Fig. 2. All-optical imaging of domain walls in a synthetic antiferromagnet.

a Simplified sketch of the scanning-NV magnetometer and the SAF structure. The two magnetic Co layers are antiferromagnetically coupled through the Ru/Pt spacer layer by RKKY exchange interaction. The exact composition of the stack is Ta(10)/Pt(8)/Co(t_Co)/Ru(0.75)/Pt(0.6)/Co(t_Co)/Ru(0.75)/Pt(3), with the thicknesses in nm. The effective perpendicular magnetic anisotropy of the SAF is controlled by varying the Co thickness t_Co. b PL quenching image recorded with the scanning-NV magnetometer above a SAF sample with perpendicular magnetic anisotropy (t_Co = 1.41 nm), showing an overview of the magnetic domain structure. c Closer view of a domain wall. d Static magnetic field distribution recorded above the area marked with the dashed rectangle in c. Only the component of the stray field along the NV quantization axis, B_NV, is measured. This axis is defined by the spherical angles $\left({\theta }_{\mathrm{NV}}=58^{\circ },{\varphi }_{\mathrm{NV}}=103^{\circ }\right)$ in the laboratory frame of reference (x, y, z).