As the old adage goes, Seeing is believing! This is particularly acute for antiferromagnets that despite their interest for low-power, ultrafast spintronics applications remain practically impossible to image at the nanoscale since their the antiparallel order of neighbouring spins results in a vanishing magnetization. Usually, reciprocal-space, bulk averaging methods such as neutron diffraction are the techniques of choice to characterize antiferromagnets, but then microscopic details remain concealed. In our recent paper just published in Nature, we report the first real-space imaging of long-range periodic order in a complex antiferromagnet, bismuth ferrite (BiFeO3). We have used a new technique exploiting the extreme magnetic sensitivity of the photoluminescence response of a single nitrogen-vacancy (NV) center located near the apex of an atomic force microscope tip. In addition, we have also taken advantage of the magnetoelectric coupling present in BiFeO3 to evidence the electrical control of the cycloid propagation direction in real space. Besides highlighting the potential of NV magnetometry for imaging complex antiferromagnetic orders at the nanoscale, our results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures on-demand.
This work was performed in collaboration with Lab. Charles Coulomb, CEA-Saclay, C2N, Synchrotron SOLEIL, Lab. Aimé Cotton and University of Basel. Left image on figure courtesy of P. Maletinsky.
Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer
I. Gross et al ; Nature 459, 252 (2017)