produced by topographic steps fabricated by ICP etching. The steps have various
angles with respect to the c-axis in-surface component, allowing us to probe different
`cuts` of the magnetization. We finally consider a simple model based on a
homogenous surface magnetization strength and orientation for the various crystal
facets. We find good agreement between this model and the recorded stray fields for
a magnetization aligned with the bulk c-axis orientation. The predicted magnitude
agrees with previous results of measurements on (001) surfaces [4]. We hope that
these findings may aid in understanding the relation between surface and bulk
magnetic order in antiferromagnets and aid in the development of antiferromagnetic
spintronic devices.